(1. 北方工業(yè)大學(xué) 機(jī)電工程學(xué)院，北京 100144；
2. 西北工業(yè)大學(xué) 凝固技術(shù)國(guó)家重點(diǎn)實(shí)驗(yàn)室，西安 710072)
摘 要: 采用定向凝固方法研究不同試樣尺寸對(duì)Al-4%Cu合金凝固固/液界面特征的影響。結(jié)果表明：當(dāng)凝固速率v=1 μm/s時(shí)，小尺寸試樣的平界面更加平直；當(dāng)v=5 μm/s時(shí)，隨著試樣尺寸的增大，界面形態(tài)分別為淺胞—深胞—初始枝晶，同時(shí)，試樣邊緣的組織比中心的組織更不穩(wěn)定；在相同凝固速率下，小尺寸試樣的溫度梯度較大，促使界面穩(wěn)定性提高；試樣尺寸的增大引起徑向溫差增大，促進(jìn)溶質(zhì)流動(dòng)，使試樣邊緣產(chǎn)生溶質(zhì)富集，從而使平界面彎曲；由于試樣中心排出的溶質(zhì)大部分流向界面前沿糊狀區(qū)的液相中，而枝晶糊狀區(qū)的液相比胞晶的多，因而形成的枝晶界面彎曲程度比胞晶的小。
關(guān)鍵字: Al-4%Cu合金；固/液界面；徑向溫差；溶質(zhì)富集
directional solidification of Al-4%Cu alloy
（1. School of Electrical and Mechanical Engineering, North China University of Technology, Beijing 100144, China;
2. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China）
Abstract: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.
Key words: Al-4%Cu alloy; solid/liquid interface; radial temperature difference; solute accumulation
