Environment-friendly free-cutting brass alloy, preparation method and application thereof

Abstract

The application discloses an environment-friendly easy-cutting brass alloy, which comprises the following components in mass percentage: Cu: 59-62%, Sn: 0.5-1.0%, Pb < 0.2%, Fe < 0.1%, As: 0.02-0.09%, Bi: 0.1-0.4%, Si: 0.1-0.4%, Sb: 0.05-0.4%, Ni+Mn: 0.1-0.3%, and the rest is Zn and inevitable impurities; the environment-friendly easy-cutting brass alloy comprises a base phase composed of an alpha phase, a beta phase and a beta' phase, and a second phase, wherein the second phase comprises a Mn-Si phase, a K phase, a gamma phase, a beta-Sn phase, a beta-Si phase, a Si phase and a Bi phase, and the area ratio is 0.01-0.5%. The application further discloses a preparation method and application of the environment-friendly easy-cutting brass alloy. The brass alloy is prepared by adding elements such as silicon Si and bismuth Bi and a refiner in a melting and casting process, and simultaneously adopting an online quenching solid solution process and a water tank cooling mode. The brass alloy disclosed by the application has fine and uniform grains, and has excellent anti-zinc loss property and cutting performance, and can be used as a production raw material of household appliances, detection and control instruments and the like.

Description

Technical Field

[0001] This invention belongs to the field of materials metallurgy technology, specifically relating to an environmentally friendly free-machining brass alloy, its preparation method, and its application. Background Technology

[0002] Brass is an alloy composed of copper and zinc. Due to its beautiful appearance and excellent physical and chemical properties, it is widely used in many fields. Because ordinary brass has poor machinability, adding a small amount of lead (approximately 1-4.5%) significantly improves the material's cutting performance. Therefore, leaded brass is widely used in everyday consumer goods and mechanical parts, especially for some complex workpieces.

[0003] However, with advancements in technology and increased public awareness of health and safety, the harmful elements in everyday products, such as lead, nickel, cadmium, mercury, and hexavalent chromium, are becoming increasingly recognized and attracting close attention from many countries. In particular, laws and regulations are being drafted or are being developed to control the content of harmful elements in industrial products, requiring that equipment providing drinking or cooking water, including pipes, valves, and faucets, must meet new lead-free standards.

[0004] Currently, commonly used lead-free copper products include H62, C46500, CuZn series, and CW511L. However, there are few lead-free copper products that can ensure good hot forging performance, resistance to dezincification corrosion, and good machinability. Moreover, they all have different degrees of defects, such as the self-cracking problem of bismuth brass, the corrosion resistance problem of silicon brass, the environmental protection problem of sulfur copper, and the machinability problem of tin brass. Therefore, it is urgent to optimize the existing lead-free copper products.

[0005] Patent document CN101624667A discloses a sintered lead-free free-machining brass and its preparation method. The mass fractions of each element in the brass are as follows: copper 48.0%-70.0%, aluminum 0.3%-0.4%, magnesium 4.0%-4.3%, manganese 0.1%-0.2%, cerium 0.08%-0.11%, lanthanum 0.01%-0.03%, boron powder 0.4%-2.4%, and the remainder being zinc and impurities totaling no more than 0.05%. This brass alloy composition is lead-free and environmentally friendly, but its machinability is poor. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides an environmentally friendly free-machining brass alloy, which has excellent machinability and anti-zincification properties, and has fine and uniform grains.

[0007] An environmentally friendly free-machining brass alloy, by mass fraction, comprises Cu: 59-62%, Sn: 0.5-1.0%, Pb < 0.2%, Fe < 0.1%, As: 0.02-0.09%, Bi: 0.1-0.4%, Si: 0.1-0.4%, Sb: 0.05-0.4%, Ni+Mn: 0.1-0.3%, with the balance being Zn and unavoidable impurities. The environmentally friendly free-machining brass alloy includes a matrix phase and a second phase. The matrix phase includes α phase, β phase, and β' phase. The second phase includes Mn-Si phase, K phase, γ phase, β-Sn phase, β-Si phase, Si phase, and Bi phase. The area ratio of the second phase is 0.01-0.5%.

[0008] Bismuth, silicon, nickel, antimony, manganese and tin are mainly used to form the second phase, including Mn-Si phase, K phase, γ phase, β-Sn phase, β-Si phase, Si phase and Bi phase. The formation of these phases improves the machinability of the material. Through these dispersed particles, they play a role in chip breaking during the cutting process.

[0009] Sb can be dispersed in the matrix and grain boundaries, which can cut the network structure formed by Bi and eliminate the risk of cracking in the material. When the content of Bi in brass is higher than 0.4 wt%, it will increase the risk of self-cracking. When it is lower than 0.1 wt%, it has little effect on improving the machinability.

