The Effect Of Bath Composition And Additives On Electrodeposit Ni-W-P Alloy Coating

In recent years, many studies were carried out to develop the electrodeposition ofNi-W-P alloy for numerous interests such as uniform thickness, high hardness, goodcorrosion resistance, easy operation and low cost. However, most studies of Ni-W-P alloyget outstdanding performance coatings by improving process parameters, the influence ofbath composition on coating performance was rarely reported.In this paper, by using electrodeposition appropriate process parameters, the Ni-W-Palloy coating on the surface of copper has shiny surface, excellent adhesion, goodcorrosion resistance. In the electrodeposition, the effect of different sodium tungstate,sodium hypophosphite, sodium citrate, additives and heat treatment temperature onstructure and performance of the coating has been studied.The results show that the higher concentration of sodium tungstate, the coating hassmaller cells, greater hardness and better corrosion resistance in the same configuration.When the concentration of sodium tungstate is70g/L, deposition rate and currentefficiency reach maximum,8.2μm/h and32%. When sodium hypophosphite concentrationhas increased, current efficiency and the size of cells has reduced, the corrosion resistanceof coating has enhanced. The deposition rate can reach8.7μm/h in sodium hypophosphiteconcentration of10g/L. With increasing of sodium citrate, hardness and current efficiencyhave reduced. When sodium citrate is80g/L, Deposition rate and corrosion resistance arebest. The Deposition rate is8.6μm/h at this time. Excessive sodium citrate make thecoating roughness and cracking. The result of adding saccharin is that enhancing cathodicpolarization, reducing the size of cells, eliminating the cracks on coating. With increasingof saccharin, hardness has increased, but corrosion resistance has increased at first andthen decreased.Coating is amorphous under state-electrodeposition. With increasing of heattreatment temperature, Ni3P, NiW have phase separated out from coating. Corrosionresistance has gradually decreased after heat treatment, the corrosion current is about30times than state-electrodeposition after700℃. Hardness has increased at first and then decreased, after600℃, hardness is about2times than state-electrodeposition and hasreached1099.17HV.