Research on the differences of mechanical properties between horizontal and vertical in Al-Cu alloy deposits fabricated by wire + arc additive manufacturing

Research on the differences of mechanical properties between horizontal and vertical in Al-Cu alloy deposits fabricated by wire + arc additive manufacturing | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Research on the differences of mechanical properties between horizontal and vertical in Al-Cu alloy deposits fabricated by wire + arc additive manufacturing Shuai Wang, Lingling Ren, lan yang, Zhu Ming, Chengde Li, Wei Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4392994/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Al-Cu alloy made by arc fuse additive has excellent microstructure and properties, but the difference between transverse and longitudinal is the key factor limiting its application.In this experiment, Al-Cu alloy deposits with different Cu contents were formed by the wire + arc additive manufacturing (WAAM) process used Al-Cu welding wire with different Cu content.The microstructure and properties of the deposits,both intralayer and interlayer,were analyzed using metallography, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and tensile tests.The results showed that the interlayer content of Cu is higher than that in the intralayer. When Cu content in the deposit was 6.3% in the as-deposited state, there was an enhanced θ (Al 2 Cu) precipitate phase in the interlayer position. After T4 treatment, there were still θ phases with a size larger than 20 µm, which were linearly distributed parallel to the accumulation layer. These θ phases led to lower mechanical properties in the vertical direction than in the horizontal direction, with a brittle fracture mode. When the Cu content of the deposit was reduced to 5.6% after T4 treatment, there were no large θ phases in the interlayer position. Furthermore, the mechanical properties of horizontal and vertical directions were consistent, and they had a ductile fracture mode.The Cu content in the deposit was the primary reason for the difference in mechanical properties between horizontal and vertical directions. Al-Cu alloy deposits with uniform mechanical properties in the horizontal and vertical directions can be obtained by controlling the Cu content,which has an important role in the application of this process. Al-Cu alloy wire + arc additive manufacturing microstructure horizontal and vertical differences Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1 Introduction Due to its excellent mechanical properties,the Al-Cu alloy has a broad application prospect in the fields of aviation and aerospace [ 1 – 3 ] . However, due to the large crystallization temperature range of the alloy, casting products are prone to produce thermal cracking,segregation, shrinkage and other defects, resulting in a low casting yield [ 4 – 6 ] . Additionally, the welding process cannot achieve equal strength between the base material and the welding seam, so it is difficult to produce high complexity products [ 7 ] . These limitations have restricted the use of Al-Cu alloys. In recent years, the production of Al-Cu alloy structural parts by the wire + arc additive manufacturing (WAAM) process has been widely studied [ 8 , 9 ] . Gu [ 10 ] examined the structure and properties of Al alloy 2219 deposits formed by the cold metal transfer (CMT) process, and found mechanical differences in the deposits between horizontal and vertical directions.Specifically, the mechanical properties in the vertical direction were smaller than those in the horizontal direction, especially the elongation rate. Cong et al. and Gu et al. investigated the distribution [ 11 ] and formation mechanism [ 12 ] of pores in the Al-6.3%Cu alloy wall fabricated by WAAM. The results showed interlayer porosity parallel to the accumulation layer, which was believed to be the reason for the differences in horizontal and vertical directions. However, These research results are not applicable to WAAMZL205A alloy and ZL114A alloy, which does not show a difference in the mechanical properties between horizontal and vertical directions of the deposits made through WAAM [ 13 , 14 ] .On the base of ZL205A alloy,Cd was replaced by Sn, the mechanical properties horizontal and vertical directions of the Al-Cu-Sn alloy deposits were still nuiform [ 15 ] .On the whole, the reasons for the difference in the horizontal and vertical directions of the Al-Cu alloy deposits fabricated by WAAM have not been clearly concluded, which limits the industrial application of this technology. Cu is the main strengthening element of Al-Cu series high-strength aluminum alloys. Its main function is to precipitate nanoscale θ (Al 2 Cu) phases after heat treatment, with the phases improving the strength of the alloy. The content of Cu during solidification determines the size, quantity and distribution of primary Al2Cu, which has an important influence on the mechanical properties of Al-Cu alloy.Xu et al. [ 16 ] studied the variation of microstructure and mechanical properties of 2219 ingots, and found that due to the different solidification sequence, the content of Cu gradually increased from the edge of the ingots to the center, with the mechanical properties tending to increase first and decrease later. Yu Fang [ 17 ] et al. studied the effect of Cu content on the size and distribution of the precipitated phase of Al-Cu alloy, and found that when Cu content in the alloy is low, the precipitation phenomenon in the structure is weakened and the anisotropy of the alloy is reduced. These studies indicate that Cu content has an important effect on the microstructure and properties of Al-Cu alloy, and may be a key factor affecting the transverse and longitudinal mechanical properties of Al-Cu alloy. In this paper, Al-6.3%Cu and Al-5.6%Cu alloys are used as raw materials, and the deposits are formed though the WAAM process. Among them, 6.3% is the typical Cu content of deformed Al-Cu alloy, and 5.6% is the maximum solid solubility of Cu in aluminum.This study aims to determine the reasons for the differences in the vertical and horizontal directions of Al-Cu alloy deposits. Specifically, the study analyzes the microstructure and properties of the deposits in different states in order to develop the materials suitable for the WAAM process, in addition to deposits with isotropic character,which has an important role in the application of this process. 2 Materials and Methods The 1.2-mm-diameter Al-Cu alloy welding wire used in this experiment was supplied by Fushun Donggong Metallurgy & Materials Technology Co., Ltd (Fushun, China). The chemical composition of the raw materials is shown in Table 1 . A 2219 Al plate with a thickness of 10 mm was used as the deposition substrate.The chemical composition was measured by an electric spark direct-reading spectrometer, and the average value is measured at 5 points. Table 1 Chemical composition of the raw materials Sample Fe Si Mg Cu Mn Ti Zr V Al-6.3%Cu 0.115 0.036 0.007 6.291 0.274 0.136 0.163 0.112 Al-5.6%Cu 0.113 0.083 0.007 5.602 0.2271 0.124 0.165 0.110 The additive manufacturing system consists of the Fronius TPS 4000 arc welding power supply and an ABB 1410 welding robot. The position definition of the deposits is shown in Fig. 1 (a). The interlayer position represents the overlap remelting zone between the two layers, and the intralayer position represents the non-remelting zone. The printing parameters are shown in Table 2 . Argon gas with a purity of 99.999% was used as the additive shield gas. The solution treatment temperature, solution treatment time, quenching temperature, ageing temperature, and ageing time of the T6 heat treatment process were 535 ℃, 360 min, 40 ℃, 180 ℃, and 120 min, respectively. Table 2 Print parameters Parameters I/A U/V ν WFS / m·min − 1 ν TS / m·min − 1 Cool time /s Gas flow/ ML/min 98 11.2 6.5 8 60 25 A WDW-300 computerized electronic universal testing machine (Changcun,China)was used to conduct the mechanical performance tests. Furthermore, a LEICA MEF4M metallographic microscope and a QUANTA FEG 250 scanning electron microscope (SEM) were used for the structural and morphological observations. Energy-dispersive X-ray spectroscopy (EDS) was conducted for the elemental and phase analysis. The sampling locations and the machining shape of the mechanical samples are shown in Fig. 1 (b) where the dimensions of the wall are 200 mm × 150 mm. The vertical and horizontal direction tensile samples were collected at locations 1 and 2 respectively, and the metallographic and transmission samples were collected at location 3. The tensile samples were processed into a plate structure with a gauge length of 30 mm and a cross-sectional area of 2.5 × 10 mm 2 . 