Revealing the microstructural evolution and strengthening mechanism of Mg-5.5Gd-3Y-1Zn-0.5Mn alloy in centrifugal casting and subsequent hot rolling

To fulfill the wider engineering application demands of Mg alloy ring parts, Mg-5.5Gd-3Y-1Zn-0.5Mn alloy was fabricated via centrifugal casting and following hot rolling. The effects of centrifugal casting, rolling temperature (420℃, 450℃ and 480℃) and cumulative rolling reduction (20%, 40% and 60%) on the microstructure and tensile properties of the Mg-RE alloy were investigated. In comparison with gravity casting, the centrifugal casting alloy has a uniform and dense microstructure, and the mechanical properties are obviously enhanced. After rolling, the strength of the alloy is further improved, and the microstructure and tensile properties exhibit regular changes with the change of rolling conditions. Affected by rapid cooling, dynamic precipitation of Mg-RE and LPSO phases and high rolling strain rate, the dynamic recrystallization degree of the rolled alloy is low. The ultimate tensile strength and elongation of the alloy at 480℃−60% rolling conditions reached 342 MPa and 11%, respectively. The good strength-ductility synergy is the result of a combination of grain refinement, nano-scale stacking faults, precipitation of the LPSO phase, activation of non-basal slips, and bimodal structure dominated by fine grains. Good comprehensive mechanical properties are expected to be obtained at higher rolling temperature and larger cumulative reduction.