Unveiling the microstructure evolution and deformation mechanisms of micro-alloying Mg-1.5Zn-0.5Zr-0.5Sr alloy via extrusion-shearing

Obtaining high strength without sacrificing ductility in Mg alloys is of great importance. However, the hexagonal close-packed crystal structure critically limits the deformation of Mg alloys. In this work, novel Mg-1.5Zn-0.5Zr0.5Sr (wt.%) alloys were fabricated through homogenization, direct extrusion (DE), and extrusion-shearing (ES) processes. The effects of three different processes on microstructures, texture, and mechanical properties were thoroughly investigated. The results show that the average grain size of the alloy was greatly refined after hot extrusion. The alloy after the DE process exhibited a typical bimodal microstructure with dynamic recrystallized (DRXed) grains showing a strong < 1010 > fiber texture parallel to extrusion direction (ED), while the smallsized unDRXed grains showed relatively weak basal texture. In addition, the strength was significantly improved, with the value of yield strength (YS) reaching -229 MPa and ultimate tensile strength (UTS) reaching -262 MPa. This is mainly attributed to grain boundary strengthening and dislocation strengthening. Compared to the DE-processed alloy, the basal texture intensity was significantly decreased and non-basal slip was activated after the ES process, which indicates that the shearing deformation during ES could improve the ductility, with the fracture elongation (FE) increased from -13.9 % to -21.4 %. This work aims to unveil the deformation mechanisms in Mg-1.5Zn-0.5Zr-0.5Sr alloy and provides an efficient way for preparing micro-alloying Mg alloys with low cost and significant improvement of comprehensive properties.