(清華大學(xué)材料學(xué)院先進(jìn)成形制造教育部重點(diǎn)實(shí)驗(yàn)室，北京 100084)
摘 要: 通過Al-7Si-0.36Mg合金定向凝固實(shí)驗(yàn)和元胞自動(dòng)機(jī)模型，開展定向凝固枝晶形貌演化和一次枝晶臂間距選擇過程的實(shí)驗(yàn)和模擬。結(jié)果表明：在給定的凝固條件下，一次枝晶臂間距范圍是一個(gè)連續(xù)的變化區(qū)間。在恒定溫度梯度和不同凝固速度條件下，測得Al-7Si-0.36Mg合金一次枝晶臂間距上限值(λmax)、下限值(λmin)和平均值(λave)以及生長速率之間的關(guān)系，且上限值和下限值的比值接近3。模擬結(jié)果與實(shí)驗(yàn)結(jié)果的吻合程度明顯優(yōu)于Hunt-Lu等解析模型的預(yù)測結(jié)果，表明CA模型在枝晶定向凝固過程枝晶形貌演化模擬和枝晶臂間距預(yù)測等方面的準(zhǔn)確性。結(jié)合模擬研究和文獻(xiàn)調(diào)研分析影響定向凝固一次枝晶臂選擇的因素，包括抽拉速度v、溫度梯度G、界面能大小、溶質(zhì)擴(kuò)散系數(shù)DL、枝晶生長取向與熱流方向的偏離角度θ等。
關(guān)鍵字: 定向凝固；枝晶臂間距；生長速度；元胞自動(dòng)機(jī)；數(shù)值模擬
（Key Laboratory for Advanced Materials Processing Technology, Ministry of Education,
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China）
Abstract:The directional solidification dendritic morphology evolution and primary dendrite arm spacing selection process of Al-7Si-0.36Mg alloy were studied by directional solidification experiments and cellular automaton model. The results indicate that there is a continuous range of primary dendrite arm spacing under the given solidification condition. Under the condition of the given temperature gradient and various solidification velocities, the relationships between the primary dendrite arm spacing parameters (λmax, λave, λmin) of Al-7Si-0.36Mg alloyand growth velocity were expressed, and λmax/λmin≈3. The simulated results show a quite good agreement with the experimental results, which is better than predicted results of Hunt-Lu model. The comparisons reveal that the present CA model has a high accuracy in simulating the evolution of dendrite morphology and predicting primary dendrite arm spacing in directional solidification. Based on the predictions and related literatures, the factors influencing the selection of primary dendrite arm spacing, such as growth velocity v, temperature gradient G, interfacial energy effect, solute diffusion coefficient DL, as well as the deviation angle θbetween the dendrite growth direction, and heat flux direction were analyzed.
Key words: directional solidification; primary dendrite spacing; growth velocity; cellular automaton; numerical simulation
