抽拉速率对定向凝固Al-4％Cu合金枝晶界面特征的影响

EFFECT OF WITHDRAWAL RATE ON DENDRITIC INTERFACIAL CHARACTERISTIC FOR A1-4%Cu ALLOY DURING DIRECTIONAL SOLIDIFICATION

采用Al-4%Cu合金,对不同抽拉速率下定向凝固枝晶界面特征进行了研究.结果表明,当抽拉速率从100μm/s增至600μm/s时,一次枝晶间距随抽拉速率的增人而减小.在枝晶固/液界面存在枝晶千的凸起,其平-凸-平-凸的程度随抽拉速率的增加呈现先加强后减弱最后几乎消失的规律.随着抽拉速率的增火,枝晶尖端温度先升高而后降低.采用KGT模型和非平衡效应研究了枝晶界面温度,分析了尖端过冷度和尖端成分对枝晶界面特征的影响,得到非平衡凝固枝品尖端过冷度的计算方程.界面平-凸-平-凸的程度与枝晶尖端成分和尖端过冷度有关.

Directional solidification experiments were carried out on Al-4%Cu alloy under withdrawal rates varying from 100 μm/s to 600 μm/s. It is showed that the primary dendrite arm spacing decreases with increasing withdrawal rate. The shape of quenched solid/liquid interface in dendrite growth morphology appears as unevenness where some dendrite trunks grow as convex parts. The ex- tent of protrusion is inconspicuous at lower withdrawal rates. With withdrawal rate increasing, those protrusions are then reinforced and finally almost faded. Dendrite interface temperature is also first increased and then decreased with increasing withdrawal rate. The KGT model and non-equilibrium effect were used to determine the dendrite interface temperature, tip undercooling and composition and the formula to describe dendrite tip undercooling was also obtained. It is found that the unevenness of interface is related to the tip undercooling and compositions.