Microstructural evolution and hot tensile behavior of Mg?3Zn?0.5Zr alloy subjected to multi-pass friction stir processing
The microstructures and hot tensile behaviors of ZK30 alloys subjected to single-and multi-pass friction stir processing (FSP) were systematically investigated. Following single-pass FSP (S-FSP),coarse grains underwent refinement to 1−2 μm,with a distinct basal texture emerging in the stir zone (SZ). Additionally,second-phase particles were fragmented,dispersed,and partially dissolved. Multi-pass FSP (M-FSP) further enhanced the homogeneity of the microstructure,reduced texture intensity differences,and decreased the fraction of second-phase particles by 50%. Both S-FSP and M-FSP SZs demonstrated superplasticity at strain rates below 1×10−3 s−1 and at temperatures of 250−350 ℃. The S-FSP SZ exhibited an elongation of 390% at 250 ℃ and 1×10−4 s−1,while the M-FSP SZ achieved an elongation of 406% at 350 ℃ and 1×10−3 s−1. The superplastic deformation of SZ was co-dominated by grain boundary sliding (GBS) and the solute-drag mechanism in S-FSP and mainly by GBS in M-FSP.