Al基难混溶合金快速定向凝固研究 Ⅰ.固/液界面的影响

INVESTIGATION OF RAPID DIRECTIONAL SOLIDIFICATION OF Al-BASED IMMISCIBLE ALLOYS Ⅰ.Effect of Solid/Liquid Interface

分析了难混溶合金凝固过程中作用在凝固界面前沿液滴上的力,建立了液滴与凝固界面相互作用行为的动力学判据．结合实验,探讨了固/液界面与液滴间相互作用对Al-Bi基难混溶合金凝固组织演变的影响．结果表明,在界面排斥和Marangoni力共同作用下。较小尺寸的富Bi液滴被凝固界面排斥并富积在凝固界面前沿．当凝固界面为枝晶/胞状晶时,临界尺寸的富Bi液滴与界面发生部分捕获,凝固后形成“蝌蚪”型的富Bi粒子;尺寸较小的富Bi液滴被捕获在枝晶/胞状晶间,凝固后富Bi粒子分布于晶界和三叉交角处．

The forces acting on the droplet in front of the S/L interface during the solidification of immiscible alloys have been analyzed. The dynamic criterion for the interaction mode between the droplet and solidification interface has been proposed. Combining experiment, the effect of the interaction between the S/L interface and the droplet on the microstructure development in the Al- Bi based immiscible alloy has been discussed. The results indicated that the small Bi-rich droplets were repelled and accumulated in front of the solidification interface due to the combined action of the interracial repulsion and Marangoni migration. If the interface morphology is dendritic or cellular, the Bi-rich droplets with critical size are partially entrapped by the interface and form tadpole-type particles, while, the smaller Bi-rich droplets will be entrapped in the interdendrite and the Bi-rich particles distribute at the grain boundaries and the triple junctions after solidification.