Experimental investigation and process parameter optimization of simultaneous staggered double-sided friction stir welding

This paper presents a novel simultaneous staggered double-sided friction stir welding technique, which offers a new approach for joining thick plates. The purpose of this study is to experimentally analyze the simultaneous staggered double-sided friction stir welding and to optimize its process parameters. This study conducts welding experiments on 12 mm-thick AA6061-T6 aluminum alloy plates using the SSDS-FSW technique. The macroscopic morphology of the joint cross-section shows that SSDS-FSW enables complete joining of thick plates. The effects of rotational speed, welding speed, and the unique offset distance of this technique on the mechanical properties are investigated. Result shows the tensile strength of SSDS-FSW joints initially increases and then decreases with increasing rotational speed, and shows a similar trend with welding speed. In contrast, increasing the offset distance leads to a continuous decrease in tensile strength. Elongation also first increases and then decreases with rotational speed, but decreases steadily as welding speed and offset distance increase. Finally, multi-objective optimization of process parameter is conducted using Taguchi experimental design and grey relational analysis. Result indicates that the joint achieves optimal mechanical properties at a rotational speed of 800 r/min, a welding speed of 150 mm/min, and an offset distance of 4.5 mm. Experimental verification confirms that, the joint exhibits a tensile strength of 231 MPa and an elongation of 13.55%. The results indicate that simultaneous staggered double-sided friction stir welding not only has the capability to weld thick plates, but also produces joints without any incomplete penetration regions.