Microstructual evolution of AZ80 magnesium alloy during multi-directional compression deformation at elevated temperature

Abstract

Microstructural evolution of AZ80 magnesium alloy during multi-directional compression deformation at elevated temperature was systematically investigated. The effects of deformation variables on the as-compressed microstructures and the deformation behavior were analyzed. Grain splitting that developed in various directions due to the formation of microbands was the main characteristic of microstructural evolution during hot multi-directional compression, which was different from that of the continuous uniaxial compression. Such microbands intersected each other, resulting in continuous subdivision of the coarse grains into misoriented fine domains, thus contributing to grain refinement. Further deformation led to increases in the number and misorientation of these boundaries and finally almost full development of fine equiaxed grains at high strain. A more homogeneous microstructure with fine dynamic recrystallization grains could be attained with the applied strain up to a critical strain, and after that, it was difficult to achieve further grain refinement. However, the higher reduction in each pass and the lower deformation temperature in the certain range aided grain refinement. The second phase Mg ₁₇Al ₁₂ with large particle size that remained after solution treatment experienced a series of changes with the process of breaking up, dissolving, precipitating and then re-dissolving. Fine precipitates were located at the grain boundaries, suppressing dislocation movement and preventing grain growth.