Effect of La2O3 addition on the microstructure of partially remelted Mg-9Al-1Zn alloy.

The effect of La2O3 addition on the microstructure of partially remelted Mg-9Al-1Zn (AZ91D) alloy was studied. The results indicate that small amounts of La2O3 additions to AZ91D alloy refined the partially remelted microstructure and caused the formation of new phase- LaAl4 in the microstructure. Moreover, the grain size of the partially remelted alloys is decreased with the increasing of La2O3 addition. In as-cast microstructure the LaAl4 phases have two morphologies: needle-like and particle-shape. The presence of more LaAl4 phases, especially, the particle-shape LaAl4 which dispersedly distributed within the grains can induce more dislocations, which can result in the occurring of a large amount of recrystallizations. Moreover, these LaAl4 phases can also restrain the growth and combination of the recrystallizations and partially remelted initial grains during the subsequent heat-treatment. [ABSTRACT FROM AUTHOR]