Strengthening of low-cost rare earth magnesium alloy Mg-7Gd-2Y–1Zn-0.5Zr through multi-directional forging

Abstract

Conventional rare-earth magnesium alloys have high strength but are not accepted by some fields because of their relatively high price. Magnesium alloys with the addition of small amounts of rare earth elements can improve the mechanical properties by severe plastic deformation while saving cost. In this paper, the effects of multidirectional forging (MDF) process on the microstructure and mechanical properties of low-cost rare earth magnesium alloy Mg-7Gd-2Y–1Zn-0.5Zr were investigated, and the plastic deformation mechanism, dynamic recrystallization mechanism and property strengthening mechanism during the MDF process were analyzed. The results showed that the yield strength, ultimate tensile strength and elongation of Mg-7Gd-2Y–1Zn-0.5Zr alloy were 395.2 MPa, 435.3 MPa and 17.6% after extrusion, MDF at reduced temperature conditions and T5 treatment. The increase in alloy strength is related to solid solution strengthening and is more attributed to the combined effect of grain refinement and aging precipitation. The dynamic recrystallization mechanism leading to grain refinement converts from discontinuous dynamic recrystallization to continuous dynamic recrystallization during MDF at reduced temperatures. And the decrease in deformation temperature leads to difficulties in prismatic and pyramidal slipping, where grain boundary sliding from fine grains and twinning in a few relatively coarse grains play a role in coordinating deformation.