Brass

What Is Brass?

Brass is an alloy composed of copper and zinc. Brass composed of copper and zinc is called ordinary brass. If it is a variety of alloys composed of more than two elements, it is called special brass. Brass has strong wear resistance. Brass is often used to make valves, water pipes, connecting pipes for internal and external air conditioners, and radiators.

Main Performance

Room temperature tissue

Ordinary brass is a binary alloy of copper and zinc, and its zinc content varies widely, so its room temperature structure is also very different. According to the Cu-Zn binary state diagram, 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 brass; containing zinc For brass with a content of 36%～46%, the microstructure at room temperature consists of (α+β) two phases, called (α+β) brass (two-phase brass); the zinc content exceeds 46 %～50% brass, the microstructure at room temperature is only composed of β phase, which is called β brass.

Pressure processing performance

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 medium temperature brittleness during hot working such as forging, and its specific temperature range varies with the Zn content. The change is generally between 200 and 700°C. Therefore, the temperature during thermal processing should be higher than 700°C. The reason for the formation of the medium-temperature brittle zone in single-phase α brass is mainly due to the existence of two ordered compounds Cu3Zn and Cu9Zn in the α-phase zone of the Cu-Zn alloy system. The orderly transformation occurs when heated at medium and low temperatures, making the alloy brittle; , There are traces of lead and bismuth harmful impurities in the alloy and copper to form a low-melting eutectic film distributed on the grain boundary, causing intergranular fracture during thermal processing. Practice has shown 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 good 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) at low temperature is hard and brittle. Therefore (α+β) brass should be forged in hot state. Beta brass with a zinc content of more than 46%-50% cannot be press-processed due to its hard and brittle properties.

Mechanical properties

Due to the different zinc content in brass, the mechanical properties are also different, and the mechanical properties of brass vary with the zinc content. For alpha brass, as the zinc content increases, both σb and δ continue to increase. For (α+β) brass, the room temperature strength continues to increase before the zinc content increases to about 45%. If the zinc content is further increased, the more brittle r-phase (a solid solution based on Cu5Zn8 compound) appears in the alloy structure, and the strength is drastically reduced. (Α+β) The room temperature plasticity of brass always decreases with the increase of zinc content. Therefore, a copper-zinc alloy with a zinc content of more than 45% has no practical value.
Ordinary 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 complex shaped punching products, small hardware parts, etc. As the zinc content increases from H63 to H59, they can withstand 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 few up to 3% to 4%, and very few 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-element alloys, which are complex brass, also known as special brass.

Zinc Equivalent Coefficient

The structure of complex brass can be calculated based on the “zinc equivalent coefficient” of elements added to brass. Because a small amount of other alloying elements are added to the copper-zinc alloy, it is usually only to move the α/(α+β) phase region in the Cu-Zn state diagram 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, adding 1% silicon to the Cu-Zn alloy is equivalent to adding 10% zinc to the Cu-Zn alloy. So the “zinc equivalent” of silicon is 10. The “zinc equivalent coefficient” of silicon is the largest, causing the α/(α+β) phase boundary in the Cu-Zn system to move significantly to 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 expanded.

The α and β phases in special brass are multi-element complex solid solutions with greater strengthening effects, while the α and β phases in ordinary brass are simple Cu-Zn solid solutions with low strengthening effects. Although the zinc equivalent is equivalent, the properties of multi-component solid solutions and simple binary solid solutions are different. Therefore, a small amount of multi-element strengthening is a way to improve the properties of the alloy.

Main classification

Lead brass

Lead is actually insoluble in brass and is distributed on the grain boundaries in the state of free particles. According to its organization, lead brass has two types: α and (α+β). Due to the harmful effects of lead, alpha-lead brass has very low high temperature plasticity, so it can only be cold deformed or hot extruded. (α+β) Lead brass has good plasticity at high temperature and can be forged.

Tin brass

Adding tin to brass can significantly improve the heat resistance of the alloy, especially the ability to resist seawater corrosion, so tin brass is called “navy brass”.
Tin can dissolve into the copper-based solid solution to play a solid solution strengthening effect. But with the increase of tin content, brittle r-phase (CuZnSn compound) will appear in the alloy, which is not conducive to the plastic deformation of the alloy, so the tin content of tin brass is generally in the range of 0.5% to 1.5%.

