Effect of Gd and Y contents on the microstructural evolution of long period stacking ordered phase and the corresponding mechanical properties in Mg-Gd-Y-Zn-Mn alloys

This study analyzes the effect of different Gd and Y contents on the microstructural evolution and mechanical properties of Mg-Gd-Y-Zn-Mn alloys. Microstructural analysis indicates the existence of both the long period stacking order and eutectic phases in the as-cast alloys. In case of alloys with high Gd and low Y contents, the main eutectic phase is (Mg,Zn)3(Gd, Y), while in alloys with high Y and low Gd contents, the main eutectic phase is Mg24(Gd,Y,Zn)5. The as-annealed alloys show only α-Mg and LPSO phases; the LPSO phases could be bulk-shaped and lamellar-shaped. The main composition of the LPSO phase with gray bulk-shaped morphology is Mg12ZnY, while the LPSO phase that penetrated thoroughly the grain is mainly Mg12ZnGd. After extrusion, the formation of distorted grains and lamellar-shaped LPSO phases in the alloys with high Gd and low Y contents tends to improve the strength of the as-extruded alloys, while the formation of isometric crystal grains in the alloys with high Y and low Gd contents enhances the alloy elongation.