Microstructure and corrosion resistance of chromate conversion coating on cold sprayed aluminum alloy 2024

This paper examines the microstructure and corrosion resistance of chromate conversion coating (CCC) on cold sprayed (CS) aluminum alloy 2024. CCC is an effective surface treatment for aluminum aircraft alloy to improve paint adhesion as well as corrosion resistance. Although the studies of CCC on wrought aluminum alloy have been extensively conducted, understanding the interaction of CCC applied to CS deposits has not yet been addressed in the literature. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and focused ion beam (FIB) were employed for investigating the microstructure of CCC on CS2024 deposits. Potentiodynamic testing, electrochemical impedance spectroscopy (EIS), and immersion testing were performed to probe into corrosion performance of CCC on CS deposit. The results demonstrated that unique intermetallic networks inside the CS deposit formed CCC with more heterogeneous microstructure compared to CCC on wrought counterparts. Although wrought and CS 2024 presented similar corrosion resistance within a short exposure time (<48 h), CCC on CS deposits was more susceptible to corrosion damage, revealed by EIS with an extended exposure time (>48 h). Additionally, distinctive corrosion propagation of CCC on CS deposits along intermetallic networks and prior particle boundaries was seen from the immersion test.