Cadmium Plating Guide: Process, Types, Processes and Applications

Cadmium plating is a well-known electroplating process which engineers use for aerospace nuts, bolts and fasteners. Out of its good conductance, low friction and remarkable corrosion resistance. Knowledge about cadmium plating will help you design optimised components with extended life and performance. We will walk you through process types, applications and much more about cadmium plating. Stay here and learn every aspect about cadmium plating, helping you evaluate you manufacturing.

What Is Cadmium Plating?

As said before, a well-known electroplating process is where cadmium is electroplated over a metal surface. It not only helps make component corrosion resistance but also helps enhance soliderability, ductility and lubricity. Cd itself acts as a sacrificial layer protecting the underlying material from corrosion. Engineers prefer using Cd plating on tiny components of the marine industry and aerospace. Electroplated Cd layers help them to maintain their performance in harsh salty and moist conditions.

What Is the Color of Cadmium Plating?

One electroplated Cd layer appears silver-white, golden-yellow, iridescent, or olive drab. Colour depends on post-treatment of chromate finish. For example, in case type II, supplementary chromate conversion coating is done. Such coating offers material with a distinct yellow or rainbow-gold look.

Is Cadmium Plating Toxic?

Yes, Cadmium plating that helps prevent damage to your components is toxic in nature. It's all because of that heavy base metal cadmium that's carcinogenic. Although its toxic, it's used by engineers and manufacturers.

Why Is Cadmium Plating Still Used?

In components where any sort of functional failure is catastrophic, Cd plating is still used because of its exceptional multiple properties. For example, it offers exceptional galvanic compatibility with aluminum airframes, a highly predictable torque-tension relationship without galling, and non-binding sacrificial corrosion products.Here is a further breakdown of why it still in use.

Protect Parts from Corrosion

Coating of Cd does not let water, air, or moisture of salt reach base material. Coating acts as a physical barrier preventing buried components from corrosion. It protects components from galvanic corrosion and stress corrosion as well as from salt water corrosion. Even in case cd plated part gets scratched or its coating gets damaged somehow, the Cd layer acts as a sacrificial layer. This means it crudes itself but does not let corrosion reach base material.

Out of this property, engineers prefer using cd plating over parts that are continuously under stress and in harsh environments. For example, in marine boat rigging and dock connectors and on mechanical parts like gears, shafts, and bearings

Reduce Friction of Parts

CD plating forms a uniform layer over base material. With its low coefficient of friction cd offer smooth mating of parts' surfaces without tearing or sticking. Under high stress, like in case threaded fasteners, layers slightly deform instead of shearing out. That's why Cd coating finds its use in hinges, latches, gears, and sliding tracks that operate in dynamic environments. Also used on landing gear components.

Improved Anti-Galling Performance

As said before cd plating results in a smooth, uniform surface with low friction. Due to this, sliding surfaces do not wear and tear. Such property is crucial in aerospace parts where seizing and galling can lead to remarkable outcomes. Not only this, but CD layer prevents galling through different mechanisms, including:

• Low Shear Strength Interlayer:Since Cd is soft and ductile in nature, whenever stress is applied on component frictional strength exceeds shear strength of Cd. Because of this, cadmium essentially acts as a sacrificial, solid-state lubricant layer. Coating deforms and slips internally rather than transferring stress to the base metal.
• Asperity Flattening and Load Distribution:Cd also prevents galling through load distribution. Micro-peaks (asperities) of a soft cadmium coating plastically deform and flatten out under load. So real contact area of surfaces increases, and load distribution occurs. Hence eliminating the localised high-stress concentrations that typically trigger galling.

Good Electrical Conductivity

Cadmium plating is preferred by engineers in aerospace fasteners and brackets and in circuits where they need conductance with minimum resistance due to its good electrical conductivity. Cd has free electrons in its lattice structure, allowing electricity to pass through it easily. With its very low electrical resistivity of approximately 7.5 microhm-cm its considered a good conductor.

Reduces Galvanic Corrosion

When bare steel fasteners or components directly touch aluminium in a moist environment, a galvanic cell forms. Cadmium plating is commonly used on steel fasteners, especially those assembled with aluminum structures. It is because cadmium electrochemical potential sits extremely close to aluminium on the galvanic series, which can reduce reduces the electrochemical mismatch between steel and aluminum. As for the steel, Cd acts as a sacrificial coating.

Types of Cadmium Plating

According to AMS-QQ-P-416, engineers divide Cad coating into three types. These types are based on post-treatment applied after primary cd coating layer. Here are the three main types including: Type I, type II and type III Cadmium Plating

Type I Cadmium Plating

A simple layer of cad plating which does not undergo any post-treatment is type I cadmium plating. Usually appear silver metallic in colour. For this coating desired component is submerged in a liquid bath of cadmium salts in presence of electric current, and a layer of Cd gets deposited on it. If your CNC part needs to retain an as-plated cadmium surface, choose Type I.

