| Aluminum and its alloys are widely used in manufacturing industry to follow the iron and steel in market consumption, because it has a series of excellent properties, such as low density, high specific strength, corrosion-resistant ability in atmosphere, good diathermancy, easily forming, easily reproducing, etc. The aluminum alloy cylinder is widely used in diesel and gasoline engines for its low density and high specific strength to reduce the vehicles' weight. But unfortunately aluminum alloy appears poor wear-resistant and corrosion-resistant. Therefore, aluminum alloy must be surface-treated in order to improve the performances of wear resistant and corrosion resistant.In all kinds of surface treatment technology, composite electroplating is one of feasible techniques on the surface of the aluminum alloy cylinder bore, because it has a series of excellent characteristics, such as simple techniques, low cost, tremendous development potential, etc. In order to improve the coating properties and seek after application of nanometer particles on composite coating, the effect of nanometer particles on the coating properties in Ni/micron SiC/nanometer Al2O3 is studied in this work. At the same time, electrolyte composition and processing parameters, such as electric current density, temperature, etc, are studied and analyzed. In addition, strengthen mechanism of coating and depositing way of particles is also discussed.It has been concluded in this work that the coating properties can be improved by adding nanometer particles, and the relations between all kinds of processing parameters and coating properties are studied. Simultaneously, the electrolyte composition and the processing parameters of Ni/micron SiC/nanometer Al2O3 composite electroplating are obtained: 500 g/L Nickel Sulfamate, 15 g/L Nickel Chloride, 46 g/L boric acid, 27 g/L micron SiC, 15 g/L nanometer Al2O3, PH≈4, anodizing pre-treatment, treat temperature 57℃, electric current density 20A/dm2, mild intensity air stirrer, stirrer intermittent time 40 s, treat time 30 min.At the same time, experimental results showed that the strengthen mechanism of coating are mainly composed of two aspects: the strengthen mechanism of nickel and the strengthen mechanism of particles. The strengthen mechanism of nickel is explained with dislocation theory. The strengthen mechanism of micro particles is due to dispersion strengthening. The strengthen mechanism of nanometer particles can becontributed to three reasons: improvement of particles deposit, dispersion strengthening rather than micro particles, notability transformation of nickel dislocation sub-structure led by dimension domino effect of nanometer particles.Because nanometer particles are adhibitting on the surface of micro particles, and both of them are deposited at one time, there is no big aggregation of nanometer particles, and nanometer particles take a condition of homogeneous distribution within the interspace of micro particles.
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