Microstructural Characteristics and Mechanical Properties of Cast Mg–3Nd–3Gd–xZn–0.5Zr Alloys

The microstructure, aging behavior and mechanical properties of cast Mg–3Nd–3Gd–xZn–0.5Zr (x = 0, 0.5, 0.8, 1 wt%) alloys are investigated in this work. Zn–Zr particles with different morphologies form during solution treatment due to the additions of Zn. As the Zn content increases, the number density of Zn–Zr particles also increases. Microstructural comparisons of peak-aged studied alloys indicate that varying Zn additions could profoundly influence the competitive precipitation behavior. In the peak-aged Zn-free alloy, β′′ phases are the key strengthening precipitates. When 0.5 wt% Zn is added, besides β′′ precipitates, additional fine β1 precipitates form. With the addition of 0.8 wt% Zn, the peak-aged 0.8Zn alloy is characterized by predominantly prismatic β1 and scanty basal precipitate distributions. The enhanced precipitation of β1 should be primarily attributable to the presence of increased Zn–Zr dispersoids. When Zn content further increases to 1 wt%, the precipitation of basal precipitates is markedly enhanced. Basal precipitates and β1 phases are the key strengthening precipitates in the peak-aged 1Zn alloy. Tensile tests reveal that the relatively best tensile properties are achieved in the peak-aged alloy with 0.5 wt% Zn addition, whose yield strength, ultimate tensile strength and elongation are 179 MPa, 301 MPa and 5.3%, respectively.