The Study On Electroless Nickel Plating Process Of Zinc Alloy Die

The zinc alloy applies in the trial manufacturing of punching, injection molding and blow molding and the small batch mold as an economical fast mold material, and has achieved good economic and social benefits. However its intensity and hardness was low, wear-resisting and anticorrosion is poor, which is opposite in the steel, the application has been limited. Electroless nickel plating can not only effectively improves the surface performance of the material, and widely uses in the surface modification of various materials, but also an important treatment craft of mold surface. Electroless nickel plating for zinc alloy die can not only make full use of the zinc alloy advantages such as the perfect forming performance and low-cost, can also effectively improve the corrosion resistance, wear resistance and service life of zinc alloy die, but the traditional electroless nickel Plating on the Zinc Alloy surface has shortcomings or defects, finding a environmental protection, high quality coating of electroless nickel plating is imperative. A clean, low power and high-quality coating of alkali + acidic electroless nickel plating process was researched, the process can avoid the shortcomings of traditional technology and maximize the reduction of the zinc in the bath melting phenomenon of the return, and solve the acid bath on the corrosion of the matrix.The pretreatment process decides the quality of plating layers. In this paper, through a great deal of experiments, a kind of pretreatment techniques suitable for die zinc alloy for electroless nickel plating is founded: chemical degreasing-weak acid corrosion-activation-alkaline pre-nickel plating. The Ni-P coating of 1.0μm～1.5μm is obtained by the process treating, the coating is compact, smooth.In this paper, the composition and the function of the electroless nickel plating solution is introduced. On this basis, the techniques of die zinc alloy for electroless nickel plating is obtained. In order to obtain reasonable processing parameter of electroless nickel plating, the influences of the concentration of NiSO₄, NaH₂PO₂, complex agent and buffering agent, pH value and temperature were studied. The reasonable process of electroless nickel plating is obtained. It was found that the concentration of lord salt NiSO₄ varied is 25～30g/L, the concentration of reductants NaH₂PO₂ varied is 30～35g/L, the concentration of complex agent varied is 20— 25ml/L, the concentration of complex agent varied is 5～10g/L, the concentration of buffer was 20～25g/L, accelerator is 2～8ml/L, stabilizing agent is 10～20 mg/L, pH value is 5.0,and the reaction temperature varied form 85℃.The appearance, adhesion, hardness and corrosion resistance of the coating were tested by thickness tester to calculate the average thickness of sedimentary layers. And the samples were detected and analyzed by SEM, EPMA and X-Ray diffraction.Observing the appearance of the Ni-P coating, it is very smooth, compact and has metal luster without small hole, grey dot, and curly skin. The content of phosphorus is 6.03% of the coating for microcrystalline structure. The results of adhesion and corrosion resistance experiment show that it can meet the requirement for use. Electroless nickel plating state hardness is HV635.