Picture of galvanized metal hanging. Photo courtesy of Wertuose // Wikimedia Commons.
Metal plating is the process of coating a metal surface with a thin layer of another metal to enhance durability, corrosion resistance, and appearance. It combines the best of durability and efficiency.
Take a pressure vessel, for example—building it entirely from stainless steel can be expensive.
Instead, using carbon steel for the main structure keeps costs down, while plating the interior surfaces exposed to corrosive substances adds the corrosion resistance of stainless steel. This approach provides strength, affordability, and protection where it’s needed most, making metal plating a smart, cost-effective solution.
Jump to a section: Finish Materials | Processes | Working Steps | Quality Control | Metal Plating on Plastic | Safety | Defects and Remedies | Everyday Uses | FAQs
Common Types of Metal Plating Finish Materials
Metal plating uses a range of materials, each chosen for specific advantages in welding projects and applications. These materials provide unique properties like corrosion resistance or durability, making them essential for different jobs.
Nickel
Nickel provides top-notch corrosion resistance, especially in demanding environments. It’s a go-to material for kitchen utensils, electronics, and vessels that handle corrosive liquids.
Gold
Gold stands out for its corrosion resistance and superior conductivity. It’s used in electronics for connectors and circuit boards, as well as in jewelry, decorative items, and medical devices.
Silver
Silver is known for its high electrical and thermal conductivity as well as its antimicrobial properties and general aesthetic appeal. It is often used in electronics, jewelry, silverware, and medical instruments and devices.
Chrome
Chrome (chromium) delivers a tough, corrosion-resistant surface that’s built to last. Its high-gloss finish makes it popular in automotive applications like rims and bumpers.
Zinc
Zinc is a cost-effective, easy-to-apply option for corrosion protection, often used in hot-dip galvanizing. You’ll find zinc coatings on steel structures, automotive parts, and marine components like boat fittings and dock hardware.
Copper
Copper is prized for its outstanding electrical and thermal conductivity, lightweight nature, and malleability. It’s commonly used in electrical wiring, heat exchangers, pipes, and decorative applications.
Rhodium
Rhodium is highly resistant to corrosion and wear, with a reflective, polished look. It’s commonly used to plate white gold for jewelry, boost the shine of silver, and protect electronic connections in harsh environments.
Cadmium
Cadmium offers strong corrosion resistance, often acting like a “sacrificial layer” to protect underlying materials. It’s frequently used in marine, aerospace, and military applications.
Tin
Tin is non-toxic and corrosion resistant, making it ideal for food and beverage uses. It’s also solderable, which suits electronic applications, and provides reliable corrosion protection as a coating.
Aluminum
Aluminum is lightweight yet durable, with natural corrosion resistance due to its oxide layer. It’s an excellent conductor of heat and electricity and is used in everything from aircraft parts and automotive components to packaging materials like foil and cans.
Common Metal Plating Processes
There are various ways to apply plating materials.
Electroplating
Electroplating uses electrical energy to create a bond in a liquid solution.
Process Overview
First, the part that needs plating (the substrate) is thoroughly cleaned of all surface contaminants. It is then placed in an electrolyte solution containing metal ions and is electrically charged with the use of a cathode (the negatively charged workpiece) and metal anode. A direct current reduces metal ions at the cathode, which results in the formation of a metal coating on the substrate.
Common Applications
Electroplating has many applications, such as improving corrosion resistance in marine environments, enhancing the aesthetic appeal of jewelry, and increasing electrical conductivity in electronics.
Electroplating also increases wear resistance in tools and machinery and restores worn components by building up the base metal where excessive wear has taken place.
Electroless Plating
Electroless plating is common in the application of nickel but is also suitable for copper and sometimes even gold and silver.
Process Overview
As its name implies, electroless plating does not use electrical energy. Instead, it uses chemical reactions in a liquid solution (typically sodium-based), which, when oxidized, creates a negative charge on the workpiece.
Common Applications
Electroless plating is a versatile process commonly used in circuit boards and connectors to improve electrical conductivity. It is also used to improve wear and corrosion resistance in engine parts and aesthetic appeal and corrosion resistance in plumbing fixtures, which extends the service life of the fixtures and fittings.
