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

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 α-Mg matrix, discontinuous β-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 α-Mg matrix and β-Mg17Al12 phase. The as-cast alloys exhibit the excellent tensile mechanical property. The tensile strength (σb) and elongation (Δ) 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 σb and Δ 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.