Study On The Composite Electroplating Of Ni/nano-Al₂O₃ Particles

Nanocomposite plating, which occurred in the 90s of 20 century, is a novel surface-finishing method of materials, wherein microparticles used in composite plating were substituted by nanoparticles. It is the trend of composite plating. So the preparation, performance, deposition mechanism and strengthening mechanism of nanocomposite Ni/ Al2O3 coatings were presented in this paper.The deposition process of nanocomposite Ni/ Al2O3 coatings was discussed from a new angle in this paper. The effect of current density, pH value of the electrolyte, the temperature of the electrolyte and Al2O3 content in electrolyte on the deposition rate, roughness, density of coatings and Al2O3 content in coatings were discussed in detail. Among the four parameters, current density was the main factor among the four parameters, but the effect of Al2O3 content in electrolyte was the most complicated one. Four maxes of Al2O3 content in coatings, 8.5%,9.3%,11.4% and 9.5%, were obtained when current density, pH value of the electrolyte, the temperature of the electrolyte and Al2O3 content in electrolyte were 2.5 A/dm2, 4.5,120g/l and 45℃ respectively. As for the performance of nanocomposite Ni/ Al2O3 coatings, the hardness, friction coefficient and wear loss of coatings were considered. And also the relationships between them and the four parameters mentioned above were discussed, besides the relationship between wear loss and Al2O3 content in coatings was also discussed. As a result, Al2O3 content in electrolyte was the main and most complicated effect on the performance of coatings, and wear loss had a close relationship with Al2O3 content in coatings. The best plating process can be derived from the discussion of this paper: current density 3.5~4 A/dm2, pH value of the electrolyte 4.5~6, the temperature of the electrolyte 55~65℃ and Al2O3 content in electrolyte 25~80g/l.The mechanism of the deposition of coatings and how Al2O3 particle strengthen the coatings were discussed in the last section of this paper. The deposition of Ni and Al2O3 particle during composite plating can be described by the most typical Guglielmi model. But in the coatings, large Al2O3 particles and small Al2O3 particles had different ways on strengthening them.