Biaxial warm forming behavior of aluminum sheet alloys

In the present investigation, biaxial warm forming behavior in the temperature range 200–350 °C is investigated for three automotive aluminum sheet alloys: Al 5754, Al 5182 containing 1% Mn (Al 5182+Mn) and Al 6111-T4. While the formability for all the three alloys improves at elevated temperatures, the strain hardened alloys Al 5754 and Al 5182+Mn show considerably greater improvement than the precipitation hardened alloy Al 6111-T4. Even without the precipitation treatment, the formability of alloy 6111 could not be improved. Formability was studied by forming rectangular parts at a rapid rate (dε/dt∼1 s−1) using internally heated punch and die in both isothermal and non-isothermal conditions. Temperature effect on drawing of the sheet was found to have a large effect on formability. Setting die temperature slightly higher than punch temperature was favorable in promoting formability. Forming limit diagram (FLD) under warm forming conditions was also determined, which showed results that are consistent with the evaluation of part depth. It is confirmed by post-forming tensile test results that rapid warm forming in the above-mentioned temperature range does not create a significant loss in yield strength. After a simulated paint-baking treatment (177 °C for 30 min) the sheet retains strength level in the part similar to current stamped parts.