Effect of pattern and coating properties on defect formation in aluminum lost foam castings

<p>"This dissertation focuses on some of the factors affecting defect formation and the characterization of these defects in aluminum lost foam castings. Several statistically designed experiments were used to evaluate the effects of various gating designs, aluminum alloy compositions, foam pattern properties, and coating properties. Metal velocity measurements, along with the number, type, and size of defects, were used as response variables.</p> <p>Foam properties of interest in this dissertation included foam density, fusion level, and bead chemistry. Decreasing the nominal density of the pattern was found to decrease the total amount of defects. The same was true when a high fusion level was used. It was determined that the current qualitative measure of fusion level is not adequate; a quantitative measure needs to be developed. This research also revealed that the use of beads containing a bromide additive significantly reduced the amount of defects found in the castings, particularly for conditions where the metal temperature is low or solidification times are short.</p> <p>Coating properties of interest were permeability and thickness. Both of these properties can be controlled via the viscosity of the coating slurry applied to the pattern. It was found that decreasing the permeability and increasing the thickness of the coating decreased the total amount of defects in the casting.</p> <p>Defect characterization was done using Auger spectroscopy, scanning electron microscopy (SEM), and optical metallography. Auger results revealed that the color of the defect changed with carbon layer thickness. SEM imaging showed the presence of wrinkles on fold surfaces while no wrinkles were found on the surface of pores"--Abstract, page iii.</p>

Name thesis:degree_name

Ph. D. in Metallurgical Engineering

Grantor

University of Missouri--Rolla

Year dc:date.available

2016

Author dc:creator

• Hess, Devin Ray

• Metallurgy

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/1449

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-2451