OPTIMIZING INTERRUPTED AGING OF Al-Zn-Mg-Cu ALLOY: INCREASING STRENGTH, IMPROVING CORROSION RESISTANCE, REDUCING PEAK AGED TIME

Abstract

Microstructure and properties of Al-Zn-Mg-Cu alloys can be altered by manipulating the phase precipitations during the age hardening. By the conventional aging process T6, the alloy obtains high strength but the peak aged time is up to 24 hours and the stress corrosion cracking resistance is insufficient. In this study, the interrupted aging of B96ц-1 (GOST), a typical alloy of Al-Zn-Mg-Cu system, was performed in two stages. The first stage is at higher temperature, the second one is at lower temperature than T6 peak aged temperature. The aging time in these stages was optimized to achieve the high strength, the sufficient corrosion resistance, and reducing the peak aged time. The experimental results showed that 180 ^oC-1 hour+ 120 ^oC-5 hours aging treatment improves the strength by 3%, the ductility by 15% and reduces the corrosion rate by 2 times while the total aging time decreases by 70% in the comparison with the conventional aging process T6 that was carried out at 130 ^oC-24 hours.