Weld metal ductility in aluminum tailor welded blanks
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I. INTRODUCTION
THE automobile industry is continually working to develop and apply technology that reduces the cost and weight of automobiles. The intent of these efforts is to minimize the energy consumption and environmental impact of vehicles. Tailor welded blanking is a technology that allows vehicle designers to reduce component weight and the number of components in a structure without compromising the final strength, stiffness, and durability of the component. Tailor welded blanks consist of multiple sheet materials joined with welds to produce a single variable thickness and/or alloy stamping blank. Automobile manufacturers are finding more and more applications for the use of steel tailor welded blanks in current vehicle designs. Currently, aluminum tailor welded blanks are being investigated for potential use in aluminum intensive vehicles to further reduce vehicle weight. A photograph of a prototype aluminum tailor welded blank is shown in Figure 1. The formability of aluminum tailor welded blanks currently is an area of considerable interest to the automobile industry.[1–3] Although tailor welded blank technology is effective at minimizing material use and thus vehicle weight, the stamping process is complicated by the existence of welds in the blank.[4,5] Product design and process reliability for components produced in this way become critical issues when compared to designs and processes based on monolithic sheet stamping. From a process modeling standpoint, the weld produces a geometric discontinuity that is more difficult to accurately model than monolithic sheet stamping. In addition, if a model does accurately predict the stress and strain imposed on the weld during stamping, the weld metal limits of formability are substantially unknown. R.W. DAVIES, Senior Development Engineer, M.T. SMITH, Technical Group Manager, and M.A. KHALEEL and S.G. PITMAN, Staff Engineers, are with Battelle Pacific Northwest National Laboratory, Richland, WA 99352. H.E. OLIVER, Team Leader of Project Engineering and Technology, is with the Reynolds Metals Company, Chester, VA. Manuscript submitted August 17, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
Prior research has focused on the problem of describing the formability of aluminum tailor welded blank material in stamping applications.[6–10] Most of this research has focused on performing simulative stamping tests and placing welds within a standard size tensile specimen. These methods provide insight into the combined properties of the material, but they offer limited quantitative means of describing the weld metal ductility individually. The research described in this article produced a series of tensile specimens with the weld oriented longitudinal to the tensile axis. The specimens were designed with varying amounts of cross-sectional gage area, which resulted in varying amounts of specimen gage area comprised of weld material. The experimental results exhibit a trend that indicates increasing the amount of weld in the specimen gage area will lead to a dec
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