Corrosion Behavior of Cold Sprayed Aluminum Alloys 2024 and 7075 in an Immersed Seawater Environment

Abstract

This paper describes the polarization and basic pitting behavior of 2024 and 7075 aluminum alloys produced by high-pressure cold-spray deposition. While cold spray is showing great promise as a solid-state repair approach for metallic structures, the corrosion behavior of these materials still needs investigation, particularly in describing the potential galvanic interactions with the repaired substrate. Potentiodynamic testing was performed on cold-sprayed (CS) aluminum alloys 2024 and 7075, and corresponding wrought AA2024-T3 and AA7075-T651 alloys for comparison. Testing used ASTM D1141 artificial seawater for potentiodynamic polarization, following the MIL-STD 889C standard for testing with consistent results. Pitting was investigated using 120 h immersion tests, with subsequent photography, scanning electron microscopy imaging, and energy-dispersive x-ray spectroscopy analysis of the surface. CS-2024 was found to be more active and reactive than wrought, with enhanced anodic kinetics; it experienced more aggressive pitting than the AA2024-T3 during the immersion test. CS-7075 was found to be less active and more reactive than wrought, with enhanced cathodic kinetics; the CS-7075 demonstrated reduced pitting compared to the AA7075-T651. Possible causes for these differences are discussed, including material homogeneity, CS powder intermetallics, and spray parameters. Overall, CS-2024 and CS-7075 should have little galvanic interaction with their corresponding substrates.