Microstructure of Mg-5Al-0.4Mn-xRE (x = 3 and 5 wt.%) alloys in as-cast conditions and after annealing

The microstructure investigations of two AME503 and AME505 experimental alloys in as-cast conditions and after long-time annealing were presented. The investigated materials were fabricated on the basis of the AM50 commercial magnesium alloy with 3 and 5 wt.% cerium rich mish metal. Analyses of the alloy microstructures were carried out by light microscopy, XRD, scanning and transmission electron microscopy. In as-cast conditions both the alloys were mainly composed of α-Mg, Al11RE3 and Al10RE2Mn7 intermetallic phases. Additionally, due to non-equilibrium solidification conditions, a small amount of α + γ divorced eutectic and Al2RE intermetallic phase were revealed. Long-time annealing at 473 K for 1000 h did not change the above main structural constituents. During annealing, the γ (Mg17Al12) secondary precipitation process took place in areas enriched in aluminium during solidification. The γ secondary precipitates were mainly observed in the interdendritic regions and around the α + γ eutectic.