The corrosion behaviors of zinc alloy （ZnAl4Cul） in 3.5% （mass fraction） NaCl, 7.3% （mass fraction） Na2SO4 and simulated acid rain solutions were investigated using electrochemical measurements. The potential noise during dry-wet cycle was monitored and analyzed by fast Fourier transform （FFT）, fast wavelet transform （FWT）, shot noise theory and stochastic theory. Cumulative probability curves of event frequency fn indicate that the corrosion events in the dry cycles are greater than those in the wet cycles. Uniform corrosion was observed in the NaCl solution compared with more localized corrosion in the Na2SO4 solution, which is evidenced by FWT and SEM. Conditional events generation rate r（t） for diffusion controlled reactions decreases with increasing the time. r（t） values for uniform corrosion and diffusion controlled process are the largest in the wet cycle in 3.5% NaCl solution. The values of r（t） for pitting corrosion in Na2SO4 solution are observed to become large during spraying periods, and r（t） for pitting corrosion has the largest value in the Na2SO4 solution. The intergranular corrosion of zinc is serious in simulated acid rain solution.
The atmospheric corrosion behavior of bronze under thin electrolyte layer （TEL） with different thicknesses was monitored using cathodic polarization curves, open circuit potential （OCP） and electrochemical impedance spectroscopy （EIS）. Cathodic polarization result indicates that the cathodic limiting current density increases with decreasing the TEL thickness. EIS result shows that the corrosion rate increases with decreasing the TEL thickness at the initial stage because the corrosion is dominated by the cathodic process, whereas after long immersion time, the corrosion degree with the TEL thickness is in the sequence of 150 μm 〉 310 μm〉 10μm ≈ bulk solution 〉 57 μm. The measurements of OCP and EIS present in-situ electrochemical corrosion information and their results are in good agreement with that of physical characterizations.
In order to improve the corrosion resistance and microhardness of AZ91D magnesium alloy, TiN nanoparticles were addedto fabricate Ni-P-TiN composite coating by electrodeposition. The surface, cross-section morphology and composition wereexamined using SEM, EDS and XRD, and the corrosion resistance was checked by electrochemical technology. The results indicatethat TiN nanoparticles were doped successfully in the Ni-P matrix after a series of complex pretreatments including activation, zincimmersion and pre-electroplating, which enhances the stability of magnesium alloy in electrolyte and the adhesion betweenmagnesium alloy and composite coating. The microhardness of the Ni-P coating increases dramatically by adding TiN nanoparticlesand subsequent heat treatment. The corrosion experimental results indicate that the corrosion resistance of Ni-P-TiN compositecoating is much higher than that of uncoated AZ91D magnesium alloy and similar with Ni-P coating in short immersion time.However, TiN nanoparticles play a significant role in long-term corrosion resistance of composite coatings.