Galvanizing
Galvanizing is commonly used on steel and iron to protect the metal from corrosion, particularly in structures exposed to inclement weather and harsh marine environments.
Process Overview
Galvanizing is performed by dipping or completely immersing the part or assembly into a molten bath of zinc (commonly known as hot-dipped galvanizing) or by applying zinc-based paint to the base metal (called zinc-rich or mechanical galvanizing).
Common Applications
Galvanizing is a common plating process, used in structural steel, such as power and light poles. It protects against harsh environmental conditions that could otherwise impact the pieces’ structural integrity. It is also used on hardware and fasteners to preserve strength and durability to extend service life.
Immersion Plating
Immersion plating involves oxidation in a solution. This causes the less noble metal to lose ions to the more noble metal.
Process Overview
Once clean, the metal substrate is lowered into a solution containing the metal ions (the plating material). During the chemical reaction, the metal ions are reduced and deposited onto the surface of the substrate, which itself may dissolve into the solution.
Different metals react differently with each other in this process. For example, if a nickel substrate is immersed in a gold solution, the gold ions will be deposited onto the nickel surface.
Control of factors like immersion time, temperature, and concentration of metal ions influence the thickness of the metal plating.
Common Applications
Immersion plating is common in electronics, such as in gold plating for connectors and circuit boards.
Hot-Dip Plating
Hot-dip plating applies a metal coating (usually zinc-based) to a metal at high temperatures.
Process Overview
After cleaning and prepping the substrate, a flux solution (typically a zinc-chloride mixture) is applied to prevent oxidation and enhance adhesion.
Common Applications
Hot-dip plating is often used in construction and automotive applications due to its protective characteristics and high durability.
Brush Plating
Also known as selective plating or “electroplating by brush,” brush plating applies the metal plating to a specific area of the substrate using a brush-like tool.
Process Overview
Brush plating is a variant of the electroplating process. An electric current is passed through a solution in which there is a brush saturated with the metal that will be deposited onto the substrate. Brush plating allows the application of metal plating on specific, targeted areas.
Common Applications
Brush plating is commonly used to build up worn components when wear has occurred due to prolonged exposure to harsh conditions and to add to existing coatings.
Vacuum Deposition: PVD & CVD
Vacuum deposition plating is performed through either physical or chemical vapor deposition. Both deposit thin films of plating material on various substrates.
Process Overview
Physical vapor deposition (PVD) is where metal from a solid source is vaporized and then deposited onto a substrate in an enclosed vacuum chamber.
Chemical vapor deposition (CVD) relies on the reaction of gasses called volatile precursors (meaning their composition is designed to trigger a specific chemical reaction with the substrate), often at elevated temperatures. This leads to the deposition of material onto the substrate in a thin film. In many cases, the reaction produces volatile by-products that must be removed from the enclosed chamber during the plating process.
Common Applications
PVD is often used in tool and die making to improve hardness and wear resistance (the process applies an anti-reflective coating to optical components) and in the semiconductor industry to deposit thin films on wafers.
CVD has similar applications. It is often used in the production of microelectronics, such as circuits and thin film transistors. CVD also makes hard coatings, like silicon carbide on cutting tools and wear-resistant components.
Plasma Spray Coating
Plasma spray coating uses a coating material in powdered form (either metal, ceramic, or composite). The coating is sprayed onto the substrate with a plasma torch.
Process Overview
The plasma torch generates an electric arc by connecting two electrodes that ionize the gas (typically argon or nitrogen). The powdered solution is then fed into the plasma torch setup and, under intense heat created by the plasma arc, is liquified and sprayed onto the substrate.
Common Applications
Plasma spray coating is often found in nuclear reactors and gas turbines due to its capability to provide corrosion resistance and thermal stability.
Chromizing
Chromizing is a surface treatment that involves adding a thin layer of chromium to a substrate to increase its hardness as well as its wear and corrosion resistance.
Process Overview
Chromizing happens in an enclosed chamber with a mixture of chromium in powdered form and an activator like ammonium chloride. Together with the activator, the substrate and chromium powder are then heated to a high temperature (sometimes as high as 1000 degrees Celsius), which causes the chromium to diffuse onto the substrate surface.
