Lead brass for thin-walled parts and preparation method thereof

Abstract

The present invention discloses a lead brass for thin-walled components, comprising the following components by weight: Cu: 57.0-59wt%, Fe: 0.1-0.3wt%, Al≤0.05wt%, Ni≤0.3wt%, Sn≤0.3wt%, Pb: 2.5-3.0wt%, impurities <0.2wt%, and the balance Zn. The lead brass for thin-walled components has a microstructure comprising an α phase, a β phase, and Pb particles, wherein the average size of the α phase is 20-30μm, the average size of the β phase is ≤15μm, and the β phase is divided into isolated particles by the α phase. The thin-walled components obtained using the lead brass for thin-walled components exhibit less cracking and better mechanical properties. The present invention also discloses a method for preparing the lead brass for thin-walled components.

Description

Technical Field

[0001] The invention belongs to the technical field of brass, and in particular relates to lead brass for thin-walled parts and a preparation method thereof. Background Art

[0002] Brass is primarily composed of Cu and Zn, often containing small amounts of alloying elements. To improve its properties, brass is often infused with lead (typically 1-3% by weight) to achieve the mechanical properties required by industry. As a result, it has become an important industrial material, widely used in pipes, faucets, metal fittings for water supply / drainage systems, and valves.

[0003] Lead brass is an extremely important and widely used complex brass, offering excellent machinability and wear resistance. Lead brass typically contains less than 3% lead, often with small amounts of iron, nickel, or tin added. The lead exists in a free state within the structure, fragmenting the matrix and imparting excellent machinability and anti-friction properties to lead brass.

[0004] CW614N (CuZn39Pb3) is a free-cutting lead brass with good machinability, high strength, and ease of welding, thread rolling, and knurling, making it suitable for high-speed machining operations. The finely dispersed lead particles in the microstructure act as a lubricant and chip breaker, making the alloy easy to machine. It also offers excellent corrosion resistance, welding, brazing, and corrosion resistance. This makes it an ideal choice for many brass components used in industry, such as nuts, bolts, valves and fittings, and pneumatic and hydraulic screws. The component processing and assembly process involves: CW614N brass rod → cutting → drilling → tapping → turning → low-temperature annealing → assembly. However, during assembly of some thin-walled components, cracking is common in areas with wall thicknesses below 2 mm.

[0005] DIN EN 12164-2016 specifies the chemical composition of CW614N as follows: Cu: 57.0-59.0wt%, Al ≤ 0.05wt%, Fe ≤ 0.3wt%, Ni ≤ 0.3wt%, Sn ≤ 0.3wt%, Pb: 2.5-3.5wt%, the balance being Zn, and impurities < 0.2wt%. Mechanical property requirements for the bar are: tensile strength Rm ≥ 430 MPa, yield strength Rp0.2 ≥ 250 MPa, elongation at break A ≥ 10%, and hardness HV5 ≥ 120.

[0006] Within the required range of alloy chemical composition and mechanical properties, cracking in thin-walled areas can be avoided by increasing the Cu content, reducing the Pb content, reducing the content of other elements, and increasing the elongation at break. However, these measures will cause the material composition to exceed the range of DIN EN 12164-2016, and the material's cutting performance will deteriorate, and the strength and hardness will not meet the standards. In addition, since copper is a precious metal, the increase in Cu content and the increase in raw material purity will also lead to a significant increase in raw material costs, making the product lose market competitiveness.

[0007] Therefore, in order to solve the above problems, the existing CW614N lead brass needs to be improved so that the chemical composition of the alloy is within the range specified by DIN EN 12164-2016 and the problem of cracking of thin-walled parts processed from bars during assembly can be solved. Summary of the Invention

[0008] The invention provides a lead brass for thin-walled parts. The thin-walled parts obtained by using the lead brass for thin-walled parts have less cracking and better mechanical properties.

[0009] The present invention provides a lead brass for thin-walled parts, the components of which are as follows by weight: Cu: 57.0-59.0wt%, Fe: 0.1-0.3wt%, Al≤0.05wt%, Ni≤0.3wt%, Sn≤0.3wt%, Pb: 2.5-3.0wt%, impurities <0.2wt%, and the balance is Zn;

[0010] The structure of the lead brass for thin-walled parts includes α phase, β phase and Pb particles. The average size of the α phase is 20-30 μm, the average size of the β phase is ≤15 μm, and the β phase is divided into isolated particles by the α phase.

