Corrosion Resistance of Aluminum-Copper Alloys with Different Grain Structures
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Corrosion Resistance of Aluminum-Copper Alloys with Different Grain Structures Alejandra S. Roma´n, Claudia M. Me´ndez, Claudio A. Gervasi, Rau´l B. Rebak, and Alicia E. Ares Submitted: 12 July 2020 / Revised: 19 October 2020 / Accepted: 7 November 2020 Electrochemical studies and microstructure analysis of directionally solidified hypoeutectic and eutectic aluminum-copper alloys were performed. Optical and scanning electron microscopy studies of corroded specimens with columnar and equiaxed microstructures in 0.1 M, 0.5 M, and 1 M NaCl solutions were conducted. Low-rate potential scanning and alternating current (AC) electrode impedance measurements were conducted to study the corrosion resistance of four aluminum-copper alloys. The concentration of Cu in the alloys proved to be a key factor in the corrosion resistance of the Al-Cu alloys, which controlled the fraction of a and h phases and the morphological distribution of these phases. The addition of Cu provides cathodic sites that increase adjacent anodic activity and higher corrosion susceptibility of the Al-Cu alloys, as compared with pure Al. Arise in the Cu amount that is linked to an increased concentration of the Al2Cu intermetallic or theta phase results in a higher susceptibility to corrosion for the studied alloys. A microstructural morphology related to a decreased area of contact between the a-phase and the Al2Cu intermetallic phase enhances the corrosion resistance of the Al-Cu alloys. For the Al-1wt.%Cu alloy increasing the content of Cl2 produces a beneficial result related to a more resistive passive film. For the rest of the studied alloys with nobler corrosion potentials, the increase in Cl2 results in a decrease in their corrosion resistance. Keywords
AC electrode impedance measurements, Al-Cu alloys, corrosion susceptibility, directional solidification, low-rate potential scanning tests
1. Introduction One of the best-known properties of aluminum is that it is light, with a density that amounts to one-third of that of steel. This makes aluminum the preferred choice for numerous applications. One of the detrimental properties of unalloyed aluminum is its poor strength rendering it unfit to be used as construction material for large structures. However, aluminum alloys of
Alejandra S. Roma´n, Misiones Institute for Materials Research, IMAM (CONICET-UNaM), Fe´lix de Azara 1552, 3300 Posadas, Misiones, Argentina; and CONICET, Godoy Cruz 2290, 1425 Buenos Aires, Argentina; Claudia M. Me´ndez, Misiones Institute for Materials Research, IMAM (CONICET-UNaM), Fe´lix de Azara 1552, 3300 Posadas, Misiones, Argentina; and Fac. Cs. Es., Quı´m. y Nat, Univ. Misiones, Fe´lix de Azara 1552, 3300 Posadas, Misiones, Argentina; Claudio A. Gervasi, Laboratory for Theoretical and Applied Research in Physicochemical Science (INIFTA), La Plata University – CONICET, Suc. 4 CC 16, 1900 La Plata, Argentina; and Electrochemistry Division, Engineering College, La Plata University, 1 y 47, 1900 La Plata, Argentina; Rau´l B. Rebak, GE G
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