Microstructures and mechanical properties of Mg-Al-Sm series heat-resistant magnesium alloys

The microstructures and phase compositions of the as-cast and die-cast Mg-6.02Al-1.03Sm, Mg-6.05Al-0.98Sm-0.56Bi and Mg-5.95Al-1.01Sm-0.57Zn alloys were investigated. Meanwhile, the tensile mechanical and flow properties were tested. The results show that the as-cast microstructure of Mg-6.02Al-1.03Sm alloy is composed of alpha-Mg matrix, discontinuous beta-Mg17Al12 phase and small block Al2Sm phase with high thermal stability. Rod Mg3Bi2 phase precipitates when Bi is added, while the added metal Zn dissolves into alpha- Mg matrix and beta-Mg17Al12 phase. The as-cast alloys exhibit the excellent tensile mechanical property. The tensile strength (sigma(b)) and elongation (delta) can reach 205-235 MPa and 8.5%-16.0% at ambient temperature, respectively. Meanwhile, they can also exceed 160 MPa and 14.0% at 423 K, respectively. The die-cast microstructures are refined obviously, and meanwhile the broken second phases distribute dispersedly. The die-cast alloys exhibit better tensile mechanical properties with the values of sigma(b) and delta of 240-285 MPa and 8.5%-16.5% at ambient temperature, respectively, and excellent flow property with the flow length of 1870-2420 mm. The die-cast tensile fractures at ambient temperature exhibit a typical character of ductile fracture.