Coating Of Magnesium Alloy Surface Ni-p/ni Combination Preparation

In this paper, AZ91 magnesium alloy was used as the test material. The Ni-P/Ni duplex coating was deposited on the surface of magnesium alloys by electroless Ni-P plating and following electroplating Ni. The influence of the pre-treatment for electroless nickel plating and the process of electorpless nickel plating on the porosity of the electroless nickel coating were studied in the guarantee of the adhesion of the coating, and the optimized concentration of the electroless nickel plating additive was determined by the orthogonal test. The effect of electroless plating time and electroplating time on the corrosion resistance properties of the duplex coating was investigated and got the optimal time of the lectroless plating and electrodplating. The influence of the electroplating nickel process on coating performance was studied and got the optimize process parameters of electroplating nickel. The results are as follows:1. The pickling process was CrO3120g/L ,HNO3 (68%) 80g/L, pickling for 60s at the room temperature2. Activation process was HF(40%) 250mL / L, Activation for 10 min at the room temperature.3. The optimum technology of electroless nickel was NiSO4?6H2O 20 g / L, NaH2PO2 ? H2O: 20g / L, C6H8O7?H2O 5g / L, NH4HF2 15g / L, HF (40%) 10 ml/L, NCSNH2 0.6mg / L, NH4OH 50ml/L , CH3CHOHCOOH 10g/L, the value of the pH and the temperatur was 6.0 and 82℃.4. The optimal Ni-P/Ni duplex coating prepared by electroless plating nickel for 40min and electroplating nickel for 30min .5. The optimal technology of electroplating Nickel were as follows: the value of electroplating current density,temperature, pH were 0.02A/cm2, 50℃and 5 respectively, the concentration of NiSO4?6H2O and brightene were 300g/L and 1.5g/L respectively .The static corrosion immersion test result of the Ni-P/Ni duplex coating prepared with the optimal parameters was longer than 30 h, the potentiodynamic polarization curves shew that the coating has good corrosion resistance both in acidic and alkaline solution , The SEM observation of the cross section of the duplex coating indicates that the coating was compact and connected well to the magnesium substrate ,there wasn't obviously interface between the Ni-P layer and Ni layer ;the photo of the metallographic microscope shew that the surface of the coating is polishing formation and there is on defect on it; the microhardness of the coating was up to 348HV.