Contact materials and alloys for electrical contacts

Importance of contact materials in electrical contacts

Contact materials are a core functional element of electrical contacts. They largely determine contact resistance, erosion behavior, tendency to weld, and the achievable electrical and mechanical service life of a contact point.

In electromechanical assemblies, contact materials act directly at the interface between two conductive parts. Simplifications during material selection are difficult to compensate later and often become visible only during field operation.

Contact materials are used in relays, contactors, installation switches, connector systems and complex contact assemblies. Selection must always be application- and system-specific.

Basic requirements for contact materials

Electrical contact materials must meet multiple, partly conflicting requirements. High conductivity must be combined with mechanical stability and controlled behavior under arcing.

Typical requirements include:

• low and stable contact resistance
• sufficient hardness and wear resistance
• controlled erosion behavior
• low tendency to contact welding
• resistance to temperature, atmosphere and environmental influences

The weighting differs significantly between AC and DC applications and between switching and continuous-current contacts.

Base materials for electrical contacts

Silver as the base material

Silver is the most important base material for electrical contacts due to its very high electrical conductivity. Pure silver, however, is relatively soft and can show unfavorable behavior under arcing (e.g., material transfer and welding). Therefore, silver is mainly used in alloyed or modified forms.

Copper and copper alloys

Copper also has high conductivity and is widely used as a carrier material, for example in contact rivets or composite designs. As a direct contact surface, copper is usually limited due to oxidation and switching behavior.

Silver alloys for electrical contacts

Silver alloys are used to combine silver’s conductivity with improved mechanical and switching performance. Alloying elements influence hardness, erosion behavior and welding tendency and must be chosen according to the application.

AgNi (silver-nickel)

AgNi is among the most common contact materials. Nickel increases hardness and wear resistance and reduces welding tendency while maintaining adequate conductivity for many applications. It is widely used for parts such as contact tips and contact rivets.

AgCu (silver-copper)

AgCu alloys offer higher mechanical strength. With increasing copper content, conductivity decreases. They are typically used where mechanical loads are higher and switching loads remain moderate.

AgSn (silver-tin)

AgSn alloys without an oxide phase can be used for moderate switching loads. They increase strength compared to pure silver but do not reach the arc performance of oxide-based materials. Suitability is application-dependent.

AgPd (silver-palladium)

AgPd is used particularly for low switching currents and low contact forces. Palladium increases hardness and improves resistance to atmospheric influences. Conductivity is lower than pure silver, but sufficient for many signal and control applications.

AgAu (silver-gold)

AgAu combines good conductivity with improved corrosion resistance. It is considered when stable contact conditions at very small currents are required. The gold content affects cost and performance and must be selected to match the application.

AgZnO (silver-zinc oxide)

AgZnO is an oxide-based silver material that may be used as an alternative to other silver metal-oxide systems in certain applications. Properties depend strongly on composition and manufacturing route.

Silver metal-oxide contact materials

AgSnO₂ (silver-tin oxide)

AgSnO₂ is widely used for applications with high inrush currents and inductive loads. The oxide phase supports stable switching behavior and reduces welding tendency. Lower ductility compared with classic alloys must be considered during forming and processing.

Powder-metallurgical materials

Many silver metal-oxide materials are produced by powder metallurgy, enabling a fine and homogeneous oxide distribution and reproducible properties. These materials are typically less ductile than melt-metallurgical alloys, which can limit forming options.

Cadmium-containing contact materials

Silver-cadmium oxide materials were historically used for high switching loads. Current use depends on application, market and the regulatory framework. In some cases, valid exemptions may exist. Blanket statements about usability are not appropriate.

Gold plating and gold coatings

Gold coatings are used when very low and stable contact resistance is required at small currents and low contact forces. Gold is highly resistant to corrosion and oxidation and does not form insulating surface layers under typical environmental conditions.

Function and typical use cases

Gold-plated contacts are typical in signal, control and measurement electronics and in connectors where very small currents are switched. In such cases, silver surfaces can become unstable depending on environmental influences.

Gold as a functional layer

The gold layer usually acts as a functional and protective layer. The base material provides mechanical stability and most of the current-carrying capability. The selection of the base material and suitable intermediate layers is important for adhesion and durability.

Limitations of gold plating

Gold plating is not suitable for high switching currents or pronounced arcing. Under such conditions, the gold layer may be rapidly worn or damaged. The decision must be made based on electrical load, contact force and expected service life.