[0010] In the brass material of the present invention, the silicon content is 0.1-0.4 wt%. When the silicon content is less than 0.1 wt%, the effect on machinability is not obvious, and the formation of Si-Mn phase is insufficient. When the silicon content is higher than 0.4 wt%, the proportion of hard and brittle phase γ+K is easily increased, which leads to an increased risk of material cracking and a significant reduction in the plasticity of the material, which is not conducive to the production, processing and engineering application of the material.

[0011] The main functions of tin in brass materials are to inhibit dezincification, improve corrosion resistance, and enhance machinability. Nickel can enter the α phase of the microstructure during the casting process, dissolving in an unlimited proportion to improve the microstructure's resistance to dezincification. Simultaneously, the addition of manganese (Mn) forms a layer of MnO2 oxide on the material surface, providing corrosion protection.

[0012] Preferably, the area ratio of the α phase in the matrix phase is 45%-50%, and the remainder is the β+β' phase.

[0013] Preferably, the average grain size of the environmentally friendly free-machining brass alloy is 30-55 μm.

[0014] Preferably, the β' phase has a particle size of 2-5 μm, and the proportion of columnar crystals in the β' phase is 15-45%.

[0015] Preferably, in the second phase, the area ratio of the Mn-Si phase is 1-5%, the area ratio of the K phase is 0.1-1%, the area ratio of the γ phase is 0.1-1%, the area ratio of the β-Sn phase is 5-10%, the area ratio of the Si phase + β-Si phase is 20-30%, and the area ratio of the Bi phase is the balance.

[0016] This invention can regulate the properties of brass alloys by controlling their microstructure. The α and β phases belong to the matrix phases of the material, acting as carriers that give the material good tensile strength, elongation, wear resistance, pressure resistance, and environmental friendliness. However, they still have shortcomings in machinability, dezincification resistance, and corrosion resistance, requiring improvement through microalloying. This involves adding metals such as bismuth, silicon, nickel, antimony, and manganese during the casting process, primarily to form second phases: Mn-Si, K, γ, β-Sn, β-Si, Si, and Bi. The formation of these phases improves the material's machinability and corrosion resistance. The main mechanism is that these dispersed second-phase particles act as chip breakers during the cutting process.

[0017] The formation of the Si-Mn phase is used to improve the corrosion resistance and machinability of the material. The area ratio of the Si-Mn phase is in the range of 1% to 5%. Above 5%, it will rapidly increase the brittle phase of the material, which will reduce the stability of the material's mechanical structure. Below 1%, the interfacial corrosion resistance is relatively weak.

[0018] K and γ phases are hard and brittle phases that need to be eliminated, but they can be produced by non-uniform crystallization. In addition to deteriorating the mechanical properties of the material, they can also help improve the machinability of the material, with a proportion of 0.1-1%.

[0019] The β-Sn phase is an allotropic transformation of metallic Sn. It has a face-centered cubic structure, which is conducive to mutual solubility, improves the machinability and corrosion resistance of the material, and can also increase the strength of the material. Generally, it is 5-10%. If it is higher than 10%, it will cause the material to become brittle, that is, the grain boundaries will become embrittled and the bonding strength will decrease.

[0020] Both Si and Bi phases are elemental phases, mainly distributed in elemental form at grain boundaries and within grains. They play a role in chip breaking during machining and are used to improve the machinability of materials. The range is 20-30%. Above 30%, the grain boundaries will be enriched with silicon-bismuth particles, forming a network structure, which will cause the material to become embrittled rapidly, causing machining cracks. At the same time, the strength and yield strength will decrease rapidly. Below 20%, the formation of Mn-Si and β-Si phases is easy to occur, and the machinability cannot be guaranteed.

[0021] This invention also provides a method for preparing the above-mentioned environmentally friendly free-machining brass. This method involves adding elements such as silicon (Si), bismuth (Bi), and antimony (Sb) and a refining agent during the smelting process, and simultaneously employing an online quenching and solution treatment process during continuous casting. This results in brass with fine and uniform grains, superior and more stable resistance to dezincification, and better machinability. Moreover, this process is simple and environmentally friendly.

[0022] A method for preparing the aforementioned environmentally friendly free-machining brass alloy includes the following process flow: batching and smelting → continuous casting → stretching → peeling and straightening, wherein the continuous casting adopts an online quenching and solution treatment process, and a water bath is used for cooling. The casting temperature is 1080-1120℃, the temperature difference between the inlet and outlet of the primary cooling water is 30-38℃, the ingot exiting the crystallizer temperature is 580-620℃, and the temperature of the copper rod after water cooling is 12-25℃.

[0023] Preferably, the water tank includes a cooling chamber and a diversion chamber composed of a flow grid, wherein the water flow direction in the water tank is opposite to the traction direction of the copper rod, and the copper rod enters the cooling chamber after being pulled out from the crystallization port.

