Junxi Zhang

Electrodeposition and corrosion resistance of Ni–P–TiN composite coating on AZ91D magnesium alloy

Abstract In order to improve the corrosion resistance and microhardness of AZ91D magnesium alloy, TiN nanoparticles were added to fabricate Ni–P–TiN composite coating by electrodeposition. The surface, cross-section morphology and composition were examined using SEM, EDS and XRD, and the corrosion resistance was checked by electrochemical technology. The results indicate that TiN nanoparticles were doped successfully in the Ni–P matrix after a series of complex pretreatments including activation, zinc immersion and pre-electroplating, which enhances the stability of magnesium alloy in electrolyte and the adhesion between magnesium alloy and composite coating. The microhardness of the Ni–P coating increases dramatically by adding TiN nanoparticles and subsequent heat treatment. The corrosion experimental results indicate that the corrosion resistance of Ni–P–TiN composite coating 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.

Effect of Alternating Electric Field on Diffusion Coefficient of Oxygen in Thin Electrolyte Layer

Effect of an applied alternating electric field on the oxygen diffusion coefficient in thin electrolyte layers on an electrode of stainless steel was investigated by chronoamperometry. The re- sults show that the oxygen diffusion coefficient increased with the decrease in TEL thickness, as well as the increase in AEF strength. The effect of AEF on the oxygen diffusion coefficient is found to be due to that the migration of oxygen form the gas/liquid interface to electrode surface was ac- celerated by the applied electric field. For a thinner electrolyte layer by a stronger applied electric field, the cathodic process of the electrode would be more intensive,which corresponds to higher corrosion rate of metal.