Corrosion resistance performance of Zr based conversion coating developed on aerospace aluminum alloy

摘要

A zirconium based conversion coating (ZrCC) was developed on aerospace aluminum alloy (AA2024) in order to improve its corrosion resistance. Various corrosion inhibitors such as Ce, Mo and W oxyanions were also added in the conversion bath and their corrosion inhibition performance was studied. Electrochemical impedance spectroscopy (EIS) results revealed that the cerium incorporated zirconium (ZrCeCC) showed higher charge transfer resistance value (13.4 kΩ.cm2) compared to zirconium-molybdenum (ZrMoCC) and zirconium-tungsten (ZrWCC) conversion coatings. The EIS results also revealed that low frequency impedance of ZrCeCC did not change significantly with respect to immersion time in 3.5% NaCl solution for up to 168h. The potentiodynamic polarization (PDP) results showed that both ZrCC and ZrCeCC exhibited lower icorr values of 0.83 and 0.6 μA.cm-2 respectively. The damage tolerance study results revealed that the ZrCeCC offered active corrosion protection to the substrate from the chloride ion attack. X-ray photoelectron spectroscopy (XPS) results revealed that both Zr and Ce elements existing in the multivalent oxidation state. The morphology (FE-SEM) and composition analysis (EDAX) of the developed coatings before and after corrosion studies were also thoroughly examined.