Role of Plastic Deformation on Elevated Temperature Tribological Behavior of an Al-Mg Alloy (AA5083): A Friction Mapping
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WHEN aluminum blanks come into contact with forming tools, a tribological system is created that determines the tool life and the surface quality of the final product. Superplastic forming (SPF) is a technique that takes advantage of superplasticity of fine-grained alloys such as AA5083[1–4] and uses gas pressure to force a heated aluminum blank to stretch into conformance with a die surface. An important improvement over SPF is the quick plastic forming (QPF) process that deforms AA5083 aluminum-magnesium (Al-Mg) alloy in the strain rate and temperature regimes of 1 9 104 to 5 9 103 s1 and T = 723 K to 818 K (450 C to 545 C), respectively.[5] A number of vital improvements in the heating/cooling and automated handling systems enable much faster forming cycles than were conventionally achieved by the SPF process.[5] QPF or, more specifically, the hot air blow forming process can be used to produce automotive body in white components with complex shapes such as present in liftgates and fenders.[6] The future advancement in aluminum hot and warm forming operations is intimately related to the control and improvement of the tribological conditions between S. DAS, PhD Student, A.R. RIAHI, Assistant Professor, X. MENG-BURANY, Research Associate, and A.T. ALPAS, Professor and NSERC/General Motors of Canada Industrial Research Chair, are with the Department of Mechanical, Automotive and Materials Engineering, University of Windsor, Windsor, ON N9B 3P4, Canada. Contact e-mail: [email protected] A.T. MORALES, Staff Research Scientist, is with the Chemical Science & Materials System Lab, General Motors Global Research and Development, Warren, MI 48090. Manuscript submitted August 7, 2010. Article published online March 29, 2011 2384—VOLUME 42A, AUGUST 2011
the aluminum blanks and the forming tool. The tribological problems that occur during these processes tend to be numerous and include metallic particle transfer to the tool, which leads to adhesion and surface damage to both the die and the workpiece.[7] The use of solid lubricants reduces adhesion of aluminum to the die surface.[8] The most commonly used lubricants in the SPF and QPF processes are boron nitride (BN) and graphite.[9] While graphite provides excellent lubricity at low cost, it decreases the efficiency of the subsequent sheet welding process, and so must be removed from the surface after forming. The use of coatings, including PVD and plasma-assisted CVD coatings based on TiAlN,[10,11] thermal spray coatings based on Cr compounds, and electroless nickel-based coatings have also been considered[12] to reduce the diesticking problem. Although improvements in achieving low friction at temperatures above 673 K (400 C) have been observed in laboratory tests, these coatings usually fall short of eliminating the industrial problems. Fundamental research aimed at understanding the factors that control friction and aluminum adhesion is essential to developing an effective lubricant or coating for improving the viability of the hot forming process that is sustain
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