Effect of gadolinium on the microstructure and mechanical properties of Mg-Nd-Zn-Zr cast magnesium alloys

The new element points was selected by adjusting Nd and Zn content based on Mg-Nd-Zn-Zr magnesium alloys, and the effects of Gadolinium on the microstructures and mechanical properties of Mg-Nd-Zn-Zr magnesium alloy were studied. The main research results are as follows: (1) The as-cast microstructure of Mg-Nd-Zn-Zr alloy and NG31 alloy consist of α-Mg grains with Mg₁₂Nd phase on the grain boundary. (2) After solution heat-treatment, Mg₁₂Nd phase of Mg-Nd-Zn-Zr alloy were dissolved in the matrix, however, there was still discontinued Mg12Nd phase at grain boundary of NG31 alloy. (3) The mechanical properties of Mg-Nd-Zn-Zr alloy and NG31 alloy at room temperature are satisfactory, with σ_b =275 MPa, σ _0.2 =158 MPa for Alloy-A2 and σ_b=280 MPa, σ_0.2 =165 MPa for NG31 alloy respectively. (4) With the increase of Nd and the decrease of Zn, the ultimate strength, yield strength and the elongation of Mg-Nd-Zn-Zr alloy at room temperature were increased slightly. The ultimate strength and yield strength of NG31 alloy are higher than those of Mg-Nd-Zn-Zr alloy at room temperature, but the elongation is lower. (5) With the temperature increasing, the ultimate strength and yield strength of Alloy-A2 at elevated temperature were decreased sharply. The ultimate strength of NG31 alloy kept at 215 MPa at 250 °C, and the yield strength also kept at 155 MPa higher than 141 MPa at 200 °C.