[0011] The α phase provided by the present invention is a solid solution of Zn in Cu, has a face-centered cubic lattice, and has good plasticity. In two-phase brass, the higher the α phase ratio, the better the plasticity and toughness of the brass, and the less likely it is to undergo brittle cracking. However, if the α phase ratio is too high, cold deformation with a high processing rate is required to obtain the required strength and hardness of the material, which in turn causes the material to become hard and brittle. Therefore, in the lead brass structure of the present invention, the area ratio of the α phase needs to be controlled at 55-70%, and the average size of the α phase needs to be controlled at 20-30 μm. This is because the smaller the average size of the α phase, the greater the amount of α phase per unit volume, and plastic deformation occurs inside the grains, so the plasticity and toughness of the α phase are also high.

[0012] The β phase provided by the present invention is a solid solution based on the electronic compound CuZn, has a body-centered cubic lattice, and has good high-temperature plasticity. However, it exists in the form of a β phase at room temperature. At this time, the β phase is hard and brittle. Its morphology and size affect the degree of its influence on the room-temperature brittleness of the alloy. Cracking is the result of crack source expansion. The crack expands along the β phase channel. When the β phase is divided by the α phase and distributed in a discontinuous granular form, the crack encounters the soft α phase during the expansion process, and the energy is absorbed, and the crack stops expanding. When the average size of the β phase is controlled to be ≤15μm, the area proportion of the α phase needs to be controlled to be 55-70%, and the average size of the α phase needs to be controlled to be 20-30μm, the more thoroughly the β phase is divided by the α phase, the better the effect of preventing crack expansion.

[0013] Among the Al, Ni, and Sn provided by the present invention, the zinc equivalent coefficient of Al is +6, the Zn equivalent coefficient of Sn is +4, and the Zn equivalent coefficient of Ni is -1.5. Al and Sn can reduce the α phase ratio of brass structure, while Ni can increase the α phase ratio of brass structure. The influence of Al content on the α phase ratio is about 4 times that of Ni, and the influence of Sn content on the α phase ratio is about 1.6 times that of Ni. Therefore, when (Al+Sn) is less than 0.02wt%, the negative effects of Al and Sn can be ignored. When (Al+Sn) is greater than or equal to 0.02wt%, the mass ratio of Ni to (Al+Sn) is: m Ni :m Al+Sn ≥5.6. Controlling the content of harmful elements such as Al and Sn at a low level will inevitably increase the purity of raw materials, resulting in an increase in raw material costs.

[0014] The Cu content provided by the present invention has a significant impact on the plasticity and toughness of the alloy. This is because the proportion of the α phase in the two-phase brass is positively correlated with the Cu content. The higher the Cu content, the higher the α phase proportion. When the Cu content is lower than 57.0wt%, by controlling the content of other elements and adjusting the processing technology of the alloy, it is impossible to obtain a metallographic structure in which the area proportion of the α phase is ≥55%. When the Cu content exceeds 58.5wt%, the area proportion of the α phase can reach more than 65%, and there is no need to regulate the size of the α phase, the morphology and size of the β phase, and the thin-walled parts processed by the alloy will not crack during assembly. Therefore, in the lead brass of the present invention, the Cu content is controlled in the range of 57.0-59.0wt%.

[0015] The lead brass for thin-walled parts provided by the present invention is a Cu-Zn binary alloy. In order to improve the cutting performance, a certain amount of Pb is added. The cutting performance of lead brass is related to the mass fraction of Pb. The higher the mass fraction of Pb, the better the cutting performance. However, simply increasing the Pb content will increase the cold brittleness of brass, causing parts to crack easily when assembled under stress. The cutting performance of lead brass is also related to the size of Pb particles and the number of Pb particles distributed in the structure. Therefore, the Pb content of the brass alloy of the present invention should be controlled according to the lower limit of the standard, that is, Pb: 2.5-3.0wt%. The problem of reduced cutting performance caused by the reduction of Pb content is compensated by optimizing the Pb distribution index. The finer the Pb particle size, the greater the number, and the more diffuse the distribution in the brass structure. The Pb particle size in the lead brass provided by the present invention is ≤2μm, and the number of Pb distribution per unit area is not less than 16000pcs / mm. 2 .

