Materials Performance

DEC 2018

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.

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Page 42 of 76

40 DECEMBER 2018 W W W.MATERIALSPERFORMANCE.COM MATERIALS SELECTION & DESIGN T The electrochemical corrosion behav- ior of 7003 aluminum alloy (AA7003) under peak aging (PA), double peak aging (DPA), and regression re-aging (RRA) in sodium chloride (NaCl) solu- tion at different temperatures have been studied by using potentiody- namic polarization and electrochemi- cal impedance spectroscopy tests in combination with scanning electron microscopy. The results showed that the electrochemical corrosion rate of AA7003 in 3.5 wt% NaCl solution increases with increasing tempera- ture, and the effect of aging treat- ments on the electrochemical corro- sion rate in descending order is as follows: PA>DPA>RRA. The 7000 series aluminum alloy, with high strength, good welding performance, and excellent corrosion resistance, has been widely used in the aerospace indus- try, vehicles, buildings, large pressure ves- sels, etc. 1-2 However, those alloys are prone to electrochemical corrosion in corrosive environments and stress corrosion crack- ing (SCC) under the interaction of the m echanical environm ent, w hich limits their broader application. 3-4 Although the electrochemical corrosion and SCC behav- ior of Al–Zn–Mg–Cu alloys in a n ear - neutral 3.5 wt% sodium chloride (NaCl) solution have been studied over the past several years, 5-10 researchers have seldom considered the effect of temperature on the electrochemical corrosion of 7003 alu- Electrochemical Corrosion Behavior of AA7003 T.S. HUA, X.Y. ZHANG, C.B. ZHENG, AND R.G. SONG, Changzhou University, Changzhou, China; and Jiangsu University of Science and Technology, Zhenjiang, China minum alloy (AA7003) under dif ferent aging treatments in NaCl solution. There- fore, this article presents a study of the electro ch emical c orrosion b ehavior of AA7003 and the morphologies of the corro- sion after etching. It can be deduced that the corrosion strength at different temper- atures provides a basis for further study of the SCC process. 11-14 Experimental Procedures Material and Heat Treatment The material used in this study was AA7003 supplied by Alcoa Co. in the form of sm o o t h sp e c i m e n s m a c h i n e d f r o m a 40-mm thick rolled plate. Its composition is as follows: 0.6 wt% Zn, 0.6 wt% Mg, 0.2 wt% Cu, 0.1 wt% Zr, 0.2 wt% Ti, 0.3 wt% Mn, 0.2 wt% Cr, 0.35 wt% Fe, 0.3 wt% Si, and the bal- ance Al. The specimens were put in a muf- fle furnace at 470 °C for 2 h, quenched with cold water, and placed in an oven at 120 °C for 50 h (peak aging [PA]), 120 h (double peak aging [DPA]), then 48 h at 205 °C for 10 min, and finally 48 h at 120 °C (retrogres- sion and re-aging [RRA]), respectively. Immersion Corrosion Test The 3.5 wt% NaCl solution was pre- pared using analytical-grade NaCl and deionized water and was used as the exper- iment solution. The specimens with dimen- sions of 1.0 by 1.0 by 0.4 cm were polished, p r o v i d i n g a sm o o t h su r f a c e w i t h o u t s c ra t c h e s . T h e n t h e sp e c i m e n s w e re immersed in 3.5 wt% NaCl solutions at dif- ferent temperatures for three days. After the three-day immersion, the specimens

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