Research On Electroless Plating Of Ni-P Alloys Of Nanocrystalline Magnesium Alloys

Recently, much attention has been attracted to magnesium alloy for many investigators, owing to low density, high specific strength and modulus of elasticity, unique casting and cutting property. However, lack of corrosion resistance limits the widespread applications in civilian industry immensely. At present, corrosion resistance of magnesium alloy can be improved by various of treatment and made progress. A process, termed electroless plating, appears especially important contribute to the favourable type-copy and adaptability on technology.In recent years, more and more research on the magnesium alloy are processed in domestic and overseas. Accordingly, the technology of electroless plating is simplification and quality of coating is promoted. All sorts of studies focus on the improvement of corrosion resistance of magnesium alloy through the plating technology. However, Ni-P coating on magnesium alloy is the cathode coating. The defect of holes can accelerate the corrosion of magnesium alloy whereas the holes exist in itself inevitably. Electroless plating can reproduct surface of workpiece perfectly but including the defect. Therefore, it must reduce the matrix surface defects in order to improve the corrosion resistance of Ni-P coating.The thesis focused on the optimum process to obtain the favourable coating of morphology, uniform thickness, wear and corrosion resistance properties. The matrix grain were tessellated and defects were reduced, so that the quality was enhanced and corrosion resistance of Ni-P coating on magnesium alloy could be improved through nano-process on the surface of magnesium alloy. In addition, the paper studied the influence of thermal treatment on the Ni-P coating of Nanocrystalline magnesium alloy.Based on the studies, the main conclusion can be drown as follows:1、 The optimal technological scheme of electroless plating which was cheap and simple was confirmed from multiple experiments. NiSO4-6H2O16g/L; NaH2PO2·H2O14g/L; CH3COONa13g/L; NH4HF8g/L; HF(40%)12ml/L; thiocarbamide0.001g/L; PH6.4±0.2; Temperature:80±2℃。2、 Through this kind of technological scheme, the typical cellular structure could be obtained with compact and uniform coating but no obvious defect (average in20-30μm) Ni-P plating was phosphorus coating with phosphorus content was between5%and8%.3、 Compared to the coarse-grained magnesium alloy, the plating rate on nanocrystalline was slower in magnesium alloy surface electroless plating which was treated by means of nano. The reason was that nanocrystalline magnesium alloy own the bigger specific surface area and encountered more resistance in stage of surface nucleation. Whereas in the nucleation stage, the activation point and plating rate of nanocrystalline magnesium alloy got more, coating thickness was also great.4、 The hardness of the Ni-P coating on the surface of magnesium alloy was reached to427HV, whereas the coating on the nanocrystalline could be attained to689HV. By means of thermal treatment, the hardness of the coating was promoted further on. Especially when the temperature was300℃, it could be reached to1130HV. The wear-resisting performance of the coating could be promoted through the hardness. Moreover, the friction coefficient is decrease slightly.5、 The corrosion resistance of magnesium alloy could be reduced by nanocrystalline, but it on Ni-P coating was increased. The corrosion resistance of coating depressed after thermal treatment. Meanwhile, it got worse and worse in the wake of temperature rose.