Influence of ultrasound irradiation on transient solidification characteristics in DC casting process: Numerical simulation and experimental verification
Influence of ultrasound irradiation on transient solidification characteristics in DC casting process: Numerical simulation and experimental verification
复制标题
超声辐照对直流铸造瞬态凝固特性的影响：数值模拟与实验验证
DOI：
10.1016/j.jmatprotec.2021.117116
复制
发表时间：
2021
影响因子：
6.3
通讯作者：
Komarov Sergey V.
中科院分区：
文献类型：
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作者：
Yamamoto Takuya;Komarov Sergey V.
众所周知，金属液的凝固是在瞬态不稳定现象的影响下发生的，在实际铸造操作中很难控制。例如浮力流动、自然热对流、糊状区反复重熔和凝固以及模具界面处的固体壳。本文的研究结果表明，将超声波照射到热顶结晶器中，为控制铝合金方坯直流铸造过程中的瞬态现象提供了一种有吸引力的方法。建立了一种考虑瞬态熔体流动、传热、超声传播、声流和凝固的直流铸造数学模型。结果表明，超声辐照改变了熔体的凝固行为和凹坑的演变，特别是在铸坯早期，但随着铸坯长度的增加，超声辐照和常规铸坯的凹坑轮廓几乎相同。在这种情况下，浇注速度成为影响熔池演化和糊状区体积的关键参数。结果表明，超声驱动的声流和湍流振荡抑制了液池内的浮力流动，导致凝固界面熔体温度振荡频率增加。这些现象的一个有用的结果可能是更频繁地重复重熔/凝固循环，并改善钢坯质量，特别是钢坯表面形貌。利用中试直流连铸机实验验证了超声辐照对铸坯形貌的影响。
It is well known that solidification of molten metals occurs under the influence of transient unsteady phenomena, which are difficult to control in actual casting operation. Examples include buoyancy flows, natural heat convection, repeated remelting and solidification in mushy zone and solid shell at the mold interface. This paper presents the results suggesting that ultrasound waves, irradiated into the hot-top mold offers an attractive way to control the transient phenomena in DC casting of aluminum alloy billets. A novel mathematical model was developed to simulate the DC casting with considering transient melt flow, heat transfer, ultrasound propagation, acoustic streaming and solidification. It was found that ultrasound irradiation alters the solidification behavior of melt and sump evolution especially in the earlier stage of casting, however as the billet length increases, the sump profile becomes almost the same for both the ultrasonic and conventional castings. In this condition, the casting speed becomes the key parameter influencing the sump evolution and mushy zone volume. The results reveal that ultrasound-driven acoustic streaming and turbulent oscillations result in a suppression of buoyancy flow in the sump and lead to an increase of frequency of the melt temperature oscillations at the solidification interface. One of the useful results of these phenomena can be a more frequent repetition of remelting/solidification cycle and improvement of the billet quality, particularly the billet surface morphology. The effect of ultrasound irradiation on the billet morphology was verified experimentally using a pilot DC caster.