Effect of rolling on the microstructure and mechanical properties of 6061-T6 DS-FSW plate

In this investigation, the 6061-T6 double-side friction stir welding (DS-FSW) plates with a thickness of 6 mm were rolled to different thickness. The microstructural evolution during rolling process was systematically studied based on the technologies of XRD, EBSD and TEM. The tensile test showed the evolution of yield strength (YS), ultimate tensile strength (UTS) and elongation during rolling process. The results revealed that the deformation mechanism of stirring zone (SZ) during rolling was grain rotation of fine grain. It contributed to a weaker dislocation density improvement in SZ. For the strengthening effect, all of the grain refine strengthening, precipitating strengthening, and solid solution strengthening of SZ were stronger than those in base metal (BM). However, the poor dislocation strengthening effect of SZ resulted in its lower YS compared with that of BM. The fracture of SZ depended on the debonding of plastic flow layers. The special fracture mode determined the lower UTS and elongation of SZ compared with those of BM.