Electroless Plating Nickel And Phosphorus On AZ31B Magnesium Alloys

Magnesium alloys with a series of unique performances in automotive industry, electronic industry, aerospace and other fields are being increasingly wider range of applications. However, poor corrosion resistance has often prevented further development and application. Electroless plating nickel is one of the important methods for surface protection on magnesium alloys because its coating is uniformity, smooth surface and has excellent corrosion resistance, wear resistance.Surface electroless plating Ni-P technology was investigated on AZ31B magnesium alloy which has good plastic deformation ability. By using SEM, EDS, XRD and electrokinetic potential polarization curve research techniques, the pretreatment for electroless nickel plating, technology of electroless nickel plating, the performance of Ni-P coating and heat pretreatment have studied systematically, the best technological conditions were confirmed for the formation of electroless nickel plating on AZ31B magnesium alloy. The initial deposited and electroless nickel plating waste water have also been investigated.The results showed that a uniform and compact and flawless Ni-P coating was formed under the conditions of the optimum condition and deposition rate on AZ31B magnesium alloy in nickel sulfate system and nickel carbonate by the electroless nickel plating technology. The nickel sulfate system: polarization curve test results show that free corrosion potential of the film approached -0.24V(SCE), so the film has better corrosion ability and provide excellent protection. EDS results showed that Ni-P coating which Ni, P contents are 90.97%(Wt), 9.03%(Wt).The formation of the Ni-P coating process in nickel sulfate system, Ni²⁺ reduction after forming a cellular sedimentary particles, outward extension, even gradually into films, covering a large area, growing in longitudinal section way, eventually the formation of the Ni-P coating.Three methods treated the electroless nickel plating waste water, the experimental results showed removal rate of nickel ion were excellent methods. However, the nickel purity: thermal alkaline method 97.56%, PdCl₂ catalytic reduction method 63.77%, and NaBH₄ reduction method 61.93%. On the terms of this experiment, thermal alkaline method has high purity nickel recycle, simple operation, and is the technology of protect environment, reduce pollution and renewable resources.