Tips to simplify designsMetal plating has a storied history that dates back centuries, using craftsman level skills using thin hammered gold (gold leaf) burnished onto lower value metals such as Silver and Bronze. This process is termed gilding and was in use from the early Bronze Age in the Middle East. It is still much used for decorative items and is a craft skill
Roman use of displacement plating is well recorded, even written off by Pliny the Elder. This uses a Gold/Mercury amalgam paste which is painted onto a metal surface, then the Mercury is evaporated with slow heating.
Electroplating and other approaches came later and is a critical industrial process used to enhance the durability, conductivity, corrosion resistance, and aesthetics of metal parts. From gold-plated jewelry to zinc-coated automotive components, plating plays a vital role in manufacturing, electronics, aerospace, and more.
However, Immersion and electroless methods are still widely used across various markets and sectors.
This guide will introduce:
- The various types of metal plating technology available
- Their key applications by industry
- The benefits and challenges of each method
- Required surface preparation and post-plating treatments
- The common defects in the processes and how to manage them
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What is Metal Plating?
Metal plating involves depositing a thin layer of metal onto a substrate – usually another metal or plastic, occasionally onto composite or natural materials. This can be achieved through electrochemical, mechanical or chemical processes. Such coatings serve to improve:
- Corrosion resistance, such as Zinc plating on steel by electroplating or hot-dip immersion.
- Wear resistance, an example being chrome on tools.
- Electrical conductivity, exemplified by Gold on PCBs.
- Aesthetic appeal, such as Nickel on costume jewelry.
Types of Metal Plating techniques
Electroplating (Most common)
An electric current reduces dissolved metal ions, depositing them onto a conductive substrate by using the ions as direct current carriers, completing the electrical circuit in which the to-be-plated part is the solution cathode. In some cases, the source metal can be the anode, rather than an ionic solution of metal salts.
Common Metals Used:
- Gold in electronics, jewelry, etc. This variously enhances conductivity, oxidation resistance and aesthetics.
- Nickel is used for corrosion resistance, low stress build-up plating and as a substrate for Chromium plating. Nickel is applied by both electroplating and electroless methods discussed in detail.
- Chrome is used decorative & hard coatings on machine wear surfaces
- Zinc can be electroplated onto steel (BZP, bright Zinc plate) or hot-dip coated (galvanizing)
The benefits in metal plating are:
- Precise thickness control
- Applicability to a wide spectrum of plating and base metals
- Highly cost-effective for high volumes
- Relatively simple technology that can give very reliable and serviceable outcomes.
Many of the processes are, however, burdened with risks and difficulties, such as; requiring toxic chemicals (cyanide, acids, hexavalent Chromium salts, Cadmium); wastewater treatment can be challenging; regulatory restrictions are growing in scope and challenge.
Electroless Plating (Autocatalytic)
In this group of methods, a chemical reaction deposits metal pulled out of ionic solution without electricity, using a reducing agent (e.g., sodium hypophosphite for Nickel, the most common execution of this plating type). These plated results are unlike electroplating – they are typically matte, powdery/rough and thicker/tougher.
Common metals Used:
- Nickel-phosphorus (Ni-P) typical for military and industrial equipment that will experience high-contact and wear-inducing use and regular wetting.
- Copper PCB manufacturing, where the uniformity of coating and the ability to coat inside drilled holes is critical in applying conductors to the insulating substrate. Later stages can be electro-or-electroless plated according to particular specific needs.
The benefits of electroless plating are;
- Uniform coating, even on complex shapes
- No power source required
- Superior corrosion resistance is easily achieved
- Thicker coatings can be produced reliably.
However, the process is slower than electroplating and applicable to a limited number of metals.
Immersion Plating (Displacement plating)
The substrate metal displaces ions from a plating solution (e.g., copper on steel). This is an electrochemical exchange process where the charge state of the substrate and the plating metal in ionic solution are favorably differentiated such that the surface atoms in the substrate trade-bonds with the plating metal ions, resulting in deposition onto the substrate.
Common metals used:
- Tin for food packaging and
- Silver (low-cost jewelry)
The utility of immersion plating lies in its simplicity and reliability, where simple equipment/chemistry and no electrical current is needed. It is excellent at producing moderately adhered, thin coatings.
