Achieving high strength and creep resistance of a Mg-13Gd-6Y-0.2Zr alloy forging fabricated by isothermal forging and artificial aging

Abstract

Mg alloys are limited in applications due to low strength and poor creep resistance. The requirement for Mg alloy components to be used at 200 °C is proposed in the aerospace industry. Although Mg-Gd-Y-Zr alloys have superior mechanical properties, the creep properties of practical Mg-Gd-Y-Zr alloy forgings have not been reported, which is related to their industrial utilization. In this work, a typical Mg-13Gd-6Y-0.2Zr (wt%) alloy forging used in the aerospace industry was fabricated by a combination of isothermal forging and artificial aging. The forging exhibits excellent creep resistance with a steady-state creep rate of 2.26×10−9 /s at 200 °C and a stress of 60 MPa, while achieving the ultimate tensile strength of 475 MPa (Engineering stress) higher than those of reported wrought Mg-RE alloys with similar elements. The occurrence of recrystallization during isothermal forging refines the grains, increasing strength. The uniformly distributed β' phase (30–50 nm) formed during aging provides effective strengthening. The low steady-state creep rate is mainly attributed to the formation of the finer precipitates (5–10 nm) during creep tests, which contribute to reducing the precipitation-free zones near the grain boundaries and retarding creep behaviors by hindering dislocation movements.