Study On Regularity Of Electroplating Zinc-nickel Alloy From Sulfate System

Steels are widely used in many fields, so, how to protect steel is an important topic. Zinc coating has been extensively used as a protective coating for steel. With the development of civilization of mankind, the corrosion resistance of zinc coating can not catch up with the demand of mankind .So , the zinc alloys are widely developed .Among the zinc alloys, the zinc-nickel alloys are widely focused in view of its excellent corrosion resistance and other engineering properties.Now, there are two types used in electroplating of zinc-nickel alloys. One is slight acidic choloride electrolyte system, another is alkaline zincate system. The features of slight acidic choloride electrolyte include high current efficiency, rapid rate of deposition, the lower hydrogen embrittlement, and waste water treated easily , however , the solution has a bad throwing power and ability of covering ,the bath is apt to corrode the equipment also, and it is easy to produce chlorine when current is high . The features of alkaline zincate system are good throwing power and ability of covering, the bath is not easy to corrode the equipment , but the current efficiency is low, the waste water is difficult to treat. The main work of this thesis is to research the sulphate bath, we find that the sulfate system has the advantage of slight acidic choloride electrolyte system and alkaline zincate system. The solution of sulphate system is very simple and easy to maintain and high current efficiency. Furthermore, the technology has the advantage of lower plating cost and broader width of the temperature.The main work of this thesis consists of the following four parts: 1. The study of technology about electroplating zinc-nickel alloys The effects of all kinds of compositions and electroplating condition on the coating are discussed. It is also put forward the best technology conditions about electroplating zinc-nickel alloys in sulfate systems and the resolvents of frequentlyquestions.2. The effects of the additives on electroplating zinc-nickel alloysThe effects of the additives (such as ceric sulfate , vanillin , ethylene thiourea and DPE) on electroplating zinc-nickel alloys were investigated by means of potentiondynamic polarization, AC impedance techniques. The results showed that ethylene thiourea has the active effect on the procession of electrodeposition and the others could increase the cathodic polarization.3.The experiment of the coating of electroplating zinc-nickel alloys from the sulfate solutionZinc-Nickel alloy were prepared by electroplating from a sulfate bath on ferrous substrate. The relative composition of the Zinc-Nickel alloy was studied using energy dispersive X-ray diffraction studies. The phase limits of Zinc-Nickel (16%) alloy is the γ phase.4. Study on the corrosion resistant of zinc-nickel alloys. Their corrosion resistant were investigated by NSS, Corrosion soaking experiment and AC impedance techniques . The experiments showed that the corrosion potential of Zinc-Nickel (16%) alloy increased 230 mV positively compared with that of pure Zinc plate . Salt spray test of Zinc-Nickel (16%) alloy was 1000 hours , which was 4.5 times of pure Zinc plate did at the same thickness . The results exhibited that the Zinc-Nickel (16%) alloy had excellent corrosion resistance.