Room temperature tissue
Generally, the brass component in the brass capillary is a copper-zinc binary alloy, and its zinc content has a large modification plan, so its room temperature structure is also very different. According to the Cu-Zn binary situation diagram (Figure 6), there are three types of brass at room temperature: brass with a zinc content of 35% or less, and the microstructure at room temperature is composed of a single-phase α solid solution, called α yellow Copper; brass with a zinc content of 36% to 46%, the microstructure at room temperature is composed of (α+β) two phases, called (α+β) brass (Two-phase brass); Brass with zinc content exceeding 46%-50%, the microstructure at room temperature is composed of β-phase only, which is called β-brass.
Pressure processing function
α single-phase brass (from H96 to H65) has excellent plasticity and can accept hot and cold processing, but α single-phase brass is prone to medium temperature brittleness during hot working such as casting, and its specific temperature plan varies with the Zn content The changes are generally between 200 and 700°C. Therefore, the temperature during thermal processing should be higher than 700°C. The reason for the occurrence of the medium temperature brittle zone of single-phase α brass is mainly due to the existence of two ordered compounds of Cu3Zn and Cu9Zn in the α phase zone of the Cu-Zn alloy system. Orderly changes occur when heated at medium and low temperatures, making the alloy brittle; , There are traces of lead, bismuth harmful impurities and copper in the alloy to form a low-melting eutectic film scattered on the grain boundary, and intergranular fracture occurs during hot working. Practice shows that adding a small amount of cerium can effectively eliminate medium temperature brittleness.
In two-phase brass (from H63 to H59), in addition to the α phase with excellent plasticity, β solid solution based on the electronic compound CuZn also appears in the alloy structure. The β phase has high plasticity at high temperature, while the β'phase (ordered solid solution) is hard and brittle at low temperature. Therefore (α+β) brass should be cast in a hot state. Beta brass with a zinc content of more than 46%-50% cannot be press-processed because of its hard and brittle function.
Because of the different zinc content in brass, the mechanical function is different. The mechanical function of brass and copper changes with the different zinc content. Regarding alpha brass, as the zinc content increases, both σb and δ continue to increase. Regarding (α+β) brass, the room temperature strength continues to advance before the zinc content increases to about 45%. If the zinc content is further increased, the more brittle r-phase (solid solution based on Cu5Zn8 compound) appears in the alloy structure, and the strength drops sharply. (α+β) The room temperature plasticity of brass has been decreasing with the increase of zinc content. Therefore, a copper-zinc alloy with a zinc content of more than 45% has no practical value.
General brass has a wide range of uses, such as water tank belts, water supply and drainage pipes, medals, bellows, serpentine tubes, condenser tubes, bullet casings, and various messy-shaped punching products, small hardware parts, etc. With the increase in zinc content from H63 to H59, they can all accept hot processing well, 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 (generally 1% to 2%, a small amount up to 3% to 4%, and most others up to 5% to 6) are added to the copper-zinc alloy. %) Tin, aluminum, manganese, iron, silicon, nickel, lead and other elements form ternary, quaternary, and even five-member alloys, which are messy brass, also known as special brass
Zinc equivalent coefficient
The organization of messy brass can be calculated based on the "zinc equivalent coefficient" of the participating elements in brass. Because a small amount of other alloying elements are added to the copper-zinc alloy, generally only the α/(α+β) phase region in the Cu-Zn situation diagram is moved to the left or right. Therefore, the organization of special brass is generally suitable for the organization with increased or decreased zinc content in general brass. For example, adding 1% silicon to the Cu-Zn alloy is suitable for adding 10% zinc to the Cu-Zn alloy. So the "zinc equivalent" of silicon is 10. The "zinc equivalent coefficient" of silicon is so large that the α/(α+β) phase boundary in the Cu-Zn system is significantly shifted to the copper side, that is, the α phase region is drastically reduced. The "zinc equivalent coefficient" of nickel is negative, that is, the α-phase region is expanded.
In particular, the α and β phases in brass are multi-element messy solid solutions and have a greater strengthening effect, while the α and β phases in general brass are simple Cu-Zn solid solutions with low strengthening effects. Although the zinc equivalent is appropriate, the properties of multiple solid solutions and simple binary solid solutions are different. Therefore, a small amount of multi-element strengthening is a way to advance the function of the alloy.
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