I. Basic Concepts of CuZn30 Brass
CuZn30 brass is a typical copper-zinc binary alloy, containing about 70% copper and 30% zinc (mass fraction). In China, it is often called H70 brass, and it also has various standard designations such as C260 in the international arena. Because it retains the ductility of copper, and substantially improves strength and wear resistance through the addition of zinc, it has a wide range of applications in machinery manufacturing, building decoration, and appliance parts.
Chemical composition and organizational structure
1. Chemical composition
Copper (Cu): about 70%, is the base metal, giving the alloy excellent electrical conductivity, thermal conductivity and ductility.
Zinc (Zn): about 30%, is the main alloying element to improve strength and hardness, but also to some extent to improve corrosion resistance.
Other trace elements (such as lead, tin, aluminum, iron, etc.) are usually very low in content, mainly to refine the grain or further improve the processing performance, does not constitute the main body of the alloy.
2. Organizational structure
According to the phase diagram of copper and zinc in different composition ratios, CuZn30 mainly forms the alpha phase (Alpha Brass), which is a kind of copper-dominated, zinc in the copper face-centered cubic (FCC) lattice to form a solid solution of the metal phase. alpha phase has good ductility and toughness at room temperature, and thus is capable of a greater degree of cold working (such as rolling, drawing, stamping, etc.).
In some compositional ranges, brass may also appear **(α + β) two-phase organization, but for CuZn30, the α-phase is still mainly dominated by the α-phase, which ensures that it has a good balance of strength and plasticity **at room temperature and in medium temperature environments.
Third, mechanical properties: high strength and good plasticity coexist
1. Solute strengthening and microstructure
Zinc in the copper matrix for solid solution, the formation of solid solution strengthening. When zinc atoms are dissolved in the copper lattice, lattice distortion occurs, which prevents dislocation movement. This results in an alloy that is stronger and harder than pure copper. As the zinc content increases, the strength of the brass usually rises as well, but the ductility decreases.
In the case of CuZn30, the zinc content is within a relatively reasonable range, ensuring a balance between strength and ductility. It has a good tensile strength, but also maintains a good plasticity, suitable for a variety of ways of machining and stamping molding.
2. Grain refinement and work hardening
By controlling the heat treatment process such as smelting, rolling and annealing, the grain of CuZn30 can be made more refined. After cold working, a large number of dislocations and substructures will be generated inside the material, and these defects will further strengthen the alloy, a phenomenon known as work hardening. Therefore, CuZn30 brass after suitable heat treatment and machining process can obtain higher yield strength and tensile strength while maintaining a certain degree of plasticity.
Fourth, the scientific principle of wear resistance
1. Intermetallic bonding and anti-wear
In the relative friction or sliding working environment, metal materials will often appear surface wear. CuZn30 brass in the copper - zinc atoms of the metal bond is relatively stable, coupled with the brass surface will often generate a layer of oxide film or passivation layer, can to a certain extent reduce the coefficient of friction, to reduce the direct contact of the metal surface, so as to reduce wear and tear.
2. Anti-seize performance
Compared with steel, brass surface is usually less likely to bite phenomenon. Especially in the mating of relatively moving parts, such as gears, bushings, bushes, etc., the use of CuZn30 brass can effectively reduce the wear, friction and galling between parts.
3. Balance of hardness and plasticity
Sufficient hardness: CuZn30 obtains higher hardness than pure copper through solid solution strengthening and work hardening of zinc, which reduces surface scratching and tearing.
Moderate plasticity: CuZn30 is not overly brittle compared to higher hardness materials, and is therefore able to cushion micro-motion wear caused by external shocks and vibrations.
