镁合金焊缝凝固枝晶生长的相场法模拟分析

Research on dendrite growth of magnesium alloy during welding solidification using the phase field method

采用六重对称各向异性的Karma模型对镁合金焊缝凝固枝晶生长过程进行模拟,研究了晶核密度、晶核位置对枝晶生长的影响。结果表明:单枝晶生长时,晶核在优先生长方向上生长迅速,形成六重对称的枝晶形貌;多枝晶生长时,受生长空间的限制,枝晶形貌的对称性被严重破坏。当晶核密度较小时,晶核平均生长空间较大,晶核之间的相互影响较弱,形成六重对称枝晶形貌;当晶核密度较大时,晶核平均生长空间较小,晶核之间的相互影响加强,形成不规则枝晶形貌;当仅有2个晶核处于计算区域对角位置时,相对生长空间充足,六重对称枝晶形貌发达。

The Karma model with the six-fold symmetrical anisotropy was used to simulate the dendrite growth of magnesium alloy during welding solidification. The effects of the crystal nucleus density and crystal nucleus position on the dendrite growth was studied. The result shows that for single dendrite growth,the crystal nucleus grows fast at the preferential growth orientation and the dendrite morphology shows six-fold symmetry. In the case of the multidendrites growth,limited by space the six-fold symmetry of the dendrite morphology is severely damaged. When the crystal nucleus density is low,the average growth space of the crystal nucleus is larger and the mutual influence between them is weak,and the dendrite morphology shows six-fold symmetry. When the crystal nucleus density is high,the average growth space of the crystal nucleus becomes smaller,and the mutual influence between crystal nuclei becomes bigger,so that the dendrite presents asymmetric morphologies. When there are only 2 nuclei in the diagonal positions of the growing region,the relative growth space is sufficient,and the developed six-fold symmetry of dendrite morphology is formed.