Thirty years of Retrogression and Re-Aging (RRA)

The first work on Retrogression and Re-Aging (RRA) was performed over thirty years ago by Cina and his colleagues in Israel, in an attempt to achieve high levels of both strength and stress-corrosion-cracking (SCC) resistance in 7075 aluminum alloy, thus combining the best features of the T6 and T73 tempers. Their process, however, involved such short heat-treatment times that its application would be effectively limited to very thin section components that typically do not exhibit SCC. Work at the NRC-IAR began in 1980, with the first goal being to explore modifications to the process in order to make it amenable to thick section parts. Since then extensive studies have been carried out on the kinetics, microstructure and structure-property relationships over a wide range of processing conditions and alloy compositions. This paper presents a review of the development of the RRA processes over the past thirty years, with an emphasis on the application of the technology to the aging aircraft problem.