The influence of warm forming conditions on the natural aging and springback of a 6016-T4 aluminum alloy

Heat treatable aluminum alloys are very attractive materials to replace traditional steels in automotive body-in-white construction. However, their reduced formability and high springback limits their application in sheet metal forming operations. Moreover, these alloys are prone to natural aging that causes variability in forming operations and increases the amount of scrap. Warm forming can be a very interesting solution to improve formability and reduce springback. However, depending on the processing time, precipitation hardening may occur during the warm forming of these heat treatable alloys. Thus, punch speed has a major influence on the success of sheet metal forming operations. The present study addresses the influence of natural aging and punch speed in the warm forming of an Al-Mg-Si alloy: EN AW 6016-T4. The thermo-mechanical behavior was studied in function of temperature (from 22 to 300 °C), punch speed (from 0.1 to 10 mm·s⁻¹) and storage time (from 1 to 18 months), using uniaxial tensile tests, cylindrical cup tests, and split ring (springback) tests. Warm temperatures between 200 and 250 °C reduce the flow stress, minimizing the effects of natural aging on the variability of the mechanical properties. A high punch speed is advantageous since it minimizes the occurrence of precipitation hardening which contributes to increase the springback. Thus, warm conditions at high punch speed can be used as an effective solution to minimize the variability caused by the natural aging in forming operations of heat treatable aluminum alloys.