Numerical and experimental investigation of the formability of AA6013-T6

Abstract

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.

Effect of Initial Temper on the Warm Forming Characteristics of a High Strength 7000-series Al-Zn-Mg-Cu Alloy

“…Formability characterization of the PA, T6 and T76 tempers was undertaken at room temperature (23°C), 150°C, 175°C and 200°C. Testing was accomplished using a double-acting hydraulic press with tooling heated by closed-loop controlled embedded heater cartridges, as described in [9] and [17]. The specimens were heated in-situ, with typical heating curves measured at the specimen flanges plotted in Figure 2c).…”

“…Necking is assumed to have initiated once changes in the surface curvature occur due to initiation of an acute neck. The curvature approach applied in this work is termed the Enhanced Curvature Method (ECM) and was built upon the method developed by DiCecco et al [9], [17]. For comparison purposes, limit strains are also computed using the ISO12004:2-2008 methodology.…”

Investigation on Yield Behavior of 7075-T6 Aluminum Alloy at Elevated Temperatures

“…Warm forming technology is a promising approach to improve the formability of peak-aged 7075 aluminum alloys (AA7075-T6) [6][7][8][9], where the AA7075-T6 blank is heated to target temperatures followed by warm forming with heated or cold dies. The formability of aluminum alloys under warm conditions can be evaluated by forming limit curves (FLCs) [10,11]. Sotirov et al [12] obtained temperature-dependent forming limits of EN AW-7075-T6 using the Nakazima tests and found that the major strain of FLC raised from 0.15 to 0.3 at plane strain condition as the temperature increased from room temperature to 230 °C.…”

Investigation on Yield Behavior of 7075-T6 Aluminum Alloy at Elevated Temperatures

“…Warm forming technology is a promising approach to improve the formability of peak-aged 7075 aluminum alloys (AA7075-T6) [5][6][7][8], where the AA7075-T6 blank is heated to target temperatures followed by warm forming with heated or cold dies. The formability of AA7075-T6 under warm conditions can be evaluated by forming limit curves (FLCs) [9][10]. Sotirov et al [11] obtained temperature-dependent forming limits of EN AW-7075-T6 using the Nakazima tests and found that the major strain of FLC raised from 0.15 to 0.3 at plane strain condition as the temperature increased from room temperature to 230℃.…”