Use of copper and bimetals in contact technology

Besides silver-based materials, copper and copper-based composites play a key role. Their use is typically not as the contact surface but as carrier material or as part of composite and multilayer designs.

Copper as conductor and carrier

Copper is widely used for carriers, contact arms, terminals and rivet shanks due to its high conductivity. As a direct contact surface it is often limited because oxide layers can increase contact resistance, especially at low contact forces.

Copper alloys in the contact environment

Copper alloys are used when higher mechanical strength or spring properties are required. They usually serve as functional carriers for applied contact materials.

Bimetal and multilayer designs

Bimetal and trimetal designs separate the functional contact surface from the mechanical carrier. These concepts are used, for example, in contact rivets, contact tips and contact profiles.

Design requires coordinated material selection, geometry and manufacturing process. Interfaces must remain stable over life to avoid increased resistance or mechanical weaknesses.

Contact materials by form and product type

Depending on function and manufacturing strategy, contact materials are used in different forms, including:

• solid contact parts
• bimetal and trimetal designs
• contact rivets
• contact tips
• contact profiles

Selection criteria for contact materials

Technical criteria

• current type (AC or DC)
• switching and continuous current
• load type (resistive, inductive, capacitive)
• contact force and contact geometry
• required electrical and mechanical life
• environmental conditions (temperature, atmosphere, contamination)

Economic criteria

• precious metal content and material cost
• availability and supply stability
• series-production suitability
• reproducibility and consistent quality
• documentation and inspection requirements

Typical applications

Contact materials are used, for example, in relays and contactors, installation and protection devices, connectors and contact assemblies. Selection must be aligned with the specific system and application context, e.g. in electrical engineering and installation technology, and may require additional considerations in the automotive sector.

Selection criteria for engineering and purchasing

Engineering typically focuses on function, lifetime and process stability, while purchasing emphasizes cost stability, availability and consistent quality. A robust selection approach considers both perspectives.

Engineering perspective

Key topics include load profile (AC/DC, currents, load type), erosion and welding tendency, contact force, geometry, counter-contact material and environmental conditions. Materials must be evaluated within the overall system.

Purchasing perspective

Typical criteria include precious metal content, options for composite solutions, supply stability, reproducible properties, and requirements for documentation and traceability.

Shared decision basis

Close coordination between engineering and purchasing reduces later field issues and change effort while enabling stable series supply and controlled piece costs.

Typical misconceptions (practical examples)

In contact engineering, simplified assumptions can lead to functional issues or unnecessary cost. Common examples include:

“Higher conductivity always means a better contact”

High conductivity alone does not guarantee stable switching behavior. Pure silver or copper can show unfavorable behavior under arcing. Alloyed or oxide-based materials are often functionally superior.

“One contact material fits all applications”

Material selection is application-specific. A material that works well for AC resistive loads may behave poorly for DC or inductive loads.

“Gold-plated contacts are always better”

Gold plating is beneficial for very small currents and low contact forces. It is not suitable for high switching currents or pronounced arcing.

“Copper is a good contact surface”

Copper is usually a carrier material. Oxide layers and switching effects can increase contact resistance, especially at low contact forces.

“Bimetal designs are only a cost-saving option”

They also enable functional separation of contact surface and carrier and can improve overall performance. Interfaces must be designed for long-term stability.

Quality assurance

Contact materials and related contact parts are typically verified for composition, microstructure/homogeneity and relevant functional properties. In many cases, switching and lifetime tests are performed in the assembled state because system factors are decisive.

FAQ about contact materials and alloys

How does AC vs. DC influence material selection?

Current type influences erosion and material transfer. DC often imposes higher demands on material and geometry than AC.

Why is pure silver rarely used for switching contacts?

Pure silver is highly conductive but relatively soft and can show welding and material transfer under arcing. Alloys and metal-oxide materials improve overall performance.

When is gold plating technically reasonable?

When very low, stable contact resistance is required at small currents and low contact forces. For high switching currents/arcing, gold plating is typically not suitable.

Why are bimetal and multilayer solutions important?

They separate contact function and carrier function and help optimize precious metal usage and mechanics. Interfaces must remain stable over life.

How to select the right material in practice?

By evaluating electrical, mechanical and economic requirements within the specific system and application context.

 

Note: Further technical information is available in the knowledge section of AX-METALS GmbH. For technical questions or project-related coordination, please contact us.