Microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy during equal channel angular pressing

Abstract

The homogenized Mg-13Gd-4Y-2Zn-0.6Zr alloy was subjected to different equal channel angular pressing (ECAP) passes to investigate the effect of long period-stacking order (LPSO) phase on microstructure evolution and mechanical properties. The heterogeneous bimodal microstructure can be obtained due to the inhibition effect of intragranular 14H-LPSO phase on dislocation slip and lattice rotation at early stage. The intragranular 14H-LPSO phase was kinked and broken, which facilitate the transformation from LAGBs to HAGBs and subdivision of the deformed grains. Furthermore, the interdendritic 14H-LPSO phase was crushed and broken with further ECAP passes, which contribute to the dynamic recrystallization (DRX) process at grain boundaries via particle-stimulated nucleation (PSN) mechanism. The microstructure after 3p-ECAP demonstrates finer randomly oriented dynamic recrystallization (DRX) grains, broken 14H-LPSO phase at grain boundaries and precipitated intragranular lamellar 14H-LPSO phase. In addition, the alloy after 3p-ECAP exhibits the ultimate tensile strength of 361 MPa, tensile yield strength of 197 MPa and fracture elongation of 9.3%. The elevated temperature ultimate tensile strength after 3p-ECAP exceeds 300 MPa at test temperature of 300 ℃ and strain rate of 0.001/0.003 s−1, which can be ascribed to the broken 14H-LPSO phase at grain boundaries and precipitated lamellar 14H-LPSO phase within DRX grains.