Microstructure evolution maps of AZ31 and AZ91–Ca–Y–MM alloys under precompression and subsequent annealing conditions

This study establishes the microstructure evolution maps of a commercial AZ31 alloy and a recently developed Mg–9Al–0.8Zn–0.9Ca–0.6Y–0.5MM (AZXWMM91100) alloy on the basis of their microstructural variations with precompression amount and subsequent annealing temperature. The fully twinned microstructure of precompressed samples of the AZ31 alloy remains unchanged after annealing at 200 °C. At annealing temperatures above 225 °C, the area fraction of twin-free grains gradually increases with increasing precompression amount and annealing temperature. The microstructure evolution map of the AZ31 alloy consists of three regions: those with a fully twinned grain structure, partially twinned grain structure, and completely twin-free grain structure. The twinned microstructure of precompressed samples of the AZXWMM91100 alloy remains unchanged after annealing even at 250 and 300 °C. At annealing temperatures above 350 °C, the microstructure drastically changes from a fully twinned microstructure to a completely twin-free microstructure irrespective of the precompression amount. Consequently, the microstructure evolution map of the AZXWMM91100 alloy does not include the region with the partially twinned grain structure. The large amount of Al solute atoms and numerous second-phase particles in the AZXWMM91100 alloy inhibit grain-boundary movement during annealing, which results in the different microstructural evolution behavior with the AZ31 alloy.