2. Brass: refers to the alloy with copper and zinc as the main components, which can be subdivided into simple brass and complex brass. The complex brass is named nickel brass and silicon brass with the third component;
3. Bronze: refers to copper-based alloys other than copper-nickel alloys and copper-zinc alloys. The main varieties are tin bronze, aluminum bronze and special bronze (also known as high copper alloy);
4. White copper: copper-nickel alloy;
The standardization of copper and copper alloys in China is progressing rapidly, and the national standards for copper are divided into four categories:
One is the basic standard, GB 5231-2001stipulates the chemical composition and product shape of processed copper and copper alloys;
The second is the standard of chemical analysis methods, which stipulates the chemical analysis methods of main components and impurity elements in copper and alloys;
Third, the physical and chemical properties testing methods, including resistance coefficient, ultrasonic flaw detection, eddy current flaw detection, residual stress, dezincification corrosion, oxygen content of oxygen-free copper, fracture, grain size and other specified methods; Fourth, product standards, including cathode copper, copper wire ingot for electrical purposes, cast brass ingot, cast bronze ingot, crude copper, copper sulfate, copper beryllium master alloy, copper master alloy, copper concentrate and copper and alloy processing material standards.
In addition to national standards, China also has industry standards and enterprise standards. In order to meet the needs of product development, the supply and demand sides can also agree on special technical conditions.
Copper and copper alloy products all over the world have been included in national standards, such as American ASTM standard, Japanese JIS standard, British BS standard, German DIN standard, French NF standard, Russian γ γγOCT standard, international ISO standard, European Union BSEN standard and so on. Standardization is very important to the development of national economy, and it is also a summary of the production, research and application of copper materials, so the standards of copper and copper alloys all over the world are constantly revised and improved.
According to the different kinds of alloy elements contained in brass, brass can be divided into ordinary brass and special brass. Brass used for pressure machining is called deformed brass.
1. Ordinary brass
(1) The room temperature microstructure of ordinary brass is a binary alloy of copper and zinc, and its zinc content changes greatly, so its room temperature microstructure is also very different. According to the binary state diagram of copper and zinc (Figure 6), there are three kinds of room temperature microstructures of brass: brass with zinc content below 35%, and the room temperature microstructure is composed of single-phase α solid solution, which is called α brass; The microstructure of brass with zinc content ranging from 36% to 46% is composed of (α+β) two phases at room temperature, which is called (α+β) brass (biphasic brass). The microstructure of brass containing more than 46% ~ 50% zinc is only composed of β phase at room temperature, which is called β brass.
(2) Pressure-machinable α single-phase brass (from H96 to H65) has good plasticity and can withstand cold and hot working, but α single-phase brass is prone to medium-temperature brittleness during hot working such as forging, and its specific temperature range varies with Zn content, generally between 200℃ and 700℃. Therefore, the temperature during hot working should be higher than 700℃. The reason for the brittle zone of single-phase α brass at medium temperature is that there are two ordered compounds, Cu3Zn and Cu9Zn, in the α phase zone of Cu-Zn alloy system, which undergo ordered transformation when heated at medium and low temperatures, making the alloy brittle. In addition, there are trace harmful impurities in the alloy, such as lead and bismuth, which form a low melting point crystal film with copper and distribute on the grain boundary, leading to intergranular fracture during hot working. The practice shows that adding trace cerium can effectively eliminate the brittleness at medium temperature.
In biphase brass (from H63 to H59), besides α phase with good plasticity, β solid solution mainly composed of electronic compound CuZn also appears in the alloy structure. β phase has high plasticity at high temperature, while β′ phase (ordered solid solution) is hard and brittle at low temperature. Therefore, (α+β) brass should be forged in hot state.
β brass containing more than 46% ~ 50% zinc cannot be pressure worked because of its hard and brittle characteristics.
(3) Mechanical Properties The mechanical properties of brass vary with the zinc content. Fig. 7 shows the curves of mechanical properties of brass with different zinc contents. For α brass, σb and δ increase with the increase of zinc content. For (α+β) brass, the room temperature strength increases continuously until the zinc content increases to about 45%. If the zinc content is further increased, the strength of the alloy will drop sharply due to the appearance of more brittle R phase (solid solution based on Cu5Zn8 compound). The room temperature plasticity of (α+β) brass always decreases with the increase of zinc content. Therefore, copper-zinc alloy with zinc content exceeding 45% has no practical value.
2. Special brass
In order to improve the corrosion resistance, strength, hardness and machinability of brass, a few elements (generally 1% ~ 2%, a few 3% ~ 4% and a few 5% ~ 6%) are added into copper-zinc alloy to form ternary, quaternary or even quaternary elements.
The microstructure of brass with complex zinc equivalent coefficient (1) can be calculated according to the "zinc equivalent coefficient" of elements added to brass. Because a small amount of other alloying elements are added to Cu-Zn alloy, the α/(α+β) 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 after adding 1% silicon to Cu-Zn alloy is equivalent to adding 10% zinc to Cu-Zn alloy. So the zinc equivalent of silicon is 10. The "zinc equivalent coefficient" of silicon is the largest, which makes the α/(α+β) phase boundary in Cu-Zn system significantly move 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 enlarged.
