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 alpha-Mg, AI(11)RE(3) and Al10RE2Mn7 intermetallic phases. Additionally, due to non-equilibrium solidification conditions, a small amount of alpha + gamma 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 gamma (Mg17Al12) secondary precipitation process took place in areas enriched in aluminium during solidification. The gamma secondary precipitates were mainly observed in the interdendritic regions and around the alpha + gamma eutectic. (C) 2015 Elsevier B.V. All rights reserved.