[0024] Preferably, the water tank is installed at the outlet of the crystallizer, 50-100mm away from the crystallizer without contacting it. The continuously cast copper rod enters the water tank immediately after being pulled out. After entering the distribution chamber, the water flow is evenly distributed into the cooling chamber by the flow grid. The copper rod can be fully and evenly cooled in the cooling chamber, and the use of traction and reverse water flow allows for the removal of more heat.

[0025] This invention employs an online quenching and solution treatment process in the continuous casting process. The matrix structure of the ingot is mainly α+β phase. During heating and holding, the microstructure changes, with the α phase continuously transforming into the β phase. Furthermore, the β phase decomposes from a network structure into isolated equiaxed crystals called β'. The β' phase has a grain size of 2–5 μm, and columnar crystals account for 15%–45% of the β' phase. Rapid cooling using a water bath method yields a stable β' phase, blocking corrosion channels and eliminating the corrosion influence of the unstable β phase. The phase transformation is α+β→β→β+β'→α+β+β'. The final microstructure consists of α phase, β phase, β' phase, Mn-Si phase, K phase, γ phase, β-Sn phase, β-Si phase, Si phase, and Bi phase.

[0026] Preferably, the steps of the batching and smelting process are as follows:

[0027] Brass alloy raw materials and refining agents are added to an industrial frequency induction furnace for smelting, with the voltage maintained above 180V. After smelting, slag is removed, and the melt composition is adjusted to meet the requirements of the brass alloy. Then, refining agents are added for melt refining. After refining, the melt is held at a temperature of 10-15 minutes, then the temperature is adjusted to 1150-1180℃, ignited for 20-25 seconds, and then the temperature is reduced to 1080-1120℃. During the smelting process, the surface of the molten copper is covered with graphite flakes and charcoal.

[0028] In some embodiments, the brass alloy raw materials include copper powder, recycled materials, bismuth ingots, copper-silicon alloys, antimony ingots, arsenic ingots, copper-nickel alloys, and copper-manganese alloys, wherein the recycled materials include processing waste, scrap, extrusion residue, and scrap ends. Preferably, the mass of copper in the recycled materials accounts for 50-60% of the mass of copper in the brass alloy raw materials. This invention reduces the cost of raw materials by adding a large amount of recycled materials.

[0029] In the smelting process, this invention adds bismuth ingots, antimony ingots, and alloys containing silicon, nickel, and manganese to form second phases such as Mn-Si phase, K phase, γ phase, β-Sn phase, β-Si phase, Si phase, and Bi phase. The formation of these easily machinable phases can significantly improve the machinability of the material.

[0030] In this invention, copper-nickel alloy is added during the smelting process mainly to refine the grains, introduce the nucleation center of the second phase, increase the probability of heterogeneous nucleation, and make the grains finer. Since nickel can enter the α phase of the structure and enter in an unlimited proportion through solid solution, it can improve the structure's resistance to dezincification. At the same time, the addition of metallic manganese (Mn) can form an oxide layer (MnO2) on the material surface, which can play a role in corrosion protection.

[0031] Preferably, the grain refiner includes at least one of boron powder, iron powder, or sodium carbonate. The addition of the grain refiner can significantly refine the grains and improve the microstructure of the ingot. More preferably, the grain refiner is a mixture of boron powder, iron powder, and sodium carbonate, wherein the mass fraction of boron powder is 20-50 wt%, the mass fraction of iron powder is 5-20 wt%, and the mass fraction of sodium carbonate is 30-70 wt%. This composition of the grain refiner has a better grain refinement effect.

[0032] Preferably, the amount of the refining agent added is 0.01-0.04% of the mass of the brass alloy melt.

[0033] In the casting process of this invention, the traction speed is determined according to actual needs. In some embodiments, the casting temperature is 1080–1120°C, and cooling is performed using a water tank with a volume of 0.016 m³. 3 The water tank has a water change rate of 0.1m. 3 ~0.5m 3 / min. Using The traction process has a traction speed of 220-230 mm / min, the temperature of the copper rod exiting the crystallizer is 580-620℃, the surface temperature of the rod after water cooling is about 12℃, and the outlet temperature of the circulating water is 30-40℃.

[0034] The extension, peeling, and straightening process of this invention includes head making—pickling—extension (30-70) filaments—straightening—punch peeling (30-40) filaments—finishing. The extension, peeling, and straightening process of this invention can be specifically designed according to actual needs. For example, in some embodiments, a Φ23.6 blank is used to produce a Φ23 finished product, with extension (30-70) filaments and peeling (30-40) filaments.

