Introduction of copper alloys (brass, bronze, cupronickel)
Copper alloys have excellent material properties and can be used in many scenarios. In the past thousands of years, pure copper has been one of the most important metals. Compared with other metals, its biggest advantages are:
Good electrical conductivity, high thermal conductivity, outstanding combination of strength and plasticity, corrosion resistance in many environments.
Many properties of copper, including diamagnetism, are also present in its alloys, and multiple alloying elements add other required properties. Although the price of copper is relatively high, its alloys of brass, bronze and cupronickel still have an unshakable position in various fields (including engineering).
Adding zinc to copper will increase the strength of the alloy, and at the same time, its plasticity will also increase, which is a very important function.
10-20% zinc alloy is called gold-plated metal, which is used in the jewelry industry and heat exchanger production; 30% zinc alloy is called cartridge brass. The highest threshold of zinc in formable brass is about 35%.
Adding other alloying elements can further improve the performance of brass. For example, tin and aluminum improve their corrosion resistance in seawater.
Applications: Jewelry, artwork, tableware, musical instruments and cartridges.
The zinc content of single-phase brass is as high as 37%. It is called alpha brass, which has a uniform crystal structure, is softer and has higher ductility. These qualities make Alpha Brass suitable for cold working, drawing, bending and other processes.
Applications: Heat exchangers, capacitors, parts made by automatic cutting tables, etc.
Dual-phase brass contains both α and β phases, that is, both α grain structure and β grain structure exist. Because dual-phase brass uses a lot of zinc, it is cheaper than single-phase brass, and it is also susceptible to corrosion. Its chemical composition makes it have greater strength and hardness, so it is suitable for hot forming and casting processes.
According to the alloying elements used, bronze alloys are divided into different types.
Applications: springs, washers, coins, handicrafts, pump parts, pressure-resistant castings, bearings, etc.
Its application depends on the percentage of tin used in the alloy. The maximum content of tin in alloys suitable for cold working is about 7%, and these copper alloys have good plasticity.
The maximum content of tin is about 20%. Starting from 5% tin, the structure of the alloy changes and some additional heat treatment is required, which leads to a porous structure, which is why they are not suitable for other forming methods besides casting .
The main application of dual-phase tin bronze is in the bearing industry. This structure has a good balance, in which the alpha phase ensures the impact resistance, while the hard and brittle compound bears the load and provides a certain degree of wear resistance.
Zinc and lead are sometimes present in tin bronze. Zinc improves the quality of castings and also makes the alloy cheaper. This bronze is also called gun copper, because in the past large guns were made of this material.
A small amount of lead helps to improve the cutting mechanical properties of bronze. The lead content in lead bronze used as bearing material is relatively high (up to 25%).
Applications: coins, ship parts, ship hardware, sleeve bearings, pumps, valves, etc.
Aluminum bronze has similar characteristics to tin bronze. Most of it has a single phase and is suitable for cold forming. It is very suitable for making coins. The content of aluminum is usually between 6-12%.
Dual-phase aluminum bronze can be used as a casting alloy or for hot working. Aluminum bronze with an aluminum content of about 10% is used to make propellers, valves, pumps, etc.
Applications: coins, ship equipment, electrical equipment, heat exchangers, cooling systems, shipbuilding, etc.
Copper-nickel alloy is strong and has strong plasticity. The addition of nickel to copper (usually 2-30%) can make the metal highly resistant to corrosion and has excellent electrical conductivity.
Copper-nickel alloy has almost no thermal expansion coefficient at 40...50% nickel and has the largest electrical resistance. Therefore, Constantan (Cu-Ni alloy containing 45% nickel) is used for electrical equipment with large temperature changes.
The corrosion-resistant copper-nickel alloy contains about 30% nickel, and a small amount of iron and manganese, and their properties in salt water are particularly stable.
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