Copper deposition during the corrosion of aluminum alloy 2024 in sodium chloride solutions

Copper and copper-rich particle clusters were observed to deposit on aging aircraft skin material (Al 2024 sheet coupons) after corrosion immersion experiments for 5 days in acidic (pH 3) neutral (pH similar to 6), and basic (pH 11) 0.6 M NaCl solutions. SEM analysis employing an EDX spectrometer showed a propensity of large Cu particle clusters on Fe-rich or Fe-containing areas while a TEM inventory of second-phase particles in the alloy sheet showed a propensity of Al-Fe-Cu-Mn and Al-Cu-Si particles along with Al-Cu-Mg and Al-Cu-Fe-Mn-Si particles and particle clusters. A modified replication technique was used to lift particles from the corroded coupon surfaces. TEM analysis employing an EDX spectrometer showed a wide range of copper deposits exhibiting microdendritic morphologies in basic and neutral environments, and botryoidal (or nodular) morphologies in acidic environments. The plating or cementation of copper from solution as an electrochemical displacement reaction appears to be a major contributor to the pitting corrosion of 2024 aluminum alloy. (C) 2000 Kluwer Academic Publishers.