3 Results and Discussion 3.1 Microstructure in as-deposited state The microstructure of Al-6.3%Cu alloy and Al-5.6%Cu alloy deposits in the as-deposited state is shown in Fig. 2 . As can be seen from Fig. 2 (a), the intralayer organization of the Al-6.3%Cu deposit is homogeneous equiaxed crystals. The interlayer organization is also homogeneous equiaxed crystals, but the grain size is larger, as shown in Fig. 2 (b). According to the heat dissipation characteristics of the WAAM process, each layer of deposit is solidified from the surface to the interior, and the sequence is as follows: surface, intralayer region, interlayer region. The grain size increases slightly due to the final solidification of the interlayer region. The same trend was observed in the microstructure of Al-5.6% alloy deposit, as can be seen from Fig. 2 (c,d). It can be seen from Fig. 2 that there are pores with diameters of 20–30 µm in the interlayer region of Al-6.3%Cu and Al-5.6%Cu alloy deposits, which are larger in number and size than in the intralayer region. This trend in the two allow deposits is consistent with the research results of Cong et al. [ 11 ] . The pores in Al alloys are mainly hydrogen pores, because hydrogen is mutated during the solubility transformation from a liquid to a solid in Al. The nucleation rate of hydrogen pores is closely related to the grain size [ 18 ] , and they grow by self-diffusion and mergers. The interlayer location of the Al-Cu alloy has a larger grain size. Therefore, the nucleation probability of hydrogen pores is greater, and the solidification time of interlayer organization is longer, allowing hydrogen pores to grow through diffusion and mergers. There are more pores in the interlayer location given that the interlayer location is the final solidification area, and the overflow channel of the pores has been closed. It can be seen from Fig. 2 (a,b) that in the intralayer structure of the Al-6.3%Cu alloy deposit, the precipitated phases are distributed along the grain boundaries. Additionally, the segregated precipitated phases can be seen in the interlayer structure, distributed in a band parallel to the deposited layer. In the intralayer structure of the Al-5.6%Cu alloy deposit, the precipitated phases are also distributed along the grain boundaries, but the width of the grain boundaries is greatly reduced, as shown in Fig. 2 (c). This indicates that the number of precipitated phases is reduced. The width of the grain boundary in the interlayer structure of the Al-5.6%Cu alloy deposit is larger than that in the intralayer, indicating that the number of precipitated phases has increased but without obvious segregation. In Fig. 3 it can be seen from the SEM and EDS of the deposits that the precipitated phase on the grain boundary is mainly θ phase. In the intralayer position of the Al-6.3%Cu alloy deposit, the θ phase size is small and intermittently precipitates. The average Cu content in the region is 5.72% (mass fraction), as shown in Fig. 3 (a). In the interlayer position, the θ phase is continuously precipitated and the size is significantly increased. The average Cu content in the region is 6.52% (mass fraction), as shown in Fig. 3 (b). In the intralayer and interlayer of Al-5.6%Cu alloy deposits, the distribution trend of precipitated phases is the same as Al-6.3%Cu. Specifically, the number and size are greatly reduced, and the regional average Cu content in the intralayer and interlayer is 5.17% and 5.61%, respectively. In the WAAM Al-Cu alloy deposits, the difference in the distribution of the precipitated phases in the intralayer and interlayer locations is caused by microsegregation during the solidification process of the molten pool. The WAAM process has the characteristics of rapid solidification. From the solute change curve of the Al-Cu alloy solidification process, under such non-equilibrium solidification conditions, the Cu content in the Al solution gradually progresses as the solidification process proceeds [ 19 ] . The Cu content in interlayers is larger than that in the intralayer location due to the solidification order of the deposit. This solidification characteristic of the Al-Cu alloy causes the Cu content to gradually increase from the edge of the ingot to the center, resulting in macrosegregation, which has been widely studied in the casting process [ 20 – 23 ] . WAAM is similar to the micro-casting process. Each layer is equivalent to a small-sized ingot. Following the solidification characteristics of the ingot, microsegregation occurs in the deposits. 3.2 Microstructure of deposits in T4 state Figure 4 shows the microstructure of Al-6.3%Cu and Al-5.6%Cu alloy deposits in T4 state. It can be seen from the figure that the grains of the deposits are all equiaxed crystals with uniform size due to the quenching and tempering effect. The grain size in intralayer locations is still smaller than that in interlayer locations due to the genetic effect of the alloy. There are two types of precipitated phases in the intralayer structure of Al-6.3%Cu alloy deposits at T4 state, small-sized black phases and larger-sized gray phases, as shown in Fig. 4 (a). In the interlayer structure, there are also two types of precipitated phases, as shown in Fig. 4 (b). However, the number of gray phases greatly increases, and the distribution is linear along the grain boundary. There are no large-scale gray precipitated phases found in the intralayer and interlayer microstructure of the Al-5.6%Cu alloy deposits at T4 state, only black phases that are dispersedly distributed along the grain boundaries. As can be seen from the SEM and EDS of Al-6.3%Cu and Al-5.6%Cu alloy deposits in Fig. 5 . The black phase in the metallographic structure is the remolded T phase (Al 12 Mn 2 Cu) containing a small amount of Fe impurity, and the gray phase is θ phase. The θ phases are not completely dissolved during the solid solution process. The size of the θ phase in the intralayer location of Al-6.3%Cu alloy deposit is about 10 µm, as shown by point A1 in Fig. 5 (a), and the size of the θ phase in the interlayer location is about 20 µm, as shown by point B1 in Fig. 5 (b). In the intralayer microstructure of Al-5.6%Cu alloy deposits in T4 state, there are θ phases smaller than 2 µm in size, as shown in Fig. 5 (c) by point C1, while the size of θ phases in interlayer location is about 5 µm, as shown in Fig. 5 (d) by point D1. After T4 treatment there are θ phases with linear distribution in the interlayer location of Al-6.3%Cu alloy deposits, due to the partial accumulation of the θ phase in the interlayer location in the as-deposited state. This is evident from EDS analysis of area scanning and matrix point of deposit with difference Cu contents. In the intralayer location of Al-6.3%Cu alloy deposits at T4 state, the average area Cu content is 5.83%, while the Cu content in the matrix is 5.11%. In the interlayer location, the average area Cu content is 6.45%, and the Cu content in the matrix is 5.20%. In the intralayer location of the Al-5.6%Cu alloy deposit at T4 state, the average area Cu content is 5.15%, while the Cu content in the matrix is 5.01%. Conversely, in the interlayer location, the average area Cu content is 5.66%, and the Cu content in the matrix is 5.12%. After T4 treatment, the amount of Cu atom in solid solution to the matrix did not increase significantly, and mainly appeared as intermetallic compounds in the grain boundary. This is because the solid solution amount of Cu is determined by temperature. At the solid solution temperature (535℃) in this experiment, the ultimate solid solution of Cu in Al was 5.29%, then the remaining Cu was distributed in the grain boundary in the form of the θ phase [ 17 ] . As can be seen from the alloy phase diagram, the ultimate solid solubility of Cu in Al is 5.65% at 548℃. Therefore, under WAAM process conditions, when the Cu content in the alloy exceeds 5.65%, there will inevitably be θ phases on the grain boundaries after solid solution treatment. The higher the content of Cu, the greater the number and size of the θ phases, and the more accumulation occurs in the interlayer locations. The higher the Cu content in deposit in T4 state, the greater the number and size of θ phases, and the more enrichment that will occur in the interlayer locations. (a) Intralayer location of Al-6.3%Cu alloy deposit. (b) Interlayer location of Al-6.3%Cu alloy deposit. (c) Intralayer location of Al-5.6%Cu alloy deposit. (d) Interlayer location of Al-5.6%Cu alloy deposit. 