Abstract Magnesium – Zirconium master alloys are the dominant grain refiner for a range of commercial magnesium alloys that exhibit good elevated temperature properties. However, the grain refining efficiency achieved by the master alloy is relatively low because Zr particles quickly settle to form sludge. In this study ultrasonic treatment (UST) is applied to investigate whether the grain refinement efficiency can be improved by increasing the Zr solute content, producing a more uniform dispersion of Zr particles and minimizing sludge formation. It was determined that, for a range of Zr contents from 0.2 to 1.0 wt% Zr, UST of the melt above the liquidus temperature decreased the grain size due to an increase in the amount of solute Zr and the number of Zr particles. For Zr contents less than 0.5 wt% the grain size decreased further when UST was applied from above to below the liquidus temperature to include the onset of nucleation of α – Mg grains. Additionally, the application of UST substantially decreased the amount of sludge which increased the number density of Zr particles and improved their likelihood of successful nucleation. The Interdependence nucleation model was successfully applied to predict the grain size of each casting condition where the parameter z relates to the temperature gradient which in turn is affected by the acoustically-induced convection. A lower value of z when UST is applied facilitates nucleation and the survival of grains. The factors affecting grain refinement under each condition are evaluated in terms of solute and particle Zr contents, cavitation and acoustic streaming and their effect on nucleation and as-cast grain size.

中文翻译：

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超声波处理对添加到亚包晶和超包晶成分的镁中的 Mg-Zr 中间合金的合金化和晶粒细化效率的影响

摘要 镁 - 锆中间合金是一系列具有良好高温性能的商业镁合金的主要晶粒细化剂。然而，母合金实现的晶粒细化效率相对较低，因为 Zr 颗粒快速沉降形成污泥。在这项研究中，超声波处理 (UST) 被用于研究是否可以通过增加 Zr 溶质含量、产生更均匀的 Zr 颗粒分散和尽量减少污泥形成来提高晶粒细化效率。已确定，对于 Zr 含量为 0.2 至 1.0 wt% Zr 的范围，高于液相线温度的熔体的 UST 由于溶质 Zr 的量和 Zr 颗粒数量的增加而降低了晶粒尺寸。Zr 含量小于 0。当 UST 从液相线温度以上到以下应用 5 wt% 时，晶粒尺寸进一步减小，包括 α - Mg 晶粒的成核开始。此外，UST 的应用大大减少了污泥量，从而增加了 Zr 颗粒的数量密度并提高了它们成功成核的可能性。相互依存成核模型成功应用于预测每个铸造条件的晶粒尺寸，其中参数 z 与温度梯度有关，而温度梯度又受声诱导对流的影响。当应用 UST 时，z 值较低有利于成核和晶粒的存活。根据溶质和颗粒 Zr 含量评估每种条件下影响晶粒细化的因素，