In some cases, CVD is used. Here, chromium compounds in gas form are introduced into the chamber to cause a chemical reaction that will deposit the chromium plating onto the substrate surface.
Common Applications
Chromizing is used in a wide range of applications due to its high corrosion resistance. Chromium is often used on gears in the automotive industry to reduce wear and friction and in many industrial machines, specifically on components susceptible to excessive wear to extend service life.
The Metal Plating Process: Working Steps
Metal plating involves a few essential steps to ensure a strong and reliable finish.
Preparation
Proper preparation is key to getting the best results. Skipping steps here can lead to weak bonds or poor durability.
Cleaning
Start by making sure the metal surface is completely clean. Dirt, rust, oil, or other contaminants will stop the plating material from sticking properly.
Surface Activation
Roughening the surface helps the plating bond better. Common methods include sandblasting, etching, or using a sanding disc. The goal is to give the surface enough texture for the plating to hold.
Masking and Racking
Before plating, areas that shouldn’t be coated need masking. Tape works for simple surfaces, but rubber, silicone, or liquid masking materials are better for tougher jobs or complex shapes. Liquid masks harden into a protective layer and are ideal for intricate designs.
Racking ensures the plating process is even and efficient. This can be done by hanging workpieces with hooks or placing them in baskets or racks that are lowered into the bath. Proper racking also makes handling safer and prevents damage during plating.
Plating
Plating Bath Preparation
Fill the bath with the plating solution, which contains metal salts or other chemicals based on the plating material. Submerge the part to ensure even plating coverage.
Immersion Time
Immersion time depends on factors like desired thickness, substrate size, shape, and material. Plan accordingly before starting the process.
Electrical Current Application (If Applicable)
For electroplating, connect the workpiece to the cathode (negative electrode) and use the anode (positive electrode) as the plating metal.
Finishing Steps
Some applications require additional steps to complete the metal plating process.
Rinsing
It may be necessary to remove excess plating solution to ensure an even and consistent plated surface.
Drying
It may also be necessary to dry the completed workpiece to prevent the formation of water spots. Buffing and polishing will give a bright, aesthetically pleasing appearance.
Quality Inspection
Examine the freshly plated workpiece. Check for a uniform coating with no voids or bare spots. Make sure the plating is of the required thickness and that the plating material adheres well to the workpiece.
Quality Control in Metal Plating
A critical step in metal plating is quality control. Inspection of the metal plating and finished product will ensure the plating will serve its intended purpose.
Visual Inspection Techniques
Start with a visual inspection to check for uniform plating and bare spots.
Measuring Thickness
Measure substrate thickness before and after plating to confirm the coating meets specifications.
To get a precise measurement, cut away a small sample of the piece and measure the exposed cross-section. If this is not possible without damaging the completed assembly, measure the plating thickness at the point where the uncoated base metal is exposed and the plated portion of the assembly begins.
Adhesion Testing
Test adhesion by checking the completed workpiece for any voids or gaps at the edges or boundaries where plated and unplated areas occur. Try prying away the plating material with either a thumbnail or a small pocket knife to assess the strength of the bond.
Another method is the tape test. Apply a strong adhesive tape to the plated surface and gently pull it away. If the plating has adhered correctly, the tape should separate from the plating without removing the plating from the workpiece.
Metal Plating on Plastic
It is also possible to apply metal plating to plastic components.
Process of Plating on Plastic
Metal plating can be applied to plastics using various methods:
Electroplating
Good for plastics with sufficient electrical conductivity.
Electroless Plating
Works for non-conductive plastics since it doesn't require electricity.
Other Methods
Includes spray-on metallic finishes and dipping techniques.
Benefits of Metal Plating of Plastics
Metal plating on plastic produces components with the lightweight and design flexibility of plastics but the strength, durability, and overall aesthetic appeal of metal.
In electronic applications, plating provides electrical conductivity in smaller assemblies and components, which makes them lightweight and cost-effective to produce.
Safety and Environmental Considerations
Safety Protocols
The plating process may generate toxic fumes that could cause severe respiratory complications and even cancer. For this reason, it is vital to use respirators with a cartridge rated for the chemicals in use. Any facility where metal plating processes are performed should have adequate ventilation through the use of exhaust fans or another means of removing toxic fumes.
