Microstructure and high temperature mechanical properties of the Mg-Gd-Y(-Nd)-Zr alloy

Mg–Gd system alloys have been widely studied because they are applied in automotive, weaponry and aerospace applications and have a wide range of application scenarios due to the excellent strength and heat resistance properties. This work aims to systematically investigate the microstructure and high temperature mechanical properties of Mg-10Gd-3Y-xNd-0.5Zr alloy, and found that the microstructure of Mg-10Gd-3Y-0.5Zr alloy was mainly composed of α-Mg matrix, Mg5(Gd, Y) phase and Mg24(Y, Gd)5 phase. In which Nd element plays a role in the alloy to promote the precipitation phase precipitation and form the new phase Mg41Nd5, and the appropriate amount of Nd can refine the grain size. Moreover, Mg-10Gd-3Y-xNd-0.5Zr alloy has excellent mechanical properties in room and high temperature, with ultimate tensile strengths above 280 MPa at 200 °C–300 °C, 309 MPa at 250 °C, and especially at 350 °C, the tensile strength is still up to 195 MPa. The main strengthening phases are β'' phase, β′ phase and 18-LPSO (Long-period stacking ordered) phase. The Mg-10Gd-3Y-2Nd-0.5Zr alloy has excellent high temperature creep resistance at (200 °C–300 °C)/(50–90 MPa). When creeping at 200 °C, β′ phase is completely transformed into β'' phase. After creeping at 250 °C, β′ phase is transformed into β phase. After creeping at 300 °C, β phase grows significantly. Meanwhile, when the creep temperature and stress increase, the creep mechanism gradually changes from diffusion and grain boundary sliding mechanism to dislocation slip and dislocation climbing mechanism.