Type II Cadmium Plating

Type II plating is where cd plated component is further treated with chromate conversion coating. The color of Type II is olive drab. An extra layer of chromate offers a more higher corrosion resistance, as it prevents formation of white rust over Cd. If your machined part will be used in harsh environments and requires better corrosion resistance, choose Type II.

Type III Cadmium Plating

Just like type II, type III cadmium plating involves post-treating the Cd plating component. But here instead of chromate a layer of phosphate is applied. Unlike types I and II, it doesn't have a smooth finish; instead, it gives a component a microporous phosphate layer surface. Such porosity is effective for subsequent painting, priming, or adhesive bonding. If you plan to apply another coating over the cadmium plating, choose Type III.

Cadmium Plating Thickness

Thickness of coating layers plays a crucial role in corrosion, assembly, dimension, and critical features like threads. Too thick coatings can provide greater corrosion protection, while may hinder component assembly. On the contrary, an uneven or thin coating can lead to corrosion and tearing without providing significant protection. For these reasons cadmium plating is divided into three classes for thickness based on their required functioning.

Classes of Thickness

Class 1

Class thickness is what offers maximum thickness among all coatings of cadmium. Here minimum thickness is kept around 0.0005 inches (13 µm). Especially used for components that can't be recoated again and again and need max protection from corrosion in harsh conditions like in marine fasteners.

Class 2

Class 2 provides a balance between protection and dimensional control. Its 0.0003-inch (7.6 µm) minimum thickness gives better corrosion protection than Class 3 while adding less coating thickness than Class 1. Engineers prefer using it for components where precision and protection are both important, like in thread fit, hole dimensions, and bearing fits

Class 3

You can use Class 3 thickness when dimensional accuracy is more important than maximum corrosion protection. Because it offers minimal resistance compared to class 1 and 2. Class 3 has a thickness of 0.0002 in or 5 µm. It is the thinnest coating among these classes.

Can thicker Cadmium Plating Increase Cost?

A thicker cadmium coating usually requires more plating time, more cadmium consumption, and tighter process control. Thicker Cadmium plating has higher requirement for dimension control, and tolerance control of the critical features like threads and holes. For indoor components that don't need much protection, you should opt for class 3 thickness without adding unnecessary cost by adopting thick coating.

How Does the Cadmium Plating Process Work?

Engineers perform Cad plating in three ways, including mechanical plating, electroplating and vapour deposition. However, mostly at industrial level, manufacturers use electroplating process. So we are going to discuss that in detail.

Step 1: Review Plating Requirements

Engineers begin Cad electroplating by reviewing plating requirements. At this stage, they check the material type, either aluminium, iron or silver and evaluate which type of coating and thickness is required.

Step 2: Clean the Machined Parts Carefully

To prevent blistering, poor adhesion and uneven coating, cleaning components properly is key. To clean a component from any sort of dirt and heavy oils, the component is subjected to water degreasing or solvent immersion. Microscopic residues are cleaned using an alkaline bath. For instance, immerse components in a heated, highly alkaline formulation for 5-10 minutes to saponify any remaining organic residues and rinse with water.

Step 3: Activate the Part Surface

Before subjecting a component to cadmium plating, part's surface is activated. Herein thin oxide or passive film from the component surface is removed. After this they expose surface to a chemically active metal. As a result, adhesion of the cadmium deposit improves.

Actual conditions and activations depend upon base metal. For example, to activate aluminium, the part is submerged in an alkaline zincate solution (525 g/L NaOH, 100 g/L ZnO) for 60 seconds. Afterward its stripped in 50% nitric acid and re-dipped for 30 seconds to form a dense, plateable zinc layer.

Step 4: Cover Unplated Areas

Engineers mask areas of components where they do not want Cd plating. For this purpose they use masking tapes like high-temperature polyester or lead foils. Not only this, but they also use Rubber-based lacquers or peelable synthetic coatings.

Step 5: Plate the Part with Cadmium

Now engineers immerse components in an electroplating bath containing cadmium ions. Components which is to be electroplated acts as an anode, and pure cadmium rod acts as a cathode. Cadmium oxide and sodium cyanide, additives and brighteners like aldehydes and dextrins are present in bath.

Exact composition of electroplating bath

• 20-25 g/L Cadmium Oxide (CadmiumO)
• 75-100 g/L Sodium Cyanide (NaCN)
• 10-12 g/L Sodium Hydroxide (NaOH)

Operating Conditions

• Temperature: 75-90°F (22-24°C)
• Current Density: 5-20 A/ft²

Step 6: Rinse the Parts

Once electroplated, they rinse components thoroughly with water to remove unwanted chemicals from surface.

