Contactless Ultrasonic Treatment in Direct Chill Casting
Contactless Ultrasonic Treatment in Direct Chill Casting
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DOI：
10.1007/s11837-020-04370-7
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发表时间：
2020-10-02
期刊：
影响因子：
2.6
通讯作者：
Pericleous, Koulis
中科院分区：
文献类型：
--
作者：
Tonry, Catherine E. H.;Bojarevics, Valdis;Pericleous, Koulis
成分均匀、晶粒细化是有色合金铸锭直接激冷(DC)铸造的理想工艺特点。超声波处理是一种经过验证的实现晶粒细化的方法，通过额外的熔体搅拌来实现成分的均匀。为此，已采用浸入式声电极技术在直流铸造之前的熔池中和在水池中直接处理合金。在这两种情况下，混合都很弱，依赖于浮力驱动的流动，或者在后一种情况下依赖于声波流动。在这项工作中，我们考虑了一种直接用于连铸机的替代电磁技术，即在强烈的熔体搅拌的同时诱导超声波振动。这种非接触式声电极技术依赖于向熔体下降的千赫兹频率感应线圈，频率可调至熔池内的声学共振。数值模拟和物理实验相结合开发的技术已成功地批量应用于细化组织和脱除坩埚中的铝。在这项工作中，我们扩展了数值模型，耦合了电磁、流体流动、气体空化、传热和凝固，以考察在直流过程中使用的可行性。模拟表明，在强烈混合的熔池中可以获得一致的共振模式，空化所需的布莱克阈值处的高压区局限于液相线温度。认为由于空化引起的糊状区的极端条件会促进枝晶的破碎，再加上强烈的搅拌，将导致细小的等轴晶。
Uniformity of composition and grain refinement are desirable traits in the direct chill (DC) casting of non-ferrous alloy ingots. Ultrasonic treatment is a proven method for achieving grain refinement, with uniformity of composition achieved by additional melt stirring. The immersed sonotrode technique has been employed for this purpose to treat alloys both within the launder prior to DC casting and directly in the sump. In both cases, mixing is weak, relying on buoyancy-driven flow or in the latter case on acoustic streaming. In this work, we consider an alternative electromagnetic technique used directly in the caster, inducing ultrasonic vibrations coupled to strong melt stirring. This 'contactless sonotrode' technique relies on a kilohertz-frequency induction coil lowered towards the melt, with the frequency tuned to reach acoustic resonance within the melt pool. The technique developed with a combination of numerical models and physical experiments has been successfully used in batch to refine the microstructure and to degas aluminum in a crucible. In this work, we extend the numerical model, coupling electromagnetics, fluid flow, gas cavitation, heat transfer, and solidification to examine the feasibility of use in the DC process. Simulations show that a consistent resonant mode is obtainable within a vigorously mixed melt pool, with high-pressure regions at the Blake threshold required for cavitation localized to the liquidus temperature. It is assumed that extreme conditions in the mushy zone due to cavitation would promote dendrite fragmentation and coupled with strong stirring, would lead to fine equiaxed grains.