Beryllium Copper Strip
Proper use of Beryllium Copper
(1) Aging Conditions and Aging Furnace , Shrinkage (Alloy25)
Aging Conditions and Aging Furnace
The increase in the mechanical properties of beryllium copper can be controlled through the heat treatment conditions and the cold rolling reduction rates, i.e. temper. This is shown by age hardening curves in Fig. 9 and 10.
Heat Treatment Conditions
Standard heat treatment conditions for beryllium copper alloy 25 age hardenable material are temperature of 315*C and retention time of 2 to 3 hours. The retention time must be counted after the material has reached 315°C. When the volume or weight of parts to be heat-treated in a furnace is relatively large, it is important to ensure that the temperature of the parts is kept at 315t for 2 to 3 hours by directly attached thermocouple. Although the required time to heat up the temperature to 315°C or to cool down to room temperature gives little influence on the properties in case of standard heat treatment conditions, it must be checked carefully when other conditions are applied, e.g. for shorter time or at higher temperature.
Atmosphere of Furnace
Heat treatment of beryllium copper is usually performed in an inert gas atmosphere, such as nitrogen, carbon dioxide or argon. It is not recommended to use air as the atmosphere of the heat treatment for electric components, because an intensive black oxide film will be formed on the surface. In order to keep the uniformity of the temperature in a furnace, it is better to circulate the atmosphere.
Fig. 9 Properties of Alloy 25 after Age Hardening at different Temperatures
(Retention Time: 2 hours)
Fig. 10 Age Hardening Curve of Alloy 25
Shrinkage (Alloy 25)
The mechanical properties of beryllium copper alloy 25 are drastically increased by age hardening, because beryllium atoms, which were dispersed in copper as a solid solution, are precipitated through various process during age hardening. This results in a shrinkage of approx. 0.15% in length. This is the reason age hardening of stamped parts may cause slight deformation.
The shrinkage varies slightly depending on the temperature of age hardening and the cold reduction prior to stamping. The following methods have proven effective in minimizing distortion.
- to select higher temper within the limitation of bending form-ability, e.g. 1/2H rather than 1/4H, H rather than 1/2H.
- to fix the parts in jigs or to place them in copper powder and apply pressure, if the shape of the parts is complicated.
- to apply lower age hardening temperature, e.g. from 315°C to 280'C. In this case the mechanical strength will be lower to some extent.
- Parts formed from mill hardened material can be further heat treated after stamping with very little distortion.