(2) Properties of Special Brass The α phase and β phase in special brass are multi-component composite solid solutions, which have great strengthening effect, while the α phase and β phase in ordinary brass are simple copper-zinc solid solutions, which have low strengthening effect. Although the zinc equivalent is equivalent, the properties of multicomponent solid solution are different from those of simple binary solid solution. Therefore, a small amount of multi-element strengthening is a way to improve the properties of the alloy.
(3) Microstructure and pressure workability of several commonly used special deformed brass.
Lead brass: Lead is actually insoluble in brass and distributed on grain boundaries as a free particle. Lead brass can be divided into α and (α+β) according to its structure. α lead brass can only be cold deformed or hot extruded because of its harmful effect and low high temperature plasticity. (α+β) lead brass has good high temperature plasticity and can be forged.
Tin brass: adding tin to brass can obviously improve the heat resistance of the alloy, especially the ability to resist seawater corrosion, so tin brass is called "navy brass"
Tin can be dissolved in copper-based solid solution, which plays a role in solid solution strengthening. However, 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% ~ 1.5%.
Commonly used tin brass are HSn70- 1, HSn62- 1, HSn60- 1 and so on. The former is α alloy, which has high plasticity and can be processed by hot and cold pressing. The alloys of the latter two brands have (α+β) two-phase structure, and a small amount of R phase often appears, which has low plasticity at room temperature and can only be deformed in hot state.
Manganese brass: Manganese has great solubility in solid brass. Adding 1% ~ 4% manganese to brass can significantly improve the strength and corrosion resistance of the alloy without reducing its plasticity.
Manganese brass has (α+β) structure, and HMn58-2 is commonly used, which has good stamping workability in cold and hot state.
Iron brass: In iron brass, iron precipitates in the form of iron-rich particles, which are used as crystal nuclei to refine grains and prevent recrystallization grains from growing, thus improving the mechanical properties and technological properties of the alloy. The iron content in iron brass is usually below 1.5%, and its structure is (α+β), which has high strength and toughness, good plasticity at high temperature and cold deformation. The commonly used brand number is Hfe59- 1- 1.
Nickel brass: Nickel and copper can form a continuous solid solution, significantly expanding the α phase region. Adding 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, which has good plasticity at room temperature and can be deformed in hot state, but the content of impurity lead must be strictly controlled, otherwise the hot workability of the alloy will be seriously deteriorated.
The earliest use of brass to cast money in China began in Jiajing period of Ming Dynasty. The word "brass" first came from Dong Fangshuo (() Shen Yi Huang Jingzhong Classic in the Western Han Dynasty: "There is a palace in the northwest, with brass as the wall, called the Imperial Palace." What copper alloy this "brass" refers to remains to be tested. The New Tang Book is also called "bronze" and "brass", which refer to the colors of ores and smelting products respectively, instead of the current copper-tin alloy and copper-zinc alloy. In the Song Dynasty poet Hong's "Daye Fu", there is another sentence: "It is brass, the pit has another name, and the mountains are numerous and plain", which refers to pure copper smelted by pyrometallurgy. The term brass refers to copper-zinc alloy, which began in Ming Dynasty, and is recorded in Ming Hui Dian: "There is an example in Jiajing, Bao Tong paid six million yuan, and Erhuo brass paid 47,272 Jin ..." Through the analysis of the composition of copper coins in Ming Dynasty, it is found that the brass in the real sense mentioned in Ming Hui Dian appeared much later than other copper alloys, because zinc in brass is hard to obtain. Zinc oxide can be rapidly reduced to metallic zinc at a high temperature of 950℃- 1000℃, while liquid zinc has boiled at 906℃, so the metallic zinc obtained by reduction exists in the form of steam. When cooling, the reaction is a reverse reaction, and the vapor zinc is oxidized from carbon dioxide to zinc oxide in the furnace, so it is necessary to have a special condensation device to obtain metallic zinc. This is the reason why zinc is used much later than copper, lead, tin and iron, and it is also one of the reasons why brass coins appear later. However, brass pieces and copper tubes containing more than 20% zinc were unearthed in Yangshao cultural site in Jiangzhai, and two kinds of brass cones were also unearthed in Longshan culture in Sanlihe, Jiaoxian County, Shandong Province. Obviously, the appearance of these brass objects does not mean that people have mastered the smelting technology of brass in prehistoric times, but that people obtained it unintentionally when using copper and zinc to produce ores. The zinc content of bronzes in Shang and Zhou Dynasties is very low, generally in the order of10-z. There are several kinds of coins in the Western Han Dynasty and Xin Mang, some of which contain 7% zinc, but this does not mean that brass coins were produced in the Western Han Dynasty and Xin Mang. Because these copper-zinc alloys are extremely rare phenomena, their zinc content is generally much smaller than that of real brass 15%-40%. Therefore, we think that these copper coins containing zinc were produced when copper and zinc were used in the "mountain casting money" in the Han Dynasty. According to the investigation of relevant mines, it is found that there are abundant copper and zinc mines in Changwei, Yantai, Linyi and Hubei in Shandong Province, which makes the smelting copper contain a small amount of zinc. In the Tang Dynasty, due to the standardization of coin materials, the zinc content in coins was constant.
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