Upscaling environment-friendly cavitation melt treatment (UltraMelt #2)

我们对金属的使用是如此重要，以至于它定义了人类文明的各个时期--从青铜时代(公元前3600年)到铁器时代(公元前1100年)。随着我们今天对金属和合金的掌握，现在越来越重视资源和环境。金属工业正在寻找新的方法，以可持续、经济和无污染的方式生产更轻、更坚固的材料。超声波空化处理为实现这些目标提供了一条途径。超声波处理第二常见的结构金属铝，通过排出导致气孔的溶解气体、细化颗粒以帮助成形性、分散和分布固体或不混溶相以改善回收过程中的机械性能等来进行除气。尽管有这些好处，但将这项有前途的技术转移到工业中一直存在困难，特别是在处理大量液态金属方面，这些液态金属通常用于‘直接冷却’连铸生产钢锭。需要基础研究来回答以下实际问题：在最大限度地提高处理效率的同时将输入功率、成本和设备复杂性降至最低的最佳熔体流动速度是什么？加速治疗效果的最佳工作频率和声功率是多少？相对于熔池几何形状，超声波电源在熔体传输系统中的最佳位置是什么？回答这些问题将为超声波熔体处理在工业上的广泛应用铺平道路，同时改善轻质结构合金的性能，同时减少目前用于脱气或昂贵的(Zr，Ti，B，Ar)颗粒细化添加剂的污染(Cl，F)。这项研究利用提出者在非常成功的UltraMelt项目(22篇出版物)期间获得的独特专业知识，旨在通过开发一个综合的数值模型来应对有效处理大量液体的挑战，该模型结合了所有涉及的物理学：流体流动、传热、凝固、声学和气泡动力学。Greenwich将在波动方程和守恒定律的基础上，领导改进的空化模型的发展，并将其应用于气泡在熔体中的破碎和传输及其与固体夹杂物(例如，铝合金或任何金属间杂质的凝固前沿)的相互作用的两相问题。为了提高超声空化处理流动金属的效率，将使用一种清洗管道。该过程对不同可调参数(源功率、频率、空化区时间、挡板位置等)的敏感性。将在洗衣机熔体流动的3D模型中用并行计算进行检验。这个计算机模型将通过在透明液体和铝中的实验来验证。水和透明有机合金实验将使用牛津布鲁克斯大学的PIV技术来测量气泡的大小、数量和位置，并将这些结果与数值预测进行比较。将使用布鲁内尔大学的高速相机和钻石光源设施的X射线照相术实时观察金属间化合物破碎和粒子团分解的机制。与Anton Paar有限公司合作，将使用独特的纳米压痕技术测量金属间杂质在与熔体加工相关的温度下的机械性能。将在布鲁内尔大学进行洗涤管道中的空化压力测量，并将经验观察结果与模型预测进行比较。全面开发的模型将用于优化直接冷却铸造过程中熔体流动中的超声波熔体处理，并使用AMCC(Brunel，在Constellium的支持下)的中试设施和凯撒铝业的工业规模设施进行验证。

Our use of metals is so important that it defines periods of human civilisation - from the Bronze Age (c. 3600 BC) to the Iron Age (c. 1100BC). With our present-day mastery of metals and alloys, the mounting emphasis is now on resources and the environment. The metals industry is looking at new ways to produce lighter, stronger materials in a sustainable, economical and pollution-free manner. Ultrasonic cavitation treatment offers a route to meet these goals. Ultrasonic treatment of the second commonest structural metal, aluminium, causes degassing through the evacuation of dissolved gases that lead to porosity, grain refinement to assist formability, dispersion and distribution of solid or immiscible phases to improve mechanical properties during recycling etc. In spite of the benefits, transfer of this promising technology to industry has been plagued by difficulties, especially in treating large volumes of liquid metal typical in processes such as 'Direct Chill' continuous casting for ingot production. Fundamental research is needed to answer the following practical questions: what is the optimum melt flow rate that maximises treatment efficiency whilst minimizing input power, cost, and plant complexity? What is the optimum operating frequency and acoustic power that accelerates the treatment effects? What is the optimum location of an ultrasonic power source in the melt transfer system in relation to the melt pool geometry? Answering these questions will pave the way for widespread industrial use of ultrasonic melt processing with the benefit of improving the properties of lightweight structural alloys, simultaneously alleviating the present use of polluting (Cl, F) for degassing or expensive (Zr, Ti, B, Ar) grain refinement additives.Capitalising on the unique expertise gained by the proposers during the highly successful UltraMelt project (22 publications), this research aims to answer the challenge of efficiently treating large liquid volumes by developing a comprehensive numerical model that couples all the physics involved: fluid flow, heat transfer, solidification, acoustics and bubble dynamics. Greenwich will lead the development of an improved cavitation model, based on the wave equation and conservation laws, and applied to the two-phase problem of bubble breakup and transport in the melt, and its interaction with solid inclusions (e.g. the solidification front of an aluminium alloy or of any intermetallic impurities present). To improve the efficiency of the ultrasonic cavitation treatment in flowing metal, a launder conduit will be used. The sensitivity of the process with respect to different adjustable parameters (source power, frequency, time in the cavitation zone, baffle location ...) will be examined with parallel computations in a 3D model of melt flow in the launder. This computer model will be validated by experiments in both transparent liquids and aluminium. Water and transparent organic alloy experiments will use a PIV technique by Oxford Brookes University to measure the size, number and positions of bubbles and compared these with the numerical predictions. Mechanisms of intermetallic fragmentation and particle cluster breakup will be observed in real time using a high speed camera at Brunel University and X-ray radiography at the Diamond Light Source facility. Mechanical properties of intermetallic impurities at temperatures relevant to melt processing will be measured using unique nano-indentation technique in collaboration with Anton Paar Ltd. Cavitation pressure measurements in launder conduits will be conducted at Brunel University and the empirical observations will be compared with model predictions. The fully-developed model will be used to optimise the ultrasonic melt treatment in melt flow during direct-chill casting and verified using pilot-scale facilities at AMCC (Brunel, with support of Constellium) and industrial-scale facilities at Kaiser Aluminum.