Electroplating 101: How Metal Plating Works

Electroplating lets you combine the strength, electrical conductivity, abrasion and corrosion resistance, and appearance of certain metals with different materials that boast their own benefits, such as affordable and/or lightweight metals or plastics.

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In this guide, you'll learn why many engineers, researchers, and artists use electroplating and metal plating in every stage of manufacturing'from prototyping to mass production.

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What Is Electroplating?

Electroplating is the process of using electrodeposition to coat an object in a layer of metal(s). Engineers use controlled electrolysis to transfer the desired metal coating from an anode (a part containing the metal that will be used as the plating) to a cathode (the part to be plated).

Diagram of copper electroplating using an electrolyte bath of copper sulfate, sulfuric acid, and chloride ions. (image source)

The anode and cathode are placed in an electrolyte chemical bath and exposed to a continuous electrical charge. Electricity causes negatively charged ions (anions) to move to the anode and positively charged ions (cations) to transfer to the cathode, covering or plating the desired part in an even metal coating. Electroplating takes a substrate material (often a lighter and/or lower-cost material) and encapsulates the substrate in a thin shell of metal, such as nickel or copper.

Electroplating is most commonly applied to other metals, because of the basic requirement that the underlying material (the substrate) is conductive. Although less common, autocatalytic pre-coatings have been developed which produce an ultra-thin conductive interface, allowing a variety of metals - most notably copper and nickel alloys - to be plated onto plastic parts. 

Electroplating vs. Electroforming

Electroplating and electroforming are both performed using electrodeposition. The difference is that electroforming uses a mold that is removed after a part is formed. Electroforming is used to create solid metal pieces, whereas electroplating is used to cover an existing part (which is made of a different material) in metal.

Electroplating Material Options

You can electroplate a single metal onto an object, or a combination of metals. Many manufacturers choose to layer metals, such as copper and nickel, to maximize strength and conductivity. Materials commonly used in electroplating include:

• Brass
• Cadmium
• Chromium
• Copper
• Gold
• Iron
• Nickel
• Silver
• Titanium
• Zinc

Substrates can be made of almost any material, from stainless steel and other metals to plastics. Artisans have electroplated organic materials, such as flowers, as well as soft fabric ribbons. 

It's important to note that non-conductive substrates such as plastic, wood, or glass must first be made conductive before they can be electroplated. This can be done by coating a non-conductive substrate in a layer of conductive paint or spray.

Electroplating (3D Printed) Plastic Parts

Thanks to scientific advances in materials and plastic manufacturing, lightweight and low cost plastic parts have replaced more expensive metal parts in a wide variety of applications serving various industries, from automobiles to plumbing pipes.

Although plastic boasts an array of advantages over metal, there are many applications where metal still reigns supreme. Try as you might, you'll never get plastic to have the same opulent finish as copper. And while plastic might be more flexible material than the majority of metals, it's not nearly as strong. This is where metal plating comes in.

3D printing offers unique advantages when combined with electroplating. Engineers often choose to 3D print substrates because of additive manufacturing's design freedom. It is often cheaper to electroplate 3D printed parts than to cast, machine, or use other manufacturing methods, especially when it comes to prototyping.

Stereolithography (SLA) 3D printing is ideal for electroplating because it creates 3D printed parts with very smooth or finely textured surfaces that make the transition between the two materials'plastics and metals'seamless. It also creates watertight parts that won't get damaged when submerged in the chemical bath required during the electroplating process.

From an engineering standpoint, the combination of 3D printing and electroplating offers unique tensile strength options for finished designs. As you can see in the chart above, the combination of these two manufacturing processes bridges the gap in tensile strength between the two material groups.

Metal plating can have a major impact on the mechanical performance of (3D printed) plastic parts. With a structural metal skin and a lightweight plastic core, parts can be produced with surprisingly high flexural strength characteristics.

In addition to improving mechanical behavior, electroplating can be used to protect plastic parts from environmental degradation. In applications where plastic parts are exposed to chemical attack or ultraviolet light, metal plating provides a permanent barrier that can extend the life of your parts from months to years.

