Copper-tin – CuSn0.15, CuSn0.2, CuSn0.5 and Copper-tin-tellurium – CuSn0.15Te

When tin (0.04–0.55%) is added to copper, the resulting copper-tin alloy has an increase in strength and softening resistance at the expense of conductivity. The maximum tin content allowed is dictated by the minimum conductivity required.

The addition of tellurium (0.005–0.05%), results in a further increase in softening resistance with little loss of conductivity.

History

These alloys, developed in the USA between 1960 and 1990 and manufactured in Europe since 1998, are available as high conductivity strip and wire. Since 1998, they have been used for lead frames (CuSn0.15, CW117C), since 2010 as automotive cables (CuSn0.5, CW129C) and since 2001 as overhead rail grooved contact wire (CuSn0.5, CW129C).

Copper-tin-tellurium (0.005-0.05% tellurium) (CuSn0.15Te, C14420) was patented in the USA between 1983 and 1987. It has good softening resistance in the temperature range 200–427^oC, with an IACS value of 99.8% and was developed as an alternative to copper-cadmium and a more cost-effective alternative to copper-silver.

Heat Treatment

These are single phase alloys and cannot be hardened by heat treatment. They may be annealed between 550–650^oC and stress relieved between 150–200^oC.

The range of mechanical properties, shown in the table below, is developed by cold working.

By comparison with alternative copper alloys, copper-tin alloys are generally stronger than electrolytic tough pitch copper, copper-silver and copper-iron, but less strong than copper-magnesium and copper-nickel-silicon.

Properties

Electrical Conductivity

As the % of tin increases, strength and hardness increase and conductivity decreases (see table below).

An alloy with a tin content which gives the required minimum electrical conductivity (with the necessary mechanical properties for a component), will be selected.

Resistance to Softening

The half-softening time, in minutes (which is defined as the heating time required for the cold worked sample to decrease its hardness to half its fully annealed value), is shown for three alloys in the table below

The beneficial effect of tin on softening is evident but the outstanding effect is that of tellurium which is effective up to 427^oC where copper-silver has softened completely. By comparison Cu-ETP will begin to soften at 150^oC.

Fabrication

This copper does not suffer from steam (hydrogen) embrittlement when heated in a hydrogen (reducing) atmosphere.

Machining

The machinability rating is 20% which is fair (free-machining brass is 100%).

Resistance to Corrosion

These alloys have good resistance to atmospheric corrosion and stress corrosion cracking.

Applications

Typical applications requiring the combination of a specific minimum electrical conductivity, high ductility and enhanced strength and softening resistance compared to pure copper include:

• Lead frames (CW117C)*
• Connector pins
• Switches and relays
• Terminals
• Automotive harness wire
• Busbars
• Rivets
• Special screws
• Automotive conductor signal cables
• Railway grooved contact wire (CW129C)*

* Listed in BS EN Standards

Available Forms

Copper-tin is available as sheet, strip and wire. Copper-tin-tellurium is available as strip.

Specifications

Below are the specifications for Europe and the US. Note that for USA, some compositions are not identical. For equivalent standards from other countries visit the Copper Key website.

• Europe: CW117C (CuSn0.15), CW129C (CuSn0.2) (European Standard EN designation).
• USA: C14415 (CuSn0.15), C14420 (CuSn0.15Te), C14410 (CuSn0.2), C18835 (CuSn0.5) (American Society for Testing and Materials ASTM designation).

Further information on copper-tin, and other conductivity materials, is available at the Copper Alloys Knowledge Base.

Application Example 1: Automotive Conductor Cables

Since 2010, copper-tin wire (0.25-0.35%), cross-sectional area 0.13 mm², with a minimum conductivity of 72% IACS and a minimum tensile strength of 620 N/mm² has been used together with copper-silver and copper-magnesium in exacting conditions for automobile conductor cables.

Automotive conductor cables (Courtesy of Leoni)

Application Example 2: Grooved Contact Wire

Copper-tin is one of the main alloys used for contact wire for the French high speed railways. It is produced to meet and exceed the requirements of the European Standard EN 50149:2012 Railway applications – Copper and copper alloy grooved contact wires.

Copper-tin contact wires have the correct balance between electrical and mechanical properties being more wear resistant compared to pure copper.

Contact wire (Courtesy of Smiley.toerist)

Quick facts

Properties
CuSn0.15 has the following combination of properties:

• Tensile strength: 250-370 N/mm²
• Yield strength: 200-250 N/mm²
• % Elongation: 9-4
• Hardness (HV): 60-110
• % IACS: 81-98
• Thermal conductivity: 300-360 W/m^oC

Applications

• Lead frames (CW117C)
• Connector pins
• Switches and relays
• Terminals
• Automotive harness wire
• Busbars
• Rivets
• Special screws
• Automotive conductor signal cables
• Railway grooved contact wire (CW129C)

Available Forms

• Sheet
• Strip
• Wire

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