Influence of Treating time of Alodine 1200S Chromate Conversion Coating on Corrosion Property of a New Type Aluminum-lithium Alloy 2198

The corrosion properties of 2198 Al-Li alloy and chromate conversion coated 2198 Al-Li alloys with different treating times were studied by polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. According to the characteristics of EIS, the electrochemical equivalent circuit was established. The formation mechanism of chromate conversion coating on the alloy was further analyzed. The results showed that Ecorr and Eb of the alloy shifted positively after chromate conversion coating treatment. The radius of capacitive arcs in Nyquist plot increased first and then decreased. The radius of capacitive arcs became the maximum when the treating time was 1 min and 30 second. Under the same condition, the modulus of corrosion resistance became the maximum, and the phase angle of corrosion resistance was the closest to -90°. Few amounts of K3Fe(CN)6 accelerator and free Cr(Ⅵ) species were adsorbed on the coating surface, and parts of them desorbed and diffused during the immersion process.