Step 7: Inspect the Finished Coating

Finally, finished coating is inspected to see if it is fully adhesive, correct thickness and no striping is there.

Cadmium Plating vs Alternative Coatings

How about alternatives to Cadmium plating? Let us compare the advantages between cadmium plating and the alternatives and know when cadmium plating is the best choice for you.

Cadmium vs Zinc Plating

Zinc plating is a standard choice if you are low on budget. It's cheaper than Cd plating and will work perfectly for normal conditions like in household equipment or over machinery parts that do not face harsh conditions. Because its not effective at high temperatures like 450°F, where Cd plating works effectively. If your project involves components working in a saltwater environment, prefer using Cd plating over Zn plating.

Cadmium vs Zinc-Nickel Plating

Cd being considered as carcinogenic, Zn-Ni plating is considered a safer alternative. Finding its use in aerospace components working at elevated temperatures and even in saltwater surroundings. In the case of Cd, it is durable, corrosion resistant, ductile and malleable, which gets a little deformed when fasteners are bonded. It does not show pitting sound threads, and there is no need to coat again and again. In case Zn-Ni coating shows high friction up to 0.25 causing cracks while installation.

Cadmium Plating vs IVD Aluminum

While IVD aluminium is known to offer excellent environmental compliance, cadmium plating completely dominates in mechanical performance. When it comes to intricate geometry and cost, manufacturers prefer cd plating over IVD aluminium. Actually, cadmium's wet electrochemical bath provides superior "throwing power". As a result, it coats deep internal cavities and blind holes where vacuum-based, line-of-sight IVD processes fail.

Moreover, cadmium's natural lubricity prevents thread galling and helps ensure precise assembly torque. In case of soft IVD aluminium, you need expensive secondary lubricants to prevent seizing. That is why for high-volume manufacturing requiring ultra-thin tolerances and low production costs, cadmium remains functionally irreplaceable.

Where Is Cadmium Plating Used?

With its remarkable lubricity, torque and corrosion resistance, cadmium plating is utilised in aerospace, electrical, hydraulic and marine components. Let's know more about its uses in detail in each industry.

Aerospace Precision Parts

Cadmium plating finds its use on precision parts like high-strength fasteners like nut bolts, landing gear actuators, hydraulic fittings, and control bushings. Because cd plating provides sacrificial corrosion protection and also prevents galvanic reactions with aluminium airframes. With its low friction, Cd prevents these critical parts from seizing under high stress.

Electrical Components

Due to its low contact resistance for reliable signal transmission and structural grounding. Cd plating is applied on avionics connectors, grounding lugs, terminal blocks, and chassis housing.

Hydraulic Components

Hydraulic components are coated with cd including:

• fluid fittings
• coupling nuts
• valve sleeves
• actuator bodies

Because Cd layer prevents catastrophic leaks by resisting high-pressure fluid corrosion. Not only this but its natural lubricity ensures tight, scratch-free thread sealing during high-torque assembly. This prevents steel components from rusting or seizing over time.

Marine and Defense Components

Cadmium plating is specified for defence and marine hardware, including torpedo housing fasteners, naval weapon mounts, amphibious vehicle track links, and salt-spray-exposed shackles. Cd plating guarantees reliable sacrificial protection in harsh marine environments.

Common Cadmium Plating Defects

While Cd plating or already cadmium-plated components show significant drawbacks duet to underlying causes. Understanding cadmium plating problems will help you avoid such circumstances to protect coating from getting defective.

Blistering

Blistering occurs due to number of reasons, including inadequate cleaning of components. If any sort of oils, acid or even fingerprints are left on sensitive parts, it does not let coating adhere to surface properly.

This results in blistering. Another factor is hydrogen embondment. It happens as, during electroplating, atomic hydrogen is introduced into the metal substrate. If you are backing components inaccurately, hydrogen gas will cause blistering. Out of this, avoid using Cd coating over high-strength steel with HRC above 32 as cadmium-coated steel is highly susceptible to hydroembodiment.

Uneven Coating Thickness

Another problem that engineers face while electroplating cd is uneven coating thickness over complex shape components. Uneven current distribution in electrochemical bath Is the key reason behind this. High current density (HCD) areas get more thick layers, like edges. However, areas like deep holes and cavities where current density is low get thin layers of Cd. To avoid this, engineers use Vacuum Deposition (per ASTM B699) for uniform coatings of Cd.

Discoloration and Staining

Discolouration and staining in cadmium plating is a result of chemical contamination. The drag-in, bath contamination, sulphur attack, or baking failures cause these stains. Presence of staining means the cadmium barrier is thin, porous, or chemically altered. A systematic and standardized cleaning process before electroplating parts can effectively prevent discoloration and staining.

