Date of Award

2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Hu, Henry

Keywords

aluminum alloy; heat transfer; squeeze casting

Rights

CC BY-NC-ND 4.0

Abstract

In automotive industry, the weight reduction in vehicles can be achieved by using new designed lighter engineering materials such as aluminum or magnesium alloys. To maintain the same performance as reducing the weight of the vehicles, high strength material has to be used. This study was aimed to develop a solution for casting high strength wrought aluminum alloys and magnesium alloys. Some critical process parameters need to be precisely pre-determined. The interfacial heat transfer coefficient is one of the most important factor. At beginning of this study, an experiment has been carried out to characterize the pressure distribution in the die cavity during squeeze casting of magnesium alloy AM50. This experiment aimed to reveal the changes of pressure distribution with the cavity geometry as well as the local cavity pressure at various locations during the solidification process. To understand the solidification and microstructure refining phenomena, squeeze casting of magnesium alloy AJ62 were performed under an applied pressure 60 MPa by using the simple cylindrical mold. A more complex shape casting mold with five different section thicknesses (2, 4, 8, 12 and 20 mm) was then developed. Wrought aluminum alloys 5083, 7075 and magnesium alloy AM60, AJ62 were squeeze casted under different applied pressures of 30, 60 and 90 MPa. With measured temperature, heat fluxes and interfacial heat transfer coefficients were determined using the inverse method. By observing the IHTC versus time curve profiles, the IHTC peak values of each step were found to increase accordingly as the applied pressure increased. In comparison with the thinner steps, the relatively thicker steps attained higher heat fluxes IHTCs values due to high local pressures and high melt temperature. Finally, the empirical equation relating IHTCs to the local pressures and solidification temperature at the casting surface were derived for wrought aluminum alloy 7075 and magnesium alloy AM60. For magnesium alloy AM60, the calculated IHTC values by using the inverse method were integrated into the casting simulation software (MAGMAsoft) to simulate the solidification process of the 5-step casting. The results indicated that the numerical calculated temperatures were in good agreement with the experimental measured temperatures.

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