3.3 Microstructure of deposits in T6 state The microstructures of Al-6.3%Cu and Al-Cu5.6 alloy deposits at T6 state are shown in Fig. 6 . It can be seen from Fig. 6 that the microstructures in the intralayer and interlayer locations of the deposits are equiaxed grains. The precipitated phases in the intralayer location of Al-6.3%Cu alloy deposits are the black T phases and the gray θ phases, as shown by points A1 and A2 in Fig. 6 (a).The precipitated phases in the interlayer position are also the black T phases and gray θ phases, as shown by points B1 and B2 in Fig. 6 (b). However, the number and size of θ phases are significantly larger than those in the intralayer, and they are linearly distributed along the grain boundary. It can be seen from Figs. 6 (c,d) that after T6 treatment of the Al-5.6%Cu alloy deposit, the precipitation phases in the intralayer and interlayer regions are consistent, where both are black T phases, and no θ phases can be seen. The size and distribution of the θ phases at the grain boundaries have a significant impact on the mechanical properties of the alloy [ 24 ] . The θ phases, which are linearly distributed in the interlayer location of Al-6.3%Cu alloy deposits, are the starting position under stress as they are large intermetallic compounds, thereby reducing the mechanical properties of the alloy.The larger θ phases exist as intermetallic compound particles. It is found that the brittle fracture of grain boundary particles is an important reason for crack initiation. When the particle spacing is small, the stress fields caused by the interaction between adjacent particles promotes crack initiation.When the number of θ phases is large, the macroscopic shear zones formed in the microstructure accelerates the crack growth [ 25 ] , so the un-dissolved θ phases in the Al-Cu6.3% deposits will reduce the mechanical properties of the alloy. The precipitated phases in intralayer location and interlayer location of Al-Cu6.3 alloy and Al-Cu5.6 alloy deposits in T6 state are shown in Fig. 7 . After the aging process, the type, quantity, size and distribution of precipitated phases in intralayer location and interlayer location of Al-Cu6.3 and Al-Cu5.6 alloys have not changed. There is an unsolvable θ phase with a size of about 5 µm in the Intralayer location of Al-Cu6.3 alloy, and the distribution is uniform. In interlayer location, a large number of unsolvable θ phases, larger than 20 µm in size, are still densely distributed along the grain boundaries parallel to the deposition direction, as shown in Fig. 7 (b). The Cu content in the deposit is reduced to 5.6%, and the unsolvable θ phase in the intralayer location and interlayer location does not accumulate, and the size is less than 5µm. The precipitated phases in the T6-state at room temperature in grain of Al-Cu6.3 alloy and Al-Cu5.6 alloy deposits are shown in Fig. 8 . As can be seen from the figure, in the T6 state of the two alloy deposits, a large number of acicular precipitates are separated out inside the grains, the size of which is less than 500nm long and 5nm wide. As can be seen by HRTEM, this phases are semi-cogrid with the matrix. This phase is the main strengthening phase θ , phase [ 26 ] in the peak aging state of Al-Cu alloy. Its transverse and longitudinal distribution can effectively hinder the dislocation movement and is the key to improving the mechanical properties of Al-Cu alloy. The phase size, distribution density and phase spacing of the two alloys have no change. Due to θ , the phase precipitation process is as follows: susaturated solid solution (α ss ) →GP region (GPⅠ region) →θ , , (GPⅡ region) →θ , phase [ 27 ] . The primary θ is dissolved in aluminum matrix by solution treatment to form a supersaturated solid solution of Cu atoms. During the aging process, Cu atoms are biased to form GP region, and then gradually grow to form θ , phase. From the precipitation process of θ , phase, it can be seen that the Cu atom content in solid solution in Al matrix is the key to determine the quantity of θ , phase. Although the Cu content of the two alloys is different, the Cu content in solid solution is basically constant, so the θ , phases are basically constant, reflecting that the upper limit mechanical properties of the two alloys are at the same level. 3.4 Mechanical properties Mechanical properties of Al-6.3%Cu alloy and Al-5.6%Cu alloy deposits in T6 state are shown in Fig. 9 . As can be seen from Fig. 9 , there are significant differences between the horizontal and vertical directions of Al-6.3%Cu alloy deposits, and the mechanical properties of the horizontal direction are higher than that of the vertical direction. In particular, the elongation is 17% in the horizontal direction, and only 7% in the vertical direction. This is mainly due to the fact that in the organization of Al-6.3%Cu deposits after heat treatment, there are θ phases in the interlayer location that are distributed linearly, parallel to the deposit. The interlayer position is parallel to the vertical sample, so it has a greater influence on the vertical mechanical properties. As for the Al-5.6%Cu alloy deposit after heat treatment, there is no large θ phase in the interlayer position of the accumulation body. This is due to the decrease in Cu content, so the mechanical properties of the two directions are consistent, as shown in Fig. 6 . In addition, after reducing Cu content, it is found that the horizontal direction mechanical properties of the accumulation body do not decrease significantly. Conversely, the vertical direction mechanical properties are greatly improved. This is mainly due to the strengthening mechanism of the Al-Cu alloy. Specifically, the Cu atoms solid solution in the matrix precipitates strengthening phases in the aging process, and as the solid solution content of Cu in the deposits of the two alloys is basically the same, so the horizontal direction mechanical properties do not decrease significantly. There are no accumulated θ phases in the interlayer location of Al-5.6%Cu alloy deposits at T6 state, so the vertical direction mechanical properties are greatly improved. 3.5 Fracture morphologies The fracture morphologies of horizontal and vertical direction of Al-6.3%Cu and Al-5.6%Cu alloy deposits are shown in Fig. 10 . The horizontal direction fracture mode of the Al-6.3%Cu alloy accumulator is a typical ductile fracture, composed of a large number of dimples. At the bottom of the dimples, there are second phase particles less than 5 µm in size, as shown in Fig. 8 (a). The vertical direction fracture of the Al-6.3%Cu alloy deposit is primarily a brittle fracture accompanied by a small number of dimples. The whole fracture is covered by the second phase particles with sizes between 20–30 µm, and the crack extends from the second phase to the dimples, as shown in Fig. 8 (b). EDS energy spectrum shows that these second phase particles are Al 2 Cu, as shown B1 in Fig. 8 (b), indicating that the vertical direction fracture corresponds to the interlayer position of the deposit, and the unsolved large θ phases in the interlayer location result in poor vertical direction mechanical properties. It can be seen from Fig. 8 (c,d) that when the Cu content in the deposit decreases to 5.6%, the horizontal and vertical direction fractures are composed of a large number of dimples, which are ductile fractures. When the sample is stressed, cracks are first generated around the larger second phase particles, and then expand to the product body. Therefore, in order to obtain excellent mechanical properties, the number and size of the second phase particles should be controlled, and the Cu content should be strictly controlled for WAAM Al-Cu alloy deposits. 4 Conclusion In this paper, Al-6.3%Cu and Al-5.6%Cu alloy accumulations were formed by the WAAM process, and the microstructures in the as-deposited and heat treatment states, as well as the horizontal and vertical direction mechanical properties and fracture morphology were compared. The conclusions drawn are as follows: From the perspective of raw materials, it is determined that the Cu content in the raw materials is the cause of the difference between horizontal and vertical direction mechanical properties of WAAM Al-Cu alloy deposits . When the Cu content is 6.3%, there are concentrated precipitated phases in the interlayer location of the accumulation body in the as-deposited state. 