Cracking

Cracking appears in Cd-plated components due to hydrogen embrittlement. Another factor is cadmium causes Solid-Metal Induced Cracking (SMIC) when it comes into intimate contact with titanium. So avoid hydrogen-embodied components that should be backed properly, and avoid using them over components with base metal titanium.

Design Guidelines for Cadmium-Plated CNC Parts

While designing cadmium plated CNC parts following guidelines will help you control final dimensions, thread fit, coating coverage, and functional performance.

Allow for Coating Thickness

You should include expected cadmium coating thickness in the finished-part dimensions. Because plating builds material on exposed surfaces. This increases external dimensions and reduces internal dimensions. For example, plating on a shaft increases its OD, while plating inside a hole reduces its ID. If the coating thickness is not considered, critical fits can fall outside tolerance after plating.

Consider Thread Fit After Plating

Since Cad plating changes both external and internal thread dimensions. So design threaded features with the specified plating thickness and thread tolerance in mind. For precision threads, define whether threads require post-plating gauging, masking, or other controlled processing to maintain functional fit.

Identify Areas That Must Not Be Plated

You must clearly identify surfaces that must remain unplated on the engineering drawing. For example, electrical contact surfaces, bearing seats, precision bores, mating faces, or dimensional reference features. Its gonna prevent unwanted coating buildup from affecting assembly. This can also reduce the cost of cadmium plating.

Consider Design for Special Features

As said before, deep holes, narrow grooves, blind cavities, and recessed features can receive less uniform plating compared to exposed surfaces. Because current distribution and solution access are limited in such areas. So prefer to design these features with adequate access for the plating solution. Also specify critical coating requirements where necessary.

Does Your Part Need Cadmium Plating?

Choose Cadmium Plating for your parts if in the following conditions:

• Your part is made of steel and will be assembled with aluminum
• Requires good corrosion resistance in humid or salt-containing environments
• Has threads or mating surfaces that need low friction and reduced galling
• Requires electrical conductivity or low contact resistance
• Is used in aerospace, defense, marine, or other specification-driven applications

How Does Tuofa Support Cadmium-Plated CNC Parts?

As a one-stop manufacturing supplier, Tuofa can ensure not only the surface quality of machined parts, but also the quality of cadmium coating. Tuofa provides custom CNC machining and cadmium plating service by following the process below:

Review Drawings Before CNC Machining

Before machining begins, Tuofa reviews the drawing and plating specifications to identify requirements that may affect both CNC machining and the final plated part.

• Confirm the specified material and material condition
• Check whether the base material is suitable for the specified cadmium plating process
• Identify critical dimensions, threads, fits, and other features that may be affected by coating buildup
• Confirm the required cadmium plating type, class, and coating thickness

Allow for Plating Thickness During Machining

Once the required coating thickness is confirmed, machining dimensions can be adjusted where necessary to account for cadmium buildup. This helps keep critical dimensions within the specified tolerances after plating and reduces the risk of fit or assembly problems.

Identify Masked Areas

Areas that must remain unplated should be clearly identified on the drawing. These may include precision fits, bearing seats, electrical contact surfaces, threads, or other functional features. Tuofa can review these areas with the customer and coordinate masking requirements before plating.

Evaluate Hydrogen Embrittlement Risks

For susceptible high-strength steels, we evaluate the hydrogen embrittlement risk associated with the plating process. We coordinate requirements for hydrogen relief baking after plating.

Inspect Critical Dimensions After Plating

We inspect threads, bores, shaft diameters, and coating thickness after plating to verify compliance with drawing requirements.

Conclusion

CAD plating is well adopted electroplating to protect critical components from corrosion and add to their surface lubricity and conductance. Although its environmental concern has made its application a bit limited in some areas, it's still used in many industries, especially in aerospace and defense, to coat key components with Cd. Understanding it is essential both for engineers and manufacturers so they can make right decisions in their fields for both economical and reliable designing and manufacturing.

FAQs

When cadmium plating should not be used?

You should not use cadmium plating if your projects involve consumer goods, electronics sold in regulated markets and general commercial hardware. Because of its severe toxicity and regulatory bans.

Is cadmium plating banned?

Yes, cadmium plating is banned in most industries due to its toxicity and hazard. But its still used in defense aerospace and marine industry under strict regulatory concerns.

Does cadmium plating cause hydrogen embrittlement?

Yes, Cd coating causes hydrogen embrittlement in high-strength material like high-strength steel. It's because of acid left over on the surface during cleaning or during electroplating that H₂ is released.

What are cadmium plating standards?

Cadmium plating standards define its thickness, post-treatment and standard conditions. Here are some major standards:

• AMS-QQ-P-416
• AMS 2400
• MIL-STD-870