The effect of RRA on the strength and SCC resistance on AA7050 and AA7150 aluminium alloys

The effect of retrogression and re-aging (RRA) on the strength and stress corrosion cracking (SCC) performance was evaluated in AA7050 and AA7150 aluminum alloys. Samples from extruded profiles, at their original condition (T77511 for AA7150 and T76511 for AA7050), were solution heat treated and aged at 120degreesC for 1440 min (T6 condition). After that, retrogression was performed at 200degreesC for times of 5, 10, 20 and 40 min, followed by a re-aging at 120degreesC for 1440 min. Hardness and electrical conductivity measurements were used to characterize the samples after different retrogression times and during re-aging. Maximum hardness after re-aging was obtained in the samples retrogressed for 20 and 40 min. Tensile and SCC testing were performed on samples retrogressed for 20 and 40 min and re-aged, and the results were compared with the alloys at their original conditions. After RRA treatment it was observed an increase of 30% in the yield strength of the AA7050 alloy, while for the AA7150 alloy the mechanical properties were similar to the original condition. Both alloys, when submitted to RRA for 40 min retrogression, had a SCC performance similar to their original condition. However, retrogression time of 20 min decreased significantly the SCC performance. (C) 2004 Elsevier B.V. All rights reserved.