| In all kinds of surface treatment technology, composite electroplating is one of feasible techniques, because of its 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, we gained Ni/micron Al2O3/nanometer Al2O3 coating on aluminum alloy by composite electroplating.There are many factors that affect the properties of the coating, among which the electric current density, temperature, PH and stirrer intensity are the main factors. Orthogonal test was carried out based on the four factors with three levels. The plating velocity, micro-hardness and wear resistance were taken as the object in orthogonal analysis. Then we got the optimized parameters. When electric current density was 4 A/dm2,stirrer intensity was 800rpm, temperature was 50°C, PH was 5 the coating had the best properties. For optimized parameter coating, micro-hardness of the composite coating was two times that of the nickel coating, relative wear resistance is 4.75.The coating morphology, worn surfaces, content of particles were respectively studied by means of SEM, OM, EDS. Micro-hardness and wear resistance were studied in this work. In addition, the relations between all kinds of processing parameters and coating properties were studied.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 particles is due to dispersion strengthening. Furthermore, the nanometer particles can be contributed to three reasons: improvement of particle deposit, dispersion strengthening rather than micro-particles, notability transformation of nickel dislocation sub-structure led by dimension domino effect of nanometer particles.
|
PDF Full Text Request