Date of Award

Summer 2021

Publication Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

H. Hu

Second Advisor

J. Sokolowski

Third Advisor

R. Riahi

Keywords

Aluminum alloy, Casting section thickness, Interfacial heat transfer coefficient, Inverse method, Magnesium alloy

Rights

info:eu-repo/semantics/openAccess

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Abstract

The weight reduction of vehicles and airplanes in the automotive and aerospace industries is urgently needed due to the government regulation and market demand. To satisfy engineering performance of lightweight auto and aero components, high strength light alloys such as aluminum (Al) or magnesium (Mg) alloys are usually adopted. This study was intended to explore a solution for casting high strength cast and wrought Al and Mg alloys. Before light alloys can be utilized for mass production, critical processing parameters need to be accurately determined. The interfacial heat transfer coefficient is one of the most important factors in casting processes.

To start with this study, a step die was designed for squeeze casting with five different section thickness of 2, 4, 8, 12, and 20 mm, which were named steps 1, 2, 3, 4 and 5. An experiment was performed to investigate the effect of casting section thicknesses on the Interfacial Heat Transfer Coefficient (IHTC) during squeeze casting of aluminum cast alloy A380. This experiment focused on revealing the dependence of the IHTC on the heat flux for a specific section thickness as well as the IHTC variation with the step casting thickness under an applied pressure of 90 MPa during the solidification process. To understand the effects of both the applied pressures and section thicknesses on the IHTCs, magnesium cast alloy AZ91, and wrought alloy AZ31 were squeeze casted under the various applied pressures of 0, 30, 60, and 90 MPa. During squeeze casting, temperatures in the different locations of the step die and at the casting surface were recorded. Heat fluxes through the interface between the die and casting and the die surface and temperatures were calculated through the inverse method. With the calculated heat flux and die surface temperature as well as the measured casting surface temperature, the interfacial heat transfer coefficients as a function of time were obtained. With the IHTC versus time relation, the IHTC peak values of each step were identified, which were noticed to increase accordingly as the applied pressure and section thickness increased. In comparison with the thinner steps, the comparatively thicker steps exhibited higher heat fluxes and IHTC values under a specific pressure.

Lastly, the empirical equations relating the IHTCs to the section thickness and casting temperature for various applied pressures were derived by multivariate linear and polynomial regression for magnesium cast alloy AZ91 and wrought alloy AZ31. To demonstrate their application, the IHTC values determined by the inverse method were imported into the casting simulation software (MAGMAsoft) to simulate the solidification sequence of the five-step casting. The performed simulation revealed that the numerically computed temperatures were in excellent agreement with the experimental measurements.

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