Warm HydroForming of the heat treatable aluminium alloy AC170PX

•Ageing is effective in the AC170PX for times larger than 400 s.•In the range 250–300 °C the UTS% is reduced when increasing the strain rate.•High strain rates and the temperature of 200 °C are optimal process conditions when forming the AC170PX.•Die cavity filling is improved from 50% to 67% and the thinning reduced.•Short forming times make the process less critical and industrially more attractive.

In this work the Warm HydroForming process of a 6xxx series Al alloy has been investigated in order to find suitable process parameters for successfully forming a benchmark component displaying varying deformation ratios due to its geometry. Since the attention was focused on the 6xxx series alloy AC170PX, belonging to the group of the age-hardenable Al alloys, the process conditions affecting the ageing, such as temperature and duration of heating exposure, the rate to increase the oil pressure, had to be determined. A preliminary mechanical characterization on artificially aged specimens was thus necessary both at room temperature and in warm conditions to investigate the influence of the ageing phenomenon on the mechanical and deformation behaviour at temperatures ranging from 150 °C to 350 °C. Based on the results of the tensile tests, preliminary Warm HydroForming experiments were conducted by changing the most influencing process parameters: working temperature, heating time and the time needed to increase the oil pressure up to the maximum value. It was found that the optimum working temperature was 200 °C and that the exposure of the material to the employed warm-forming temperature had to be minimized. Final Warm HydroForming tests were thus carried out using different rates to increase the oil pressure for comparison purposes, revealing that employing higher rates, i.e. increasing the strain rate, was beneficial, in terms of die cavity filling and sheet thinning, to obtain sound products.