变速生长条件下Al－Cu合金的定向凝固枝晶组织

CELLULAR TO DENDRITIC TRANSITION OF DIRECTIONALLY SOLIDIFIED Al-Cu ALLOYS UNDER DIFFERENT GROWTH VELOCITIES

应用改进的定向凝固装置研究了Ａｌ－２ｗｔ－％Ｃｕ和Ａｌ－４ｗｔ－％Ｃｕ合金在阶跃和不同加速度线性变速生长条件下，定向凝固组织的动态转变。实验结果表明：尽管定向生长的胞－枝晶动态转变过程随加速度的降低而减缓，但胞晶组织都是在经历了一定的胞晶形貌扰动之后才发生快速失稳、分枝细化并向树枝晶组织过渡，加速度不同，由失稳胞晶演变成的树枝晶可具有多种分枝形式。

Dendrite evolution from cellular structures of directionally solidified Al-2wt-% Cu and Al-4 wt-% Cu specimens under step and linear change of displacement velocity was studied with an improved experiment apparatus of directional solidification.The experimental results show that, although the dynamic process of cellular to dendritic transition becomes slow with decrease in the velocity change of specimen displacement,the instability and branching of the cellular structure will rapidly develop a dendritic strucutre after a certain disturbance of the cellular morphology.These dendrites could have various morphologies which are related to the acceleration.