The zinc-nickel alloy electroplating process is an important metal surface treatment technology that can form a zinc-nickel alloy coating on the metal surface to improve the corrosion resistance, hardness and aesthetics of the metal.
The basic principle of zinc-nickel alloy electroplating
Zinc-nickel alloy electroplating is a process of depositing a layer of zinc-nickel alloy on the metal surface using the principle of electrolysis. The electroplating solution contains zinc ions and nickel ions. When the power is turned on, the cations discharge on the cathode (i.e. the metal to be plated) to form a zinc-nickel alloy coating. This alloy coating combines the excellent properties of zinc and nickel, such as the sacrificial anode protection of zinc and the corrosion resistance of nickel.
Electroplated zinc-nickel alloy is divided into high nickel and low nickel
1. High nickel generally has a nickel content of 12-15%. Due to the need for trivalent chromium passivation, nickel can also reach 12-18%
Generally, this is a requirement, especially in the automotive industry, which is basically in this range.
2. The nickel content of low-nickel zinc-nickel alloy coating is 5-10%, which is relatively small. Generally, zinc-nickel alloy coating with low nickel content has good corrosion resistance and good ductility, so it will be used in some workpieces that need to be pressed or drawn after electroplating.
3. What kind of zinc-nickel alloy process is suitable for roller zinc-nickel alloy electroplating process?
There are two types: alkaline and acidic. The alkaline zinc-nickel alloy electroplating process has good stability and excellent coating quality. Most electroplating companies now use alkaline process.
When alkaline zinc-nickel alloy electroplating is applied to roller plating, the process characteristics should be required
According to the characteristics of roller plating:
1. The process has good deep plating ability. It is understood that the process deep plating ability provided by most additive suppliers with a nickel content of more than 10% on the market is suitable for roller plating requirements.
2. The current efficiency is high and good. The alkaline zinc-nickel alloy coating will dissolve under alkaline conditions. If the current efficiency is too low, especially in the low current zone, the coating may not be plated. The characteristics of the barrel plating itself determine that the coating is slow to plate and takes a long time to dissolve. If the current efficiency is too low, it takes more patience to plate a tank. At present, many alkaline zinc-nickel alloy electroplating processes on the market have an efficiency of about 35%. It is normal to take 4-5 hours to plate 8 microns thick. There are also high-efficiency alkaline zinc-nickel alloy processes on the market with an efficiency of about 75%, which can save more than half of the time.
3. For the alkaline zinc-nickel alloy process, the electroplating temperature is required to be below 35 degrees, so refrigeration equipment is required.
4. Additive selection. At present, many companies on the market need to add 5 or 6 additives at the same time when electroplating zinc-nickel alloy processes, which brings great inconvenience to the initial users, addition and maintenance. The fewer the types of additives, the clearer the functions of various additives, the better. What is the difference between the black zinc-nickel alloy and the transparent zinc-nickel alloy? Is the zinc-nickel alloy black and transparent after electroplating, or is it directly electroplated black? If it is the former, the change is that the passivation agent has nothing to do with the alloy. If it is the latter, there should be a black light agent in the additives during electroplating, otherwise the electroplated color should be silver-white.
Process flow of zinc-nickel alloy electroplating
1. Pre-plating treatment: including degreasing, rust removal, activation and other steps to ensure that the metal surface is clean and has good conductivity.
2. Electroplating process: The metal to be plated is immersed in the electroplating solution as the cathode and electroplated by electricity. The zinc ions and nickel ions in the electroplating solution are discharged on the cathode to form a zinc-nickel alloy coating.
3. Post-plating treatment: including cleaning, drying, passivation and other steps to protect the coating and improve its performance.
Key points of zinc-nickel alloy electroplating
1. Preparation of electroplating solution: The concentration of zinc ions and nickel ions in the electroplating solution needs to be precisely controlled to ensure that the ratio of zinc and nickel in the coating is appropriate. At the same time, an appropriate amount of additives must be added to the electroplating solution to improve the performance and appearance of the coating.
2. Control of electroplating conditions: Parameters such as current density, electroplating time and electroplating temperature have an important influence on the quality of the coating. It needs to be adjusted according to the actual situation to obtain the best electroplating effect.
3. Post-treatment process: The post-treatment process is crucial to protect the coating and improve its performance. The cleaning process needs to be thorough to avoid corrosion of the coating by residual electroplating solution; the drying process needs to control the temperature and time to prevent cracking or discoloration of the coating; passivation treatment can enhance the corrosion resistance of the coating.
In short, the zinc-nickel alloy electroplating process is an important metal surface treatment technology. By precisely controlling the preparation of the electroplating solution, the electroplating conditions and the post-treatment process, a zinc-nickel alloy coating with excellent performance can be formed on the metal surface.
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