Metal plating: Processes, applications and future prospects

Electroplating is a process in which a thin layer of other metals or alloys is plated on certain metal surfaces using the principle of electrolysis. The principle is that the gold-plated workpiece is used as the cathode, the electroplated metal is used as the anode (sometimes the metal that is insoluble in the electroplating solution is used as the anode), and the electroplating liquid is the electroplated metal compound and conductive salts, additives, etc. When the poles are connected to the power supply (direct current), the metal ions in the plating solution move to the cathode, where the electrons are obtained, which are reduced and deposited on the cathode surface to become the coating.

Metal plating has a long history of development. The earliest published electroplating literature is the silver plating process proposed by Professor Brugnatelli in Italy in 1805, and later he proposed the gold plating process. By 1840, Elkington, England, applied for the first patent for cyanide plated silver and used it in industrial production, which marked the beginning of the plating industry. In the same year, Jaeobi received the first patent for electroplating copper from an acidic solution.

In the 1840s, electroplating alloys began to appear, such as copper zinc alloy (brass) and precious metal alloy plating. By the 1850s, techniques such as electroplating nickel, copper, tin and zinc were developed one after another. In the early 20th century, people realized the use of acid sulfate galvanizing on the surface of steel strips, Proctor proposed cyanide electrogalvanizing, Fink (C.G. ink) and Eldridge (C.H.Eldridge) proposed the industrial method of chromium plating, and electroplating gradually developed into a complete electrochemical engineering system.

The subsequent two world wars and the growing aviation industry promoted the further development and improvement of electrodeposition, the development of commercial technologies such as electroplating hard chromium and electroplating copper alloy, and electroplating equipment was developed from manual operation to modern fully automated assembly line operation.

Because the alloy coating has better performance than the single metal coating, it has been developed from the initial purpose of obtaining decorative alloy coating to the study of decorative, protective and functional alloy coating. Electroplating After more than 200 years of application and development, new electroplating materials and electroplating process technology methods continue to emerge, and the application field continues to expand. The coating material can be metal, alloy, semiconductor, etc., and the matrix material is also expanded from metal to ceramic and polymer materials.

Pre-treatment stage

Surface cleaning is an important step in the pretreatment of metal plating. Common methods include chemical cleaning, mechanical cleaning and ultrasonic cleaning. Chemical cleaning removes oil and impurities from surfaces by using specific chemical agents; Mechanical cleaning with the help of grinding, sandblasting and other ways to remove the surface of the oxide layer and dirt; Ultrasonic cleaning uses high-frequency acoustic vibration to enhance the cleaning effect. The purpose of these cleaning methods is to provide a clean surface for subsequent plating processes, ensuring the adhesion and uniformity of the coating.

Pickling is mainly used to remove oxides and rusts from metal surfaces. The common pickling solution includes sulfuric acid, hydrochloric acid, etc. The pickling process can activate the metal surface and improve the binding force between the coating and the substrate.

Pre-plating treatment also includes activation, passivation and other steps. The activation treatment can enhance the activity of the metal surface and make the electroplating process smoother. Passivation treatment forms a protective film on the metal surface to improve the corrosion resistance of the coating.

Electroplating stage

In the electroplating process, the adjustment of parameters such as current and temperature is very important. The current density directly affects the deposition speed and quality of the coating. Low current density leads to slow deposition rate and coarse crystallization of coating. However, too high current density may cause the coating to burn and the surface to be rough. Therefore, it is necessary to select the appropriate current density according to the composition of the bath and the requirements of the coating.

Temperature also has a significant effect on electroplating effect. Increasing the temperature can accelerate the ion diffusion rate and improve the uniformity and density of the coating. However, the high temperature may lead to the decomposition of the composition of the bath and affect the quality of the coating.

The preparation of plating solution is the key to ensure plating quality. Different coating materials require different bath formulations, and the proportion and concentration of various components should be strictly controlled when preparing. At the same time, factors such as the pH and conductivity of the bath should be considered to ensure the stability of the bath and achieve good electroplating results.

Post-processing stage

Cleaning is the first step of post-treatment, which can remove the residual plating solution and impurities on the surface of the coating and prevent the coating from discoloration and corrosion.

Polishing can improve the surface flatness and gloss of the coating and make its appearance more beautiful.

Drying helps to remove moisture from the surface of the coating, preventing water marks and rust.

The sealing treatment forms a dense protective film on the surface of the coating, further improves the corrosion resistance and wear resistance of the coating, and prolongates the service life of the coating. These post-treatment methods cooperate with each other to ensure the quality and performance of the coating.

Advantages

Metal plating has many significant advantages. First of all, electroplating can greatly enhance the corrosion resistance of metals. By forming a protective coating on the metal surface, it effectively blocks the contact between the metal and oxygen, water and other corrosive substances in the external environment, significantly extending the service life of the metal. For example, the corrosion resistance of galvanized steel products in harsh environments has been greatly improved.

Secondly, electroplating can significantly increase the hardness of the metal. Some coated metals such as chromium and nickel have high hardness, which can improve the wear resistance of the metal after plating on the metal surface, making it more durable in the friction and wear environment.

In addition, electroplating can also improve the electrical conductivity of the metal. For example, gold plating, silver plating and other processes can form a good conductive layer on the metal surface, reduce resistance, and improve current conduction efficiency, which is of great significance in electronic equipment and circuit manufacturing.

