Development of microstructural solidification simulation code for light alloys

候选人研究的最终目标是基于热力学数据库和动力学模型开发高温工业冶金过程的虚拟仿真工具。为了实现这一目标，上一个发现基金（DG）专注于高温冶金和合金热力学数据库的开发。在过去的五年里，许多热力学数据库都是作为DG和其他研究赠款的结果而开发的。在这个DG中，候选人希望开发一个动力学凝固模型，以利用真实的铸造过程的热力学数据库。 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，铸态组织的演变与铸造参数仍然没有得到很好的研究。在铸造行业中，FLUENT和MAGMA等商业软件包执行的计算流体动力学和热流模拟主要用于了解非常复杂的铸造模具中的填充行为。不幸的是，这样的软件不能提供关于铸造条件的精确的微观结构信息。另一方面，相场模型被用来模拟二维和三维视图中的铸态组织的发展，但计算太慢，不能直接应用于多组分合金的实际铸造模拟。因此，铸造材料的计算机设计需要一个简单实用的动态组织模拟模型。 在本研究计划中，将开发一个通用的1-D微观组织凝固模型与用户界面，以涵盖广泛的商业镁和铝合金在广泛的铸造条件下。目前没有这样的专用凝固模拟工具可用于镁和铝合金。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Mg-Al-Zn合金的铸态显微组织的演变和Mg单晶扩散偶实验，以测量Mg-Al和Mg-Zn系统的扩散率。所有关键的凝固理论来解释凝固过程中的微观结构的发展将被考虑在1-D微观结构凝固模型。此外，热力学数据库，可以计算固相线，液相线和平衡第二相，将动态连接到动力学凝固模型。该凝固模型将在短时间内（小于10 min）计算所有重要的凝固微观结构特征，如一次和二次枝晶间距、枝晶中的溶质偏析以及根据给定合金的铸造参数的二次析出物的量。为了验证模型计算，将对Mg和Al合金进行良好控制的铸造实验。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。 该动力学模型和实验结果可为镁铝合金凝固过程的研究提供科学依据。动力学凝固模型最终可以直接或间接地连接到CFD模拟工具，以预测铸态显微组织。加拿大的许多铸造公司，包括Alcan，Novelis和Sapa以及最终材料用户，如GM-Canada，将能够在铸造工艺优化和新材料开发中使用开发的知识。4位博士学生和0.5 PDF将接受培训超过5年的拟议研究计划。

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.