The effect of pH and heat treatment on the characteristic of Ni-P-GO electroless nanocomposite coating on AZ31D alloy

Document Type : Research Article


Msc Student,, Karaj Islamic Azad University


In the present study, Ni-P-GO nanocomposite coating with different pH values in an electroless bath was applied on the AZ31D alloy surface. After applying the coating, heat treatment was carried out at 400⸰C for one hour. The results of microstructural investigations using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy emission spectroscopy (EDS) showed that The coating was formed with a semi-amorphous structure and cauliflower morphology on the surface of substrate. According to the EDS results, with increasing the pH of the electroless bath, the amount of coating phosphorus and graphene oxide (GO) nanoparticles increased. After heat treatment, by preserving the morphology and growth of the colonies, the coating became completely crystalline and nickel phosphide compounds such as Ni2P, Ni3P and Ni5P3 were formed, which increased the hardness. The results of microhardness showed that with increasing phosphorus, the hardness and toughness of the coating decreases. Hardness increased and toughness decreased with heat treatment. With heat treatment, the maximum hardness reached 1151 HV and the toughness was reduced to 2.3 (MPa/√m). The results of the polarization test showed that coating leads to an increase in corrosion resistance of substrate and a decrease in corrosion density up to 0.443 µA/cm2. However, heat treatment reduced the corrosion resistance compared to before. Also, the increase in matrix phosphorus due to the increase in the density of the hypophosphite layer and more adsorption of GO leads to an increase in corrosion resistance.


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