Multiscale Modeling and Experimental Study of Defect Formation during Aluminum Alloy Solidification

在金属合金铸造过程中发生的凝固（液体到固体的转变）在确定纳米级所得材料的结构以及它们的机械性能方面起着重要作用。在铸造过程中的凝固过程中，液态金属表面与环境反应，导致金属氧化物的生成，其被称为氧化物双膜。 这些双膜可以导致材料中不同类型的缺陷，特别是在铝合金中，因为它们的高氧化速率。氧化物双膜在降低铝铸件的质量和可靠性方面起着重要作用，并且可以占铸件中总有效问题的80%之多。该奖项支持基础研究，研究氧化物双膜的形成和演变过程中的铝合金凝固。本研究的结果将为控制和减少铝铸件缺陷提供实用建议。 这项研究在汽车、航空航天和其他需要轻质、高强度和耐疲劳金属合金的工业中有应用。该项目还将有助于制造更轻、更节能的车辆。氧化物双膜现在被认为是微裂纹、微孔和其他疾病的主要原因，这些疾病会大大削弱铸件的机械性能。虽然有实验证据表明，这是与此假设相一致的，双膜在产生缺陷和缺陷产生的机制的作用主要是推测，因为没有直接的观察一直是可能的，双膜的机械性能是未知的，和双膜的演变和相互作用的物理过程中的结晶枝晶凝固不了解。研究小组将进行原子模拟，以确定氧化物双膜的高温机械性能。这些结果将被转移到一个新的多相场模型来模拟，第一次，双膜和凝固枝晶之间的相互作用，并跟踪双膜在凝固过程中的演变和变形。将进行宏观尺度的热流体分析，以确定相场模型的微观尺度区域的流体流动和热边界条件。将进行铸造和表征实验，以验证模型预测。

Solidification (liquid to solid transition) occurring during the casting of metallic alloys plays an important role in determining the structures of the resulting materials at the nanometer scale, as well as their mechanical properties. During solidification in a casting process, the liquid metal surface reacts with the environment, resulting in generation of metallic oxides, which are called oxide bifilms. These bifilms can lead to different types of defects in materials, especially in aluminum alloys because of their high rate of oxidation. Oxide bifilms play a major role in reducing the quality and reliability of aluminum castings and can account for as much as 80% of the total effective problems in castings. This award supports fundamental research to study oxide bifilm formation and evolution during solidification of aluminum alloys. The outcomes of this research will enable practical recommendations for controlling and reducing defects in aluminum casting. This research has applications in the automobile, aerospace, and other industries that demand lightweight, high strength and fatigue-resistant metallic alloys. This project will also contribute to the manufacture of lighter and more energy-efficient vehicles.Oxide bifilms are now believed to be the main cause of micro-cracks, microporosity, and other ailments that greatly weaken the mechanical properties of cast parts. While there is experimental evidence that is consistent with this hypothesis, the role of bifilms in producing defects and the mechanisms of defect creation are mostly conjecture, because no direct observation has been possible, the mechanical properties of bifilms are unknown, and the physics of bifilm evolution and interaction with crystalline dendrites during solidification is not understood. The research team will perform atomistic simulations to determine the high temperature mechanical properties of oxide bifilms. These results will be transferred to a new multi-phase-field model to simulate, for the first time, the interactions between bifilms and solidifying dendrites and to track the evolution and deformation of bifilms during solidification. Macro-scale thermal-fluid analysis will be performed to determine fluid flow and thermal boundary conditions for the micro-scale regions of the phase-field model. Casting and characterization experiments will be performed to validate the model predictions.