浇注温度对砂型铸造Mg-10Gd-3Y-0.4Zr合金凝固行为、组织与性能的影响（英文）

Influence of pouring temperature on solidification behavior, microstructure and mechanical properties of sand-cast Mg-10Gd-3Y-0.4Zr alloy

研究砂型铸造过程中浇注温度（680～780℃）对Mg－10Gd－3Y－0．4Zr合金凝固行为、组织与性能的影响。结果表明：随着浇注温度从680℃先提高至750℃再提高至780℃，α-Mg的形核过冷度从2．3℃提高到6．3℃后不再提高；α-Mg的平均晶粒尺寸先由44μm增加至71μm而后减小到46μm；共晶组织先由网格状转变为不连续的块状继而转变为大块的岛状；β-Mg_24RE_5相的体积分数增加，由颗粒状转变为短棒状；溶质富集的现象变得更加明显；合金的屈服强度由138MPa提高至151MPa，抗拉强度由186MPa提高至197MPa。750℃浇注的合金具有最佳的强度与延展性。断口形貌特征由准解理断裂转变为穿晶韧性断裂，并伴随着不同程度的缩松与氧化夹杂等铸造缺陷。相对于铸造缺陷、共晶组织以及溶质富集，α-Mg的晶粒尺寸是砂型铸造Mg一10Gd_3Y一0．4Zr合金屈服强度最主要的影响因素。

Influence of the pouring temperature ranging from 680 to 780 ℃ on the solidification behavior, the microstructure and mechanical properties of the sand-cast Mg-10Gd-3Y-0.4Zr alloy was investigated. It was found that the nucleation undercooling of the a-Mg phase increased from 2.3 to 6.3 ℃. The average a-Mg grain size increased from 44 to 71 μm, but then decreased to 46 μm. The morphology of the eutectic compound transformed from a continuous network into a discontinuous state and then subsequently into an island-like block. The volume fraction of β-Mg_24RE_5 phase increased and its morphology transformed from particle into rod-like. The increase in pouring temperature increased the solute concentration. YS increased from 138 to 151 MPa, and UTS increased from 186 to 197 MPa. The alloy poured at 750 ℃ had optimal combining strength and ductility. The fracture surface mode transformed from quasi-cleavage crack into transgranular fracture, all plus the dimple-like fracture, with the micro-porosity and the re-oxidation inclusion as major defects. The average a-Mg grain size played a main role in the YS of sand-cast Mg-10Gd-3Y-0.4Zr alloy, besides other factors, i.e. micro-porosity, morphology of eutectic compounds, re-oxidation inclusion and solute concentration.