Improved mechanical properties of highly alloyed Mg-10Gd-5Y-5Er-xZn alloys via tailoring LPSO phase structure

The highly alloyed Mg-10Gd-5Y-5Er alloy exhibits high strength, however, the brittle Mg 24 RE 5 phase accelerates the initiation and development of micro-cracks and significantly deteriorate the plastic deformation ability. Therefore, it is necessary to regulate the type of precipitates to improve the comprehensive mechanical properties of the alloy. In this work, the influence of Zn content on mechanical properties and microstructure evolution of highly alloyed Mg-10Gd-5Y-5Er- x Zn alloys ( x ​= ​0, 1, 2, 3, and 5 ​wt%) was investigated. It was found that the tensile strength increases with increasing Zn content, without deterioration of elongation. The maximum tensile yield strength and ultimate tensile strength are achieved to be 298 ​MPa and 406 ​MPa, respectively, within the studied concentration range. Thermodynamic calculations and microstructural characterization results indicate that with the increase of Zn content the precipitate transform from Mg 24 RE 5 phase to long-period-stacking-ordered (LPSO) phase and lamellar structure. This transition will change the solute atom concentration in the matrix and affect the dynamic recrystallization behavior, thereby changing the contributions of solid solution strengthening and grain refinement strengthening to the yield strength of alloy. In particular, the blocky LPSO phase can significantly contribute to the increased strength at relatively high Zn contents ( x ​> ​2 ​wt%) by a mechanism similar to short-fiber strengthening. Moreover, the strategy of improving the mechanical properties by increasing the volume fraction of blocky LPSO phase can be applied to many Mg alloy systems containing LPSO phase.