Ordinary brass is a binary alloy of copper and zinc, and its zinc content varies widely, so its room temperature microstructure is also very different. According to the Cu Zn binary state diagram, there are three kinds of room temperature microstructure of brass: the brass with zinc content less than 35%, and the microstructure at room temperature consists of single phase α The composition of solid solution is called α Brass; The microstructure of brass containing 36% - 46% zinc at room temperature is composed of two parts（ α+β） The two-phase composition is called（ α+β） Brass (two-phase brass); The microstructure of brass containing more than 46% ～ 50% zinc at room temperature is only composed of two parts β Phase composition, called β Brass.
α Single phase brass (from H96 to H65) has good plasticity and can withstand cold and hot working, but it has good mechanical properties α Single phase brass is prone to medium temperature brittleness during forging and other hot working. The specific temperature range varies with the content of Zn, generally between 200 ℃ and 700 ℃. Therefore, the temperature of hot working should be higher than 700 ℃. single-phase α The brittle zone of brass is mainly caused by Cu Zn alloy system α There are two ordered compounds, cu3zn and cu9zn, in the phase region. The ordered transition occurs when the alloy is heated at medium and low temperature, which makes the alloy brittle; In addition, a small amount of lead and bismuth impurities in the alloy form eutectic films with low melting point and distribute on the grain boundaries, resulting in intergranular fracture during hot working. The practice shows that the medium temperature brittleness can be effectively eliminated by adding a small amount of cerium.corrugated metal roofing sheet supplier
Two phase brass (from h63 to H59) has good plasticity α In addition, the Cu Zn based electronic compounds also appeared β Solid solution. β The phase has high plasticity at high temperature, while the phase at low temperature has high plasticity β′ The phase (ordered solid solution) is hard and brittle. So（ α+β) Brass shall be forged in the hot state. The zinc content is more than 46% ～ 50% β Brass can't be pressed because of its hard and brittle properties.
The mechanical properties of brass vary with the zinc content. about α Brass, with the increase of zinc content, σ B and δ All of them increased continuously. For（ α+β) When the zinc content of brass increases to about 45%, the room temperature strength of brass increases continuously. If the zinc content is further increased, the strength of the alloy will decrease sharply due to the appearance of R phase (solid solution based on cu5zn8 compound) with greater brittleness（ α+β） The room temperature plasticity of brass always decreases with the increase of zinc content. Therefore, the Cu Zn alloy with more than 45% zinc content has no practical value.
Common brass is widely used, such as water tank belt, water supply and drainage pipe, medal, bellows, serpentine pipe, condensing pipe, cartridge case and various complex shaped stamping products, hardware and so on. With the increase of zinc content, from h63 to H59, they can well withstand hot processing, and are mostly used in various parts of machinery and electrical appliances, stamping parts and musical instruments.
In order to improve the corrosion resistance, strength, hardness and machinability of brass, a small amount of tin, aluminum, manganese, iron, silicon, nickel, lead and other elements (generally 1% ～ 2%, 3% ～ 4%, 5% ～ 6%) are added into the copper zinc alloy to form ternary, Quaternary, or even pentagonal alloy, which is also called special brass.that cold rolled steel coil
Zinc equivalent coefficient
The microstructure of complex brass can be calculated according to the "zinc equivalent coefficient" of elements added in brass. Because a small amount of other alloying elements are added to the Cu Zn alloy, it usually only makes the difference in the Cu Zn state diagram α/(α+β) The phase region moves to the left or right. Therefore, the structure of special brass is usually equivalent to that of ordinary brass with increased or decreased zinc content. For example, the microstructure of Cu Zn alloy with 1% silicon is equivalent to that of Cu Zn alloy with 10% zinc. So the zinc equivalent of silicon is 10. The "zinc equivalent coefficient" of silicon is the largest, which makes the "zinc equivalent coefficient" in Cu Zn system the largest α/(α+β) The phase boundary moves to the copper side significantly, that is, it narrows strongly α Phase region. The "zinc equivalent coefficient" of nickel is negative, i.e. expanding α Phase region.304 Stainless Steel Seamless Tubing
Copper in special brass α Xianghe β The results show that the strengthening effect is better than that of ordinary brass α and β The strengthening effect of Cu Zn solid solution is low. Although the zinc equivalent is equal, the properties of multi-component solid solution are different from that of simple binary solid solution. Therefore, a small amount of multi-element strengthening is a way to improve the properties of the alloy.