Mold temperature governed microstructural evolution and mechanical performance in cast Mg-Gd-Zn alloy

Mold temperature stands as a pivotal control parameter in the casting process, directly influencing the quality of the cast products. However, systematic studies addressing the effect of mold temperature on the microstructure and mechanical performance of cast magnesium (Mg) alloys are limited. This study delves into the influence of mold temperature on the microstructural evolution and mechanical properties of cast Mg-10Gd-0.2Zn-0.4Zr (wt.%) alloys under various thermal conditions. A quantitative prediction model for mechanical properties based on mold temperature was also developed. The results indicate that increasing mold temperature significantly reduces the cooling rate during solidification, leading to a coarser microstructure in the as-cast alloy. Additionally, the content and size of the secondary phases increase, resulting in a notably lower dissolution efficiency of these phases during solution treatment and a decrease in solute supersaturation within the matrix. Consequently, the number density and coarsening rate of the β’ phase during ageing are diminished. The undissolved secondary phases and coarse grains significantly impair the mechanical properties of the alloy, particularly its elongation. Specifically, when the mold temperature rises from 200 °C to 600 °C, the elongation of the solution-treated and peak-aged alloys decreases by 15% and 50%, respectively. Nonlinear regression analysis revealed a statistically significant quadratic relationship between mold temperature ( x ) and the mechanical properties ( y ) of peak-aged alloy, expressed mathematically as y = ax 2 + bx + c . This quantitative model enables precise prediction of the mechanical properties of Mg-Gd-Zn alloys, providing a robust experimental basis for their accurate regulation.