Effect of Partially Substituting Ca with Mischmetal on the Microstructure and Mechanical Properties of Extruded Mg–Al–Ca–Mn-Based Alloys

Abstract

Mg-2Al-1.2Ca-0.2Mn (at%)-based alloys with Ce-rich mischmetal (MM) substitution of 0–0.6 at% for Ca were hot extruded at 400 °C. The effect of MM substitution on the microstructure and mechanical properties of the extruded alloys was investigated. The as-cast Mg-2Al-1.2Ca-0.2Mn alloy is mainly composed of α-Mg, Mg₂Ca and (Mg,Al)₂Ca phases and Al₈Mn₅ precipitates, whereas the substitution of MM brings about the formation of Al₁₁MM₃, Al₂MM phases and Al₁₀MM₂Mn₇ particles with the absence of (Mg,Al)₂Ca phase. The volume fraction of MM-containing phases increases with increasing MM contents. All of the extruded alloys exhibit bimodal microstructure comprising fine dynamically recrystallized grains with almost random orientation and coarse deformed grains with strong basal texture. Dense nanosized planar Al₂Ca and spherical Al–Mn phases precipitate inside the deformed grains. High tensile yield strengths of ~ 350 MPa and moderate elongations to failure of > 12% are obtained in all extruded alloys; the MM substitution induces negligible difference in the tensile properties at ambient temperature, while the highest MM substitution improves the strength at 180 °C due to the better thermal stability of the fragmented MM-containing phases.