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Mater Sci Eng A 191:185–191 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 01 Jun, 2024 Reviewers invited by journal 01 Jun, 2024 Editor invited by journal 29 May, 2024 Editor assigned by journal 20 May, 2024 First submitted to journal 18 May, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4392994","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":309355931,"identity":"0e782732-6e6f-4aea-b383-cd6486b19c9f","order_by":0,"name":"Shuai Wang","email":"","orcid":"","institution":"Inner Mongolia Metal Material Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Shuai","middleName":"","lastName":"Wang","suffix":""},{"id":309355932,"identity":"ed0231a1-7df3-48c7-832d-2a5aa666f278","order_by":1,"name":"Lingling Ren","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxElEQVRIiWNgGAWjYBACeWb2AwcSeNjk+NkbiNRi2M6TeOCDDJ+xZM8BYq05z2B8cIaNXOKGGQlE6mBsZkg4zJNjlrhB8vHGGww1NtEEtbAzMx44zHMmzXi7dFqxBcOxtNwGomzh7Tkmu3N2jpkEY8NhwloYDjMYHOb9959xw80zJGg5OIOHTXHDDR4itRg28yQc+MDDBgxkoF8SiPGLPP/xwx8gUXl4440PNTZEOAwJGEgkkKIcooVUHaNgFIyCUTAyAAA7zUEKB0o/aAAAAABJRU5ErkJggg==","orcid":"","institution":"Inner Mongolia Metal Material Research Institue","correspondingAuthor":true,"prefix":"","firstName":"Lingling","middleName":"","lastName":"Ren","suffix":""},{"id":309355933,"identity":"e485e137-6c8d-48fe-8199-653ec52431ec","order_by":2,"name":"lan yang","email":"","orcid":"","institution":"Jinxi Industry Group Co.LTD","correspondingAuthor":false,"prefix":"","firstName":"lan","middleName":"","lastName":"yang","suffix":""},{"id":309355934,"identity":"121db06f-89b0-48eb-9e34-a7ebb9af8d81","order_by":3,"name":"Zhu Ming","email":"","orcid":"","institution":"Inner mognolia metal material research institute","correspondingAuthor":false,"prefix":"","firstName":"Zhu","middleName":"","lastName":"Ming","suffix":""},{"id":309355935,"identity":"b36de4dd-bf09-4ccf-8c2f-526e577be1a9","order_by":4,"name":"Chengde Li","email":"","orcid":"","institution":"Inner Mongolia Metal Material Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Chengde","middleName":"","lastName":"Li","suffix":""},{"id":309355936,"identity":"fe42ed06-db33-4ce9-8a1d-b720ac5ebe41","order_by":5,"name":"Wei Wang","email":"","orcid":"","institution":"Inner Mongolia Metal Material Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2024-05-09 06:24:48","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4392994/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4392994/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":58389066,"identity":"684d94a2-733b-46b4-809d-616c2b45eb4e","added_by":"auto","created_at":"2024-06-14 19:43:16","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":28274,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Position definition of the deposits. (b) Sampling locations and additive manufacturing process.\u003c/p\u003e","description":"","filename":"F1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/3325c175262dc50a1016f981.jpg"},{"id":58389075,"identity":"3da71465-e711-4745-9b7d-720fcbcc9637","added_by":"auto","created_at":"2024-06-14 19:43:16","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":69767,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructures of Al-6.3%Cu and Al-5.6%Cu alloy depositsin the as-deposited state. (a) Intralayer location of Al-6.3%Cu alloy deposit. (b) Interlayer location of Al-6.3%Cu alloy deposit. (c) Intralayer location of Al-5.6%Cu alloy deposit. (d) Interlayer location of Al-5.6%Cu alloy deposit.\u003c/p\u003e","description":"","filename":"F2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/862e79f6ce172c0668dc6748.jpg"},{"id":58389067,"identity":"8f2c1945-e7b4-4413-859b-49258dc1b407","added_by":"auto","created_at":"2024-06-14 19:43:16","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":96954,"visible":true,"origin":"","legend":"\u003cp\u003eSEM and EDS of Al-6.3%Cu alloy and Al-5.6%Cu alloy deposits in as-deposited state. (a) Intralayer location of Al-6.3%Cu alloy deposit. (b) Interlayer location of Al-6.3%Cu alloy deposit. (c) Intralayer location of Al-5.6% alloy deposit. (d) Interlayer location of Al-5.6%Cu alloy deposit.\u003c/p\u003e","description":"","filename":"F3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/56a2cc6d5b3d3711f5eee33b.jpg"},{"id":58389173,"identity":"69e8ccb5-7f2f-4681-906f-c874c9513931","added_by":"auto","created_at":"2024-06-14 19:51:16","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":62121,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructures of Al-6.3%Cu and Al-5.6%Cu alloy depositsin T4 state. (a) Intralayer location of Al-6.3%Cu alloy deposit. (b) Interlayer location of Al-6.3%Cu alloy deposit. (c) Intralayer location of Al-5.6%Cu alloy deposit. (d) Interlayer location of Al-5.6%Cu alloy deposit.\u003c/p\u003e","description":"","filename":"F4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/32d62939c9d20a303b5dd43b.jpg"},{"id":58389175,"identity":"d3894824-a5a8-4f0e-b585-10ed7713581f","added_by":"auto","created_at":"2024-06-14 19:51:16","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":69474,"visible":true,"origin":"","legend":"\u003cp\u003eSEM and EDS of Al-6.3%Cu alloy and Al-5.6%Cu alloy deposits in T4 state.\u003c/p\u003e\n\u003cp\u003e(a) Intralayer location of Al-6.3%Cu alloy deposit. (b) Interlayer location of Al-6.3%Cu alloy deposit. (c) Intralayer location of Al-5.6%Cu alloy deposit. (d) Interlayer location of Al-5.6%Cu alloy deposit.\u003c/p\u003e","description":"","filename":"F5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/b16af88e5336a7be98833f29.jpg"},{"id":58389068,"identity":"51f1ee9d-ffb3-4f7e-b69a-5b3ab96bd160","added_by":"auto","created_at":"2024-06-14 19:43:16","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":71581,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructures of Al-6.3%Cu and Al-5.6%Cu alloy deposits in T6 state. (a) Intralayer location of Al-6.3%Cu alloy deposit. (b) Interlayer location of Al-6.3%Cu alloy deposit. (c) Intralayer location of Al-5.6%Cu alloy deposit. (d) Interlayer location of Al-5.6%Cu alloy deposit.\u003c/p\u003e","description":"","filename":"F6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/ec49bf6c32f58d10452c8aba.jpg"},{"id":58389074,"identity":"696e4d43-3d73-4e53-a6e4-d4d106996e8d","added_by":"auto","created_at":"2024-06-14 19:43:16","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":71514,"visible":true,"origin":"","legend":"\u003cp\u003eSEM of Al-6.3%Cu and Al-5.6%Cu alloy deposits in T6 state. (a) Intralayer location of Al-6.3%Cu alloy deposit. (b) Interlayer location of Al-6.3%Cu alloy deposit. (c) Intralayer location of Al-5.6%Cu alloy deposit. (d) Interlayer location of Al-5.6%Cu alloy deposit.\u003c/p\u003e","description":"","filename":"F7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/a53e040284e303b07007e0ea.jpg"},{"id":58389174,"identity":"316ca927-f869-44cf-9311-66954f7fd8da","added_by":"auto","created_at":"2024-06-14 19:51:16","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":64961,"visible":true,"origin":"","legend":"\u003cp\u003eTEM and HRTEM of Al-6.3%Cu and Al-5.6%Cu alloy deposits in T6 state. (a) Al-6.3%Cu alloy . (b) Al-5.6%Cu alloy. (c) Al-6.3%Cu alloy. (d) Al-5.6%Cu alloy.\u003c/p\u003e","description":"","filename":"F8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/f198b8b4aef80304d7ba1f9d.jpg"},{"id":58389072,"identity":"213b3ad0-5ac9-422f-9a32-effa79e9f20c","added_by":"auto","created_at":"2024-06-14 19:43:16","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":50528,"visible":true,"origin":"","legend":"\u003cp\u003eMechanical properties of Al-6.3%Cu and Al-5.6%Cu alloy depositsin T6 state.\u003c/p\u003e","description":"","filename":"F9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/fe911ee07b68006a555fcc08.jpg"},{"id":58389070,"identity":"3d0b917b-9694-40a2-b5ec-cb932536b57e","added_by":"auto","created_at":"2024-06-14 19:43:16","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":93026,"visible":true,"origin":"","legend":"\u003cp\u003eFracture morphologies of Al-6.3%Cu alloy and Al-5.6%Cu alloy deposits in T6 state. (a) Horizontal direction of Al-6.3%Cu alloy deposit. (b) Vertical direction of Al-6.3%Cu alloy deposit. (c) Horizontal direction of Al-5.6%Cu alloy deposit. (d)Vertical direction of Al-5.6%Cu alloy deposit.