Investigations into Improvement in Formability of AA5754 and AA6082 Sheets at Elevated Temperatures
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JMEPEG https://doi.org/10.1007/s11665-019-04030-1
Investigations into Improvement in Formability of AA5754 and AA6082 Sheets at Elevated Temperatures Sudhy S. Panicker and Sushanta Kumar Panda (Submitted September 29, 2018; in revised form February 28, 2019) Warm forming is an attractive formability improvement technique which can be utilized to intensify the usage of aluminum alloy sheets in autobody constructions. In the present work, laboratory-scale stretch forming and deep drawing experiments were performed to demonstrate the comparative formability improvement in AA6082-O and AA5754-H22 aluminum alloy sheets at elevated temperatures. Significant enhancement of limiting dome height and forming limit diagram (FLD) was observed when stretch forming was performed at 200 °C. Warm deep drawing under both isothermal and nonisothermal conditions was carried out, and drastic improvement in drawability was found only under nonisothermal condition with an initial temperature gradient of 93 °C across the blank. Thermomechanical finite element (FE) models of the warm forming processes were developed using temperature-dependent Barlat-89 yield model coupled with Cowper–Symonds strain rate sensitivity model. The limiting dome heights, failure locations and strain distributions were well predicted by implementing experimental FLD as the failure criterion. Further, the effect of evolution of nonisothermal temperature gradient on the improvement in drawability of both the materials was analyzed in terms of cup height, earing profile, thickness distribution and surface strain evolution. Keywords
aluminum alloy, FE model, formability, strain distribution, warm forming
1. Introduction The automotive sector is exploring different strategies to attain noise-free, and green or even zero emission due to increasing environmental concerns. Lightweighting with aluminum alloys emerged as an important strategy to improve the vehicle performance without compromising the safety features, ease in use and aesthetic appeal. The body-in-white produced by replacing the ubiquitously used low carbon steels with aluminum alloys results in a 40-60% reduction in overall car weight and 32% increase in fuel efficiency (Ref 1, 2). However, the low formability hindered the extensive applications of aluminum alloys in the automotive sector (Ref 3). Warm forming is a promising technique, where the sheet metal is deformed at elevated temperature but below the recrystallization temperature of the material. An existing setup may be modified to accommodate the heating arrangements. This method drastically improves the sheet metal formability with lower deformation load (Ref 4). Panicker et al. (Ref 5) reported a substantial reduction in uniaxial tensile strength of AA5052-H22, AA2014-T6 and AA6082-T6 sheets at 350 °C under different deformation velocities. Ozturk et al. (Ref 6) discussed that Portevin–Le Chatelier (PLC) phenomenon due to the activation of Dynamic
Sudhy S. Panicker and Sushanta Kumar Panda, Department of Mechanical Engineering, Indian Institute o
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