Microstructure and mechanical properties of ZA104 (0.3–0.6Ca) die-casting magnesium alloys

In this paper, the microstructure of die-cast and slowly cooled specimens of two new experimental magnesium alloys (ZA104 + 0.3Ca and ZA104 + 0.6Ca) is examined. Microanalysis of specimens has revealed the presence of α-Mg phase (matrix) and two intermetallic compounds containing calcium with different Zn/Al ratios. These compounds, which have a crystal structure close to that of τ phase [Mg32(Al,Zn)49], were also found in slowly cooled ZA104 + 0.3Ca specimens and identified as ( τ ′ 1 and τ ′ 2 ). The microhardness of these intermetallic compounds has been obtained from specimens having the intermetallic composition and slowly cooled from the melt. The tensile and creep resistance of the two die-cast alloys (ZA104 + 0.3Ca and ZA104 + 0.6Ca) are also presented. Tensile properties are equivalent to those of the AZ91D reference alloy, but their creep deformation rate is significantly reduced by a factor 3.5–3.8 at 150 °C and 4.0–7.2 at 175 °C. Besides, it was found that the ultimate tensile strength and elongation of ZA104 + 0.3Ca alloy are superior to those of ZA104 + 0.6Ca alloy. It is then established that the intermetallic phases τ ′ 1 and τ ′ 2 containing calcium are harder than τ phase and improve substantially the creep resistance of these new ZA experimental alloys.