Effects of tool translation direction and tool rotation direction on mechanical and metallurgical properties of two-pass FSW joint of dissimilar AA6061-T6 and AA7075-T6 alloys

Abstract In the current research, the experimental investigation of the Friction Stir Welding (FSW) of two dissimilar aluminum alloys, AA6061-T6 and AA7075-T6, was done. The effect of three parameters, the number of welding passes, the tool translation direction in the second pass, and the tool rotation direction in the second pass, on the tensile properties, microhardness, and microstructure of the joint was carried out. Based on the results, the value of UTS and the elongation percentage of the welded samples are significantly dependent on the number of welding passes, the tool translation direction in the second pass, and the tool rotation direction in the second pass. Adding a secondary pass significantly increased the tensile strength of the welding samples. All samples welded with two passes experienced higher strength and elongation than the singlepass welded sample. The highest tensile strength belonged to TP-D sample. The TP-D sample experienced a 44% increase in tensile strength compared to the CF sample, and the tensile strength efficiency of this sample compared to the softer alloy (AA6061-T6) was equal to 89.6%. Also, the highest elongation percentage belonged to TP-D, TP-B, TP-C, TP-A, and CF samples, respectively. Regardless of the placement of dissimilar alloys on the Advancing side (AS) and Retreating side (RS), the number of welding passes, the tool translation direction in the second pass, and the tool rotation direction in the second pass, the lowest hardness values in all samples occurred in the HAZ region. It was found that the increase in the number of welding passes increased the microhardness in different weld areas. The highest and lowest average hardness belonged to the TP-D and CF welded samples, respectively.