Formability of AA6061- AA2017 dissimilar FSW joints: effects of weld passes, material positioning, and post-weld shot peening

Abstract Lightweight structural components in automotive and aerospace industries often undergo complex forming operations, making formability a critical factor in their performance. However, achieving high formability in friction stir-welded (FSW) dissimilar aluminium alloys remains a significant challenge due to variations in material properties and weld characteristics. This study aims to investigate the formability enhancement of such joints through optimized welding and surface treatment techniques like shot peening (SP). Experimental and simulation-based approaches were employed to examine the effects of weld pass number (i.e., single and double passes), base material positioning, and post-weld SP on formability. Welding was carried out under constant, optimized parameters, and experimental formability was evaluated using the Limiting dome height (LDH) test, while simulations were performed using ANSYS Workbench. The tailor-welded blanks (TWBs) were divided into five different zones to accurately analyse strain distribution and forming limits. Results revealed that double-pass friction stir welding (DP-FSW) combined with SP significantly improved formability, with less than ±5% deviation between experimental, simulated LDH values and load. The U-turn double-pass FSW combined with SP enhanced the limiting dome height from 23.5 mm to 33.7 mm, yielding a 43.4% improvement in formability. Overall, the study demonstrates that integrating DP- FSW and post-weld SP effectively enhances the strength and formability of dissimilar aluminium TWBs, making them suitable for advanced lightweight structural applications.