Abstract: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 a-Mg matrix, discontinuous b-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 a-Mg matrix and b-Mg₁₇Al₁₂ phase. The as-cast alloys exhibit the excellent tensile mechanical property. The tensile strength (s_b) and elongation (d) 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 s_b and d 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.

Key words: heat-resistant magnesium alloy; Mg-Al-Sm alloy; microstructure; mechanical property; flow property; fracture morphology