Copper-magnesium – CuMg0.2, CuMg0.5

The addition of 0.1 to 0.7% magnesium to copper results in a cold workable solid solution strengthened alloy with good electrical conductivity.

History

The two grades of copper-magnesium, CW127C and CW128C, first appear in European Technical Specification CEN/TS 13388:2008 which is Copper and Copper Alloys – Compendium of Compositions and Products. CEN is Comité Européen de Normalisation.

They appear in the earliest version of BS EN 50149:2001 Railway Applications – Copper and Copper Alloys Grooved Contact Wires, and are included in the current 2012 Standard.

In Europe, the railway applications for copper-magnesium wire alloys were developed from 1992 and in 1995 the high speed rail line from Hanover to Berlin used 120 mm wire for catenary and contact wire. Copper-magnesium automotive cables have been used since 2010.

Heat Treatment

Copper-magnesium alloys cannot be hardened by heat treatment. They may be stress relieved between 140-200^oC and fully annealed between 400-500^oC.

Mechanical Properties at Room Temperature CuMg0.2

Physical Properties CuMg0.2

Mechanical Properties at Room Temperature CuMg0.5

Physical Properties CuMg0.5

Electrical conductivity               41-64% IACS
Thermal conductivity                 270 W/m^oC

The strength of copper-magnesium wire is developed by cold drawing; this results in the highest strength in the smallest cross section (80mm²).

The CuMg0.5 alloy is stronger than the CuMg0.2 alloy; this is at the expense of lower electrical and thermal conductivities.

Fabrication

Machining

This is rated at 20% which is satisfactory. Free-machining brass is 100%.

Resistance to Corrosion

The resistance to atmospheric and marine corrosion is good.

Applications

All of the applications are found in electrical wire and cable. The combination of high strength, good conductivity, good solderability and resistance to corrosion leads to the following applications.

• Conductor wire
• Connector wire
• Pins
• Telecommunications cable
• Automotive switches and relays
• Contacts
• Terminals
• Catenary cables
• Automobile wire harnesses
• Contact wire for high speed trains
• Automobile cables

Available Forms

CW127C and CW128C are available in rod and wire.

Specifications

Below are the standards and 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: CW127C (CuMg0.2), CW128C (CuMg0.5), BS EN 50149:2012.
• USA: C18661, ASTM B250 (covers range of magnesium content from 0.1 to 0.7%).

Further information on copper-magnesium, and other conductivity materials, is available at the Copper Alloys Knowledge Base (CuMg0.2 and CuMg0.5).

Application Example 1: Catenary and Contact Wire

A railway electrification system supplies electric current from a generating system by means of Cu-ETP copper cables to bare overhead conductor wires which run above the length of the railway track. The current to drive the electric motor in the train is collected by means of a pantograph which is attached to the roof of the train. To complete the circuit and thereby allow the current to flow, the track is used to make the return connection. The conductor wire is supported from above by a catenary wire. During motion, a wave forms along the conductor wire resulting in alternating stresses which may lead eventually to fatigue failure. To minimise this wave, the conductor wire is kept in tension by weights suspended at each end of its length; hence the need for a high strength wire such as copper-magnesium.

In addition, the conductor wire must have good wear and corrosion resistance and be able to withstand high and low atmospheric temperatures.

Alternative conductor wires

Alternatives to copper-magnesium include copper-cadmium, copper-silver and copper-tin.

Copper-cadmium has a good combination of properties but is no longer accepted in most applications as a conductor alloy on account of the toxicity hazard and risk of respiratory disease associated with cadmium, both in initial manufacturing and later in recycling. In service, copper-cadmium poses no threat to health.

Europe and the UK, with High Speed 2, is witnessing a surge in high speed rail services, all made possible by the development of high conductivity copper alloys, shown below in increasing order of tensile strength, and giving the maximum train speed in km/h. Cu-ETP is shown for comparison.

Electric transmission system (Courtesy of Liljedahl)

Application Example 2: Copper-magnesium Automotive Cables

Electricity is a fundamental part of the working of automobiles and apart from the main charging, starting and ignition circuits, there are other circuits that power lights, air conditioning, electric motors, the sensors and gauges of electrical instruments, heating elements, magnetically operated locks and the entertainment systems.

For this reason, insulated copper cables made from electrolytic tough pitch copper (Cu-ETP) have long been the choice of vehicle engineers for automotive electrical systems due to their very high electrical conductivity, flexibility, corrosion resistance and availability in a wide range of sizes.

Weight reduction
European regulations require a reduction in vehicle pollutant emissions. Since 75% of fuel consumption is related directly to weight, changes in automobile design and materials are being made to reduce the weight of vehicles. The weight of copper used in the construction of a car ranges from 15 kg up to 28 kg in luxury vehicles. One method of reducing vehicle weight is by replacing Cu-ETP cables by copper-magnesium CW127C (Mg 0.14 to 0.26%), conductivity 75% IACS The copper-magnesium cables first introduced in 2010 are up to 25% stronger than Cu-ETP which enables smaller diameter (0.29 mm) cables to be used, resulting in a weight saving of up to 50% compared to Cu-ETP cables, whilst not jeopardising performance or reliability.

Fuel is saved as a result of this change from Cu-ETP to copper-magnesium with a consequence of less harmful emissions.

Alternative automotive materials
Alternative copper alloys to the highest conductivity Cu-ETP (100% IACS) are copper-silver which has a slightly lower conductivity (95% IACS) but higher strength than Cu-ETP and better temperature resistance. Copper-tin is an alternative with a much higher strength (620 N/mm²) but with a lower conductivity of 72% IACS.

Automotive cable (Courtesy of Leoni)

Wire harness (Courtesy of Leoni Automobile Cables)

Quick Facts

Properties (CuMg0.2)
At room temperature the alloy has the following combination of properties:

• Tensile strength: 420-460 N/mm²
• % Elongation: 3-10
• Electrical conductivity: 62-82 % IACS
• Thermal conductivity: 310 W/m^oC

Applications

• Conductor wire
• Connector wire
• Pins
• Telecommunications cable
• Automotive switches and relays
• Contacts
• Terminals
• Catenary cables
• Automobile wire harnesses
• Contact wire for high speed trains
• Automobile cables

Available Forms

• Rod
• Wire