冷却速率对Mg-Gd-Y三元镁合金凝固组织影响的相场模拟

结合Mg-Gd-Y体系热、动力学模型,首次考虑冷却速率,建立了Mg-Gd-Y三元镁合金的相场模型。应用该模型模拟了GW103(Mg-1.69mol%Gd-1.32mol%Y)合金在不同冷却速率下的凝固组织微观形貌和成分分布。采用重力铸造法制备GW103合金并对其进行实验表征以验证相场模型。结果表明,GW103合金呈不发达枝晶形貌且一次枝晶臂具六次对称性,二次枝晶臂呈突起状且无更高次枝晶臂。在多晶粒相场模拟中,随着冷却速率的增加GW103微观组织细化,晶粒尺寸减小、一次枝晶臂变细、二次枝晶臂数目减少。较高的冷却速率加剧了Gd和Y在枝晶间的溶质富集现象,令成分分布更不均匀。

Phase-field simulation on the influence of cooling rate on the solidification microstructure of Mg-Gd-Y ternary magnesium alloy

A phase-field model of ternary Mg-Gd-Y magnesium alloy was developed by coupling with the thermodynamics of Mg-Gd-Y system and considering cooling rate for the first time. It was applied to simulate the solidification microstructure and concentration distribution of GW103 (Mg-1.69mol%Gd-1.32mol%Y) alloy at different cooling rates both in one-grain and multigrain simulation cases. Then GW103 alloys were prepared via gravity casting method and characterized to verify the model. Results give new understanding that the GW103 alloy exhibits thick sixfold primary dendrite, a few protuberance-like secondary arms and even no higher-order arms, instead of developed dendrite. The ascending cooling rate results in refinement of microstructure of GW103, which exhibits smaller grain size, slimmer primary dendrite and less secondary arms in multigrain simulation case. Besides, higher cooling rate aggravates the solute enrichment and inhomogeneous distribution of Gd and Y in interdendritic area. The simulation and the experimental results are matched well.