Development of microstructural solidification simulation code for light alloys

候选人研究的最终目标是开发基于热力学数据库和动力学模型的高温工业冶金过程虚拟模拟工具。为了实现这一目标，以前的发现基金(DG)专注于开发火法冶金和合金的热力学数据库。在过去的五年里，根据DG和其他研究资助的结果，开发了许多热力学数据库。在这个DG中，应聘者希望开发一个动力学凝固模型，以便将这些热力学数据库用于实际铸造过程。 大多数轻合金产品都是通过铸造工艺生产的。因此，铸态组织是控制力学性能的决定因素之一。然而，铸态组织随铸造工艺参数的变化规律仍未得到很好的研究。在铸造行业中，计算流体力学和热流模拟主要用于了解非常复杂的铸造模具中的充型行为。不幸的是，这样的软件不能提供关于铸造条件的准确的显微组织信息。另一方面，相场模拟是从二维和三维的角度模拟铸态组织的发展过程，但计算速度太慢，不能直接应用于多组分合金的实际铸造模拟。因此，需要一种简单而实用的动力学微观组织模拟模型来进行铸造材料的计算设计。 在目前的研究计划中，将开发一个通用的具有用户界面的一维微观组织凝固模型，以涵盖各种铸造条件下的各种商业镁合金和铝合金。目前还没有这种专门的凝固模拟工具可用于镁合金和铝合金。在过去的几年里，候选人的研究小组进行了基础和全面的铸造实验，以了解镁铝锌合金铸态组织的演变，并进行了镁单晶扩散偶实验，以测量镁铝和镁锌系统的扩散系数。在一维微组织凝固模型中，将考虑所有用于解释凝固过程中组织发展的关键凝固理论。此外，可以计算固相线、液相线和平衡第二相的热力学数据库将动态连接到动力学凝固模型。该凝固模型能在较短的时间内(不到10min)计算出一次枝晶和二次枝晶间距、枝晶中溶质偏析以及二次析出物的数量等所有重要的凝固组织特征。为了验证模型计算的有效性，将对镁合金和铝合金进行良好的控制铸造实验。此外，还将进行扩散偶实验，以确定各种溶质在镁合金中的扩散系数。 所建立的动力学模型和实验结果可以对镁铝合金的凝固过程有更科学的认识。动力学凝固模型最终可以直接或间接地与CFD模拟工具相连接，以预测铸态组织。加拿大的许多铸造公司，包括阿尔坎、Novelis和Sapa，以及通用汽车加拿大公司等最终材料用户将能够在他们的铸造工艺优化和新材料开发中使用先进的知识。4名博士生和0.5名PDF将在拟议的研究计划的5年内接受培训。

The ultimate goal of the candidate’s research is the development of virtual simulation tools for high temperature industrial metallurgical processes based on thermodynamic databases and kinetic models. In order to achieve this goal, the previous Discovery Grant (DG) focused on the development of thermodynamic database for pyrometallurgy and alloys. Many thermodynamic databases have been developed as the results of DG and also other research grants over the last five years. In this DG, the candidate would like to develop a kinetic solidification model to utilize such thermodynamic database for real casting process. Most of light alloy products are produced through the casting process. Therefore, the as-cast microstructure is one of the determining factors that control the mechanical properties. However, the evolution of as-cast microstructures with casting parameters is still not well investigated. In the casting industry, computational fluid dynamics and heat flux simulations performed by commercial software packages like FLUENT and MAGMA are mostly used to understand the filling behavior in very complex casting molds. Unfortunately, such software cannot provide accurate microstructural information about the casting conditions. On the other hand, phase field modeling was pursued to simulate the development of as-cast microstructures in 2-D and 3-D views, but the calculation is too slow to be directly applied to the practical casting simulation of multicomponent alloys. So, a simple but practical kinetic microstructure simulation model is needed for computational materials design in casting. In the present research program, a versatile 1-D microstructural solidification model with a user interface will be developed to cover a wide range of commercial Mg and Al alloys under a wide range of casting conditions. No such dedicated solidification simulation tool is currently available for Mg and Al alloys. In the past years, the candidate’s research group has carried out fundamental and comprehensive casting experiments to understand the evolution of the as-cast microstructure of Mg-Al-Zn alloys and Mg single crystal diffusion couple experiments to measure the diffusivity in Mg-Al and Mg-Zn systems. All key solidification theories to explain the microstructure development during solidification will be taken into account in the 1-D microstructural solidification model. Moreover, the thermodynamic database, which can calculate solidus, liquidus and equilibrium secondary phases, will be dynamically linked to the kinetic solidification model. This solidification model will calculate, within a short time (less than 10 min), all the important solidification microstructural features such as the primary and secondary dendrite spacing, the solute segregation in dendrite, and the amount of secondary precipitates according to casting parameters at a given alloy. In order to validate the model calculations, well-controlled casting experiments will be performed for Mg and Al alloys. In addition, diffusion couple experiments will be carried out to determine the diffusivities of various solutes in Mg alloys. The kinetic model and experiment can give deep scientific understanding of the solidification process of Mg and Al alloys. The kinetic solidification model can be eventually linked directly or indirectly to CFD simulation tools to predict the as-cast microstructure. Many casting companies in Canada including Alcan, Novelis and Sapa and final materials users like GM-Canada will be able to use the developed knowledge in their optimization of casting processes and the development of new materials. 4 Ph.D. students and 0.5 PDF will be trained over 5 years of the proposed research program.