Microstructure of AJ62 magnesium alloy after long-term annealing

Abstract

The paper presents results of SEM investigations of AJ62 magnesium alloy in as cast condition and after long-term annealing. The AJ62 contains approximately 6% aluminum and about 2,5% strontium. The Mg-Al-Sr alloys exhibit good elevated-temperature tensile properties, excellent creep resistance (better than Mg-Al-RE) and good castability [1]. The alloys have also Zn, Si And Mn. Strontium is added for creep resistance in die casting and gravity casting alloys or to reduced shrinkage porosity. Sr level may range from 0,02% to 3% [2]. The Mg-Al-Sr alloys (AJ52, AJ62) show different microstructure based on the Sr/Al ratio. For Sr/Al ratio below 0.3, the microstructure consists of α-Mg with precipitates of Al₄Sr phase. When the Sr/Al ratio increases, a second intermetallic phase (probably Al₃Mg₁₃Sr) is observed together with Al₄Sr phase. This ratio also controls the precipitation of Mg₁₇Al₁₂ phase. When Sr/Al ratio is very low this phase occur in the α-Mg matrix [3,4].