Study On The Technique And Property Of Direct Electroless Ni-P Plating On ZM-1Magnesium Alloy

In this paper, the current status and prospect of pretreatment processes andelectroless nickel plating on magnesium alloy have been summarized. Byoptimizing the pretreatment process and electroless plating process, the uniformNi-P coating with good adhesion and corrosion resistance was obtained on ZM-1magnesium alloy surface.A chromium-free and fluorine-free acid pickling pretreatment process wasproposed in this paper by single-factor experiment which was based onevaluating of pickling film appearance, corrosion resistance, coating appearanceand binding force. The morphologies of magnesium alloy surface and picklingfilm were observed by SEM，and the element contents and composition wereanalyzed by EDS. The result indicated that the magnesium alloy substrate wasselectively etched in the picking process and a selected layer of phosphate filmwas formed on the surface of the magnesium alloy. The film could not only formmore chemical bond sites between the substrate and the coating, but also protectthe magnesium alloy from the erosion of the electroless nickel plating solution.Effect of the electroless nickel bath components and plating conditions onthe performance of electroless Ni-P alloy coating were studied in this paper.Among the three different main salts, nickel sulfate, basic nickel carbonate andnickel acetate, the electroless Ni-P coating prepared from the bath containingnickel sulfate showed the best corrosion resistance. Considering environmentalprotection and stability of various evaluation indicators, the stabilizer DS, anorganic compound containing sulfur, stabilized the bath most significantly.Micro-morphology observation, Tafel test, measurement of deposition rate andporosity have been used to optimize the electroless nickel plating process forZM-1magnesium alloy. The uniform and amorphous Ni-P coating with finecorrosion resistance was obtained by the optimized electroless nickel plating.The reaction kinetics of electroless nickel plating was also studied in thispaper, and the deposition rate equation of electroless nickel plating was obtained.The growth process of eletroless nickel plating was tested and analyzed by open circuit potential test, SEM, and EDS. The result indicated two stages of theelectroless nickel plating. The first stage was the replacement reaction betweennickel ions and magnesium, and the second stage was the Ni-P co-depositionreaction. The research with the influence of the plating solution composition andprocess conditions on the stable potential demonstrated that nickel sulfate andcoordinating agent AC held the most influence.