When used as an aesthetic treatment, plating offers an easy way to create prototypes that both look and feel like metal. Depending on the plate thickness, electroplated plastic can be thin and light, or add noticeable weight to a part. Thicker electroplated coatings can even be texturized or polished to achieve a variety of metal finishes, from cast aluminum to mirrored chrome. More complex textures can be achieved by 3D printing a textured resin substrate.

Given the potential combinations of 3D printable materials, a variety of plating metals, and plate thickness ratios, it's easy to see how electroplating gives engineers a new field of design options to consider.

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The Benefits of Electroplating

Electroplating offers many benefits, including increased strength, lifespan, and conductivity of parts. Engineers, manufacturers, and artists capitalize on these benefits in a variety of ways.

Engineers often use electroplating to increase the strength and durability of various designs. You can increase the tensile strength of various parts by coating them in metals such as copper and nickel. Place a metallic skin on parts and you can improve their resistance to environmental factors like chemical exposure and UV light for outdoor or corrosive applications.

Artists often use electroplating to preserve natural elements prone to decay, such as leaves, and turn them into more durable works of art. In the medical community, electroplating is used to make medical implants that are corrosion-resistant and can be properly sterilized.

Electroplating is an effective way to add cosmetic metal finishes to customer products, sculptures, figurines, and art pieces. Many manufacturers also choose to electroplate a substrate to create more lightweight parts that are easier and cheaper to move and ship.

Electroplating also offers the benefit of conductivity. Because metals are inherently conductive, electroplating is a great way to increase the conductivity of a part. Antennas, electrical components, and other parts can be electroplated to increase performance.

The Limitations of Electroplating

Though electroplating boasts plenty of benefits, its limitations lie in the complexity and hazardous nature of the process itself. Workers performing electroplating can suffer from hexavalent chromium exposure if they don't take proper precautions. It is essential for workers to have a properly ventilated workspace. The U.S. Department of Labor Occupational Safety and Health Administration has published numerous documents outlining the risks involved in electroplating.

Although it is possible to electroplate resin parts yourself, amateur users may run into difficulty. The main reason is quality and capability. Laminate adhesion strength using DIY electroplating methods is usually lower than what is achieved by a professional plating service. Structural plating, which requires long plate times, multiple baths, and compatibility between metals, is quite difficult to execute reliably. Successful applications of in-house plating are typically simple and small, such as jewelry prototyping, and thin (single layer) RF copper coatings.

Because of the expertise required and the dangers involved, many engineers and designers choose to hire a third-party electroplating manufacturer specializing in this process. Luckily, several companies, such as RePliForm and Sharretts Plating, specialize in custom electroplating projects. Download our white paper for a list of electroplating services by region and job size.

The video above shows how to electroplate with easy-to-acquire tools, such as a cell charger and spare copper pipe. We recommend you wear a mask, gloves, and eye protection while electroplating and only work in a well-ventilated space.

The Many Applications of Electroplating

Numerous industries use electroplating to make everything from engagement rings to electrical antennas. Here are some common examples:

Aerospace

Many airplane components are electroplated to add a 'sacrificial coating,' which increases the lifespan of parts by slowing down corrosion. Because aircraft components are subject to extreme temperature changes and environmental factors, an additional metal layer is added to a metal substrate so that the functionality of a part isn't compromised by normal wear and tear.

Many steel bolts and fasteners designed for the aerospace industry are electroplated in chromium (or, more recently, zinc-nickel, due to changing restrictions).

Art and Home Decor

Type the word 'electroplated' into Etsy, and you'll be presented with a vast array of electroplated home decor and one-of-a-kind keepsakes. Artisans often turn biodegradable items, including flowers, branches, and even bugs, into durable and long-lasting pieces of art with this process. You can employ electroplating to show off and preserve fine details in items that would otherwise quickly decompose.

