The effect of Al_8Mn_5 intermetallic particles on grain size of as-cast Mg—Al—Zn AZ91D alloy

摘要

Al_8Mn_5 intermetallic particles are usually present in most of commercial Mg–Al based alloys. In recent years, the ability for the Al_8Mn_5 particles to act as potent nucleation sites for the α-Mg grains during the solidification of the Mg–Al alloys has been the subject of debate. In this work, the effect of Al_8Mn_5 particles on grain size of an Mg-9Al-1Zn (AZ91D) alloy was assessed. The experimental result from two AZ91D alloys with different Mn concentrations, i.e., 0.02 wt.% and 0.22 wt.% respectively, indicated that the grain size did not show any notable change. Further, high resolution transmission electron microscopy (HRTEM) was conducted on samples with concentrated Al_8Mn_5 particles collected by pressurised filtration of the AZ91D alloy melt. The extensive TEM examination on the Al_8Mn_5/α-Mg interfaces revealed no crystallographic orientation relationship (OR) between the Al_8Mn_5 and α-Mg crystals. It is therefore concluded that Al_8Mn_5 particles are unlikely to act as effective nucleation sites for the α-Mg during solidification of Mg–Al based alloys.