Plastic Deformation and Ductility of AA7075 and AA6013 at Warm Temperatures Suitable to Retrogression Forming

A warm forming process with a simultaneous retrogression heat treatment, termed retrogression forming, can achieve good formability in high-strength aluminum alloys and recover their high strength through a single reaging heat treatment after forming. Tensile data from two commercial aluminum alloy sheet materials, AA7075-T6 and AA6013-T6, are presented for conditions suitable to retrogression forming. AA7075-T6 sheet was tested at temperatures from 180 °C to 220 °C and strain rates from 3.2 × 10−3 to 10−1 s−1. AA6013-T6 sheet was tested from 230 °C to 250 °C and 3.2 × 10−3 to 10−1 s−1. Both materials exhibit nearly steady-state flow at these temperatures and produce a modest strain-rate sensitivity of m = 0.039. The activation energies for plastic flow under these conditions are 221 kJ/mol for AA7075-T6 and 253 kJ/mol for AA6013-T6. Test data are used to construct predictive models for flow stress as a function of temperature and strain rate. AA7075-T6 demonstrates an excellent potential for retrogression forming at 200 °C and strain rates up to 10−1 s−1 if time at temperature is held to under 12 minutes. AA6013-T6 exhibits a modest potential for retrogression forming at 240 °C and strain rates up to 10−1 s−1 if time at temperature is held to under 7 minutes.