\u003c/p\u003e","description":"","filename":"F10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/ca990d654229819eb4b2efbb.jpg"},{"id":58389824,"identity":"07b22483-6f4b-4c41-814b-ea0592e0ca75","added_by":"auto","created_at":"2024-06-14 19:59:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1102136,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4392994/v1/d3047f63-cfc7-4d80-bf57-c9f93accd0c8.pdf"}],"financialInterests":"","formattedTitle":"Research on the differences of mechanical properties between horizontal and vertical in Al-Cu alloy deposits fabricated by wire + arc additive manufacturing","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eDue to its excellent mechanical properties,the Al-Cu alloy has a broad application prospect in the fields of aviation and aerospace \u003csup\u003e[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. However, due to the large crystallization temperature range of the alloy, casting products are prone to produce thermal cracking,segregation, shrinkage and other defects, resulting in a low casting yield\u003csup\u003e[\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. Additionally, the welding process cannot achieve equal strength between the base material and the welding seam, so it is difficult to produce high complexity products \u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. These limitations have restricted the use of Al-Cu alloys.\u003c/p\u003e \u003cp\u003eIn recent years, the production of Al-Cu alloy structural parts by the wire\u0026thinsp;+\u0026thinsp;arc additive manufacturing (WAAM) process has been widely studied \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. Gu \u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e examined the structure and properties of Al alloy 2219 deposits formed by the cold metal transfer (CMT) process, and found mechanical differences in the deposits between horizontal and vertical directions.Specifically, the mechanical properties in the vertical direction were smaller than those in the horizontal direction, especially the elongation rate. Cong et al. and Gu et al. investigated the distribution\u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e and formation mechanism\u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e of pores in the Al-6.3%Cu alloy wall fabricated by WAAM. The results showed interlayer porosity parallel to the accumulation layer, which was believed to be the reason for the differences in horizontal and vertical directions. However, These research results are not applicable to WAAMZL205A alloy and ZL114A alloy, which does not show a difference in the mechanical properties between horizontal and vertical directions of the deposits made through WAAM \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e.On the base of ZL205A alloy,Cd was replaced by Sn, the mechanical properties horizontal and vertical directions of the Al-Cu-Sn alloy deposits were still nuiform\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e.On the whole, the reasons for the difference in the horizontal and vertical directions of the Al-Cu alloy deposits fabricated by WAAM have not been clearly concluded, which limits the industrial application of this technology.\u003c/p\u003e \u003cp\u003eCu is the main strengthening element of Al-Cu series high-strength aluminum alloys. Its main function is to precipitate nanoscale θ (Al\u003csub\u003e2\u003c/sub\u003eCu) phases after heat treatment, with the phases improving the strength of the alloy. The content of Cu during solidification determines the size, quantity and distribution of primary Al2Cu, which has an important influence on the mechanical properties of Al-Cu alloy.Xu et al. \u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e studied the variation of microstructure and mechanical properties of 2219 ingots, and found that due to the different solidification sequence, the content of Cu gradually increased from the edge of the ingots to the center, with the mechanical properties tending to increase first and decrease later. Yu Fang \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e et al. studied the effect of Cu content on the size and distribution of the precipitated phase of Al-Cu alloy, and found that when Cu content in the alloy is low, the precipitation phenomenon in the structure is weakened and the anisotropy of the alloy is reduced. These studies indicate that Cu content has an important effect on the microstructure and properties of Al-Cu alloy, and may be a key factor affecting the transverse and longitudinal mechanical properties of Al-Cu alloy.\u003c/p\u003e \u003cp\u003eIn this paper, Al-6.3%Cu and Al-5.6%Cu alloys are used as raw materials, and the deposits are formed though the WAAM process. Among them, 6.3% is the typical Cu content of deformed Al-Cu alloy, and 5.6% is the maximum solid solubility of Cu in aluminum.This study aims to determine the reasons for the differences in the vertical and horizontal directions of Al-Cu alloy deposits. Specifically, the study analyzes the microstructure and properties of the deposits in different states in order to develop the materials suitable for the WAAM process, in addition to deposits with isotropic character,which has an important role in the application of this process.\u003c/p\u003e"},{"header":"2 Materials and Methods","content":"\u003cp\u003eThe 1.2-mm-diameter Al-Cu alloy welding wire used in this experiment was supplied by Fushun Donggong Metallurgy \u0026amp; Materials Technology Co., Ltd (Fushun, China). The chemical composition of the raw materials is shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A 2219 Al plate with a thickness of 10 mm was used as the deposition substrate.The chemical composition was measured by an electric spark direct-reading spectrometer, and the average value is measured at 5 points.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition of the raw materials\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMg\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCu\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eZr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eV\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl-6.3%Cu\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.115\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.036\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.291\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.274\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.136\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.163\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.112\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl-5.6%Cu\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.113\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.083\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.602\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.2271\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.124\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.165\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.110\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe additive manufacturing system consists of the Fronius TPS 4000 arc welding power supply and an ABB 1410 welding robot. The position definition of the deposits is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a). The interlayer position represents the overlap remelting zone between the two layers, and the intralayer position represents the non-remelting zone.\u003c/p\u003e \u003cp\u003eThe printing parameters are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Argon gas with a purity of 99.999% was used as the additive shield gas. The solution treatment temperature, solution treatment time, quenching temperature, ageing temperature, and ageing time of the T6 heat treatment process were 535 ℃, 360 min, 40 ℃, 180 ℃, and 120 min, respectively.