There is always a risk of electric shock with electrical plating processes. Keeping electrical equipment in proper working order and handling electrical connections with care will mitigate this risk.
Some chemicals used in metal plating are highly flammable. It is important to store and handle chemicals with care, keep the work area free of combustible materials at all times, and have an adequately rated fire extinguisher (typically class C rated) in the work area in case of emergencies.
Hazardous Materials Handling
One of the main risks of metal plating is the necessity to handle chemicals and toxins that pose risks to both people and the environment. Chemicals such as acids, cyanides, and heavy metals (such as chromium and nickel) may cause respiratory issues and an increased risk of certain cancers in cases of long-term exposure.
Waste Management and Disposal
Improper disposal of plating chemicals can harm both people and the environment. Contaminants in the water supply can lead to severe ecological damage and health risks, so always follow local regulations for waste disposal.
There are plenty of resources to help with the proper disposal of hazardous materials, such as local recycling centers and municipal waste programs.
Regulations and Compliance
Regulatory agencies like OSHA (Occupational Safety and Health Administration) and the EPA (Environmental Protection Agency) have strict standards and regulations for the handling and disposal of chemicals involved in the metal plating process. Violating these standards may result in steep penalties and fines or even imprisonment in severe cases or repeat offenses.
Common Defects and Remedies
Some of the most common defects involved in metal plating include lack of bonding and inconsistency.
Lack of Bonding
If the plating isn’t bonding properly, check the surface prep. Contaminants or a super-smooth surface can prevent proper adhesion. Try blasting, sanding, or wire brushing the surface to create a better texture for the plating material to grip.
Inconsistency
Inconsistent plating can result from improper surface prep or incorrect handling during the plating process. Make sure the substrate is fully submerged in the bath and not making contact with the sides or bottom where the plating can’t reach. Hanging parts or using racks ensures an even coat.
Everyday Uses of Metal Plating
Metal plating has become standard practice in the manufacture of many products and components.
Automotive Industry
Chrome plating is a classic in the automotive industry, giving rims, bumpers, exhaust components, and accessories like door handles a durable, shiny finish.
Aerospace Industry
In aerospace, where lightweight and durability are critical, metal plating improves wear resistance and reduces friction, especially in high-stress components like turbine blades.
Art
Artists use plating to create striking sculptures and structures, combining a strong frame made of carbon steel with the high-gloss finish of metals like copper or brass for a standout aesthetic.
Electronics and Power
In electronics, plating enhances conductivity, making it possible to produce critical components at a lower cost without compromising performance.
Jewelry and Fashion
From watches to bracelets, metal plating creates the signature shiny finish that makes jewelry stand out. Plating with metals like gold, silver, and copper adds luxury and detail to designs.
Medical and Dental
In medical devices, plating offers corrosion resistance and biocompatibility, which extends the lifespan of equipment and ensures safe use in the body.
FAQs
What are some key advantages to using metal plating?
Metal plating enhances desirable properties that would not be available without the plate material. For example, plating can enhance the artistic appeal of a structure. Metal plating also provides wear resistance for equipment in abrasive conditions and corrosion resistance inside vessels storing corrosive chemicals.
What is the most common metal plating process?
Electroplating is the most common method for a variety of reasons. It is suitable for a variety of materials, both in terms of the substrate and the plating material itself. It is relatively low cost in comparison to other plating methods, which makes it suitable for large-scale operations and high-volume production.
Proper electroplating creates a strong bond to the substrate. The precise nature and high degree of control over the electroplating process make consistency in greater plating thickness attainable.
What is the most common challenge faced with material plating?
The biggest plating challenge is forming a strong bond between the substrate and the plating material. To prevent problems, proper material preparation is crucial.
First, it is necessary to remove all potential contaminants on the substrate surface. Oils, paint, dirt, rust, and other debris will inhibit bonding and may result in surface irregularities in the finished product or even a lack of adhesion entirely. Any solvents used in cleaning must themselves be fully removed for the same reason.
Second, a highly smooth, shiny, or reflective surface may prove difficult for metal plating. Roughing up the surface with sanding, blasting, or wire wheels on a grinder should provide subtle surface imperfections for the plating material to adhere to.
Featured photo courtesy of Wertuose // Wikimedia Commons
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