Properties of electroless thick nickel-phosphorus coating on SiCp/Al composite surface in acidic conditions

Electroless thick Ni-P plating cannot only improve the corrosion resistance of the SiCp/Al composite substrate but also enhance the optical properties of materials. The influence of pH value on the properties of electroless thick Ni-P coatings were investigated in this work. Morphology, structure, component, microhardness, coefficient of thermal expansion (CTE) and corrosion resistance of the Ni-P coating were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), in situ energy dispersive X-ray spectroscopy (EDS), Vickers microhardness, thermal mechanical analyzer (TMA) and electrochemical workstation, respectively. The experimental results indicate that the electroless Ni-P coatings have amorphous structure in the phosphorus content ranging from 10.63 and 12.45 wt% at different bath pH values. The bath pH value has great influence on the phosphorus content of the coating. The effect law is that the phosphorus content of the coating decreases with the increase in pH value. The surface roughness, thickness and expansion coefficient gradually increases with the increase in the content of phosphorus element in the coating. Hardness and corrosion resistance decrease with the decrease in phosphorus content.