强制对流作用下镁合金枝晶生长的相场法数值模拟

Numerical simulation of dendritic growth of magnesium alloys using phase-field method under forced flow

基于Wheeler等提出的纯扩散相场模型,针对hcp晶系镁合金建立耦合温度场、溶质场和流场的相场模型,研究强制对流作用下镁合金凝固过程中单枝晶和多枝晶的生长行为。结果表明:在流速为17.19m/s的垂直强制对流作用下,流体逆流侧3个方向的枝晶臂明显比流体顺流侧3个方向的枝晶臂生长得快,逆流方向枝晶臂的稳态生长速度比纯扩散时的增加78.0%,顺流方向枝晶臂的稳态生长速度比纯扩散时的减小53.7%;各枝晶的臂长存在很大差异,枝晶形貌的六重对称性被严重破坏;在多枝晶生长时,相向生长的枝晶互相影响并竞相生长,不同枝晶的枝晶臂彼此抑制,最终形成不对称的枝晶形貌。

Based on the diffusion Wheeler model which couples the temperature field,concentration field and flow field,the phase-field model for the magnesium alloys with hcp structure was established to simulate both of the single and multi-grain dendritic growths of magnesium alloys during solidification in a forced flow.The results show that when the flow velocity is 17.19 m/s,the growths of three directions on the upstream side are much faster than those of three directions on the downstream side,the tip velocity at steady state on the upstream is increased by about 78.0% compared with the case without flow,the tip velocity at the steady state on the downstream is decreased by about 53.7% compared with the case without flow.There exists much difference in the length of dendrite arm,so that the six-fold symmetry of the dendrite morphology is severely damaged.Under the case of the multi-grain,the grains grown face to face influence mutually and grow competitively.The dendrite arms of different dendrite are mutually inhibited,ultimately,form asymmetric dendrite morphology.