5. ConclusionsThis study investigated the microstructures and the mechanical properties of Mg-8.5Gd-4.5Y-0.3Zr (wt%) alloys with and without Zn addition, which led to the following conclusions:(1) The microstructures of alloys are remarkably refined and homogeneous microstructures are obtained, while the alloy with Zn addition has finer grains due to the existence of LPSO phase.(2) Dynamic precipitation occurs during the extrusion process, and the distributions of the dynamic precipitations in both alloys are uneven, which is beneficial for the grain refinement.(3) The alloy with Zn addition has high yield strength and elongation, and the elongation and yield strength of the peak-aged alloy with Zn addition are about two times and 56 MPa higher than that of the alloy without Zn addition.(4) The Zn addition to the Mg-Gd-Y-Zr alloy causes the formation of γ phase during the aging process, and it can effectively block the basal slip and pyramidal slip systems, which result in high strengths while maintaining high elongation.(5) The main strengthening mechanisms for the peak-aged alloy without Zn addition are SS, GBS, and PS. Besides these strengthening mechanisms, the LPSO and γ phases strengthening is helpful to improve the yield strength and elongation of the alloy with Zn addition.