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Abstract. AA6013 is an age-hardenable, aluminum alloy with the potential for structural applications in weight-sensitive automotive components. The alloy is at peak strength in the T6 temper, but exhibits relatively low room temperature formability. In an effort to avoid costly post-forming heat-treatments, warm forming of the AA6013 in the T6 temper is investigated in the current work. The experimental formability of the alloy is characterized from room temperature to 250°C through limiting dome height (LDH) tests with a Nakazima hemispherical punch and in-situ stereoscopic digital image correlation (DIC) strain measurement. A forming limit diagram (FLD) is generated from the application of a curvature-based necking criterion to the elevated temperature LDH test results. The evolution of the strain distribution prior to necking is explored using models of the plane strain LDH tests at room temperature and 200°C. At 200°C, strain rate effects are explored relative to the local temporal strain evolution. Modelling efforts include development of a Barlat Yld2000 yield surface to capture the anisotropy of the alloy and use of experimentally obtained isothermal flow-stress curves. The effects of different tensile gage lengths on flow-stress and yield surface calibration for warm tensile testing are discussed. The room temperature model was found to accurately depict the thinning strain distribution consistent with the "safe" thinning strain distribution at room temperature. At 200°C, it is shown that the temporal strain evolution is strongly influenced by strain-rate effects. IntroductionThe application of aluminum in vehicle design and fabrication has seen a steady rise over the past two decades in an effort to meet increasingly stringent emissions and fuel economy mandates. To continue the trend of light-weighting, heat-treatable high-strength 6xxx and 7xxx aluminum alloys are under consideration for the fabrication of structural components that have historically been reserved for high-strength low-alloy steels. Heat-treatable aluminum alloys are at peak strength in the T6 temper, but have relatively low room temperature (RT) formability. To improve the formability of heattreatable alloys without altering the final temper, the warm forming processing route is considered [1].Before developing a warm forming processing route, the warm formability response of the intended alloy, often characterized in terms of a forming limit curve, must be established under processing parameters comparable to the intended application. So-called time-dependent methods have recently been proposed for use in elevated temperature forming applications [2], [3], [4], [5] and are a focus of the current work.

High temperature isothermal tensile tests were performed on an aluminized 1800 MPa press hardening steel with a Gleeble thermal-mechanical test system. A procedure was developed to enable the use of digital image correlation (DIC) analysis of the tensile specimens. Flow curves ranging from 500°C - 900°C with strain rates ranging from 0.01 s−1 – 1 s−1 were obtained. To validate this DIC procedure, flow curves for the more common PHS1500 (22MnB5) steel were also obtained in an identical manner and compared to results found in the existing literature. The resultant flow curves were then post-processed and fit to a thermal-viscoplastic constitutive equation for numerical simulation implementation. Finally, a finite element model of the tensile test was created to evaluate the accuracy of the constitutive results.

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