Zinc and Zinc Nickel Coating Surface Treatment

Application of magnets in the automotive industry

Over the past few decades, cars have transitioned from electrical control systems to complex electronic control systems. In contrast to the more widely used pneumatic, hydraulic and mechanical control systems of the past, this transition to electronic control has greatly increased The need for magnets to support various systems within the vehicle, including sensors, actuators, and motors.

In the automotive industry, magnetic applications are a key component of vehicle performance, safety and convenience. For example, ceramic ferrite magnets can be used in anti-lock braking systems (ABS) to improve driver safety and enable road Be a safe place for everyone to drive. Neodymium magnets concentrate extremely high power into smaller size magnets compared to other magnet materials available, and are a great pole for magnetic applications that require lightweight magnets or magnets that can be installed within a limited size. Good choice. Today, rare earth magnets are used in electric vehicle drivetrains as an environmentally friendly way to increase vehicle efficiency without sacrificing performance.

Our Ningbo Bestway Magnet Co., Ltd. is a company dedicated to the production of high-quality magnets. The company has obtained IS09001 quality system certification, and has a set of production and processing technology in terms of corrosion resistance, working temperature, low temperature coefficient, coercivity and other products, which a set of production and processing technology.

The meaning of surface treatment

The demand for zinc-nickel coatings in the automotive industry has grown globally over the past few years, making it more important to improve corrosion and improved corrosion protection, especially in high temperature areas such as engine compartments. Due to the formation of γ-phase zinc-nickel alloys, zinc-nickel coatings (12-16% Ni) have better corrosion protection against red rust than pure zinc coatings. X-ray diffraction and FIB (Focused Ion Beam) techniques were applied in order to develop coatings with optimum electroplating performance over the entire current density range, and the corrosion rates determined by neutral salt spray tests clearly exceeded automotive industry requirements.

Compared with the pure zinc process, the zinc-nickel coating can only appear foggy for a long period of time and produce less white rust in a large area, which simplifies the maintenance work during use. In addition, increased service life is also associated with anti-wear properties, especially in vehicle  bottom applications. Because of the high hardness of zinc-nickel plating, it has become the preferred object. In addition, the zinc-nickel coating provides the minimal contact corrosion when assembled with aluminum parts, because the small potential difference between them can slow down the galvanic corrosion of aluminum, although zinc-nickel alloys are more inert than zinc, but Zinc-nickel plating also provides sacrificial protection.

Main features of zinc-nickel alloy coating

1. Excellent corrosion resistance

Comparison table of neutral salt spray test of zinc coating and zinc-nickel alloy coating

After color or black passivation, the corrosion resistance of the alloy coating containing Ni <10% is 3-5 times higher than that of the zinc coating, and 3 times higher than that of the cadmium coating. The corrosion resistance of the alloy coating containing Ni10-15% is higher than The galvanized layer is increased by 6-10 times.

The reason why zinc-nickel alloys have excellent corrosion resistance is that the stable potential of the alloy coating is between Zn and the substrate (steel), and a smaller potential difference leads to slower corrosion of the coating. The corrosion product of zinc-nickel alloy is mainly ZnCl2 4Zn(OH)2, which covers the surface uniformly and compactly, is not easy to conduct, and has a good protective effect, while the corrosion product of zinc coating is mainly ZnO, which has a loose structure and is ineffective to protection. In addition, the zinc-nickel alloy containing Ni13% belongs to the γ phase (intermetallic compound), which has the highest thermodynamic stability and thus has better corrosion resistance, while the zinc coating has an η-phase structure (compact hexagonal system), which has better thermodynamic stability. Difference.

2. Almost no hydrogen embrittlement

Ultra-high-strength steel is sensitive to hydrogen embrittlement, and it is difficult to remove hydrogen from zinc-plated and cadmium-plated layers. Usually, stress is removed before plating, and hydrogen removal is also required for 24 hours after plating. It is difficult to ensure complete hydrogen removal, and zinc-nickel alloys The coating has moderate pores, which is easy to remove hydrogen, and the coating itself has less hydrogen embrittlement, so it has a wider application space in the aerospace industry.

Comparison table of hydrogen embrittlement of several coatings

3. Excellent toughness and bonding force

The zinc-nickel alloy coating has good toughness, can withstand extrusion deformation without embrittlement during assembly, and has the advantages of cadmium coating.