[0035] This invention also provides the application of the aforementioned environmentally friendly free-machining brass alloy as a raw material in the production of components for household appliances, communication equipment, testing and control instruments, and the plumbing industry. The environmentally friendly free-machining brass alloy of this invention possesses excellent machinability and anti-zincification properties, and has fine and uniform grains, making it suitable as a raw material for the production of components for household appliances, testing and control instruments, etc.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] (1) This invention improves the machinability of brass alloys by controlling the microstructure of the alloys. By adding elements such as bismuth, silicon, nickel, antimony, manganese and tin and controlling their addition amounts to generate a second phase, the machinability of the material is improved. These dispersed particles play a role in chip breaking during the cutting process.

[0038] (2) The process for preparing environmentally friendly free-cutting brass in this invention is simple and green. By adding elements such as silicon (Si), bismuth (Bi), and antimony (Sb) and refining agents during the casting process, and by using an online quenching and solution process during the continuous casting process and cooling in a water bath, a brass alloy with fine and uniform grains, better and more stable anti-zincification performance, and better cutting performance is obtained.

[0039] (3) The environmentally friendly free-cutting brass alloy of the present invention has excellent machinability and anti-zinc descaling properties, and has fine and uniform grains, which can be used as raw material for the production of components such as household appliances, testing and control instruments. Attached Figure Description

[0040] Figure 1 The diagram below shows the water tank structure in an embodiment of the present invention, wherein: 1, cooling chamber; 2, flow distribution chamber; 3, flow grid; 4, overflow port; 5, copper rod inlet; 6, copper rod outlet; 7, cooling water inlet; 8, cooling water outlet.

[0041] Figure 2 Metallographic images of the brass alloy obtained in Example 1 of this invention ( Figure 2 a) and cutting sample ( Figure 2 b).

[0042] Figure 3 Metallographic images of the brass alloy obtained in Example 2 of this invention ( Figure 3 a) and cutting sample ( Figure 3 b).

[0043] Figure 4 Metallographic images of the brass alloy obtained in Example 3 of this invention ( Figure 4 a) and cutting sample ( Figure 4 b).

[0044] Figure 5 Metallographic images of the brass alloy obtained in Comparative Example 1 of this invention ( Figure 5 a) and cutting sample ( Figure 5 b). Detailed Implementation

[0045] Example 1

[0046] We produce straight bars with a diameter of 20mm.

[0047] The mixture includes 30wt% tin-plated brass tubing, 40wt% recycled material (mainly including processing waste, scrap, extrusion residue, and scrap ends), copper powder, bismuth ingots, copper-silicon alloy, antimony ingots, copper-nickel and copper-manganese alloys, and arsenic ingots (where the copper mass fraction in the copper powder and copper alloy is 30wt%, and the copper mass fraction in the tin-plated brass tubing, recycled material, copper powder, and copper alloy is calculated based on the copper element in the brass alloy raw material). The composition of the ingredients must meet the following requirements: Cu: 59.3%, Sn: 0.55%, Pb < 0.2%, Fe < 0.1%, As: 0.08%, Bi: 0.2%, Si: 0.25%, Sb: 0.08%, Ni+Mn: 0.15%, with the balance being Zn and unavoidable impurities. The specific alloy composition in this embodiment is shown in Table 1.

[0048] A 3t industrial frequency furnace is used. Copper powder, recycled material, bismuth ingots, copper-silicon alloy, antimony ingots, arsenic ingots, copper-nickel and copper-manganese alloys, and a refining agent (25wt% boron powder, 10wt% iron powder, and 65wt% sodium carbonate) are added sequentially. The amount of refining agent added is 0.03% of the melt mass. After the raw materials are melted, the voltage is maintained above 180V. After melting, slag is removed, and samples are taken to test the spectral composition. Based on the spectral composition, the melt composition ratio is adjusted to meet the required range. Once the composition is qualified, a refining agent is added, and the melt is refined. After refining, the temperature is held for 10 minutes, then adjusted to 1150℃, ignited for 20 seconds, and then lowered to 1100℃ before casting begins.

[0049] assembled The crystallizer is configured with the following casting parameters: casting temperature 1100℃, traction speed 240mm / min, primary cooling water inlet and outlet temperature difference 35℃, water tank distance from crystallizer outlet 100mm, ingot exiting crystallizer temperature 590℃, and copper rod temperature after water cooling 18℃. The water tank structure used in this embodiment is as follows: Figure 1 As shown, the system includes a copper rod inlet, a copper rod outlet, a cooling water inlet, a cooling water outlet, an overflow outlet, a cooling chamber, and a distribution chamber composed of flow grids. The continuously cast copper rod immediately enters the cooling chamber after being pulled out. Water seal rings are used to seal the beginning and end of the water tank to prevent water overflow. Simultaneously, after entering the distribution chamber, the water flow is evenly distributed into the cooling zone by the flow grids, allowing the copper rod to be fully cooled. The use of traction and reverse water flow removes more heat. The overflow outlet acts as a safety valve to release excess water pressure. In this embodiment, the water tank volume is 0.016 m³. 3 The water bath has a water exchange rate of 0.3m / s. 3 / min.