Electroplating is often used to create art, such as this copper-plated beetle and honeycomb. (image source)

Digital designers sometimes use electroplating to produce sculptures. Designers can 3D print a substrate using a desktop 3D printer and then electroplate the design in copper, silver, gold, or any metal of choice to achieve their desired finish. Combining 3D printing with electroplating in this manner produces pieces that are easier (and cheaper) to manufacture, while still having the same look and finish as a sculpture that is solid cast metal.

Automotive

Electroplating is very common in the automotive industry. Many major automotive companies use electroplating to create chrome bumpers and other metal parts.

Electroplating can also be used to create custom parts for concept vehicles as well. For example, VW teamed up with Autodesk to create hubcaps for their 'Type 20' concept vehicle. The prototype hubcaps were 3D-printed and then electroplated. 

Restoration companies and vehicle customization businesses also use electroplating to apply nickel, chrome, and other finishes to various car and motorcycle parts.

Jewelry

Electroplating is perhaps most commonly associated with the jewelry industry and precious metals. Jewelry designers and manufacturers rely on this process to enhance the color, durability, and aesthetic appeal of rings, bracelets, pendants, and a wide range of other items.

When you see jewelry that is described as being 'gold plated' or 'silver plated,' there's a high chance the piece you're looking at was electroplated. Combinations of various metals are used to achieve uniquely hued finishes. For example, gold is often combined with copper and silver to create rose gold.

Medical and Dental

Electroplating is used to add resilient exteriors to all sorts of medical and dental elements. Gold plating is often employed to create tooth inlays and aid in various dental procedures. Implanted parts such as replacement joints, screws, and plates are frequently electroplated to make parts more corrosion-resistant and compatible with pre-insertion sterilization. Medical and surgical tools, including forceps and radiological parts, are also commonly electroplated.

Power

Numerous electrical and solar components are electroplated to increase conductivity. Solar cell contacts and various types of antennas are routinely manufactured using electroplating. Wires can be electroplated in silver, nickel, and many other types of metal. Gold plating is often used (in conjunction with other metals) to increase durability. Gold is also frequently used to increase the lifespan of parts because it is conductive, very ductile, and doesn't interact with oxygen.

Prototyping

Producing custom or low-volume metal parts for prototyping can be very costly and time-consuming with traditional manufacturing processes. As a result, engineers often combine electroplating with 3D printing for a low-cost and time-saving solution.

For example, Andreas Osterwalder of the Swiss Federal Institute of Technology in Lausanne (EPFL) has been able to speed up the prototyping process and reduce costs of advanced experimental setups by 3D printing new designs himself on his Formlabs resin 3D printer and working with Galvotec to have those parts electroplated.

Andreas Osterwalder used 3D printing and electroplating to manufacture this beam splitter.

RF and Microwave Products

Antennas need to have electrical conductivity to propagate radio waves. While plastic 3D printed parts don't conduct electricity, they offer almost infinite design freedom and materials with good mechanical and thermal properties. These benefits can be combined with electroplating to achieve the desired conductivity, resulting in a great solution for custom antennas for research and development in the automotive, defense, medicine, and education.

Electroplating plastic parts creates conductive parts that enable high performance RF applications.

Best Practices for Electroplating 3D Printed Parts

Electroplated composites are a means to a wide variety of ends. Because of its versatility, electroplating opens up countless possibilities across different industries. Want to learn more about electroplating 3D printed parts?

Download our white paper to learn how engineers are adding metal to resin 3D prints, and why hybrid metal parts can open doors to a surprising range of applications, including (but not limited to) enduse strength and durability. By the end of the white paper, you will learn new ways to apply electroplating, as well as design considerations and practical tips on using metal electroplating to amplify the performance of your SLA parts.

Surface covering of metal on a conductor

"Plated" redirects here. For the online meal kit company, see Plated (meal kits)

Plating is a finishing process in which a metal is deposited on a surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, to improve IR reflectivity, for radiation shielding, and for other purposes. Jewelry typically uses plating to give a silver or gold finish.

Thin-film deposition has plated objects as small as an atom,[1] therefore plating finds uses in nanotechnology.

