试样尺寸对定向凝固Al-4%Cu合金固/液界面特征的影响

Effect of sample size on solid/liquid interfacial characteristic in directional solidification of Al-4%Cu alloy

采用定向凝固方法研究不同试样尺寸对Al-4%Cu合金凝固固/液界面特征的影响。结果表明:当凝固速率v=1μm/s时,小尺寸试样的平界面更加平直;当v=5μm/s时,随着试样尺寸的增大,界面形态分别为浅胞—深胞—初始枝晶,同时,试样边缘的组织比中心的组织更不稳定;在相同凝固速率下,小尺寸试样的温度梯度较大,促使界面稳定性提高;试样尺寸的增大引起径向温差增大,促进溶质流动,使试样边缘产生溶质富集,从而使平界面弯曲;由于试样中心排出的溶质大部分流向界面前沿糊状区的液相中,而枝晶糊状区的液相比胞晶的多,因而形成的枝晶界面弯曲程度比胞晶的小。

The effect of sample sizes on solid/liquid interfacial characteristic of Al-4%Cu alloy was studied by adjusting sample sizes in directional solidification.The results show that the smaller the sample sizes are,the flatter the planar interface is at solidification rate（v） of 1 μm/s.However,at v=5 μm/s,with increasing sample sizes,the interface morphologies show shallow cells-deep cells-initial dendrites,respectively.For all of the samples,the microstructure at the boundary is not so stable as that in the center.The temperature gradient increases as the sample sizes decrease at the same growth velocity,which makes the interface more stable.The increasing sample sizes can strengthen the radial temperature difference,which can enhance the convection,thus makes the planar interface convex and non-planar interface flatter.In conclusion,the radial temperature difference can weaken the interface stability.The solute rejected from the center of sample flows into the liquid in the mushy zone,and the liquid in dendrite is more than that in the cellular,the curvature at the dendrite interface can be less than that at the cellular.