Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Anthony G. Straatman

2nd Supervisor

Jeffrey T. Wood

Joint Supervisor

Abstract

A formulation used to simulate the solidification process of magnesium alloys is developed based upon the volume averaged finite volume method on unstructured collocated grids. To derive equations, a non-zero volume fraction gradient has been considered and resulting additional terms are well reasoned. For discretization the most modern approximations for gradient and hessians are used and novelties outlined. Structure-properties correlations are incorporated into the in-house code and the proposed formulation is tested for a wedge-shaped magnesium alloy casting. While the results of this study show a good agreement with the experimental data, it was concluded that a better understanding of the boundary condition that existed during the experiment would result in a more agreeable result.

A variety of boundary conditions are considered at the mold-casting interface to replicate the existing conditions during the casting process. The predicted cooling rates and experimental correlations are used to predict the local grain size and average yield strength. The grain size and thickness of the skin and core regions are taken into account to modify the local yield strength. Results are compared to previously reported experimental data. The outcome of this comparison emphasizes the importance of the influence of cooling rate on the mechanical properties of castings. The effect of different boundary conditions, which resulted in variation of the cooling rates, various grain sizes and, hence, various yield strengths are studied and discussed.

It is concluded that the formulation and the numerical treatment presented in this work can be used as an excellent framework to capture the key features of the solidification process, and also provides sufficient microstructural information for estimating the local mechanical properties of die-cast components.