Beryllium-Copper Alloys

What are beryllium-copper alloys?

Beryllium-copper alloys are known for their unique combination of strength, hardness and corrosion resistance.

One important characteristic of this alloy is that beryllium-copper can be softened or hardened at will by two simple heat treatment processes.

In a fully heat-treated preparation, beryllium-copper alloys are the hardest and strongest of all copper-rich alloys (to 1400MPa), to the extent that it is similar to many high-grade alloy steels.

Of course, its advantage over steel is a higher resistance to corrosion, higher thermal and electrical conductivity and its non-sparking qualities. It is also non-magnetic and can be formed from strips or wires in the soft condition, and later hardened by heat treatment.

Generally, alloys that contain from 1.7 to 1.9 percent beryllium and are precipitation hardened for two hours within a temperature range of 315°C to 350°C will provide properties ideal for most commercial purposes. For softer grades, higher temperatures can be used.

A high elastic limit, along with a low modulus of elasticity and fatigue resistance are valued in specific technical applications. The alloy is also ductile, weldable and machinable.

Beryllium copper is most often used for producing small springs, pressure responsive diaphragms, flexible bellows, Bourdon tubes and components of measuring instruments for electrical and barometric applications.

Castings and forgings of the alloy are used in areas that require high strength combined with good electrical and thermal conductivity. Examples include electrodes for resistance welding appliances and dies for moulding plastics.

Applications for beryllium-copper can be classified into four groups based on the unique qualities each requires:

  • Spring, diaphragms and pressure sensitive instruments (elasticity and strength)
  • Dies for deep drawing and forging metals and moulding plastics (high strength and hardness)
  • Resistance welding electrodes (strength, resistance to corrosion and conductivity)
  • Non-sparking tools (non-sparking, strength and hardness)

While most alloys contain about 2 percent beryllium, this can range from 1.5 to as high as 3.0 percent depending on the application. Pressure sensitive uses, including springs, generally use a lower amount of beryllium, which is itself brittle. While dies, which require greater hardness, contain an amount of beryllium at the higher end of this spectrum.

Cobalt and nickel are also regularly included in such alloys, in very low quantities, to improve the response to heat treatment.

Low beryllium alloys contain much less beryllium (less than 1 percent) and a greater amount of cobalt (2 to 3 percent). While these alloys have lower strength and hardness, they have a much higher conductivity. Newer, proprietary alloys have also been developed with compositions falling in between regular and low beryllium copper alloys.

All commercial grades of beryllium copper are precipitation hardening alloys.

That is, they can be softened by quenching and hardened by heating to a moderate temperature.

In both normal and salt water environments, beryllium-copper's resistance to corrosion is very similar to that of pure copper. While applications for the metal (e.g. in springs and pressure sensitive applications) are most often in competition with steel, this provides a significant comparative advantage.

While beryllium-copper is attacked by sulphur and compounds of the element, it can be safely exposed to most organic liquids, including petroleum products, refined oils and industrial solvents.

Like copper, beryllium-copper alloys form a protective oxide layer on their surface that resist against oxidization and deterioration.

Sources:
Beryllium Copper. Copper Development Association. CDA Publication No.

54, 1962
URL: www.copperinfo.co.uk
Bauccio, Michael (Ed.). ASM Metals Reference Book, Third Edition. Materials Park, Ohio: ASM International. p. 445.