Semisolid microstructure evolution of the predeformed AZ91D alloy during heat treatment

The semisolid microstructure evolution process of the predeformed AZ91D alloy during heat treatment was studied. After being compressed by a ratio of 20.6% in height at 220 °C, all the dendrites oriented in the same way. With increasing heat-treatment temperature, the dissolution of eutectic β-Mg17Al12 first took place, resulting in the primary dendritic grains coarsening into interconnected non-dendritic grains. With heating continuously, a large amount of polygon recrystallization grains occur in the microstructure. Subsequently, the residual interdendritic β-Mg17Al12 at the edges of the primary grains and the new recrystallization grains melted in succession at higher heat-treatment temperature and the primary grains separated into small polygon grains. After being heat-treated at the semisolid temperature, the amount of liquid increased until the solid-liquid system reached its equilibrium state, and the grains spheroidized.