[0050] Diameter of continuously cast billets According to the process: head making—pickling—stretching —Straightening—Puncture of the protrusion mold —Finishing. The key process parameters for this embodiment are shown in Table 2.

[0051] Performance tests on the finished bar stock revealed dezincification resistance values ​​of 30 / 40 / 45 / 30 / 40 μm (H) and 75 / 60 / 35 / 50 / 70 μm (Z), a hardness of 120 / 125 / 130 HV5, and good machinability. The specific properties of the brass alloy obtained in this embodiment are shown in Table 3.

[0052] The microstructure of the prepared brass alloy was analyzed by microstructure detection method: the β phase ratio was determined according to the method specified in Clause 4.6 (Image Analyzer Measurement Method) of GB / T 15749-2008 (Quantitative Metallographic Method); the α phase and the second phase size were determined according to the method specified in Clause 4.3.3 (Grid Cut-off Method) of GB / T 15749-2008 (Quantitative Metallographic Method).

[0053] Depend on Figure 2Analysis revealed that the brass alloy prepared in this embodiment has fine and uniform microstructure, with a predominantly segmental rod-like and island-like structure, uniformly distributed, and no local microstructural anomalies observed. The matrix phase is mainly α+β phase, with a small amount of β' phase. The second phase is mainly Mn-Si phase, K phase, γ phase, β-Sn phase, Si phase, and Bi phase. The dispersed distribution of the second phase acts as chip-breaking points during cutting. The area ratio of the matrix phase α+β+β' phase is 99.7%, with the remainder being the second phase. Among the matrix phase, the area ratio of the α phase is 46.5%, and the grain size is 50 μm. Among the second phase, the area ratio of the β-Sn phase is 7%, the area ratio of the Mn-Si phase is 2%, the area ratio of the K phase + γ phase is 0.5%, the area ratio of the Si phase + β-Si phase is 25%, and the remainder is the Bi phase. Figure 2 As can be seen from b, the cutting material is basically crescent-shaped, indicating good machinability.

[0054] Example 2

[0055] We produce straight bars with a specification of 35mm.

[0056] The alloy is composed of 30wt% tin-plated brass tubing, 40wt% recycled material (mainly including processing waste, scrap, extrusion residue, and scrap ends), copper powder, bismuth ingots, copper-silicon alloy, antimony ingots, copper-nickel and copper-manganese alloys, and arsenic ingots. The composition requirements are Cu: 60.2%, Sn: 0.75%, Pb < 0.2%, Fe < 0.1%, As: 0.08%, Bi: 0.2%, Si: 0.3%, Sb: 0.1%, Ni+Mn: 0.2%, with the balance being Zn and unavoidable impurities. The specific alloy composition in this embodiment is shown in Table 1.

[0057] A 3t industrial frequency furnace is used. Copper powder, recycled material, bismuth ingots, copper-silicon alloy, antimony ingots, arsenic ingots, copper-nickel and copper-manganese alloys, and a refining agent (30wt% boron powder, 15wt% iron powder, and 55wt% sodium carbonate) are added sequentially. The amount of refining agent added is 0.03% of the melt mass. After the raw materials are melted, the voltage is maintained above 180V. After melting, slag is removed, and samples are taken to test the spectral composition. Based on the spectral composition, the melt composition ratio is adjusted to meet the required range. Once the composition is qualified, a refining agent is added, and the melt is refined. After refining, the temperature is held for 10 minutes, then adjusted to 1150℃, ignited for 20 seconds, and then lowered to 1100℃ before casting begins.

[0058] assembled The crystallizer is set with the following casting parameters: casting temperature 1100℃, traction speed 220mm / min, primary cooling water inlet and outlet temperature difference 35℃, water tank distance from crystallizer outlet 100mm, ingot outlet temperature 600℃, copper rod temperature after water cooling 20℃. The structure and operating parameters of the water tank are the same as in Example 1.

[0059] Diameter of continuously cast billets According to the process: head making—pickling—stretching —Straightening—Puncture of the protrusion mold —Finishing. The key process parameters for this embodiment are shown in Table 2.

[0060] Performance tests on the finished bar stock revealed dezincification resistance values ​​of 30 / 30 / 40 / 30 / 40 μm (H) and 70 / 60 / 50 / 50 / 40 μm (Z), with a hardness of 120 / 119 / 118 HV5 and good machinability. The specific properties of the brass alloy obtained in this embodiment are shown in Table 3.

