When the testing temperature increa

When the testing temperature increases from RT to 250 ◦C, the UTS of (A) alloy decreased from 180 to 157 MPa, and the YS also decreased from 161 to 101 MPa, respectively. The strengths of (C) alloy exhibited maximum value at 250 ◦C, the UTS and YS are 199 and 128 MPa, respectively, which are about 1.27 times higher than those of (A) alloy. The results reveal that addition of Gd can remarkably improve the mechanical properties for the ascast alloys at elevated temperature. It is because that the high melting point -phase and Mg5RE phase can effectively hind basal plane slip and inhibit the deformation of matrix at the testing temperature. Comparing with the fracture surfaces of (A) and (C) alloys (in Fig. 7), it was found that the volume fraction of phase in (C) alloy is higher than that in (A) alloy obviously. Furthermore, the grain boundary gliding occur during tensile test at the 250 ◦C. The (C) alloy has a smaller grain size than (A) alloy. It will lead to increase the amount of grain boundary, which is not benefit to enhance the mechanical properties of the alloy at elevated temperature. On the other hand, increase the amount of grain boundary can disperse -phase and Mg5RE phase mainly along grain boundary, which benefits to hinder grain boundary gliding.