No abstract

Manganese phosphate conversion coating was prepared by adding addition agent towards phosphate bath. The structure was investigated using SEM/EDX, and the anti-corrosion performance was evaluated by electrochemical technique. It was found that the film presented in crystal structure, and the crystalloid grain transformed from large grain toward small particles upon the addition. The corrosion resistance was studied by polarization curves and EIS in 3.5%NaCl. Polarization curves showed that the corrosion potential of the coating shifted remarkably towards positive direction comparing with that of AZ91 substrate. EIS results indicated that the radius of the capacity impedance for phosphate film increased distinctly, which validated the excellent anti-corrosion performance of the film.

A phosphate conversion coating was deposited on diecast AZ91D magnesium alloys, the film was a complex phosphate containing Mg and Al,which showed amorphous structure. Corrosion resistance of conversion coating in 3.5%NaCl was investigated by polarization curve. It was showed that the anodic branch of polarization curve for the phosphate conversion coating presented typical passivation characteristic. Immersion test results showed that the corrosion rate of phosphate conversion coating was less than that of chromate Dow7 film.

Phosphate conversion coatings was investigated on the surface of AZ91D magnesium alloy in a manganese dihydro phosphate baths. The influence of Ca2+ on coating microstructure was evaluate by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques, and the corrosion resistance of the coating was tested by polarization curve methods in 3.5%NaCl. Surface observation results show that the conversion coating presents in crystal feature, and the coating containning Ca was uneven with large grains and small grains. The adding of Ca2+ compound in the bath was found to be important for the attainment of good combination between the coating and Mg alloy substrate. Polarization curve results indicate that the phosphate conversion coating containing Ca could enhance the corrosion potential and improve corrosion resistance.

PANI coating was electrochemically synthesized by cyclic voltammetry (CV) method on the surface of 316L stainless steel plate. The surface morphology of PANI coating was observed by scanning electron microscopy. The effect of oxygen gas on corrosion behavior of PANI coating in PEMFC environment was investigated. The corrosion performance of the coating was evaluated by potential-time curve and polarization curve as well as electrochemical impedance spectroscopy in a bath containing 1M H2SO4and 2ppM NaF, and the air with a flow rate of 10 ml/min was piped into the testing corrosion cell to simulate the positive cathode condition of PEMFC at 70°C. The potential-time curves illustrated that oxygen gas resulted in the potential decline towards negative direction. Polarization curves showed that corrosion potential of the sample with O2was lower than that of the sample without O2, and the corrosion current density was higher than that of the sample without O2. EIS results indicated that the Nyquist plots were constitute of a capacitive impedance arc and a incline line, and the oxygen gas reduced the anti-corrosion performance of the PANI coating.