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.