Synchronous improvement of mechanical properties and stress corrosion resistance by stress-aging coupled with natural aging pre-treatment in an Al-Zn-Mg alloy with high recrystallization fraction

Abstract

Enhancing the strength of Al-Zn-Mg alloys is critical to the weight-lightening of structural components in the application of high-speed trains and aerospace industries, while high stress corrosion cracking (SCC) susceptibility of Al-Zn-Mg alloys (especially the alloy with high recrystallization fraction) with high strength makes it difficult. In this study, the influence of tensile stress-aging coupled with natural aging pre-treatment on the mechanical properties and SCC resistance of Al-Zn-Mg alloy with high recrystallization fraction has been investigated. The results show that tensile stress-aging at 160 ℃ can inhibit the dissolution of clusters/Guinier-Preston (GP) zones formed during long-term natural aging pre-treatment, which increases the number density of matrix precipitates (MPts), narrow the width of precipitate free zone (PFZ), and dramatically improve the mechanical properties of the experimental Al-Zn-Mg alloy. Meanwhile, the precipitation of the high density of MPts within the matrix will assume a large number of solute atoms during artificial aging, which will reduce the supplement of solute atoms to grain boundaries. As a result, the volume of anodic active grain boundary precipitates (GBPs) and the content of free solute atoms at grain boundaries are reduced, which reduces the possibility of initial nucleation and propagation of SCC crack. The coupled treatment method proposed in this study proves efficient in resolving the contradiction between the strength and SCC resistance in Al-Zn-Mg alloy.