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 ex periments 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 sh owed 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 s howed a propensity of Al-Fe-Cu-Mn and Al-Cu-Si particles along with Al-Cu-M g and Al-Cu-Fe-Mn-Si particles and particle clusters. A modified replicatio n technique was used to lift particles from the corroded coupon surfaces. T EM analysis employing an EDX spectrometer showed a wide range of copper dep osits exhibiting microdendritic morphologies in basic and neutral environme nts, and botryoidal (or nodular) morphologies in acidic environments. The p lating or cementation of copper from solution as an electrochemical displac ement reaction appears to be a major contributor to the pitting corrosion o f 2024 aluminum alloy. (C) 2000 Kluwer Academic Publishers.