Electrochemical corrosion behaviors of a stress-aged Al-Zn-Mg-Cu alloy
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Long Zhang, Ming-Song Chen, and Ying Zhou School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, Hunan Province, China; and State Key Laboratory of High Performance Complex Manufacturing, Changsha 410083, Hunan Province, China
Xiang Ma SINTEF Materials and Chemistry, Blindern, 0314 Oslo, Norway (Received 26 March 2016; accepted 1 June 2016)
The effects of stress-aging processing on corrosion resistance of an Al–Zn–Mg–Cu alloy were investigated. It is found that the one-stage stress-aged alloy is strongly sensitive to the electrochemical corrosion. The poor corrosion resistance of the one-stage stress-aged alloy can be attributed to fine intragranular aging precipitates and continuous distribution of grain boundary precipitates. Meanwhile, the incomplete precipitation of solute atoms results in high electrochemical activity of aluminum matrix. However, when the alloy is two-stage stress-aged, the corrosion resistance is greatly improved. Furthermore, the corrosion resistance decreases firstly and then increases with increasing the first stage stress-aging temperature. Increasing external stress can enhance the corrosion resistance of the two-stage stress-aged alloy. These phenomena are mainly related to aging precipitates within grains and along grain boundaries. The coarse and relatively low-density intragranular aging precipitates, as well as the discontinuously distributed grain boundary precipitates can enhance the corrosion resistance of the stress-aged alloy. I. INTRODUCTION
Due to the low density, high fracture toughness, high fatigue durability, and ease of fabrication, Al–Zn–Mg–Cu alloys have been widely used as the ideal materials in aerospace industries for several decades.1–3 In recent years, with the development of aviation and aerospace industries, the excellent mechanical performance and satisfactory corrosion resistance of Al–Zn–Mg–Cu alloys are increasingly demanded considering the safety, service life, and reliability of modern aircraft components.4,5 Generally, the desired properties of Al–Zn–Mg–Cu alloys are mainly related to the microstructures,6 which highly depend on the heat treatment processes. In the past, great efforts have been made on heat treatment processing of aluminum alloys.7–10 Besides the one-stage aging,11 some other heat treatment procedures, including multistage aging,12,13 retrogression and re-aging (RRA) treatment,14–16 nonisothermal aging,17
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected], [email protected] DOI: 10.1557/jmr.2016.232 J. Mater. Res., 2016
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pre-aging,18 and stress-aging (or creep-aging),19,20 are also developed. Among these heat treatment processings, stress-aging or creep-aging, which combines the mechanical and aging treatment processes, is considered as a favored method for fabricating the integral and complex panels. Due to the low residual stress in formed components, high accuracy and low forming equipmen
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