Annealing technology for copper and copper alloys

Copper and copper alloy in machining process, often is the copper pieces of hardening, while hardening can improve the strength and hardness of copper and copper alloy, but also reduces the material plasticity and toughness, cold working (after cold rolling, cold or cold drawn) profiles (rods, bars, plates) to further cold deformation will be difficult. So in the process of cold rolling or cold drawing, a recrystallization annealing must be carried out between a and a, restore its plasticity, make the copper soft, in order to facilitate cold working, such recrystallization annealing for intermediate (recrystallization) annealing.

In order to improve the structure of the material and make the material uniform to meet the requirements of the service conditions, the finished product Z should undergo a recrystallization annealing, namely Z final recrystallization annealing. Usually in the middle of annealing, rapid heating is adopted, the amount of furnace is large, and the upper limit of temperature is taken, so as to improve the recrystallization temperature, refine the grain, shorten the heating time, reduce oxidation, and improve the productivity. Annealing, slow heating, control the amount of furnace, temperature lower limit, especially for thin-walled parts, to ensure uniform product performance.

The temperature is controlled within ±5℃. The annealing temperature is 1.5 ~ 3h for brass and 1 ~ 3h for tin bronze, aluminum bronze and beryllium bronze. For the copper alloy that can be strengthened by heat treatment, it must be cooled slowly after intermediate annealing, and the cooling rate of other copper alloys has little effect on the properties. The intermediate annealing temperature is related to the degree of cold deformation, the composition of the metal, the heating rate and the size of the original grain.

The heating temperature is above the recrystallization temperature. If the temperature is too low, the recrystallization is not complete, but if the temperature is too high, the grain will be coarse, so that the surface of the material will appear "orange peel" when the next cold processing, which is very harmful, especially in single-phase materials. Billet with fine grain should be used when forming processing quantity is small, billet with coarse grain should be used when forming processing quantity is large. The mechanical properties of copper alloy after recrystallization are not only related to its composition, but also related to the annealing temperature and the amount of cold processing before annealing.

Annealing process has another important role - annealing stress! Its function is to remove the internal stress of castings, welded parts and cold formed parts, to prevent deformation and cracking of parts, but also to improve corrosion resistance, because parts with tensile stress, in corrosive media, easy to produce stress corrosion. Stress relief annealing can also improve the elasticity and strength of cold formed brass, zinc white copper and phosphor bronze.

The annealing time of general alloy is 1-3 h, and that of beryllium bronze is 15-20 min. General copper alloy elastic material strengthening and heat treatment: some copper alloy through cold plastic deformation and low temperature annealing to improve its elastic limit, the production of elastic elements. The higher the degree of cold plastic deformation, the more the elastic limit increases after low temperature annealing.