Mechanical properties
Brass has different mechanical properties due to different zinc content. Fig. 7 is a graph showing the change of mechanical properties of brass with different zinc content. For brass, σb and δ increase with the increase of zinc content. For ( plus ) brass, the strength at room temperature increases continuously before the zinc content increases to about 45 percent . If the zinc content is further increased, the R phase with greater brittleness (solid solution based on Cu5Zn8 compound) appears in the alloy structure, and the strength decreases sharply. The room temperature plasticity of ( plus ) brass always decreases with the increase of zinc content. Therefore, the copper-zinc alloy containing more than 45 percent zinc has no practical value.
Ordinary brass is widely used, such as water tank belt, water supply and drainage pipe, medal, corrugated pipe, serpentine pipe, condenser pipe, shell casing, various complex punched 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 elements such as tin, aluminum, manganese, iron, silicon, nickel, lead, etc. (generally 1 percent 2 percent , a few up to 3 percent 4 percent , and a few up to 5 percent ) are added to copper-zinc alloy to form ternary, quaternary or even quinary alloys, which is complex
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 Cu-Zn alloy, the /( plus ) phase region in Cu-Zn state diagram usually moves to the left or right. Therefore, the microstructure 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 percent silicon is equivalent to the alloy structure with 10 percent zinc added in Cu-Zn alloy. So the "zinc equivalent" of silicon is 10. The "zinc equivalent coefficient" of silicon is the largest, which makes the /( plus ) phase boundary in Cu-Zn system significantly move to the copper side, that is, the phase region is strongly reduced. The "zinc equivalent coefficient" of nickel is negative, that is, the phase region is enlarged.
The -phase and -phase in special brass are complex multi-element solid solutions, which have great strengthening effect, while the -phase and -phase in common brass are simple Cu-Zn solid solutions, which have low strengthening effect. Although zinc equivalent is equivalent, the properties of multicomponent solid solution and simple binary solid solution are different. Therefore, a small amount of multi-element strengthening is a way to improve alloy properties.