There are several plating methods, and many variations. In one method, a solid surface is covered with a metal sheet, and then heat and pressure are applied to fuse them (a version of this is Sheffield plate). Other plating techniques include electroplating, vapor deposition under vacuum and sputter deposition. Recently, plating often refers to using liquids. Metallizing refers to coating metal on non-metallic objects.

Electroplating

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In electroplating, an ionic metal is supplied with electrons to form a non-ionic coating on a substrate. A common system involves a chemical solution with the ionic form of the metal, an anode (positively charged) which may consist of the metal being plated (a soluble anode) or an insoluble anode (usually carbon, platinum, titanium, lead, or steel), and finally, a cathode (negatively charged) where electrons are supplied to produce a film of non-ionic metal.

Electroless deposition

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Electroless deposition, also known as chemical or auto-catalytic plating, is a non-galvanic plating method that involves several simultaneous reactions in an aqueous solution, which occur without the use of external electrical power. The reaction is accomplished when hydrogen is released by a reducing agent, normally sodium hypophosphite (Note: the hydrogen leaves as a hydride ion) or thiourea, and oxidized, thus producing a negative charge on the surface of the part. The most common electroless deposition method is electroless nickel plating, although silver, gold and copper layers can also be applied in this manner, as in the technique of angel gilding.

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Gold plating

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Gold plating is a method of depositing a thin layer of gold on the surface of glass or metal, most often copper or silver.

Gold plating is often used in electronics, to provide a corrosion-resistant electrically conductive layer on copper, typically in electrical connectors and printed circuit boards. With direct gold-on-copper plating, the copper atoms have the tendency to diffuse through the gold layer, causing tarnishing of its surface and formation of an oxide/sulfide layer. Therefore, a layer of a suitable barrier metal, usually nickel, has to be deposited on the copper substrate, forming a copper-nickel-gold sandwich.

Metals and glass may also be coated with gold for ornamental purposes, using a number of different processes usually referred to as gilding.

Sapphires, plastics, and carbon fiber are some other materials that are able to be plated using advance plating techniques. The substrates that can be used are almost limitless.[2]

Silver plating

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This section is about the method of adding a thin layer of silver to an object. For the Manhattan Project operation, see Silverplate

This bracelet has zircon gemstones. The metal is zinc alloy base with silver coating.

Silver plating has been used since the 18th century to provide cheaper versions of household items that would otherwise be made of solid silver, including cutlery, vessels of various kinds, and candlesticks. In the UK the assay offices, and silver dealers and collectors, use the term "silver plate" for items made from solid silver, derived long before silver plating was invented from the Spanish word for silver "plata", seizures of silver from Spanish ships carrying silver from America being a large source of silver at the time. This can cause confusion when talking about silver items; plate or plated. In the UK it is illegal to describe silver-plated items as "silver". It is not illegal to describe silver-plated items as "silver plate", although this is ungrammatical.

The earliest form of silver plating was Sheffield Plate, where thin sheets of silver are fused to a layer or core of base metal, but in the 19th century new methods of production (including electroplating) were introduced. Britannia metal is an alloy of tin, antimony and copper developed as a base metal for plating with silver.

Another method that can be used to apply a thin layer of silver to objects such as glass, is to place Tollens' reagent in a glass, add glucose/dextrose, and shake the bottle to promote the reaction.

AgNO3 + KOH ' AgOH + KNO3

3 ' [Ag(NH3)2]+ + [OH]' (Note: see

AgOH + 2 NH' [Ag(NH+ [OH](Note: see Tollens' reagent

3)2]+ + [OH]' + 3 + H2O

[Ag(NH+ [OH] aldehyde (usually glucose/dextrose) ' Ag + 2 NH+ H

For applications in electronics, silver is sometimes used for plating copper, as its electrical resistance is lower (see Resistivity of various materials); more so at higher frequencies due to the skin effect. Variable capacitors are considered of the highest quality when they have silver-plated plates. Similarly, silver-plated, or even solid silver cables, are prized in audiophile applications; however some experts consider that in practice the plating is often poorly implemented, making the result inferior to similarly priced copper cables.[3]

Care should be used for parts exposed to high humidity environments because in such environments, when the silver layer is porous or contains cracks, the underlying copper undergoes rapid galvanic corrosion, flaking off the plating and exposing the copper itself; a process known as red plague. Silver plated copper maintained in a moisture-free environment will not undergo this type of corrosion.

