Effect of variable temperature repetitive upsetting-extrusion on microstructure and texture of Mg-Gd-Y-Zr alloy

Abstract

The Mg-Gd-Y-Zr alloy was subjected to the variable temperature repetitive upsetting-extrusion process, a kind of severe plastic deformation. The evolution of microstructure, texture and deformation mechanism under different passes was analysed. It is found that when the deformation temperature was relatively high at 420℃, the morphology of the grains was approximately equiaxed. Some precipitated phases were distributed at the grain boundaries and the fraction of them was relatively low. When the deformation temperature was decreased, the precipitation phases increased remarkably, playing the pinning effect and stimulate the particle stimulated nucleation (PSN) mechanism to significantly refine the grain. As the number of deformation passes increased, The grains were remarkably refined from the 80.45 μm of initial billet to 4.08 μm of 4-pass sample, gaining the more uniform microstructure. With the increase of deformation amount, the coarse grains decreased with the fraction of dynamic recrystallization increased and secondary dynamic recrystallization occurred inside the grown dynamic recrystallized grains. The (1010) fiber texture disappeared and the texture was weakened. The random of the high-temperature deformation texture was obvious due to the non-basal slip of alloy which was easier to activate.