Effect of elevated temperatures on the drawability of aluminium sheet components

Because of the need for weight reduction in transport industry, in order to save energy as well as to reduce CO2-emission, the use of light weight aluminium sheet is taken increasingly into consideration [1]. But although aluminium is lighter than steel, the formability is less, hence press operations are often more critical. Alloys used are typically 5xxx alloys for inner panels because of the better formability and 6xxx alloys for outer panels because of the absence of stretcher lines. It is of course preferable to use one alloy type, especially from the point of view of re-use of the materials. Press operations could be improved by optimising the mechanical properties (distribution) of the sheet by using (local) heating or cooling [2-4]. An extra benefit of warm forming is that stretcher strains do not occur in 5xxx series alloys at elevated temperatures. A study is carried out on warm drawing (in the temperature range up to 250C) of 1.2 mm gauge 5754-O and 6016-T4 alloy sheet with respect to process limits and product properties and on modelling of the drawing process and sheet material. In the next sections results are presented of drawing and tensile tests at elevated temperatures, of room temperature (RT) tensile tests on samples that are prestrained at an elevated temperature and of FEM process simulations. The latter yielded information on the temperature distribution and evolution in tooling and blank. The required sheet material modelling is subject of an accompanying paper [5].