CELLULAR TO DENDRITIC TRANSITION OF DIRECTIONALLY SOLIDIFIED Al-Cu ALLOYS UNDER DIFFERENT GROWTH VELOCITIES
变速生长条件下Al－Cu合金的定向凝固枝晶组织

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.