Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.
Issue link: http://mp.epubxp.com/i/889936
58 NOVEMBER 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 11 CHEMICAL TREATMENT W The electrochemical corrosion behav- ior of 7050 aluminum alloy (UNS A97050) in various states of aging under different hydrogen charging conditions was investigated by cathodic hydro- gen-permeation, hydrogen determina- tor, and electrochemical testing. Hydro- gen concentration in this alloy increased with increased charging time under the same aging state, and the polarization curves indicated that corrosion resis- tance decreased with increased charg- ing time. Moreover, the aging states had a significant influence on the corro- sion resistance under the same charg- ing conditions (i.e., the corrosion resis- tance in the underaged state was the worst, while the over-aged state alloy showed the best corrosion resistance, and corrosion resistance of the peak- aged alloy was between the two). Widely used in the aeronautical and civil industries, 7050 aluminum alloy (UNS A97050) is an important structural material because of its low density, high strength, and excellent workability. 1 However, 7xxx series aluminum alloys have shown signifi- cant susceptibility to stress corrosion cracking (SCC), which has limited their application and development. 2 For quite some time, an anodic dissolution mecha- nism has been proposed as a model for SCC in 7xxx series aluminum alloys, 3 w hile many researchers have suggested since the 1980s that hydrogen effects account for crack propagation in 7xxx series aluminum alloys. 4 Various types of hydrogen embrittle- ment (HE) mechanisms have been pro- posed, including the decohesion of HE, 5 hydrogen-enhanced localized plasticity mechanism, 6 hydrogen-dislocation interac- tion theory, 7 and hydrogen-induced delayed plasticity theory. 8 Many believe that mag- nesium segregation that occurs at grain boundaries has a decisive influence on the susceptibility of aluminum alloys to HE, 9 w h ereby Vi swanadham 10 proposed th e "phase transformation-Mg-H " theor y to account for HE. Nevertheless, there cur- rently i s no consensus on th e preci se mechanism. Hydrogen-induced cracks always prop- agate along the grain boundary, and hydro- gen introduced in aluminum alloys always concentrates at the grain boundar y. A series of in situ observations showed that hydrogen can facilitate dislocation emis- sion , multiplication , and motion (i .e., hydrogen facilitates localized plastic defor- mation); and when deformation reaches a critical condition, hydrogen-induced crack- ing will nucleate and propagate. 11 The hydrogen-induced additive stress caused by hydrogen in specimens can assist the external stress in enhancing the plastic deformation. 12-13 Study on Electrochemical Corrosion of 7050 Aluminum Alloy W.J. Qi, X. Qi, B. Sun, C. Wang, J. r . Jin, and r . g . Song, Jiangsu Key Laboratory of Materials Surface Science and Technology; Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Changzhou, China