Electrochemical behavior and localized corrosion associated with Al₇Cu₂Fe particles in aluminum alloy 7075-T651

Initiation of localized corrosion upon high strength aluminum alloys is often associated with cathodic intermetallic particles within the alloy. Electrochemical measurements and metallurgical characterization have been made to clarify and quantify the physical properties of Al₇Cu₂Fe particles in AA7075-T651. Prior studies regarding either the stereology or electrochemical properties of Al₇Cu₂Fe are scarce. Quantitative microscopy revealed a significant population of Al₇Cu₂Fe in the alloy; comprising up to 65% of the constituent particle population and typically at a size of 1.7 ± 1.0 μm. It was determined that Al₇Cu₂Fe may serve as a local cathode in the evolution of localized corrosion of AA7075-T651 and is capable of sustaining oxygen reduction reactions at rates of several hundreds of μA/cm² over a range of potentials typical of the open circuit potential (OCP) of AA7075-T651 in NaCl solution of various concentrations and pH. The presence of Al₇Cu₂Fe leads to the development of pitting at the particle-matrix interface.