Copper plating

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Copper plating is the process of electrolytically forming a layer of copper on the surface of an item. It is commonly used as an even cheaper alternative to silver plating as it is much cheaper than silver.

Rhodium plating

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Rhodium plating is occasionally used on white gold, silver or copper and its alloys. A barrier layer of nickel is usually deposited on silver first, though in this case it is not to prevent migration of silver through rhodium, but to prevent contamination of the rhodium bath with silver and copper, which slightly dissolve in the sulfuric acid usually present in the bath composition.[4]

Chrome plating

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Chrome plating is a finishing treatment using the electrolytic deposition of chromium. The most common form of chrome plating is the thin, decorative bright chrome, which is typically a 10-μm layer over an underlying nickel plate. When plating on iron or steel, an underlying plating of copper allows the nickel to adhere. The pores (tiny holes) in the nickel and chromium layers work to alleviate stress caused by thermal expansion mismatch but also hurt the corrosion resistance of the coating. Corrosion resistance relies on what is called the passivation layer, which is determined by the chemical composition and processing, and is damaged by cracks and pores. In a special case, micropores can help distribute the electrochemical potential that accelerates galvanic corrosion between the layers of nickel and chromium. Depending on the application, coatings of different thicknesses will require different balances of the aforementioned properties. Thin, bright chrome imparts a mirror-like finish to items such as metal furniture frames and automotive trim. Thicker deposits, up to  μm, are called hard chrome and are used in industrial equipment to reduce friction and wear.

The traditional solution used for industrial hard chrome plating is made up of about 250 g/L of CrO3 and about 2.5 g/L of SO4'. In solution, the chrome exists as chromic acid, known as hexavalent chromium. A high current is used, in part to stabilize a thin layer of chromium(+2) at the surface of the plated work. Acid chrome has poor throwing power, fine details or holes are further away and receive less current resulting in poor plating.

Zinc plating

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Zinc coatings prevent oxidation of the protected metal by forming a barrier and by acting as a sacrificial anode if this barrier is damaged. Zinc oxide is a fine white dust that (in contrast to iron oxide) does not cause a breakdown of the substrate's surface integrity as it is formed. Indeed, the zinc oxide, if undisturbed, can act as a barrier to further oxidation, in a way similar to the protection afforded to aluminum and stainless steels by their oxide layers. The majority of hardware parts are zinc-plated, rather than cadmium-plated.[5]

Zinc-nickel plating

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Zinc-nickel plating is one of the best corrosion resistant finishes available offering over 5 times the protection of conventional zinc plating and up to 1,500 hours of neutral salt spray test performance. This plating is a combination of a high-nickel zinc-nickel alloy (10'15% nickel) and some variation of chromate. The most common mixed chromates include hexavalent iridescent, trivalent or black trivalent chromate. Used to protect steel, cast iron, brass, copper, and other materials, this acidic plating is an environmentally safe option.[6] Hexavalent chromate has been classified as a human carcinogen by the EPA and OSHA.[7][8]

Tin plating

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The tin-plating process is used extensively to protect both ferrous and nonferrous surfaces. Tin is a useful metal for the food processing industry since it is non-toxic, ductile and corrosion resistant. The excellent ductility of tin allows a tin coated base metal sheet to be formed into a variety of shapes without damage to the surface tin layer. It provides sacrificial protection for copper, nickel and other non-ferrous metals, but not for steel.

