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Extrusion of alumina particulate reinforced metal matrix composites

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Title: Extrusion of alumina particulate reinforced metal matrix composites
Author: Chen, Wei Chang
Degree: Doctor of Philosophy - PhD
Program: Materials Engineering
Copyright Date: 1995
Issue Date: 2009-06-04
Series/Report no. UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/]
Abstract: Alumina particulate reinforced metal matrix composite is a new kind of material, which has wide potential applications in automobile industry. The study of its physical nature during extrusion process is essential to optimize the process which may improve its mechanical properties and increase its productivity to finally reduce its cost and make it more competitive to other materials. Constitutive equations were developed for the alumina particulate reinforced metal matrix composites (Duralcan materials) based on the hot deformation tests on a ‘Gleeble 1500’ machine. Plant trials were conducted for the same materials in both a laboratory extrusion device at Kingston R & D Center (KRDC), and an industrial extrusion press at Universal Alloy Corporation, California. Different temperatures and extrusion ratios with different ram speeds were adopted during extrusion. Low speed cracking was observed at the front end of some extrudates, which has not been observed with the unreinforced aluminum alloy (AA6061). Microstructure change with particle fracture and particle distribution was studied using an optical microscope and an image analyzer in the deformation zone of a billet and the extrudates from the plant trials. The extrusion processes have been simulated with the aid of a finite element model. The plant trial data were used to validate the model predictions. The model predictions at both a macroscopic and a microscopic level were correlated with microstructural changes. Extrusion Jimit diagrams for both composites of 6/0230l6O1/Ap1 and 6/02302610/Ap1 were developed with low speed cracking boundaries included for the press at UAC. The mechanism of the low speed cracking was proposed based on the FEM and SEM analysis. Although low-speed cracking was proposed to be associated with void formation in the surface layer of the extrudates, the voids were not significant to the effect of tensile properties, because the elastic modulus, the yield stress and the ultimate tensile strength measured from extrudates of the plant trials at KRDC did not decline at extrusion ratios from 10 to about 30. Minimization of void formation in the composites was discussed and recommendations have been provided for optimization of the extrusion of the alumina particulate reinforced MMCs.
Affiliation: Applied Science, Faculty of
URI: http://hdl.handle.net/2429/8767
Scholarly Level: Graduate

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