The punch speed influence on warm forming and springback of two Al-Mg-Si alloys

Abstract

The punch speed has a major influence on the success of sheet metal warm forming of aluminum alloys, particularly in the part’s final geometry and in-service behavior. However, this process parameter has not often been analyzed in the literature. Additionally, in warm forming of heat-treatable aluminum alloys under non-isothermal conditions no study has been reported concerning the influence of the punch speed on springback. In the present work, two heat-treatable Al–Mg–Si alloys (EN AW 6016-T4 and EN AW 6061-T6) are studied between 22 °C and 200 °C, using tensile tests and cylindrical cup forming followed by split ring (springback) tests. Monotonic tensile tests and stress relaxation tensile tests were performed at strain rates from 2 × 10−4 to 2 × 10−2 s−1. Dynamic strain aging (Lüders bands) was observed at 22 °C after each stress relaxation stage. When using low strain rates and stress relaxation stages at 200 °C, the occurrence of dynamic precipitation for the EN AW 6016-T4 alloy becomes more evident due to the higher test time. Cylindrical cup tests were performed for punch speeds from 0.1 to 10 mm∙s−1. In warm forming, a higher punch speed is advantageous since it minimizes the occurrence of dynamic precipitation and the heat transfer between the sheet and the tools. Thus, formability and springback remained stable or improved with the increase in punch speed. Additionally, a higher punch speed is advantageous in the industrial field since it makes higher production rates possible with a better control of the temperature difference between the tools.