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePrint parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eI/A\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eU/V\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eν\u003csub\u003eWFS\u003c/sub\u003e/\u003c/p\u003e \u003cp\u003em\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eν\u003csub\u003eTS\u003c/sub\u003e/\u003c/p\u003e \u003cp\u003em\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCool time\u003c/p\u003e \u003cp\u003e/s\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eGas flow/\u003c/p\u003e \u003cp\u003eML/min\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eA WDW-300 computerized electronic universal testing machine (Changcun,China)was used to conduct the mechanical performance tests. Furthermore, a LEICA MEF4M metallographic microscope and a QUANTA FEG 250 scanning electron microscope (SEM) were used for the structural and morphological observations. Energy-dispersive X-ray spectroscopy (EDS) was conducted for the elemental and phase analysis. The sampling locations and the machining shape of the mechanical samples are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b) where the dimensions of the wall are 200 mm \u0026times; 150 mm. The vertical and horizontal direction tensile samples were collected at locations 1 and 2 respectively, and the metallographic and transmission samples were collected at location 3. The tensile samples were processed into a plate structure with a gauge length of 30 mm and a cross-sectional area of 2.5 \u0026times; 10 mm\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Microstructure in as-deposited state\u003c/h2\u003e \u003cp\u003eThe microstructure of Al-6.3%Cu alloy and Al-5.6%Cu alloy deposits in the as-deposited state is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. As can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a), the intralayer organization of the Al-6.3%Cu deposit is homogeneous equiaxed crystals. The interlayer organization is also homogeneous equiaxed crystals, but the grain size is larger, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b). According to the heat dissipation characteristics of the WAAM process, each layer of deposit is solidified from the surface to the interior, and the sequence is as follows: surface, intralayer region, interlayer region. The grain size increases slightly due to the final solidification of the interlayer region. The same trend was observed in the microstructure of Al-5.6% alloy deposit, as can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c,d).\u003c/p\u003e \u003cp\u003eIt can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e that there are pores with diameters of 20\u0026ndash;30 \u0026micro;m in the interlayer region of Al-6.3%Cu and Al-5.6%Cu alloy deposits, which are larger in number and size than in the intralayer region. This trend in the two allow deposits is consistent with the research results of Cong et al. \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe pores in Al alloys are mainly hydrogen pores, because hydrogen is mutated during the solubility transformation from a liquid to a solid in Al. The nucleation rate of hydrogen pores is closely related to the grain size\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e, and they grow by self-diffusion and mergers. The interlayer location of the Al-Cu alloy has a larger grain size. Therefore, the nucleation probability of hydrogen pores is greater, and the solidification time of interlayer organization is longer, allowing hydrogen pores to grow through diffusion and mergers. There are more pores in the interlayer location given that the interlayer location is the final solidification area, and the overflow channel of the pores has been closed.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003cdiv class=\"Heading\"\u003e\u003c/div\u003e \u003cp\u003eIt can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a,b) that in the intralayer structure of the Al-6.3%Cu alloy deposit, the precipitated phases are distributed along the grain boundaries. Additionally, the segregated precipitated phases can be seen in the interlayer structure, distributed in a band parallel to the deposited layer. In the intralayer structure of the Al-5.6%Cu alloy deposit, the precipitated phases are also distributed along the grain boundaries, but the width of the grain boundaries is greatly reduced, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c). This indicates that the number of precipitated phases is reduced. The width of the grain boundary in the interlayer structure of the Al-5.6%Cu alloy deposit is larger than that in the intralayer, indicating that the number of precipitated phases has increased but without obvious segregation. In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e it can be seen from the SEM and EDS of the deposits that the precipitated phase on the grain boundary is mainly θ phase. In the intralayer position of the Al-6.3%Cu alloy deposit, the θ phase size is small and intermittently precipitates. The average Cu content in the region is 5.72% (mass fraction), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a). In the interlayer position, the θ phase is continuously precipitated and the size is significantly increased. The average Cu content in the region is 6.52% (mass fraction), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b). In the intralayer and interlayer of Al-5.6%Cu alloy deposits, the distribution trend of precipitated phases is the same as Al-6.3%Cu. Specifically, the number and size are greatly reduced, and the regional average Cu content in the intralayer and interlayer is 5.17% and 5.61%, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the WAAM Al-Cu alloy deposits, the difference in the distribution of the precipitated phases in the intralayer and interlayer locations is caused by microsegregation during the solidification process of the molten pool. The WAAM process has the characteristics of rapid solidification. From the solute change curve of the Al-Cu alloy solidification process, under such non-equilibrium solidification conditions, the Cu content in the Al solution gradually progresses as the solidification process proceeds \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. The Cu content in interlayers is larger than that in the intralayer location due to the solidification order of the deposit. This solidification characteristic of the Al-Cu alloy causes the Cu content to gradually increase from the edge of the ingot to the center, resulting in macrosegregation, which has been widely studied in the casting process \u003csup\u003e[\u003cspan additionalcitationids=\"CR21 CR22\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. WAAM is similar to the micro-casting process. Each layer is equivalent to a small-sized ingot. Following the solidification characteristics of the ingot, microsegregation occurs in the deposits.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Microstructure of deposits in T4 state\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the microstructure of Al-6.3%Cu and Al-5.6%Cu alloy deposits in T4 state. It can be seen from the figure that the grains of the deposits are all equiaxed crystals with uniform size due to the quenching and tempering effect. The grain size in intralayer locations is still smaller than that in interlayer locations due to the genetic effect of the alloy. There are two types of precipitated phases in the intralayer structure of Al-6.3%Cu alloy deposits at T4 state, small-sized black phases and larger-sized gray phases, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a). In the interlayer structure, there are also two types of precipitated phases, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b). However, the number of gray phases greatly increases, and the distribution is linear along the grain boundary. There are no large-scale gray precipitated phases found in the intralayer and interlayer microstructure of the Al-5.6%Cu alloy deposits at T4 state, only black phases that are dispersedly distributed along the grain boundaries.