Retrogression Forming and Reaging of an AA7075-T6 Alclad Sheet Material

Retrogression forming and reaging is a new scientific approach to producing components of high-strength aluminum alloys through warm forming followed by a single reaging heat treatment to restore T6 strength. Retrogression forming was applied to stamp 1.6-mm-thick AA7075-T6 Alclad sheet at 200 degrees C to a depth of 45 mm without visible defects or splitting. During stamping, the sheet material was subjected to multiple deformation modes common in automotive stamping processes, producing local major strains in excess of 20%. Time and temperature were controlled during retrogression forming using the concept of accumulated reduced retrogression time to enable recovery of the original T6 sheet strength by a single reaging heat treatment after forming. Tensile specimens extracted from the formed parts were tested to evaluate the effects of retrogression forming on strength. Reaging with a previously recommended reaging heat treatment of 120 degrees C for 24 h produced strengths approximately 5% greater than those of the original T6 temper. Reaging with a simulated paint-bake cycle of 185 degrees C for 25 min produced strengths nearly equivalent to those of the original T6 temper. Exceeding the maximum reduced time for retrogression during forming produced a strength loss that could not be recovered.