Abstract: An universal method of numerical simulation on near-rapid directional solidification of Al round bar in a vertical Bridgman furnace was developed, in which the transient heat transfer equations were used and the longitudinal heat conduction is taken into account. The influence of pulling velocity on the temperature gradient and growth velocity of liquid-solid interface was analyzed. The results indicate that, in the pulling velocity range of 30~3000μm/s, the change of pulling velocity on the temperature gradient and growth velocity of liquid-solid interface is hardly obvious. With pulling velocity increasing, the temperature gradient is changed from 135 to 155K/cm, and the difference of growth velocity and pulling velocity is within the range of 5%. The numerical simulation of the near-rapid directional solidification of Al sample can provide an available tool for the investigation on the selection of microstructure of binary sing-phase Al-Zn alloy under near-rapid directional solidification condition.
Numerical simulation on near-rapid directional solidification process of Al bar sample
Abstract:
An universal method of numerical simulation on near-rapid directional solidification of Al round bar in a vertical Bridgman furnace was developed, in which the transient heat transfer equations were used and the longitudinal heat conduction is taken into account. The influence of pulling velocity on the temperature gradient and growth velocity of liquid-solid interface was analyzed. The results indicate that, in the pulling velocity range of 30~3 000 (μm/s,) the change of pulling velocity on the temperature gradient and growth velocity of liquid-solid interface is hardly obvious. With pulling velocity increasing, the temperature gradient is changed from 135 to 155 K/cm, and the difference of growth velocity and pulling velocity is within the range of 5%. The numerical simulation of the near-rapid directional solidification of Al sample can provide an available tool for the investigation on the selection of microstructure of binary sing-phase Al-Zn alloy under near-rapid directional solidification condition.
以试样和石墨坩埚为模拟对象。 纯Al和石墨坩埚的物性参数见文献
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。 选择的坩埚抽拉速度在30~3 000 μm/s之间。 试样直径为5 mm, 长度为120 mm; 坩埚外径为7 mm, 内径为5 mm, 长度为125 mm。 炉膛的结构尺寸: 绝热区上下宽度为10 mm, 以绝热区几何中心为原点, 炉膛上部的长度为140 mm, 径向直径为10.5 mm、 下部的长度为140 mm, 径向直径为16 mm。
采用单区域方法, 即对于计算域内试样的液相和固相以及坩埚用统一网格进行划分。 图2所示为对计算区域进行的网格划分示意图, 计算长度xL=0.125 m, 其网格长度Δx=0.001 m, 计算的径向半径rL=0.003 5 m, 其网格宽度r=0.000 5 m, 计算的总节点数为N1×M1=127×9=1 143。 图中的i, j分别表示x方向和r方向的节点序号, 其中xL1=0.005 m, 则与其界面相邻的节点单元为(6, j) 和(7, j), j=1, 6; rL1=0.002 5 m, 则与其界面相邻的节点单元为(i, 6) 和(i, 7), i=7, N1。
式中
αE=rPΔr(δx)e/ke;
αW=rPΔr(δx)w/kw;
αN=rnΔx(δr)n/kn;
αS=rsΔx(δx)s/ks; αP=αE+αW+αN+αS+α0P-SPΔV;
α0P=(ρcp)PΔVΔt; b=ScΔV+α0PT0P; ΔV=0.5(rn+rs)ΔrΔx。 e, w, n, s为控制容积的界面节点, E, W, N, S为节点P的邻点, 它们之间的位置见图4。 控制方程离散为一组代数方程组后, 采用交替方向隐式迭代法(ADI)求解。
图3 控制容积
Fig.3 Control volume for derivation of fundamental equation