Fri, 17 Aug 2018 02:44:58 +0000

Intense heat treatment for processing copper alloys

1. Work hardening

Some copper alloys, such as brass, tin bronze, aluminum less than 9 percent, manganese bronze, chromium bronze, copper and manganese copper, cannot be strengthened by heat treatment.

2. Hardened and tempered copper alloy

Is a kind of copper alloy strengthening is obtained by quenching and tempering, principle and the strengthening of the steel, its typical alloy is the aluminum bronze aluminum content is more than 9%, the alloy in beta phase heated to high temperature, quenching after the beta phase transition into metastable beta ‘martensite, the process will be broken down into tiny (alpha + gamma 2) eutectoid structure, make the strength, hardness and rise, aluminum bronze quenching tempering process are shown in table 9.2 5.

 

Intense heat treatment for processing copper alloys

 

3. Solid solution and aging strengthened copper alloy

One kind of copper alloy is strengthened by solid solution and aging. Its principle is similar to that of aluminum alloy. Its typical alloy is beryllium bronze. The maximum solubility of beryllium in copper is 2.7%, which decreases significantly with temperature drop, and has obvious effect of precipitation hardening. It can obtain good comprehensive mechanical properties, such as strength, hardness, plasticity, conductivity, elastic limit and elastic modulus, and reduce the elastic lag of alloy. Cold deformation can also be achieved before aging, and higher strength and hardness can be obtained after aging.

The solid solution aging process of beryllium bronze is shown in table 9.2-6. For general bar materials, bar materials and parts with large section thickness, the heating insulation time is calculated as per 25.4mm/h. For thin parts, the heating insulation time is shown in table 9.2-7. The solid solution temperature should be strictly controlled to ensure the dissolution of the alloy elements and not to make the grains grow rapidly. The grain size of beryllium bronze after the solid solution treatment is shown in table 9.2-8. Solid solution after heating, quenching into below 25 ℃ water, immediately transfer time should not exceed 3 ~ 5 s.

Beryllium bronze is characterized by high temperature aging and low temperature aging, low temperature aging is easy to control, and the maximum strength and hardness can be obtained. However, it can remove internal stress better at high temperature, and obtain higher fatigue strength, zero drift resistance and relaxation resistance. No matter high or low temperature aging, the temperature and time of material aging with more beryllium content and after cold processing shall take the lower limit, and conversely the upper limit.

Solid solution heating should be carried out in vacuum furnace or protective atmosphere furnace, but not in salt bath furnace to avoid grain boundary corrosion and beryllium removal.

Beryllium bronze profiles are generally supplied in a solid solution state (soft state), which can be directly cold-formed and then aged. With the release of the stress, the parts will deform during the aging process, so the parts must be fixed in the fixture for aging treatment. The weight of the fixture should be as light as possible and the strength should be appropriate. Where the shape of the part allows, the fixture can be used to overlap the part (figure 9.2-1). Aging treatment can be carried out by stacking, so the aging can be divided into two times. The first time does not use the clamping device, the second time USES the clamping device, and the first time after the first aging is rapidly cooled.

Silicon bronze, chromium bronze, zirconium bronze and aluminum-copper are also capable of solid solution strengthening.