Brass is an alloy composed of copper and zinc. Brass composed of copper and zinc is called ordinary brass. If it is a variety of alloys composed of two or more elements, it is called special brass. Brass has strong wear resistance, and brass is often used to manufacture valves, water pipes, connecting pipes for internal and external air conditioners, and radiators.
Ordinary brass is a copper-zinc binary alloy, and its zinc content varies widely, so its room temperature structure is also very different.
α single-phase brass (from H96 to H65) has good plasticity and can withstand hot and cold processing, but α single-phase brass is prone to moderate temperature brittleness during hot processing such as forging
Two-phase brass (from H63 to H59), in addition to the α phase with good plasticity, the β solid solution based on the electronic compound CuZn also appeared in the alloy structure. The β phase has high plasticity at high temperature, while the β′ phase (ordered solid solution) at low temperature is hard and brittle. Therefore, (α+β) brass should be forged in a hot state. Beta brass with a zinc content of more than 46% to 50% cannot be processed by pressure due to its hard and brittle properties.
Because of the different zinc content in brass, the mechanical properties are also different. The mechanical properties of brass vary with the zinc content. For α brass, with the increase of zinc content, both σb and δ increase continuously. For (α+β) brass, the room temperature strength increases continuously until the zinc content increases to about 45%. If the zinc content is further increased, the strength decreases sharply due to the appearance of a more brittle r-phase (solid solution based on Cu5Zn8 compound) in the alloy structure. The room temperature plasticity of (α+β) brass always decreases with the increase of zinc content.
In order to improve the corrosion resistance, strength, hardness and machinability of brass, a small amount (generally 1% to 2%, a few up to 3% to 4%, and very few up to 5%) is added to the copper-zinc alloy. %～6%) elements such as tin, aluminum, manganese, iron, silicon, nickel, lead, etc., form ternary, quaternary, and even quinary alloys, which are complex brass, also known as special brass.
Pb is actually insoluble in brass, and is distributed on the grain boundary in the state of free particles. Lead brass has two types: α and (α+β) according to its organization. Alpha lead brass can only be cold-deformed or hot-extruded due to the harmful effects of lead and low high-temperature plasticity. (α+β) lead brass has good plasticity at high temperature and can be forged.
Commonly used tin brass are HPB58-3, HPb59-1, etc.
The addition of tin to brass can significantly improve the heat resistance of the alloy, especially the ability to resist seawater corrosion, so tin brass is called "navy brass".
Tin can dissolve into copper-based solid solution and play a role in solid solution strengthening. However, with the increase of tin content, brittle r-phase (CuZnSn compound) will appear in the alloy, which is not conducive to the plastic deformation of the alloy. Therefore, the tin content of tin brass is generally in the range of 0.5% to 1.5%.
The commonly used tin brass are HSn70-1, HSn62-1, HSn60-1 and so on. The former is an alpha alloy, which has high plasticity and can be processed by cold and hot pressure. The alloys of the latter two grades have a (α+β) two-phase structure, and a small amount of r-phase often appears. The room temperature plasticity is not high, and they can only be deformed in a hot state.
Manganese has a large solubility in solid brass. Adding 1% to 4% manganese to brass can significantly improve the strength and corrosion resistance of the alloy without reducing its plasticity.
Manganese brass has a (α+β) structure, and the commonly used one is HMn58-2. The pressure processing performance in cold and hot states is quite good.
In iron brass, iron is precipitated as iron-rich particles, which serve as crystal nuclei to refine the grains and prevent the growth of recrystallized grains, thereby improving the mechanical properties and process properties of the alloy. The iron content in iron brass is usually less than 1.5%, and its structure is (α+β), which has high strength and toughness, good plasticity at high temperature, and can be deformed in cold state.
The commonly used iron brass grade is Hfe59-1-1
Nickel and copper can form a continuous solid solution, which significantly expands the α-phase region. The addition of nickel to brass can significantly improve the corrosion resistance of brass in the atmosphere and seawater. Nickel also increases the recrystallization temperature of brass, promoting the formation of finer grains.
HNi65-5 nickel brass has a single-phase α structure, which has good plasticity at room temperature and can also be deformed in a hot state.
Ordinary brass has a wide range of uses, such as water tank belts, water supply and drainage pipes, medals, bellows, serpentine pipes, condenser pipes, bullet casings and various complex shaped stampings, small hardware, etc.
With the increase of zinc content from H63 to H59, they can withstand hot processing well, and are mostly used in various parts of machinery and electrical appliances, stamping parts and musical instruments.