Commonly used tin brasses are HSn70-1, HSn62-1, HSn60-1 and so on. The former is an alpha alloy with high plasticity and can be processed under cold and hot pressure. The alloys of the latter two grades have (α+β) two-phase structure, and a small amount of r-phase is often present, and the plasticity at room temperature is not high, and it can only be deformed in the hot state.

Manganese Brass

Manganese has greater solubility in solid brass. Adding 1% to 4% of manganese to brass can significantly increase the strength and corrosion resistance of the alloy without reducing its plasticity.
Manganese brass has a (α+β) structure, and HMn58-2 is commonly used, and its pressure processing performance under cold and hot conditions is quite good.

Iron brass

In iron brass, iron precipitates with iron-rich phase particles, which serve as crystal nuclei to refine the crystal grains and prevent the growth of recrystallized grains, thereby improving the mechanical properties and process performance of the alloy. The iron content in iron brass is usually below 1.5%, its structure is (α+β), it has high strength and toughness, it has good plasticity at high temperature, and it can be deformed under cold conditions. The commonly used grade is Hfe59-1-1.

Nickel brass

Nickel and copper can form a continuous solid solution, which significantly expands the α-phase region. The addition of nickel to brass can significantly improve the corrosion resistance of brass in the atmosphere and seawater. Nickel can also increase the recrystallization temperature of brass and promote the formation of finer grains.

HNi65-5 nickel brass has a single-phase α structure, has good plasticity at room temperature, and can also be deformed in hot state, but the content of impurity lead must be strictly controlled, or it will seriously deteriorate the hot workability of the alloy.

Composition

Purity measurement

The purity of brass can be measured by Archimedes principle, the volume and mass of the sample are measured, and then the ratio of copper in brass can be calculated based on the density of copper and the density of zinc.

Ordinary brass

It is an alloy composed of copper and zinc.

When the zinc content is less than 35%, zinc can be dissolved in copper to form a single-phase α, called single-phase brass, which has good plasticity and is suitable for cold, hot, and pressurized processing.

When the zinc content is 36%~46%, there are α single phase and β solid solution based on copper and zinc, called dual-phase brass. β phase reduces the plasticity of brass and increases the tensile strength, which is only suitable for Hot pressure processing.

If you continue to increase the mass fraction of zinc, the tensile strength will decrease and there will be no use value.

The code name is represented by “H + number”, H represents brass, and the number represents the mass fraction of copper.

For example, H68 means brass with a copper content of 68% and a zinc content of 32%. For cast brass, add “Z” before the code, such as ZH62.

For example, ZCuZnzn38 represents a cast brass with a zinc content of 38% and the balance being copper.

H90 and H80 belong to single-phase brass, golden yellow.

H59 is a two-phase brass, which is widely used in structural parts of electrical appliances, such as bolts, nuts, washers, springs, etc.

In general, single-phase brass is used for cold deformation processing, and dual-phase brass is used for hot deformation processing.

Special brass

The multi-element alloy formed by adding other alloying elements to ordinary brass is called special brass. Commonly added elements include lead, tin, aluminum, etc., which can be called lead brass, tin brass, and aluminum brass accordingly. The purpose of adding alloying elements. Mainly to improve the tensile strength and improve the processability.
Code: It means “H + the symbol of the main element (except zinc) + the mass fraction of copper + the mass fraction of the main element + the mass fraction of other elements”.
For example: HPb59-1 means that the mass fraction of copper is 59%, the mass fraction of lead containing the main element is 1%, and the balance is lead brass with zinc.

Heat treatment specification

Thermal processing temperature is 750～830℃; annealing temperature is 520～650℃; low temperature annealing temperature to eliminate internal stress is 260～270℃.

Environmental protection brass C26000 C2600 has excellent plasticity, high strength, good machinability, welding, good corrosion resistance, heat exchanger, paper pipe, machinery, electronic parts.

Specifications (mm): Specifications: thickness: 0.01-2.0mm, width: 2-600mm;

Hardness: O, 1/2H, 3/4H, H, EH, SH, etc.;

Applicable standards: GB, JISH, DIN, ASTM, EN;

Specialty: Excellent cutting performance, suitable for high-precision parts processed by automatic lathes and CNC lathes.