Microstructure evolution and strengthening mechanisms of Mg-6Gd-4Y-0.5Zn-0.5Zr alloy during hot spinning and aging treatment

The work aims to investigate the optimized spinning temperature of Mg-6Gd-4Y-0.5Zn-0.5Zr alloy and reveal the microstructure evolution and strengthening mechanism of Mg-6Gd-4Y-0.5Zn-0.5Zr alloy during hot spinning and aging treatment. The study shows that the optimized spinning temperature window of Mg-6Gd-4Y-0.5Zn-0.5Zr alloy ranges from 420 °C to 460 °C, in which the high-performance Mg-6Gd-4Y-0.5Zn-0.5Zr alloy tube with a thickness of 1.5 mm can be successfully fabricated. The multi-pass heating and deformation during hot spinning lead to the precipitation, kinking and break-up of γ′ phase. While the precipitation of γ′ phase aggravates the microstructure inhomogeneity through the thickness of spun tube by restraining dynamic recrystallization. Solid solution strengthening, grain boundary strengthening and shearing strengthening of β′ phase are the dominant strengthening mechanisms of spun Mg-6Gd-4Y-0.5Zn-0.5Zr alloy tube. It is worth noting, finally, that the precipitation of γ′ phase decreases the precipitation density of β’ phase, and thus reduces the age hardening response in the spun tube compared to the extruded Mg-6Gd-4Y-0.5Zn-0.5Zr alloy.