Double side friction stir welding of AA6082 sheets: Microstructure and nanoindentation characterization

Friction stir welding (FSW) of aluminum alloys is currently used in modern automotive and transportation industry. The welded sheets must possess adequate elastic-plastic response and formability levels similar to that of the base alloy sheet. In the last few years different FSW processing and configurations have been proposed. In this study, a double side friction stir welding (DS-FSW) process was compared to conventional pin and pinless FSW of AA6082 sheet. The microstructure modifications and the local mechanical response, namely, hardness and elastic modulus, were here investigated. Nanoindentation was used to mechanically characterize the different welded zones of interest, the thermomechanical heat affected zone (TMAZ), the stirred zone (SZ), in the advancing and the retreating side, at different sheet section depths. The better microstructure uniformity, at the stirred zone, and the closer hardness and elastic modulus values to those of the base metal can explain the better formability showed by the DS-FSW, with respect to the conventional FSW.