The Main Properties Of Brass

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, and its specific temperature range varies with different Zn content, generally between 200 ℃ and 700℃. Therefore, the temperature of hot processing should be higher than 700℃. The main reason for the brittle zone of single-phase α brass is that there are two ordered compounds Cu3Zn and Cu9Zn in α phase of Cu-Zn alloy system. In addition, there are trace harmful impurities of lead and bismuth in the alloy and copper to form eutectic films with low melting point, which distribute on the grain boundary and produce intergranular rupture during hot processing. Practice shows that adding trace amount of cerium can effectively eliminate the middle temperature brittleness.

The microstructure of two-phase brass (from H63 to H59) is characterized by β solid solution based on electron compound CuZn in addition to α phase with good plasticity. The β phase is highly plastic at high temperature, while the β 'phase (ordered solid solution) is hard and brittle at low temperature. Therefore (α+β) brass should be forged under hot state. The β brass containing more than 46% ~ 50% zinc cannot be processed by pressure because of its hard and brittle properties. Brass has different mechanical properties due to different zinc content. Fig.7 shows the curve of brass mechanical properties changing with different zinc content. For α brass, σ B and δ increase with the increase of zinc content. For (α+β) brass, the strength at room temperature increases when the zinc content is increased to about 45%. If the zinc content is further increased, the strength of the alloy decreases sharply due to the appearance of a more brittle R phase (solid solution based on Cu5Zn8 compound) in the microstructure. The ductility of (α+β) brass decreases with increasing zinc content. Therefore, copper-zinc alloys containing more than 45% zinc have no practical value.

Common brass is widely used such as water tank belt, water supply and drainage pipe, medal, bellows, serpentine pipe, condensing pipe, shell case and a variety of complex shaped products, hardware and so on. With the increase of zinc content from H63 to H59, they can withstand hot processing very well, mostly used in various parts of machinery and electrical appliances, stamping parts and Musical Instruments.

In order to improve the corrosion resistance of brass, strength, hardness and the machinability and so on, add a small amount of in copper and zinc alloy (commonly 1% ~ 2%, 3% ~ 4% minority, extremely individual was 5% ~ 6%) of tin, aluminum, manganese, iron, silicon, nickel, lead and other elements that constitute the three yuan, four yuan, five yuan alloy, even is the complex of brass, which is also called special brass. The structure of complex brass can be calculated according to the "zinc equivalent coefficient" of the added elements in brass. Because the addition of a small amount of other alloying elements to the cu-Zn alloy usually only shifts the α/ (α+β) phase region in the Cu-Zn state diagram to the left or right. Therefore, the tissue of special brass is usually equivalent to that of ordinary brass with increased or reduced zinc content. For example, adding 1% silicon to the cu-Zn alloy is equivalent to adding 10% zinc to the cu-Zn alloy. So silicon has a zinc equivalent of 10. The α/ (α+β) phase boundary in The Cu-Zn series moves significantly towards the copper side, that is, the α phase region is strongly reduced. The "zinc equivalent coefficient" of nickel is negative, that is, the α phase region is enlarged.

The α and β phases in special brass are multi-complex solid solutions, and their strengthening effect is greater, while the α and β phases in ordinary brass are simple Cu-Zn solid solutions, and their strengthening effect is lower. Although zinc equivalents are equivalent, the properties of the multiple solid solution are different from those of the simple binary solid solution. Therefore, a small amount of multiple strengthening is a way to improve the properties of the alloy.

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