Heat treatment of copper and copper alloys
Annealing of copper and processed copper alloys
Work hardening can improve the strength and hardness of copper and copper alloys, but also reduce the plasticity and toughness of materials. It will be difficult for the profile (wire, rod, plate) to deform further after cold working (cold rolling, cold punching or cold drawing). Therefore, in the process of cold rolling or cold drawing, recrystallization annealing should be carried out between one and the other to restore its plasticity so as to facilitate cold processing. Such recrystallization annealing is intermediate (recrystallization) annealing.
In order to improve the structure of the material and make the material homogenized to meet the requirements of using conditions, the finished product shall finally undergo recrystallization annealing, that is, final recrystallization annealing.
In general, during intermediate annealing, rapid heating is adopted with large amount of charging and maximum temperature is taken, so as to increase recrystallization temperature, refine grains, shorten heating time, reduce oxidation and increase productivity. Finally annealing, slowly heating up, control the amount of furnace, and take the lower limit of temperature, especially the thin wall parts, to ensure the product performance is even. Temperature control, within + / - 5 ℃ annealing on insulated brass was 1.5 ~ 3 h, tin bronze, aluminum bronze, beryllium bronze for 1 ~ 3 h. The recrystallization annealing process of pure copper is shown in table 9.2-1. The recrystallization annealing process of copper alloy is processed. For copper alloy that can be heat treated and strengthened, the cooling speed of other copper alloys has little influence on the performance. The temperature of the intermediate annealing is related to the degree of cold deformation in advance, the composition of the metal, the heating speed and the original grain size. Heating temperature and above the recrystallization temperature, the temperature is too low to recrystallize completely, but too high will make the grain bulky, so that the next cold processing, the surface of the material appears "orange peel", which is very harmful, especially in single-phase materials. It is advisable to use a billet of fine grain for a small amount of forming, and a billet of coarse grain for a large amount of forming. The mechanical properties of copper alloy after recrystallization are not only related to its composition, but also to annealing temperature and cold processing quantity before annealing.
2. De-stress annealing
Its function is to remove the internal stress of castings, welding parts and cold formed parts, so as to prevent the parts from deformation and cracking, and also to improve the corrosion resistance (due to the tensile stress of the parts, it is easy to generate stress corrosion in the corrosive medium). Stress relief annealing can also improve the elasticity and strength of cold formed brass, zinc-white copper and phosphorous bronze. Generally, the insulation time of de-stressed annealing is 1 ~ 3h, and beryllium bronze is 15 ~ 20min.
3. Strengthening and heat treatment of common copper alloy elastic materials
Some copper alloys increase their elastic limit by cold plastic deformation and low temperature annealing to make elastic components. The higher the plastic deformation degree, the higher the elastic limit after annealing. The best elastic limit and stress relaxation of low temperature annealing of copper alloy are obtained.