铝合金大铸锭超声半连铸多场耦合的数值模拟与实验研究

Numerical simulation and experimental study of multi-field coupling for semi-continuous casting of large-scale aluminum ingots with ultrasonic treatment

建立了超声场下直径630 mm的铝合金大铸锭热顶半连铸过程中多场耦合的数学模型,采用有限体积法及自定义函数获得超声作用下结晶器内声场、流场和温度场的分布,并进行工业化实验研究.综合工业实验和仿真结果分析超声对热顶半连铸铝合金大铸锭细晶的机理.模拟结果表明,超声波对宏观物理场的影响非常明显,施加超声后,辐射杆端面下方形成向上的回流区,强烈的紊流促进铝熔体的传质传热,减小液穴深度,使液穴更加平缓,同时初始凝壳点下移,过渡带变窄,铸锭中心处过渡带宽度从342 mm减小到120 mm左右.分析实验结果发现,经超声处理,铸锭组织普遍变得细小、均匀,平均晶粒尺寸减小103μm,最大最小晶粒尺寸差从135μm减小到64μm,且凝固组织晶界变细.

A multi-field coupling mathematical model was established to analyze the hot-top semi-continuous casting of a large-scale aluminum alloy of 630 mm in diameter with ultrasonic treatment （ UST） . The finite volume method combined with the self-com-piled function was used to get the distribution of the acoustic field, flow field and temperature field, and the industrial experimental re-search was also performed. The mechanism of ultrasonic treatment on the grain refinement of the large-scale aluminum alloy produced by hot-top semi-continuous casting was analyzed based on the simulation and experiment results. The simulation results show that ultra-sonic markedly influences the macroscopic physic field. With ultrasonic treatment, an upward recirculation zone forms beneath the end face of the radiation rod, the heat and mass transfer is promoted by the strong turbulence, the sump gets shallower and gentler, the ini-tial solidifying point on the ingot surface in the mold moves down, the transition zone becomes narrower, the width of it in the center drops from 342 mm to nearly 120 mm. The experimental results show that with ultrasonic treatment, the grain size becomes smaller and more homogeneous, the average grain size reduces by 103μm, the gap between the maximum and minimum grain size decreases from 135 to 64μm, and the grain boundary of the solidification structure becomes thinner.