Comprehensive improvement of stress corrosion cracking resistance and strength by retrogression and re-aging in Al-8.9Zn-2.6Mg-1.7Cu alloy

The effect of different retrogression and re-aging (RRA) treatment on the microstructure, strength and stress corrosion cracking (SCC) resistance of a high Zn content Al alloy was investigated. The peak microhardness values after retrogression and re-aging at 180 degrees C/30 min and 200 degrees C/10 min were 214 HV and 215 HV, respectively, which are higher than that after T6 and T7 aging. The retrogression re-aged samples have large numbers of eta ' precipitate (MgZn2), resulting in high mechanical properties of the alloy. The SCC resistance order of the alloys was found to be: T6 < RRA (120 degrees C/24 h + 180 degrees C/30 min + 120 degrees C/24 h) < RRA (120 degrees C/ 24 h + 200 degrees C/10 min + 120 degrees C/24 h) < T7, and the optimal retrogression re-aging process is 120 degrees C/ 24 h + 180 degrees C/30 min + quenching + 120 degrees C/24 h. The improvement in the stress corrosion cracking resistance of the retrogression re-aged samples can be attributed to the increased interspaces of grain boundary precipitates and uniform distribution of the elements (Cu and Mg) in the grain boundary precipitates. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

Different retrogression and re-aging treatments were found to improve the microstructure, strength, and stress corrosion cracking resistance of a high Zn content Al alloy. The optimal retrogression re-aging process was identified to enhance the alloy's mechanical properties and resistance to stress corrosion cracking.