The Effect Of Adding Particles To The Plating Of Surface On The Aluminum Alloy

Traditional electroless plating has low hardness and weak wear resistance. Electroless composite plating is a new surface treatment technology on the basis of the traditional plating. In addition to having the characteristics of the metal, the electroless composite plating also has the properties of particles, and it has been widely applied to the field of aviation, aerospace, petroleum chemical industry, machinery, textile and automobile industry, etc. Aluminum alloys are structure materials which are widely used, and the properties of hardness can significantly improved by electroless composite plating.In this work, SiO2, CeO2particles are added into plating bath which is on aluminum alloy surface. Process parameters are controlled to temperature of60-90℃, particle concentration of5-30g/L, pH value of the bath4-7to obtain the aluminum alloy surface of Ni-P-SiO2and Ni-P-CeO2. On the other hand, the plating has been processed by heat treatment under400℃.The microstructure and properties of the composite plating as well as its change under heat treatment have been researched. The research results are obtained as follows:(1) Ni-P plating exhibits amorphous structure. The Ni-P-SiO2, Ni-P-CeO2electroless composite plating exhibit partial amorphous structure. The Ni-P-SiO2, Ni-P-CeO2electroless composite plating mainly belongs to Ni and Ni3P phase and also appears SiO2CeO2phase. After heat treatment under400℃×1h, the amorphous structures of the Ni-P-SiO2, Ni-P-CeO2plating are disappeared.(2) The surface morphology of the Ni-P, Ni-P-SiO2, Ni-P-CeO2plating are cellular structure, and the content of phosphorus is greater than7%. When the plating temperature is80℃, the added particle concentration lOg/L and the pH value of the bath4, the surface morphology of the plating is homogeneous and dense.After the heating treatment under400℃×1h, the grain size has a tendency to increase and the surface becomes more dense and smooth.(3) The deposition rates of three plating were improved with the increasing of the applied plating temperature. And the hardness of Ni-P, Ni-P-SiO2plating correspondingly increases. But under the same temperature, the hardness of Ni-P-SiO2plating is much higher than that of Ni-P plating. And the hardness of Ni-P-CeO2plating presents a decrease trend after increasing. With the increasing of particle concentration, the deposition rate of Ni-P-SiO2plating decrease, and the deposition rate and thickness of Ni-P-CeO2plating increase linearly; the hardness of Ni-P-SiO2plating decreases after increasing. The hardness of Ni-P-CeO2plating presents a trend that first increases then decreases and finally increases. With the rising of pH, the deposition rate of Ni-P-SiO2plating increase and the hardness decrease. The deposition rate of Ni-P-CeO2plating present a increased trend after decreasing, and a trend of the hardness present a decrease after increasing;(4) After one hour heat treatment under400℃, the hardness of the plating is improved to a different degree. The hardness of Ni-P-SiO2plating is830HV, which is2.3times as hard as that untreated plating (355HV). The Ni-P-CeO2plating is380HV, which is1.8times as hard as that untreated plating.(5) The alkali corrosion test shows that SiO2makes the corrosion resistance of Ni-P decrease, and the CeO2makes a small effect on the corrosion resistance of Ni-P.(6) In the plating state or after heat treatment, the adhesive strength of the composite plating and the base metal is better.