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs can be seen from the SEM and EDS of Al-6.3%Cu and Al-5.6%Cu alloy deposits in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The black phase in the metallographic structure is the remolded T phase (Al\u003csub\u003e12\u003c/sub\u003eMn\u003csub\u003e2\u003c/sub\u003eCu) containing a small amount of Fe impurity, and the gray phase is θ phase. The θ phases are not completely dissolved during the solid solution process. The size of the θ phase in the intralayer location of Al-6.3%Cu alloy deposit is about 10 \u0026micro;m, as shown by point A1 in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a), and the size of the θ phase in the interlayer location is about 20 \u0026micro;m, as shown by point B1 in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b). In the intralayer microstructure of Al-5.6%Cu alloy deposits in T4 state, there are θ phases smaller than 2 \u0026micro;m in size, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c) by point C1, while the size of θ phases in interlayer location is about 5 \u0026micro;m, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(d) by point D1. After T4 treatment there are θ phases with linear distribution in the interlayer location of Al-6.3%Cu alloy deposits, due to the partial accumulation of the θ phase in the interlayer location in the as-deposited state. This is evident from EDS analysis of area scanning and matrix point of deposit with difference Cu contents. In the intralayer location of Al-6.3%Cu alloy deposits at T4 state, the average area Cu content is 5.83%, while the Cu content in the matrix is 5.11%. In the interlayer location, the average area Cu content is 6.45%, and the Cu content in the matrix is 5.20%. In the intralayer location of the Al-5.6%Cu alloy deposit at T4 state, the average area Cu content is 5.15%, while the Cu content in the matrix is 5.01%. Conversely, in the interlayer location, the average area Cu content is 5.66%, and the Cu content in the matrix is 5.12%. After T4 treatment, the amount of Cu atom in solid solution to the matrix did not increase significantly, and mainly appeared as intermetallic compounds in the grain boundary. This is because the solid solution amount of Cu is determined by temperature. At the solid solution temperature (535℃) in this experiment, the ultimate solid solution of Cu in Al was 5.29%, then the remaining Cu was distributed in the grain boundary in the form of the θ phase \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e. As can be seen from the alloy phase diagram, the ultimate solid solubility of Cu in Al is 5.65% at 548℃. Therefore, under WAAM process conditions, when the Cu content in the alloy exceeds 5.65%, there will inevitably be θ phases on the grain boundaries after solid solution treatment. The higher the content of Cu, the greater the number and size of the θ phases, and the more accumulation occurs in the interlayer locations. The higher the Cu content in deposit in T4 state, the greater the number and size of θ phases, and the more enrichment that will occur in the interlayer locations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e(a) Intralayer location of Al-6.3%Cu alloy deposit. (b) Interlayer location of Al-6.3%Cu alloy deposit. (c) Intralayer location of Al-5.6%Cu alloy deposit. (d) Interlayer location of Al-5.6%Cu alloy deposit.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Microstructure of deposits in T6 state\u003c/h2\u003e \u003cp\u003eThe microstructures of Al-6.3%Cu and Al-Cu5.6 alloy deposits at T6 state are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e that the microstructures in the intralayer and interlayer locations of the deposits are equiaxed grains. The precipitated phases in the intralayer location of Al-6.3%Cu alloy deposits are the black T phases and the gray θ phases, as shown by points A1 and A2 in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a).The precipitated phases in the interlayer position are also the black T phases and gray θ phases, as shown by points B1 and B2 in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b). However, the number and size of θ phases are significantly larger than those in the intralayer, and they are linearly distributed along the grain boundary. It can be seen from Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c,d) that after T6 treatment of the Al-5.6%Cu alloy deposit, the precipitation phases in the intralayer and interlayer regions are consistent, where both are black T phases, and no θ phases can be seen. The size and distribution of the θ phases at the grain boundaries have a significant impact on the mechanical properties of the alloy \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. The θ phases, which are linearly distributed in the interlayer location of Al-6.3%Cu alloy deposits, are the starting position under stress as they are large intermetallic compounds, thereby reducing the mechanical properties of the alloy.The larger θ phases exist as intermetallic compound particles. It is found that the brittle fracture of grain boundary particles is an important reason for crack initiation. When the particle spacing is small, the stress fields caused by the interaction between adjacent particles promotes crack initiation.When the number of θ phases is large, the macroscopic shear zones formed in the microstructure accelerates the crack growth\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e, so the un-dissolved θ phases in the Al-Cu6.3% deposits will reduce the mechanical properties of the alloy.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e\u003c/h3\u003e\n\u003cdiv class=\"Heading\"\u003e\u003c/div\u003e \u003cp\u003eThe precipitated phases in intralayer location and interlayer location of Al-Cu6.3 alloy and Al-Cu5.6 alloy deposits in T6 state are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. After the aging process, the type, quantity, size and distribution of precipitated phases in intralayer location and interlayer location of Al-Cu6.3 and Al-Cu5.6 alloys have not changed. There is an unsolvable θ phase with a size of about 5 \u0026micro;m in the Intralayer location of Al-Cu6.3 alloy, and the distribution is uniform. In interlayer location, a large number of unsolvable θ phases, larger than 20 \u0026micro;m in size, are still densely distributed along the grain boundaries parallel to the deposition direction, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e (b). The Cu content in the deposit is reduced to 5.6%, and the unsolvable θ phase in the intralayer location and interlayer location does not accumulate, and the size is less than 5\u0026micro;m.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe precipitated phases in the T6-state at room temperature in grain of Al-Cu6.3 alloy and Al-Cu5.6 alloy deposits are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. As can be seen from the figure, in the T6 state of the two alloy deposits, a large number of acicular precipitates are separated out inside the grains, the size of which is less than 500nm long and 5nm wide. As can be seen by HRTEM, this phases are semi-cogrid with the matrix. This phase is the main strengthening phase θ\u003csup\u003e,\u003c/sup\u003e phase \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e in the peak aging state of Al-Cu alloy. Its transverse and longitudinal distribution can effectively hinder the dislocation movement and is the key to improving the mechanical properties of Al-Cu alloy. The phase size, distribution density and phase spacing of the two alloys have no change. Due to θ\u003csup\u003e,\u003c/sup\u003e the phase precipitation process is as follows: susaturated solid solution (α\u003csub\u003ess\u003c/sub\u003e) \u0026rarr;GP region (GPⅠ region) \u0026rarr;θ\u003csup\u003e, ,\u003c/sup\u003e (GPⅡ region) \u0026rarr;θ\u003csup\u003e,\u003c/sup\u003e phase \u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e. The primary θ is dissolved in aluminum matrix by solution treatment to form a supersaturated solid solution of Cu atoms. During the aging process, Cu atoms are biased to form GP region, and then gradually grow to form θ\u003csup\u003e,\u003c/sup\u003e phase. From the precipitation process of θ\u003csup\u003e,\u003c/sup\u003e phase, it can be seen that the Cu atom content in solid solution in Al matrix is the key to determine the quantity of θ\u003csup\u003e,\u003c/sup\u003e phase. Although the Cu content of the two alloys is different, the Cu content in solid solution is basically constant, so the θ\u003csup\u003e,\u003c/sup\u003e phases are basically constant, reflecting that the upper limit mechanical properties of the two alloys are at the same level.