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Retrogression forming and reaging (RFRA) is a new warm-forming process designed to produce automotive structural components from high-strength aluminum alloys. A scientific approach is described to determine appropriate RFRA conditions for AA7075-T6 and is applied to laboratory-scale forming experiments. The concept of reduced time is used with the activation energy of retrogression measured for AA7075-T6 to predict appropriate times and temperatures for retrogression forming. Conditions recommended for AA7075-T6 are retrogression at 200 °C for 3 to 12 min while forming at strain rates of up to 10^{–1} s^{−1}. The recommended reaging heat treatment to fully restore strength to the T6 condition after retrogression forming is 120 °C for 24 h. These RFRA conditions were successfully applied in laboratory-scale experiments to form AA7075-T6 Alclad sheet and produce a final strength equivalent to the T6 condition. Data from tensile tests provide flow stresses and tensile ductilities across the range of conditions appropriate for RFRA. 

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 sim- ulated 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 sacri- ficing strength. 

Combining a retrogression heat treatment with simulta- neous warm forming can increase the formability of peak-aged, high-strength aluminum alloys while allowing peak-aged strength to be recovered through a single reaging heat treatment after forming. This process is termed retrogression-forming-and-reaging (RFRA). This study investigates the applicability of RFRA to AA6013- T6 sheet material. Elevated-temperature tensile tests were performed at temperatures from 230 to 250 °C and strain rates from 3.2
10 −3 to 10 −1 s −1 . Tensile tests were followed by reaging with a simulated paint-bake heat treatment. Flow stress at a true strain of 0.10 ranges from 230 MPa (250 °C and 3.2
10 −3 s −1 ) to 290 MPa (230 °C and 10 −1 s −1 ), significantly lower than the room-temperature yield strength of 360 MPa in the T6 condition. The average elongation to rupture and reduc- tion in area from elevated-temperature tests are 22% and 56%, respectively, which are similar to the room- temperature values for the T4 condition. Elevated- temperature testing reduced material hardness compared to the original T6 condition. Subsequent reaging with a simulated paint-bake raised hardness to 96% of the T6 condition in un-deformed material, but slightly decreased the hardness of the deformed material. Recommendations for implementing RFRA of AA6013-T6 are presented. 

Combining retrogression heat treatment with simultaneous warm forming provides an opportunity to significantly increase the formability of high-strength aluminum alloy AA7075-T6 sheet material while subsequently regaining nearly peak-aged strength through a single reaging treatment. This new technological approach to forming high-strength aluminum alloy sheet is termed retrogression forming. Times and temperatures suitable to the retrogression forming of AA7075-T6 sheet material are examined. Differential scanning calorimetry is used to determine the activation energy associated with precipitate dissolution during retrogression. Heat treating experiments determine the changes in hardness during retrogression as a function of temperature and time. The concept of temperature-compensated time is used to construct a master curve that predicts appropriate retrogression forming conditions.