4. Excellent solderability

Ordinary galvanized steel sheet is difficult to spot welding and cannot be used for automobile covers, while zinc-nickel alloy steel sheet has excellent weldability and can be widely used as automobile covers. After conventional phosphating and coating, its corrosion resistance is greatly improved.

5. Higher hardness

The hardness of the alkaline zinc coating is HV90-120, while the hardness of the zinc-nickel alloy coating can reach HV220-270, so it is more resistant to scratches.

Zinc-nickel alloy has a high melting point (750-800℃), good heat resistance, and excellent corrosion resistance after dehydrogenation heat treatment, which is suitable for use in engines.

Zinc-nickel alloy and galvanized

Among zinc-based alloys, zinc-nickel alloy coating is a new type of excellent protective coating suitable for use in harsh industrial atmospheres and harsh marine environments. The corrosion resistance of zinc-nickel alloy with nickel content of 7~9% is more than 3 times that of zinc coating; the corrosion resistance of zinc-nickel alloy coating with nickel content of about 13% is more than 5 times that of zinc coating, and it has the best corrosion resistance. sex.

Due to its excellent properties such as high corrosion resistance, low hydrogen embrittlement, weldability and machinability, zinc-nickel alloys have long attracted people's attention, and their applications are becoming more and more extensive. The zinc-nickel alloy coating has a high melting point and is suitable for electroplating of automobile engine parts; it has low hydrogen embrittlement and is suitable for electroplating on high-strength steel; it can be used as a substitute for cadmium coating and is mostly used for military products.

Zinc-nickel alloy plating solutions are mainly divided into two types: one is weak acid system, which has simple composition, high cathode current efficiency (generally above 95%), stable plating solution and easy operation. The other is alkaline zincate plating solution, its main advantages are: good dispersion ability of the plating solution, relatively uniform alloy composition ratio of the coating layer in a wide range of current density, uniform coating thickness, less corrosion to equipment and workpieces, and process operation. Easy, stable process, low cost, etc.

Compared with Zn coating

1. Corrosion resistance

Zinc-nickel alloys and zinc-nickel alloys are functional coatings, and zinc-nickel alloys are far superior in corrosion resistance to zinc-nickel alloys, which is the main reason why researchers spend a lot of time developing zinc-nickel alloys. After color passivation, the zinc-nickel alloy coating can easily pass 1000 hours without white rust under neutral salt spray, while the zinc-nickel alloy coating can pass 120 hours after color passivation. The zinc-nickel alloy coating can pass 400 hours without white rust under neutral salt spray after white passivation treatment, while the zinc-nickel alloy coating can pass 96 hours after blue-white passivation.

2. Appearance

In general, the color passivation layer of zinc-nickel alloy is not as bright as the zinc-plated layer, especially when the nickel content in the alloy coating is high; the white passivation color of zinc-nickel alloy is not as bright as that of the zinc-nickel alloy. When it needs to be explained, people's perception of things is often preconceived, and the same is true of the color of the product. With the increase of zinc-nickel alloy products on the market, people have been able to accept the color difference between zinc-nickel alloy passivation layer and zinc-nickel passivation layer.

3. Production cost.

Since the zinc-nickel alloy coating contains about 13% metallic nickel, the price of nickel is much higher than that of zinc (nickel: 191,000 yuan/ton, zinc 18,000 yuan/ton), so the production cost of electro-galvanized nickel alloy is much higher than that of electro-galvanized zinc.

4. Process maintenance

Alkaline zincate galvanizing is now widely accepted by the market, while the zinc-nickel alloy process as a "new" electroplating process has not yet been widely popularized, and the knowledge is limited. In fact, zinc-nickel alloys have been used in the market for more than 20 years and are developing rapidly. Now the process is quite mature, and the stability even exceeds that of galvanizing.

Conclusion

Alkaline cyanide-free zinc-nickel alloy coating has good corrosion resistance, low hydrogen embrittlement and excellent heat resistance. Although the zinc-nickel alloy electroplating process has the disadvantage of low current efficiency in the alkaline system, a larger current density can be used to ensure a faster deposition rate. In general, the alkaline plating solution is less sensitive to oil contamination of the workpiece and less corrosive to equipment. The alloy composition in the solution is easy to control stably, the passivation film is less prone to discoloration, and the wastewater treatment is simple and the pollution is small, so at present, the alkaline system of zinc-nickel alloy technology at home and abroad has become a development trend.

If you have any questions and needs about the magnet or surface treatment, please feel free to drop question to NINGBO BESTWAY MAGNET Co., Ltd. at any time. We will provide professional answers in a timely manner.