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Mechanical properties\u003c/h2\u003e \u003cp\u003eMechanical properties of Al-6.3%Cu alloy and Al-5.6%Cu alloy deposits in T6 state are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. As can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, there are significant differences between the horizontal and vertical directions of Al-6.3%Cu alloy deposits, and the mechanical properties of the horizontal direction are higher than that of the vertical direction. In particular, the elongation is 17% in the horizontal direction, and only 7% in the vertical direction. This is mainly due to the fact that in the organization of Al-6.3%Cu deposits after heat treatment, there are θ phases in the interlayer location that are distributed linearly, parallel to the deposit. The interlayer position is parallel to the vertical sample, so it has a greater influence on the vertical mechanical properties. As for the Al-5.6%Cu alloy deposit after heat treatment, there is no large θ phase in the interlayer position of the accumulation body. This is due to the decrease in Cu content, so the mechanical properties of the two directions are consistent, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. In addition, after reducing Cu content, it is found that the horizontal direction mechanical properties of the accumulation body do not decrease significantly. Conversely, the vertical direction mechanical properties are greatly improved. This is mainly due to the strengthening mechanism of the Al-Cu alloy. Specifically, the Cu atoms solid solution in the matrix precipitates strengthening phases in the aging process, and as the solid solution content of Cu in the deposits of the two alloys is basically the same, so the horizontal direction mechanical properties do not decrease significantly. There are no accumulated θ phases in the interlayer location of Al-5.6%Cu alloy deposits at T6 state, so the vertical direction mechanical properties are greatly improved.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Fracture morphologies\u003c/h2\u003e \u003cp\u003eThe fracture morphologies of horizontal and vertical direction of Al-6.3%Cu and Al-5.6%Cu alloy deposits are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. The horizontal direction fracture mode of the Al-6.3%Cu alloy accumulator is a typical ductile fracture, composed of a large number of dimples. At the bottom of the dimples, there are second phase particles less than 5 \u0026micro;m in size, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a). The vertical direction fracture of the Al-6.3%Cu alloy deposit is primarily a brittle fracture accompanied by a small number of dimples. The whole fracture is covered by the second phase particles with sizes between 20\u0026ndash;30 \u0026micro;m, and the crack extends from the second phase to the dimples, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(b). EDS energy spectrum shows that these second phase particles are Al\u003csub\u003e2\u003c/sub\u003eCu, as shown B1 in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(b), indicating that the vertical direction fracture corresponds to the interlayer position of the deposit, and the unsolved large θ phases in the interlayer location result in poor vertical direction mechanical properties. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(c,d) that when the Cu content in the deposit decreases to 5.6%, the horizontal and vertical direction fractures are composed of a large number of dimples, which are ductile fractures. When the sample is stressed, cracks are first generated around the larger second phase particles, and then expand to the product body. Therefore, in order to obtain excellent mechanical properties, the number and size of the second phase particles should be controlled, and the Cu content should be strictly controlled for WAAM Al-Cu alloy deposits.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eIn this paper, Al-6.3%Cu and Al-5.6%Cu alloy accumulations were formed by the WAAM process, and the microstructures in the as-deposited and heat treatment states, as well as the horizontal and vertical direction mechanical properties and fracture morphology were compared. The conclusions drawn are as follows:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eFrom the perspective of raw materials, it is determined that the Cu content in the raw materials is the cause of the difference between horizontal and vertical direction mechanical properties of WAAM Al-Cu alloy deposits .\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eWhen the Cu content is 6.3%, there are concentrated precipitated phases in the interlayer location of the accumulation body in the as-deposited state. After heat treatment, there are a large number of precipitated phases larger than 20 \u0026micro;m that are distributed linearly along the grain boundary, resulting in uneven horizontal and vertical direction mechanical properties.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eWhen the Cu content is 5.6% in the microstructure of the intralayer and the interlayer locations, the precipitated phases do not appear to be biased. Furthermore, there are no large precipitated phases after heat treatment, with consistent horizontal and vertical direction mechanical properties.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe advice and assistance provided by Wei Wang and Zhu Ming from Inner Mongolia Metal Material Research Institute are greatly appreciated.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLiu J, Kulak M (2000) A new paradigm in the design of aluminum alloys for aerospace applications [J]. 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Mater Sci Eng A 191:185\u0026ndash;191\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Al-Cu alloy, wire + arc additive manufacturing, microstructure, horizontal and vertical differences","lastPublishedDoi":"10.21203/rs.3.rs-4392994/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4392994/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAl-Cu alloy made by arc fuse additive has excellent microstructure and properties, but the difference between transverse and longitudinal is the key factor limiting its application.In this experiment, Al-Cu alloy deposits with different Cu contents were formed by the wire\u0026thinsp;+\u0026thinsp;arc additive manufacturing (WAAM) process used Al-Cu welding wire with different Cu content.The microstructure and properties of the deposits,both intralayer and interlayer,were analyzed using metallography, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and tensile tests.The results showed that the interlayer content of Cu is higher than that in the intralayer. When Cu content in the deposit was 6.3% in the as-deposited state, there was an enhanced θ (Al\u003csub\u003e2\u003c/sub\u003eCu) precipitate phase in the interlayer position. After T4 treatment, there were still θ phases with a size larger than 20 \u0026micro;m, which were linearly distributed parallel to the accumulation layer. These θ phases led to lower mechanical properties in the vertical direction than in the horizontal direction, with a brittle fracture mode. When the Cu content of the deposit was reduced to 5.6% after T4 treatment, there were no large θ phases in the interlayer position. Furthermore, the mechanical properties of horizontal and vertical directions were consistent, and they had a ductile fracture mode.The Cu content in the deposit was the primary reason for the difference in mechanical properties between horizontal and vertical directions. Al-Cu alloy deposits with uniform mechanical properties in the horizontal and vertical directions can be obtained by controlling the Cu content,which has an important role in the application of this process.\u003c/p\u003e","manuscriptTitle":"Research on the differences of mechanical properties between horizontal and vertical in Al-Cu alloy deposits fabricated by wire + arc additive manufacturing","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-14 19:43:11","doi":"10.21203/rs.3.rs-4392994/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-06-01T09:32:33+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-01T09:01:40+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Welding in the World","date":"2024-05-29T13:55:54+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-20T10:07:47+00:00","index":"","fulltext":""},{"type":"submitted","content":"Welding in the World","date":"2024-05-19T02:11:45+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d19677a4-3504-4628-a1ce-74557300d6e4","owner":[],"postedDate":"June 14th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-09-22T06:19:19+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-14 19:43:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4392994","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4392994","identity":"rs-4392994","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}