[0061] Depend on Figure 3 Analysis revealed that the brass alloy prepared in this embodiment has fine and uniform microstructure, with a predominantly segmental rod-like and island-like structure, uniformly distributed, and no local microstructural anomalies observed. The matrix phase is mainly α+β phase, with a small amount of β' phase. The second phase is mainly Mn-Si phase, K phase, γ phase, β-Sn phase, Si phase, and Bi phase. The dispersed distribution of the second phase acts as chip-breaking points during cutting. The area ratio of the matrix phase α+β+β' phase is 99.6%, with the remainder being the second phase. Among the matrix phase, the area ratio of the α phase is 48.7%, and the grain size is 55 μm. Among the second phases, the area ratio of the β-Sn phase is 8%, the area ratio of the Mn-Si phase is 3%, the area ratio of the K phase + γ phase is 0.6%, the area ratio of the Si phase + β-Si phase is 26%, and the remainder is the Bi phase. Figure 3 As can be seen from b, the cutting material is basically crescent-shaped, indicating good machinability.

[0062] Example 3

[0063] We produce straight bars with a specification of 45mm.

[0064] The alloy is composed of 30wt% tin-plated brass tubing, 40wt% recycled material (mainly including processing waste, scrap, extrusion residue, and scrap ends), copper powder, bismuth ingots, copper-silicon alloy, antimony ingots, copper-nickel and copper-manganese alloys, and arsenic ingots. The composition requirements are Cu 61.2%, Sn 0.75%, Pb < 0.2%, Fe < 0.1%, As 0.085%, Bi 0.25%, Si 0.3%, Sb 0.1%, Ni + Mn 0.3%, with the balance being Zn and unavoidable impurities. The specific alloy composition in this embodiment is shown in Table 1.

[0065] A 3t industrial frequency furnace is used. Copper powder, recycled material, bismuth ingots, copper-silicon alloy, antimony ingots, arsenic ingots, copper-nickel and copper-manganese alloys, and a refining agent (35wt% boron powder, 15wt% iron powder, and 50wt% sodium carbonate) are added sequentially. The amount of refining agent added is 0.03% of the melt mass. After the raw materials are melted, the voltage is maintained above 180V. After melting, slag is removed, and samples are taken to test the spectral composition. Based on the spectral composition, the melt composition ratio is adjusted to meet the required range. Once the composition is qualified, a refining agent is added to refine the melt. After refining, the temperature is held for 10 minutes, then adjusted to 1150℃, ignited for 20 seconds, and then reduced to 1100℃ before casting begins.

[0066] assembled The crystallizer is configured with the following casting parameters: casting temperature 1100℃, traction speed 200mm / min, primary cooling water inlet and outlet temperature difference 38℃, water tank distance from crystallizer outlet 100mm, ingot exiting crystallizer temperature 610℃, and copper rod temperature after water cooling 25℃. The structure and operating parameters of the water tank are the same as in Example 1.

[0067] Diameter of continuously cast billets According to the process: head making—pickling—stretching —Straightening—Puncture of the protrusion mold —Finishing. The key process parameters for this embodiment are shown in Table 2.

[0068] Performance tests on the finished bar stock revealed dezincification resistance values ​​of 70 / 60 / 60 / 30 / 40 μm (H) and 60 / 50 / 50 / 40 / 30 μm (Z), a hardness of 128 / 128 / 120HV5, and good machinability. The specific properties of the brass alloy obtained in this embodiment are shown in Table 3.

[0069] Depend on Figure 4 Analysis revealed that the brass alloy prepared in this embodiment has fine and uniform microstructure, with the microstructure mainly consisting of segmental rods and islands, uniformly distributed, and without local microstructural anomalies. The matrix phase is α+β phase, also including a small amount of β' phase. The second phase consists of Mn-Si, K, γ, and β-Sn phases, with the dispersed distribution of the second phase acting as chip-breaking points during cutting. The area ratio of the matrix phase α+β+β' phase is 99.65%, with the remainder being the second phase. Among the matrix phase, the area ratio of the α phase is 49.5%, and the grain size is 50 μm. Among the second phases, the area ratio of the β-Sn phase is 5%, the area ratio of the Mn-Si phase is 3%, the area ratio of the K phase + γ phase is 0.8%, the area ratio of the Si phase + β-Si phase is 24%, and the remainder is Bi phase. Figure 4 As can be seen from b, the cutting material basically presents a crescent shape.

[0070] Example 4

[0071] We produce straight bars with a diameter of 41mm.

[0072] The alloy is composed of 30wt% tin-plated brass tubing, 40wt% recycled material (mainly including processing waste, scrap, extrusion residue, and scrap ends), copper powder, bismuth ingots, copper-silicon alloy, antimony ingots, copper-nickel and copper-manganese alloys, and arsenic ingots. The composition requirements are Cu: 60.5%, Sn: 0.82%, Pb < 0.2%, Fe < 0.1%, As: 0.088%, Bi: 0.32%, Si: 0.27%, Sb: 0.05%, Ni+Mn: 0.25%, with the balance being Zn and unavoidable impurities. The specific alloy composition in this embodiment is shown in Table 1.

