Effect mechanism of serrated joint design on microstructure and mechanical properties of AA2024 and AA7075 alloy friction stir welding

In this study, three different parameters of the serrated joint interface design are proposed to improve the strength of the joint,and the relationship between joint design and mechanical properties was studied in detail. In addition, the influence of joint design on welding was also studied.The results show that the joint strength increases first and then decreases with the increase of the width of the serrated joint. When the width of serrated joint is 1.5mm, the ultimate tensile strength of the joint is the highest (383Mpa). With the width of the serrated joint increases, the effective load bearing area increases and the energy caused by work hardening increases. When the width of the joint is too wide, defects such as holes will occur at the bottom of the material, ultimately resulting in decreased strength.In addition, the number of fine hook structures formed at the interface is related to the width of the joint design. The wider the width of the serrated joint, the more hook structures are formed.