Research On Electroless Nickel Plating's Electroless Technique On The Surface Of Zinc Aluminum And Heat Treatment

Zinc Aluminum alloy has excellent properties of physical and machinery treatment, which is widely used in every industry field. The most familiar way is electroless nickel plating on the surface of Zinc Aluminum alloy. This is a very important technology of surface modification. The nickel plating can improve the surface property of Zinc Aluminum material effectively. Electroless nickel plating on the surface of Zinc Aluminum is central to the improvement of friction and corrosive resistance, and can greatly enhance surface hardness. At the same time it also can display the characteristic of low cost and the fine shaping property of Zinc Aluminum alloy fully. The traditional electroless nickel plating technology on Zinc Aluminum alloy surface has deficiencies on resource waste, environment pollution and so on.Our laboratory researchers studied a electroless nickel plating craft which possesses good plating, low consumption and environment pollution. But in the process of nickel plating technical, some craft methods and experiment parameters are not good enough, which are waited for further exploration. We has conducted to study important production processes and experiment parameters furtherly, basing on earlier achievements, and found two other ways of nickel plating with different contents of phosphorus.Through the contrasting of experiments, alkaline pre-coating function has been analyzed. Pre-coating has important influence on guaranteeing properties of the whole coating.In this paper, agitation crafts were evaluated by comparing the qualities of plating under different agitation crafts. 1. Agitation crafts. We can know that deposition rate and hardness will increase with the increasing agitation velocity vie comparing four platings under different agitation crafts (120,240,360 and 480r/min). The deposition rate of 360r/min is up to 13.33μm /h. Hardness of the plating reaches a maximum when agitation velocity is 240 r/min. Hardness and deposition rate are only 321HV and 8.53μm /h, respectively, while direction turning. 2. Loadage. The hardness and deposition rate of plating are respectively 395HV and 8.55μm /h when loadage is 0.64 dm² /L . 3. Electroless solution temperature. Properties of the plating under 80℃and 85℃has little difference. When the temperature goes down to 75℃, hardness and thickness of the plating appear obvious decrease.During the heat treatment process, hardness, wear-resistance, and corrosion resistance of the nickel plating are enhanced. Through massive experiment analysis, changing mechanism of the plating performance in heat treatment process is systematically elaborated. The Ni-P plating's state is the mixture of crystal and amorphous, which possesses a trend in transforming to crystalline state during heat treatment. The sub-stable Ni₁₂P₅ phases occur firstly and then disappear with increasing heat treatment temperature. Finer hard phases Ni₃P becomes the principal constituent which is the main reason of improvement of the plating.The low and high phosphorus plating respectively with 4.6% P and10.15%P have been obtained by adjusting the electroless nickel solution.