[0073] A 3t industrial frequency furnace is used. Copper powder, recycled material, bismuth ingots, copper-silicon alloy, antimony ingots, arsenic ingots, copper-nickel and copper-manganese alloys, and a refining agent (38wt% boron powder, 12wt% iron powder, and 50wt% sodium carbonate) are added sequentially. The amount of refining agent added is 0.03% of the melt mass. After the raw materials are melted, the voltage is maintained above 180V. After melting, slag is removed, and samples are taken to test the spectral composition. Based on the spectral composition, the melt composition ratio is adjusted to meet the required range. Once the composition is qualified, a refining agent is added, and the melt is refined. After refining, the temperature is held for 10 minutes, then adjusted to 1150℃, ignited for 20 seconds, and then lowered to 1100℃ before casting begins.

[0074] assembled The crystallizer is configured with the following casting parameters: casting temperature 1100℃, traction speed 200mm / min, primary cooling water inlet and outlet temperature difference 38℃, water tank distance from crystallizer outlet 100mm, ingot exiting crystallizer temperature 610℃, and copper rod temperature after water cooling 25℃. The structure and operating parameters of the water tank are the same as in Example 1.

[0075] Diameter of continuously cast billets According to the process: head making—pickling—stretching —Straightening—Puncture of the protrusion mold —Finishing. The key process parameters for this embodiment are shown in Table 2.

[0076] Performance tests on the finished bar stock revealed dezincification resistance values ​​of 60 / 55 / 65 / 40 / 35 μm (H) and 20 / 40 / 30 / 50 / 60 μm (Z), with a hardness of 123 / 125 / 130 HV5 and good machinability. The specific properties of the brass alloy obtained in this embodiment are shown in Table 3.

[0077] The brass alloy prepared in this embodiment has fine and uniform microstructure, mainly in the form of segmental rods and islands, with a uniform distribution and no local microstructural anomalies. The matrix phase is α+β phase, with a small amount of β' phase. The second phase consists of Mn-Si, K, γ, and β-Sn phases, with the dispersed distribution of the second phases acting as chip-breaking points during cutting. The area ratio of the matrix phase α+β+β' phase is 99.65%, with the remainder being the second phase. Among the matrix phase, the area ratio of the α phase is 47.5%, and the grain size is 35 μm. Among the second phases, the area ratio of the β-Sn phase is 6%, the area ratio of the Mn-Si phase is 3.5%, the area ratio of the K phase + γ phase is 0.1%, the area ratio of the Si phase + β-Si phase is 26%, and the remainder is Bi phase. The brass alloy cutting chips in this embodiment are basically crescent-shaped.

[0078] Comparative Example 1

[0079] We produce straight bars with a specification of 30mm using conventional processes.

[0080] The alloy is composed of 30% tin-plated brass tubing, 40% recycled material (mainly including processing waste, scrap, extrusion residue, and scrap ends), copper powder, copper-silicon alloy, and arsenic ingots. The composition requirements are Cu: 60.5%, Sn: 0.65%, As: 0.08%, Si: 0.15%, with the balance being Zn and unavoidable impurities. The specific alloy composition in this embodiment is shown in Table 1.

[0081] A 3t industrial frequency furnace is used. Copper powder, recycled material, bismuth ingots, copper-silicon alloy, antimony ingots, arsenic ingots, copper-nickel and copper-manganese alloys, and a refining agent (100% potassium fluoroborate) are added sequentially. The amount of refining agent added is 0.03% of the melt mass. After the raw materials are melted, the voltage is maintained above 180V. After melting, slag is removed, and samples are taken to test the spectral composition. Based on the spectral composition, the melt composition ratio is adjusted to meet the required range. Once the composition is qualified, a refining agent is added, and the melt is refined. After refining, the temperature is held for 10 minutes, then adjusted to 1150℃, ignited for 20 seconds, and then lowered to 1100℃ before casting begins.

[0082] assembled The crystallizer is set with the following casting parameters: casting temperature 1100℃, traction speed 230mm / min, primary cooling water inlet and outlet temperature difference 38℃, water pipe distance from crystallizer outlet 100mm, ingot outlet temperature 580℃, and copper rod temperature after water cooling 20℃.

[0083] Diameter of continuously cast billets According to the process: head making—pickling—stretching —Straightening—Puncture of the protrusion mold —Finishing. The key process parameters for this comparative example are shown in Table 2.

