Heat Treatment of Copper Alloys
Copper and its alloys are used in a wide range of applications:
- electrical wiring, cables and busbars
- heat exchangers
- cooking utensils
- power transmission lines
- building products
As with many metallic alloys, these are frequently heat treated to improve their mechanical and electrical properties. Davis Scientific Treatments [DST] has been offering such processes for many years.
Properties of Copper Alloys
Copper is a tough, ductile and malleable metal. It is very suitable for wire drawing, spinning, and tube forming. In addition, when alloyed with suitable metals, these alloys have:
- excellent electrical conductivity
- excellent heat conductivity
- good corrosion resistance
- good machinability
- non-magnetic property
Alloying improves many properties. Addition of Beryllium increases hardness and strength. Copper with Nickel, or Aluminium, reduces corrosion, especially aluminium bronzes.
Heat treatment of copper alloys is performed for many purposes, and these heat treatment processes include:
- stress relieving
- precipitation and age hardening
The aim is to obtain a desired microstructure, which achieves certain pre-determined properties.
Homogenising is used to dissolve the various phases in the material, to form a uniform microstructure. This process is especially necessary for cast and hot worked products, chiefly those containing nickel or tin.
It is a slow treatment, frequently taking several hours. It is a process often used prior to specialised heat treatments.
Cold worked alloys are softened by heating to a temperature which causes recrystallisation of the grain structure.
There are commonly two annealing processes, light and soft.
Light anneal is performed just above the recrystallisation temperature.
Soft anneal is carried out several hundred degrees higher. This latter process promotes grain growth, and hence an improvement in material softening.
Stress relieving eliminates, or substantially reduces, any residual stresses in the material, usually obtained through manufacturing.
Otherwise, parts can fail in service, through corrosion fatigue, or even by cracking under repeated loading. Typical alloys include those with 15 % zinc, and aluminium and silicon bronzes.
Components are heated to a temperature which is below the annealing range. Recrystallisation therefore does not take place.
Using a high stress relieving temperature, for a short time, is generally considered the optimum balance between inprovement in properties, and cost of the process.
High strength in many copper alloys is usually obtained through cold working of the material.
Special types of alloys are strengthened by solution treatment, followed by precipitation hardening.
These alloys include: copper-chromium alloys, beryllium coppers, copper-silicon-nickel, copper-phosphorus-nickel, and copper-zirconium.
The process commences with treatment to a soft condition, by cooling from a high temperature [solution treatment].
Subsequently, the precipitation hardening is carried out, at quite a low temperature, during which the grain structure is altered by the precipitation of certain phases. The exact blend of property improvement depends on the solution treatment, and extent of precipitation hardening time.
This process is sometimes known as Age Hardening.
Davis Scientific Treatments (DST)
At Davis Scientific Treatments, we have extensive experience of performing these treatments, usually under vacuum, where a blemish-free condition is obtained after processing.
We are always ready and willing to discuss any new projects or applications.