Corrosion Resistance of Aluminum-Copper Alloys with Different Grain Structures

Abstract

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 α and θ 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 α-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 Cl− 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 Cl− results in a decrease in their corrosion resistance.