[0084] Performance tests on the finished bar stock revealed dezincification resistance values ​​of 60 / 150 / 120 / 80 / 40 μm (H) and 110 / 100 / 80 / 40 / 30 μm (Z), with a hardness of 98 / 118 / 125HV5 and poor machinability. The specific properties of the brass alloy obtained in this comparative example are shown in Table 3.

[0085] Depend on Figure 5 Analysis revealed that the matrix phase of the brass alloy prepared in this embodiment was α+β phase, with an area ratio of 99.4%, and the remainder being second phases; among the matrix phases, the α phase accounted for 44.8% of the area. In the second phases, the γ phase accounted for 54% of the area, and the β-Sn phase accounted for 46%. The alloy in this comparative example exhibited coarse-grained microstructure, predominantly segmental rod-like and dendritic structures, with a very uniform distribution and abnormal microstructure. The second phase distribution was uneven. Figure 5 As can be seen from b, the cutting material basically presents a spiral shape, which is very unfavorable for machining.

[0086] Table 1. Brass Alloy Composition Table

[0087] Group Cu Pb Sn Fe Ni+Mn Bi As Sb Si Example 1 59.3 0.15 0.55 0.07 0.15 0.2 0.08 0.08 0.25 Example 2 60.2 0.15 0.75 0.06 0.2 0.2 0.08 0.1 0.3 Example 3 60.2 0.15 0.75 0.06 0.2 0.2 0.08 0.1 0.3 Example 4 60.5 0.15 0.82 0.06 0.25 0.32 0.08 0.05 0.27 Comparative Example 1 60.5 0.16 0.65 0.06 - - 0.08 - 0.15

[0088] Table 2 Key Process Parameters

[0089]

[0090] Table 3 Properties of Brass Alloys

[0091]

Claims

1. An environmentally friendly free-machining brass alloy, characterized in that, The composition, by mass fraction, includes Cu: 59-62%, Sn: 0.5-1.0%, Pb < 0.2%, Fe < 0.1%, As: 0.02-0.09%, Bi: 0.1-0.4%, Si: 0.1-0.4%, Sb: 0.05-0.4%, Ni+Mn: 0.1-0.3%, with the balance being Zn and unavoidable impurities. The environmentally friendly free-machining brass alloy comprises a matrix phase and a second phase, with the second phase having an area ratio of 0.01-0.5%. The matrix phase includes an α phase, a β phase, and a β' phase, wherein the area ratio of the α phase in the matrix phase is 45-50%. The second phase includes Mn-Si phase, K phase, γ phase, β-Sn phase, β-Si phase, Si phase and Bi phase. In the second phase, the area ratio of Mn-Si phase is 1~5%, the area ratio of K phase is 0.1~1%, the area ratio of γ phase is 0.1~1%, the area ratio of β-Sn phase is 5~10%, the area ratio of Si phase + β-Si phase is 20~30%, and the area ratio of Bi phase is the balance.

2. The environmentally friendly free-machining brass alloy according to claim 1, characterized in that, The average grain size of the environmentally friendly free-machining brass alloy is 30-55 μm.

3. The environmentally friendly free-machining brass alloy according to claim 1, characterized in that, The β' phase has a particle size of 2~5 μm, and the proportion of columnar crystals in the β' phase is 15~45%.

4. The method for preparing the environmentally friendly free-cutting brass alloy according to any one of claims 1-3, comprising the following process flow: batching and smelting → continuous casting → stretching → peeling and straightening, wherein the continuous casting adopts an online quenching and solution treatment process, and is cooled by a water bath, the casting temperature is 1080~1120℃, the temperature difference between the inlet and outlet of the primary cooling water is 30~38℃, the ingot exiting the crystallizer temperature is 580~620℃, and the temperature of the copper rod after water cooling is 12~25℃.

5. The preparation method according to claim 4, characterized in that, The water tank includes a cooling chamber and a diversion chamber composed of flow grids. The water flow direction in the water tank is opposite to the traction direction of the copper rod. The copper rod is pulled out from the crystallization port and enters the cooling chamber.

6. The preparation method according to claim 4, characterized in that, In the batching and smelting process, brass alloy raw materials and refining agents are added together to an industrial frequency induction furnace for smelting. The refining agent includes at least one of boron powder, iron powder, or sodium carbonate. The amount of refining agent added is 0.01-0.04% of the mass of the brass alloy melt.

7. The preparation method according to claim 6, characterized in that, The refining agent is a mixture of boron powder, iron powder and sodium carbonate, wherein the mass fraction of boron powder is 20-50 wt%, the mass fraction of iron powder is 5-20 wt%, and the mass fraction of sodium carbonate is 30-70 wt%.

8. The application of the environmentally friendly free-machining brass alloy according to any one of claims 1-3 as a raw material in the production of components for household appliances, communication equipment, testing and control instruments, and the plumbing industry.

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