Stress corrosion inhibition mechanism of hot rolled medium thickness Al–Zn–Mg–Cu plate by cryogenic-aging treatment

Abstract

In this article, a novel cryogenic-aging treatment was realized by introducing the deep cryogenic treatment (DCT) in liquid nitrogen prior to artificial aging. The stress corrosion performance of the hot rolled medium thick Al–Zn–Mg–Cu plate after cryogenic-aging treatment was investigated by mechanical properties test, in-situ electrochemical test and microstructure analysis. It was found that the DCT-8 h and 24 h prior to double-stage aging treatment were optimum parameters. Cryogenic-aging treatment prolonged the duration of Al–Zn–Mg–Cu alloy under the coupling of stress and corrosion media. In addition, cryogenic-aging treatment promoted the multiplication of dislocations aggregated on the grain boundary or sub-grain boundary, which provided nucleation sites of precipitates and reduced the width of precipitates-free zone (PFZ). In-situ electrochemical test and microstructure observation were combined to analyze the inhibition mechanism of stress corrosion by cryogenic-aging treatment, which effectively inhibits the rupture of oxide film and the propagation of crack during the initial stage. This study proposes a simple and efficient process to enhance stress corrosion performance, which has important guidance for the application of Al–Zn–Mg–Cu alloys in the aerospace and transportation industries.