The Effect Of High Temperature Pre-precipitation On Strengthening-toughening Of Al-Zn-Mg Series Aluminum Alloy

The problem of improving resistance to stress corrosion cracking (SCC) of moderate and high strength weldable Al-Zn-Mg series aluminum alloys with non-deteriorated strength by heat treatment was not still resolved. The effects of the high temperature near-solvus pre-precipitation following after higher temperature solution treatment on matrix and grain groundary (GB) precipitates and mechanical properties and stress corrosion cracking resistance were investigated .Alloys structure after heat treatment indicated that high temperature pre-precipitation after solution could enlarge the difference of precipitates of grain and grain boundary, high temperature pre-precipitation above 400 ℃ could limit pre-precipitation to the GB, yet precipitates hardly existed in the grain. Pre-precipitation treatment at 370℃ incurred pre-precipitates in the grain and GB.High temperature pre-precipitation had a certain influence on age-hardening and tensile properties of 7A52 and 7039 alloys, high temperature pre-precipitation at 400 ℃ could retain ageing precipitation hardening, tensile strength and hardness were invariable basically, yield strength was enhanced slightly, and elongation was 13%.The measurement of electrical conductivity and stress corrosion cracking show that high temperature pre-precipitation could enhance electrical conductivity and resistance to stress corrosion cracking of 7A52 and 7039 alloys at different tempers evidently, and pre-precipitation temperature was lower, resistance to stress corrosion cracking was higher; pre-precipitation treatment above 400 ℃ could improve resistance to stress corrosion cracking obviously with retaining alloys strength.