Effect of Alloying with Al, Nd and Ca and Heat Treatment on Microstructures and Mechanical Properties of Vacuum Die-Cast AM50 Alloy

In this paper, Mg–Al–Mn (AM) series alloys were studied to develop high strength and toughness die-cast magnesium alloys by micro-multi-alloying method. AM50-X (Al, Nd, Ca) alloy samples were prepared by vacuum die casting using Al, Ca, Nd elements with obvious alloying effect. The microstructures and mechanical properties of AM50, AM70 and AM70–0.5Nd–0.5Ca alloys after die casting and heat treatment were investigated by means of microstructure observation and mechanical properties test. The results showed that the tensile strength of the die-cast AM70 alloy was higher than that of the die-cast AM50 alloy, but the elongation was lower. The AM70–0.5Nd–0.5Ca alloy showed a further increase in tensile strength and a slight decrease in plasticity. The addition of small amounts of Nd and Ca led to a refinement of the microstructure, and the elements Nd and Ca did not form new phases and dissolve mainly in the Mg₁₇Al₁₂ phase. T4 heat treatment slightly reduced alloy hardness, while T6 heat treatment could increase alloy hardness. AM70–0.5Nd–0.5Ca alloy had the optimal overall mechanical properties after T4 treatment. The ultimate tensile strength, yield strength, elongation and hardness of AM70–0.5Nd–0.5Ca alloy reached 243.6 MPa, 145.2 MPa, 6.7% and 60.9 HBS, espectively. The improvement in the mechanical properties of AM70–0.5Nd–0.5Ca–T4 alloy could be attributed to comprehensive effect of fine grain strengthening, solid solution strengthening and dispersion strengthening caused by the improvement of Mg₁₇Al₁₂ (Ca, Nd) phase.