Tin is also widely used in the electronics industry because of its ability to protect the base metal from oxidation thus preserving its solderability. In electronic applications, 3% to 7% lead may be added to improve solderability and to prevent the growth of metallic "whiskers" in compression stressed deposits, which would otherwise cause electrical shorting. However, RoHS (Restriction of Hazardous Substances) regulations enacted beginning in require that no lead be added intentionally and that the maximum percentage not exceed 1%. Some exemptions have been issued to RoHS requirements in critical electronics applications due to failures which are known to have occurred as a result of tin whisker formation.

Alloy plating

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In some cases, it is desirable to co-deposit two or more metals resulting in an electroplated alloy deposit. Depending on the alloy system, an electroplated alloy may be solid solution strengthened or precipitation hardened by heat treatment to improve the plating's physical and chemical properties. Nickel-Cobalt is a common electroplated alloy.

Composite plating

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Metal matrix composite plating can be manufactured when a substrate is plated in a bath containing a suspension of ceramic particles. Careful selection of the size and composition of the particles can fine-tune the deposit for wear resistance, high temperature performance, or mechanical strength. Tungsten carbide, silicon carbide, chromium carbide, and aluminum oxide (alumina) are commonly used in composite electroplating.

Cadmium plating

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Cadmium plating is under scrutiny because of the environmental toxicity of the cadmium metal. Cadmium plating is widely used in some applications in the aerospace, military, and aviation fields. However, it is being phased out due to its toxicity.[9] Military and Aerospace components manufacturers, such as Amphenol Aerospace, have recently been exploring drop-in electroplating replacements for use with currently fielded equipment in order to support the phaseout of the dangerous finish.[10]

Cadmium plating (or cad. plating) offers a long list of technical advantages such as excellent corrosion resistance even at relatively low thickness and in salt atmospheres, softness and malleability, freedom from sticky and/or bulky corrosion products, galvanic compatibility with aluminum, freedom from stick-slip thus allowing reliable torquing of plated threads, can be dyed to many colors and clear, has good lubricity and solderability, and works well either as a final finish or as a paint base.[5][11]

If environmental concerns matter, in most aspects cadmium plating can be directly replaced with gold plating as it shares most of the material properties, but gold is more expensive and cannot serve as a paint base.

Nickel plating

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Nickel is electroplated by using a Watts bath, an electrolytic cell having a nickel anode and electrolyte containing nickel sulfate, nickel chloride, and boric acid.[12] Other nickel salts such as nickel ammonium sulfate are sometimes used instead of nickel sulfate.

Electroless nickel plating

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Electroless nickel plating, also known as enickel and NiP, offers many advantages: uniform layer thickness over most complicated surfaces, direct plating of ferrous metals (steel), superior wear and corrosion resistance compared to electroplated nickel or chrome. Much of the chrome plating done in aerospace industry can be replaced with electroless nickel plating, again environmental costs, costs of hexavalent chromium waste disposal and notorious tendency of uneven current distribution favor electroless nickel plating.[13]

Electroless nickel plating is self-catalyzing process, the resultant nickel layer is NiP compound, with 7'11% phosphorus content. Properties of the resultant layer hardness and wear resistance are greatly altered with bath composition and deposition temperature, which should be regulated with 1 °C precision, typically at 91 °C.

During bath circulation, any particles in it will become also nickel-plated; this effect is used to advantage in processes which deposit plating with particles like silicon carbide (SiC) or polytetrafluoroethylene (PTFE). While superior compared to many other plating processes, it is expensive because the process is complex. Moreover, the process is lengthy even for thin layers. When only corrosion resistance or surface treatment is of concern, very strict bath composition and temperature control is not required and the process is used for plating many tons in one bath at once.

Electroless nickel plating layers are known to provide extreme surface adhesion when plated properly. Electroless nickel plating is non-magnetic and amorphous. Electroless nickel plating layers are not easily solderable, nor do they seize with other metals or another electroless nickel-plated workpiece under pressure. This effect benefits electroless nickel-plated screws made out of malleable materials like titanium. Electrical resistance is higher compared to pure metal plating.

Aluminum plating

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"Aluminum plating" can refer to either plating on aluminum[14] or the plating of aluminum on other materials.[15]

See also

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References

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