Fundamentals of grain coalescence and applications to aluminum alloy industrial solidification processes

近终形铸造为复杂形状的轻金属合金零件的制造提供了最经济有效的方法。然而，热裂等铸造缺陷降低了产品质量和工艺效率。热裂的特征是半固态金属合金由于晶粒之间的液膜破裂而自发失效，并且在接近凝固结束时发生，其中变形变得局部化到晶界。热裂的发生与半固体从被液体包围的孤立颗粒逐渐演变成连贯和分散的固体网络密切相关，这一过程称为颗粒聚结。如果晶粒聚结被延迟并因此在较低温度下完成，则热裂敏感性显著增加。 该发现资助研究计划的目标是开发晶粒聚结过程的新知识，然后应用新知识来提高用于汽车和航空航天领域的高强度Al-Cu铸造合金的质量。在接下来的5年里，我的研究团队将利用实验和模拟来量化合金含量和工艺参数对晶粒聚结动态演变的影响，以及该过程对半固态本构行为和热撕裂的影响。通过这项研究，7 HQP将在开发过程/结构/缺陷的现象学模型，并在铝合金铸造过程的数学模型中应用这些关系进行培训。 研究方法：作为第一步，将开发一个数值模型来预测颗粒聚结。同时，将创建具有已知微观结构的模型材料，然后将其用作聚结过渡的原位（约束铸造试验）和非原位（半固态拉伸试验）表征的一部分。然后，实验和数值结果将被用来提出一个半固态力学行为的本构关系的动态演变的聚结的基础上。最后，新的工具将被应用到用于生产潮汐涡轮机应用由B206（工业铝铜铸造合金）制成的组件的砂型铸造过程的有限元模拟，以证明在工业过程中预测热裂的改进能力。 工业影响：热裂是降低铝合金铸造和锻造产品生产率的主要缺陷。在许多情况下（例如高可靠性的复杂形状铸件），由于这种缺陷的高发生率，产品甚至无法制造。这项研究的结果预计将导致一个大大改善的理解聚结，因此热撕裂，并将提供一个预测工具，供工业使用的宏观尺度的工艺模拟的铝铜铸件。

Near-net-shape casting provides the most cost-effective way to manufacture light metal alloy components of complex shape. However, casting defects such as hot tearing reduce product quality and process efficiency. Hot tearing is characterized as a spontaneous failure of semi-solid metallic alloys due to the rupture of liquid films between grains, and occurs near the end of solidification where deformation becomes localized to the grain boundaries. The occurrence of hot tearing is intimately linked with the semi-solid's gradual evolution from isolated grains surrounded by liquid to a coherent and percolated solid network, a process known as grain coalescence. If grain coalescence is retarded and therefore finishes at lower temperatures, hot tearing susceptibility is significantly increased. The objective of this Discovery Grant research program is to develop new knowledge of the process of grain coalescence, followed by application of the new knowledge to improve the quality of high-strength Al-Cu casting alloys that are used in the automotive and aerospace sectors. Over the next 5 years, my research team will utilize experimentation and simulation to quantify the influence of alloy content and processing parameters on the dynamic evolution of grain coalescence, and the impact of this process on semi-solid constitutive behaviour and hot tearing. Through this research, 7 HQP will be trained in developing processing/structure/defect phenomenological models, and in applying these relationships within mathematical models of aluminum alloy casting processes. Research Approach: As a first step, a numerical model will be developed to predict grain coalescence. Concurrently, model materials with known microstructure will be created and then used as part of in-situ (restrained casting tests) and ex-situ (semi-solid tensile tests) characterization of the coalescence transition. Then, the experimental and numerical results will be used to propose a constitutive law of semi-solid mechanical behaviour based on the dynamic evolution of coalescence. Finally, the new tools will be applied to a finite element simulation of the sand casting process used to produce components made from B206 (an industrial Al-Cu casting alloy) for a tidal turbine application to demonstrate the improved ability to predict hot tearing in an industrial process. Industrial Impact: Hot tearing is a major defect that lowers the productivity of aluminum alloy casting and wrought products. In many cases (e.g. high reliability complex shape castings), products cannot even be manufactured because of the high occurrence of this defect. The results of this research are anticipated to lead to a greatly improved understanding of coalescence and hence hot tearing, and will provide a predictive tool for use by industry in macro-scale process simulations of Al-Cu castings.