Semisolid microstructure evolution of the predeformed AZ91D alloy during heat treatment

Abstract

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-Mg 17Al 12 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-Mg 17Al 12 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.