Abstract
Localized corrosion of Al-alloys in the aircraft industry can cause expensive catastrophic failures, especially in aging aircraft. To further aggravate conditions, aircraft maintenance with conventional cleaning solutions can gradually destroy the protective Al oxide film and accelerate corrosion in crevices and lap joints. VCI 415, a solution with corrosion inhibition properties used for washing/rinsing aircraft was investigated to determine the corrosion susceptibility for several Al alloys. The VCI 415 chemical composition, as determined from XPS analysis, is a mixture of sodium compounds and hydrocarbon surfactant with uniform chemistry across the surface and minor variation of concentration with depth. Inhibitor effectiveness was confirmed with EIS and elevated temperature studies. Polarization resistance increased with concentration of VCI 415 due to film formation and displacement of water molecules. Cyclic polarization behavior for samples in the vapor phase inhibitor showed a shift in the passive film breakdown potential by roughly +600 mV. The substantial increase in the passivation range has favorable consequences for pitting and localized cell chemistry. The strain at failure and tensile strength from the stress corrosion cracking studies showed pronounced effects at -300mV; the fractographs showed an improved morphology with ductile overload as the primary failure mode.
