Mathematical modeling of the extrusion of 6061/Al 2 O 3 /20 p composite
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I.
INTRODUCTION
METAL matrix composites (MMCs) are now used in or being considered for use in a variety of applications, including automotive drive shafts, cylinder linings, brake rotors,[1] bicycle frames and components, and tire studs.[2] These MMCs are primarily particulate-reinforced aluminum alloys; for cast products, the composite is typically an aluminum casting alloy reinforced with SiC or Al2O3; while wrought products are based on an age-hardenable alloy, such as 6061 reinforced with Al2O3. The volume fraction of reinforcement is usually between 0.1 and 0.2.[1,2] One of the most cost-effective methods of producing large volumes of MMCs is to incorporate the ceramic into a stirred melt. The MMC billet material costs between US$4 and $8 per kg, and extrusions made using this billet stock are reported to sell for little more than their unreinforced counterparts.[2] However, even a slight increase in unit cost may lead to a large absolute cost when the volumes of components required in, for example, the automobile industry are considered.[1] It is essential to use conventional manufacturing equipW.C. CHEN, formerly Graduate Student, The Centre for Metallurgical Process Engineering, The University of British Columbia, is Senior Research Engineer, DSI, Poestenkill, NY 12140. C.H.J. DAVIES, formerly Postdoctoral Fellow, The Centre for Metallurgical Process Engineering, The University of British Columbia, is Lecturer, Department of Materials Engineering, Monash University, Clayton, Victoria 3168, Australia. I.V. SAMARASEKERA, Dofasco Chair in Advanced Steel Processing, J.K. BRIMACOMBE, Alcan Chair in Materials Process Engineering and Director, and E.B. HAWBOLT, Professor, are with The Centre for Metallurgical Process Engineering, The University of British Columbia, Vancouver, BC, Canada V6T 1Z4. Manuscript submitted December 15, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS A
ment for the extrusion of MMCs in order to reduce production costs and facilitate the penetration of MMCs into large-volume markets. However, MMCs suffer from poor workability and high cost when compared with their unreinforced counterparts. These factors mean that it is perhaps even more essential to optimize extrusion limits for MMCs than for unreinforced alloys. As the limits on workability become more restrictive, modeling plays a role in the characterization of the extrusion process. This article is a first step toward addressing these issues. A. Previous Work Several studies on the extrusion of particulate-reinforced MMCs have been reported.[1–5] An extensive review on extrusion of particulate-reinforced MMCs can be found in the literature.[6] Based on early extrusion trials done by Hains et al.,[3] it was found that (1) two kinds of defects occurred during extrusion of 6061 and 2014 with alumina-reinforced MMCs and (2) their behavior was very different from unreinforced alloys. First, considerable surface tearing occurred at the front end of the extrusion at low extrusion speeds, which persisted over the entire extruded length. How
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