Retrogression and re-aging application for high strength aluminum alloy

High strength aluminum alloys have been favored in applications requiring high strength-to-weight ratios. Many of these alloys are prone to corrosions damage such as exfoliation and pitting. The intermediate heat treatment known as Retrogression and Re-aging (RRA) has been shown to increase the corrosion resistance of 7075-T6X aluminum to a level approaching the T73 temper, without significantly reducing the strength properties. To take advantage of this beneficial heat treatment, the Air Force contracted the University of Dayton Research Institute (UDRI) to develop procedures to apply the RRA treatment to selected corrosion-prone 7075-T6X aircraft parts and sections of parts, and to demonstrate the procedures. This paper will briefly outline the theory behind the RRA process, and then describe the process control methods, heat treat equipment developed, and the resulting material properties.