However, it is an intrinsically self limiting reaction as an integral coating excludes the electropotential difference and stops the reaction, so it can provide only limited thickness
Tin immersion plating of steel for canning was widely used, though less so now. It enabled large scale and low cost food preservation for the first time in human history.
Mechanical Plating
In this process, metal powder (e.g., zinc) is cold-welded onto a substrate using tumbling media and impact forces.
Common Metals Used:
- Zinc, for fasteners, corrosion proofing of steel hardware.
- Cadmium, used in military/aerospace, though this is rapidly declining due to the extreme toxicity of the metal.
This process offers the benefit of not inducing Hydrogen embrittlement in the substrate, making it well suited to high-strength steel components. Additionally, it is a cold process which can avoid thermal distortion in thin, precise parts.
Given that it requires surface peening at the impact points to create adhesion, it is not suited to non-ductile materials – although it can work well on some non-metals.
It offers much lower corrosion resistance than electroplating, as well as relatively low abrasion resistance.
Vacuum Plating (PVD/CVD)
Metal vapor is deposited in a vacuum chamber in processes termed Physical Vapor Deposition and Chemical Vapor Deposition.
In PVD, the metal is vaporized using a strong AC current and then deposits onto all exposed surfaces, with a moderate to strong directionality that creates localized shadows and potential for highly varied deposition thickness on more complex shapes. It is best suited to simple and geometrically fast parts.
CVD uses a distributed vapor of metal salts to coat a target surface by one of several chemical reactions – reduction, substitution and others. This process is more amenable to more complex shapes and tends to produce more complete and uniform coating.
Common materials used are:
- Titanium nitride (TiN) for cutting tools and precious metals such as Gold for specialist scientific instruments, optical coatings and signal modulators/gratings in optical fiber systems
- Aluminum for decorative coatings such as automotive trim, and silvering for mirrors.
- Indium Tin oxide (ITO) for transparent conductive coatings in electronics
This delivers extremely hard, wear-resistant coatings that are environmentally friendly, generating no toxic waste.
However, they suffer high equipment and part cost and severe limitations in coating complex parts.
Key Applications by Industry
Surface preparation & post-treatment
Critical Pre-Plating steps
- Degreasing – Remove oils with alkaline cleaners and surfactants, often assisted with use of an ultrasonic bath.
- Acid pickling – Remove rust/oxides (e.g., hydrochloric acid for steel).
- Activation – Ensures adhesion (e.g., nickel strike before gold plating).
Post-Plating treatments
- Passivation (chromate conversion coating for zinc) – enhances corrosion resistance.
- Heat treatment – Reduces hydrogen embrittlement in high-strength steel.
- Polishing/Buffing – Improves aesthetics.
Common Electroplating defects & fixes
Future trends in Metal Plating
- Nanoparticle coatings – thinner, stronger layers, improved barrier properties and enhanced adhesion (e.g., graphene-enhanced Nickel).
- Green plating – Cyanide-free gold plating, trivalent chromium (replaces hexavalent that suffers very high toxicity).
- Smart coatings – Self-healing or color-changing finishes that remain chemically active after application..
- Tubular rivets: Similar to solid rivets but with a tubular body for easier peening.
- Drive/hammer rivets: Installed by hammering them into place or pushing a central distorting mandrel pin into the body, typically used for sheet metal or thin materials.
Metal Plating Techniques Comparison Chart
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Conclusion
Choosing the right plating method depends on a variety of factors that are particular to each application.
Metal plating techniques play a pivotal role in the durability, appearance, and functionality of many components and products. Each method offers unique advantages suited to different applications and materials. Whether it’s improving corrosion resistance, adding aesthetic value, or increasing surface hardness, the right plating technique can improve the lifespan and performance of products.
As technology continues to develop, innovations in metal plating offer more efficient, eco-friendly, and cost-effective solutions. Understanding the characteristics and benefits of each method enables manufacturers and engineers to make informed choices that align with their project requirements. Ultimately, mastering these techniques is key to producing high-quality, reliable, and resilient metal parts.
