Contactless Ultrasonic Processing for Liquid Metals

在为运输和航空航天工业寻求更轻、更强的金属的过程中，我们的目标是在这项研究中开发和评估一种非接触式电磁激励装置，该装置在液态金属熔体中产生振动，用于超声波处理（UST）。轻质合金金属（铝或镁）在液态的UST已被证明可以改善其最终的机械性能，导致更精细的微观结构，去除溶解气体，或分散强化颗粒。浸入熔体中的“声纳电极”探头通常用于这种UST工艺，以超声波频率（~20-100 kHz）振动，并在熔融金属中产生强烈的声波。这些压力波使溶解的气体以微气泡的形式从溶液中出来（想想香槟），然后在大小上振荡，要么内爆产生高速射流和冲击波，要么扩大到它们漂浮到表面并脱离熔体的点。这种空化现象有助于晶体成核和/或破坏新出现的枝晶，从而减小晶粒尺寸，从而改善材料性能。氧化物形式的强化颗粒用于金属复合材料以改善其性能。然而，很难将这些颗粒均匀分散，以确保最终组件的均匀性能。此外，非常小的颗粒容易聚集在一起成为缺陷。众所周知，气泡坍塌产生的冲击波会破坏颗粒团，但随后还需要强烈的搅拌才能均匀地分散它们。在铝回收中也需要同样的颗粒分散要求，以分散不需要的夹杂物，如氧化物或铁素体金属间颗粒。因此，UST是一种非常有用的工艺，但即使在低温熔体（Al, Mg）中，也存在阻碍工业广泛应用的问题：浸入式探针被消耗污染熔体；被处理的物质被限制在声极喇叭周围的小体积内，然后需要进一步的机械搅拌来传播效果。这里提出的非接触式UST将避免污染和外来探针材料的成本，将UST的潜在优势转移到更广泛的合金中，避免了大多数缺点：(a)批量自动产生的电磁搅拌的洛伦兹力,(b)扩大是很容易的,自感应线圈可以设计适合应用程序,提供了电源频率调谐促进共振,(c)由于没有接触,没有污染的融化,或需要更换频繁的调查最后(d)高温或活性金属用于电力或航空发动机应用程序可以以同样的方式对待(viz.核钢,获得专利的“非接触式Sonotrode”概念源于理论工作和在格林威治进行的计算机模拟；但要将其巨大的理论潜力转化为实用的制造技术，还需要通过伯明翰大学和牛津大学提出的实验项目进行仔细的实际验证。伯明翰的原型装置将研究坩埚熔体中的轻合金、钢和镍，而牛津大学将在铝锭生产的直接冷却（DC）连续铸造工艺中测试这一想法。

In the quest for lighter, stronger metals for the transport and aerospace industry we aim in this research to develop and evaluate a contactless electromagnetic excitation device producing vibration in liquid metal melts, for the purpose of Ultrasonic treatment (UST). UST of light alloy metals (aluminium or magnesium) at the liquid state, has been shown to improve their final mechanical properties, leading to finer microstructure, removal of dissolved gases, or dispersion of strengthening particles. A 'sonotrode' probe immersed in the melt is commonly used for this UST process, vibrating at ultrasonic frequency (~20-100 kHz) and generating intense sound waves in the molten metal. These pressure waves cause dissolved gas to come out of solution in the form of micro-bubbles (think of champagne), then oscillate in size and either implode generating high speed jets and shock waves or enlarge to the point where they float to the surface and out of the melt. This cavitation phenomenon assists crystal nucleation and/or breaks up emerging dendritic crystals to reduce grain size and so improve material properties. Strengthening particles in the form of oxides are used in metal composites to improve their properties. However, it is difficult to disperse these particles evenly, ensuring homogeneous performance in the final component. Furthermore, very small particles tend to cluster together becoming defects. The action of shock waves produced by collapsing bubbles is known to break up particle clusters, but then strong stirring is also needed to disperse them evenly. The same particle dispersion requirement is needed in aluminium recycling, to disperse unwanted inclusions, such as oxides or ferritic intermetallic particles. So UST is a very useful process but even in low temperature melts (Al, Mg), there are problems preventing widespread use by industry: the immersed probe is consumed contaminating the melt; the mass treated is restricted to a small volume surrounding the sonotrode horn, and further mechanical stirring is then necessary to spread the effect. Contactless UST as proposed here will avoid contamination and the cost of exotic probe materials, transferring the potential benefits of UST to a wider range of alloys, avoiding most of the drawbacks: (a) Bulk stirring is automatically generated by the electromagnetic 'Lorentz' force, (b) Scale-up is easy, since the induction coil can be designed to fit the application, provided the supply frequency is tuned to promote resonance, (c) Since there is no contact, there is no contamination of the melt, or need for a frequent probe replacement and finally (d) high temperature or reactive metals used in power or aeroengine applications can be treated in the same way (viz. nuclear steels, nickel and titanium alloy blades) The patented 'Contactless Sonotrode' concept originated from theoretical work and computer simulations carried out in Greenwich; but to translate its immense theoretical potential into a useful manufacturing technique, careful practical validation is needed through the proposed experimental programme at Birmingham and Oxford Universities. A prototype installation at Birmingham will investigate light alloys, steel and nickel in crucible melts, whilst Oxford will test the idea in the Direct Chill (DC) continuous casting process for aluminium ingot production.