Retrogression Forming and Reaging of AA7075-T6 Alclad to Produce Stampings with Peak Strength

Abstract

A retrogression heat treatment was combined with simultaneous warm forming to produce cross-shaped stampings from AA7075-T6 Alclad sheet. This process is termed retrogression forming. A maximum-allowed-retrogression-forming-time, which includes sheet heat up, transfer, and stamping, was predicted by calculation to achieve peak-aged strength through a single reaging heat treatment after forming. Sheets of 1.6-mm-thick AA7075-T6 Alclad were stamped at 200 °C to a depth of 45 mm within 2 s without splitting. The formed geometry exhibits a complexity appropriate to automotive structural components. These stampings were then subjected to one of two reaging heat treatments. A full reaging heat treatment of 120 °C for 24 h produced strength levels in excess of the original, peak-aged T6 alloy sheet. A simulated paint bake heat treatment at 185 °C for 25 min recovered 95% of the strength lost during warm forming. Successful retrogression forming and reaging of AA7075-T6 provides new possibilities for stamping high-strength aluminum alloys into complex geometries without sacrificing strength.