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, beta '' phases are the key strengthening precipitates. When 0.5 wt% Zn is added, besides beta '' precipitates, additional fine beta(1) precipitates form. With the addition of 0.8 wt% Zn, the peak-aged 0.8Zn alloy is characterized by predominantly prismatic beta(1) and scanty basal precipitate distributions. The enhanced precipitation of beta(1) 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 beta(1) 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.