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Magnesium alloy due to the proportion of small, good machining performance advantages, applications increasingly widespread, but poor corrosion resistance of magnesium alloy. Electroless nickel plating layer having excellent uniformity, hardness, wear, and corrosion resistance, etc. Comprehensive physical and chemical properties, the active magnesium alloys is very high, when in contact with air, the surface will rapidly formed a layer of oxide film, therefore, before the chemical plating The need for a special pretreatment in order to obtain good adhesion of the coating. The pretreatment method for magnesium alloys are very cumbersome and due to the magnesium alloy and the strong electric plating between dual role so that the binding force of the coating is not ideal. This article was first explored in the surface of the magnesium alloy AZ31 NI, Cu, Fe, Co, and Ni-Co, Ni-Cu, Ni-Fe, Ni,-Zn substitution by orthogonal experiment to determine the optimum conditions of the various displacement film . Determine the replacement membrane plating, heat shock and rasp experiments to determine the best replacement membrane binding force, the best replacement membrane process conditions were as follows: CuSO4 · 5H2O: 5g / L; sodium dodecyl sulfate : 100mg / L; pH = 5.3; t = 1min. then study the the copper replacement film formation process, follow-up coating the surface morphology, hardness, corrosion resistance, the corrosion potential of the test, the following conclusions: (1) studied by scanning electron microscopy of the the copper replacement film growth process, start the random growth of small particles, and then the center of these small particles grow to the surrounding, and finally completely cover the surface of the magnesium alloy, but the copper replacement film is not uniform. (2) the corrosion potential of the electroless plating of copper replacement film about 0.9V than no replacement film coating, the copper replacement membrane can significantly improve the corrosion potential of the coating. (3) In the chemical coating thickness is reached in the case of 30 μm, no replacement of the specimen only in the salt spray test chamber 5h corrosion. Copper replacement film test piece 10h corrosion occurs, however, the copper displacement film can effectively improve the corrosion resistance of the coating. (4) surface morphology of coating microstructure showed typical cellular morphological characteristics, there is no obvious surface defects, dense uniform coating formation, in the organizational structure to ensure the coating has good corrosion resistance. (5) for replacement of copper by electroless plating hardness is 530HV, no permutation copper electroless plating hardness of 520HV film copper replacement had no significant effect on the hardness of the coating.
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