In addition, electroplating can also improve the appearance of the metal, making it more smooth, bright, with better decorative, to meet different aesthetic needs.

Disadvantages

However, metal plating also has some shortcomings that cannot be ignored. First of all, the electroplating process will produce serious environmental pollution. Electroplating wastewater usually contains a large number of heavy metal ions, such as chromium, nickel, cadmium, etc., as well as various acid-base substances and organic pollutants. If the waste water is discharged directly without proper treatment, it will cause serious pollution to the soil and water source, endangering the ecological environment and human health.

Secondly, improper treatment during electroplating may have a counterproductive effect. For example, hydrogen embrittlement problems can cause the coating and base metal to become brittle, reducing their mechanical properties. If the post-treatment steps in the plating process are not perfect, it may lead to defects in the coating, affecting its performance and service life.

In addition, electroplating needs to consume a lot of energy and resources, and the process is relatively complex and the cost is high. At the same time, for some small enterprises, there may be a lack of effective pollution control equipment and technology, and it is difficult to meet environmental protection requirements.

Field of protective decoration

In the field of protective decoration, metal plating has a wide range of applications. Sanitary faucets are usually treated with copper/nickel/chromium plating, which not only gives them a bright appearance, but also provides certain protective properties to prevent rust and wear on the faucet surface. Artificial jewelry is also a common application case, such as electroplating imitation gold, gold, silver and other metal coating, or the use of aluminum anodizing process, so that it has a similar color and texture of precious metals, to meet people's needs for beauty and decoration. In addition, hardware with frequent daily contact, such as doorknobs, is often electroplated to enhance beauty and durability.

Field of corrosion protection

In the field of corrosion protection, metal plating plays an important role. Galvanized sheet is a common anticorrosive material, plating a layer of zinc on the iron plate can significantly improve the corrosion resistance of the iron plate, and is widely used in construction, automobile and other industries. Chromium plating is also a common anticorrosive coating, and this process is often used in the wheel rims of old bicycles in the past. In addition, processes such as electroless nickel plating and anodizing can also effectively enhance the corrosion resistance of metals, provide reliable protection for metal products in harsh environments such as industry and outdoor, and extend their service life.

Improved performance areas

In terms of improving performance, metal plating performs well. We know that plastics are originally non-conductive, but under some special requirements, a layer of conductive metal is plated on the surface of plastics through a special process, such as silver or copper plating, which can make plastics have conductive properties, so as to be used in electronic equipment, integrated circuits and other fields. This plating method gives the material new properties and expands its range of applications.

Areas of special performance requirements

For special performance requirements, metal plating can also be met. In the need for wear-resistant occasions, such as the surface of some mechanical parts, a layer of wear-resistant materials can be plated, such as a layer of tungsten carbide or diamond-like carbon (DLC) coating, significantly improve the wear resistance of parts, reduce wear and damage, and extend the service life. In the case of self-lubrication, a layer of graphite nanocomposite coating can be plated on the surface of the material to reduce the friction coefficient, achieve self-lubrication effect, and improve the operating efficiency and stability of the equipment.

Market prospect

With the continuous development of the automotive industry, the demand for metal plating will continue to rise. Automotive exterior and interior components, such as bumpers, wheels, dashboards, etc., in order to pursue higher aesthetics and corrosion resistance, there is an increasing demand for high-quality electroplating processes. At the same time, the rise of new energy vehicles, for battery components, electronic components and other protective plating requirements are also more stringent. In the home appliance industry, high-end and intelligent products have become the mainstream, and consumers' requirements for product appearance and durability have prompted home appliance manufacturers to adopt more advanced electroplating technologies, such as nano-plating, to enhance the competitiveness of products. In the field of aerospace, with the advancement of space exploration and the continuous improvement of aircraft performance, higher requirements are put forward for the characteristics of high temperature resistance, wear resistance and corrosion resistance of parts, which will promote the development of metal plating technology to a more refined and high performance direction. It is expected that the demand for metal plating in these industries will continue to maintain a strong growth trend in the future.

Technological innovation

In terms of new electroplating materials, the application of nanomaterials and composite materials is expected to become the focus of research and development. Nano-plating technology will further improve the properties of the coating, such as hardness, wear resistance and corrosion resistance. At the same time, new alloy materials, such as copper alloys with special properties, nickel alloys, etc., will also be developed to meet different industrial needs. In terms of process innovation, intelligent and automated electroplating production lines will become the development trend, which can improve production efficiency, ensure the consistency of product quality, and reduce labor costs. In addition, the development and application of cyanide-free electroplating and low chromium electroplating processes based on green environmental protection concepts will be more extensive to reduce environmental pollution.

Environmental protection and sustainability

In the development process of metal plating, environmental protection and energy saving and emission reduction are crucial. The requirements of the government and society for environmental protection are increasingly strict, and enterprises need to increase investment in environmental protection equipment and technology to ensure that waste water, waste gas and waste residue are discharged up to standard. Research and development and use of more environmentally friendly plating processes, such as plating technology without plating solution emissions, will become the future development direction. At the same time, by optimizing the production process, improve the efficiency of energy utilization, reduce resource consumption, and achieve sustainable development. Strengthening the recycling and reuse of electroplating waste can not only reduce environmental pollution, but also create certain economic value. In short, only by focusing on environmental protection and sustainable development, the metal plating industry can have a broad future.