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Advisory Committee Chair

Charles Monroe

Advisory Committee Members

Robin Foley

John Griffin

Document Type

Thesis

Date of Award

2017

Degree Name by School

Master of Science in Materials Engineering (MSMtE) School of Engineering

Abstract

The theory of predicting the formation of microporosity in specific alloy fami-lies—steel, aluminum, nickel, and magnesium— is particularly well developed, and it has become a common practice over the past several years. Combining a long solidification range, low thermal gradient, high cooling rate, and dissolved gases can lead to significant amounts of microporosity formation in these alloys. The use of the Niyama criterion has become a common tool for predicting the formation of microporosity in these alloy families. While the use of the Niyama criterion to predict microporosity formation has become routine for the alloys stated above, it is still not commonly used in the prediction of microporosity formation in copper-based alloys. This research aims to study the formation of microporosity formation in low-leaded copper alloys in order to gain a better understanding of the mechanisms that cause microporosity to form and develop methods for reducing its formation. In an attempt to understand the formation of microporosity in copper alloys, a high-leaded, low-leaded, and bismuth-containing copper alloy as well as a traditional leaded copper alloy were analyzed. A wedge casting with variations in cooling rates and the thermal gradient was studied. Cooling curves were generated, and simulation-based models were developed to evaluate the effects of composition on the microstructure and formation of microporosity in the alloys. Experimental results showed a maximum microporosity formation of approximately 3.8% in the leaded alloy and a maximum amount of approximately 7.6% microporosity formation in the unleaded alloy. The highest amount of microporosity in the copper-bismuth alloy falls approximately halfway between the other two compositions. There appeared to be a correlation between the simulation results and experimental results for all the compositions studied. All the information led to the development of a simulation-based model that could accurately predict the macrosegregation of the major alloying additions in these copper alloys.

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Engineering Commons

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