Effect of Slow Solidification Rate on Microstructure of AZ91D Magnesium Alloy

In order to discuss the microstructure under slower cooling rate of as-cast AZ91D magnesium alloy,the slow solidification treatment was carried out. The solidification process of AZ91D and the reason of dendritic segregation decreasing in slow solidification were analyzed using metal solidification principle. The results indicate that with the decrease of cooling rate, the form of β-Mg17Al12 phase gradually changes from the continuous network distribution to intermittent bit or strip distribution along the grain boundary, the dendrites segregation reduces. The cooling rate achieves 0.003 0 K/s, the volume fraction of β is 2%, but the grains grow up remarkably.