[0016] The Fe provided by the present invention has very low solubility in the lead brass for thin-walled components, primarily existing as hard particles, which act as nuclei. An appropriate amount of Fe is beneficial in brass, controlling the grain size. When the Fe content in the brass of the present invention is below 0.1 wt%, the effect on grain size is minimal. Within the DIN EN 12164-2016 standard, the Fe content in the brass of the present invention is controlled within the range of 0.1-0.3 wt%.

[0017] Furthermore, the lead brass for thin-walled components provided by the present invention has a tensile strength (Rm) of 440-490 MPa, a yield strength (Rp0.2) of 260-310 MPa, an elongation (A) of 12-20%, and a Vickers hardness (HV5) of 120-145. Elongation and hardness reflect the plasticity of a material; lower hardness and higher elongation indicate better plasticity. However, as a load-bearing component, it is important to maintain high strength and hardness to prevent deformation under assembly stress.

[0018] The present invention also provides a method for preparing lead brass for thin-walled parts, comprising:

[0019] (1) mixing, smelting and continuously casting the lead brass for thin-walled parts according to the mass percentage of each component to obtain an ingot;

[0020] (2) Extruding the ingot obtained in step (1), the billet obtained after extrusion is kept at 420-540°C for 15-30 minutes and then cooled to obtain an extruded billet, wherein the extrusion process is as follows: the extrusion temperature is 540-600°C, and the extrusion speed is 8-14 mm / s:

[0021] (3) The extruded billet obtained in step (2) is subjected to drawing, low-temperature annealing and fine straightening to obtain lead brass for thin-walled parts.

[0022] The present invention adopts a low-temperature rapid extrusion process for the ingot. Under the control of appropriate extrusion temperature and extrusion speed, the dynamic recrystallization temperature of the ingot during extrusion deformation is reduced to obtain a blocky α phase with an average size of 10-20 μm. The extruded billet flows out of the die hole into the take-up groove. When entering the take-up reel, the surface temperature of the extruded billet is detected and controlled at 420-540°C. The cooling fans of the first 4-8 take-up reels are turned off, and the cooling fans of the 5th-15th take-up reels are turned on. The fan flow rate is 6-18m 3 / h, so that the extruded billet is kept in the range of 420-540℃ for 15-30min, with the purpose of promoting the proper growth of 10-20μm α phase to form an interconnected organizational morphology with an average size increased to 20-30μm and β phase divided by α phase to form isolated granular distribution. After the extruded billet is kept in the temperature of 420-540℃ for a short time, it is strongly cooled to below 300℃. Combined with the hard points formed by the appropriate Fe content, the growth of β phase is prevented, and the average size of β phase is controlled to be no more than 15μm. Rapid extrusion can avoid the situation where low-temperature extrusion cannot be extruded.

[0023] The extruded billet provided by the present invention does not undergo intermediate stretching annealing and directly enters the finished product stretching process. The purpose is twofold: first, to avoid the influence of intermediate stretching annealing on the Pb particle size and the distribution number of Pb, and to obtain a Pb particle size of ≤2μm and a Pb distribution number of >16000pcs / mm 2 The first is to improve the Pb distribution characteristics, because after long-term annealing at a high temperature, the Pb particles will aggregate and grow, and the amount of Pb distribution will decrease; the second is to retain the organizational morphology obtained in the extrusion process to the finished product.

[0024] Furthermore, in step (1), the mixed material is smelted, and after all the metals are melted, molten copper is obtained, and the molten copper is kept warm at a converter temperature of 1050-1090° C. The converter temperature is the temperature at which the molten copper is transferred to the holding furnace, and is generally higher than the holding temperature of the molten copper in the holding furnace.

[0025] Furthermore, in step (1), the molten copper obtained by smelting is continuously cast, and the continuous casting process is as follows: ingot specification: Φ140-260mm, casting temperature: 990-1050℃, traction stroke: 3-15mm, traction speed: 5-20mm / s, traction pause time: 0.1-0.6s, reverse thrust stroke: 0.5-5mm, reverse thrust speed: 1-5mm / s, reverse thrust pause time: 1-8s, ingot sawing length 400-1000mm.

[0026] Furthermore, the extrusion process is as follows: the extrusion temperature is 540-600° C., and then extrusion is performed on a 1250-3150T extruder, the extrusion flow number is 1-2, the extrusion ratio is 100-200, and the extrusion speed is 8-14 mm / s.

[0027] Furthermore, in step (2), the cooling process is: cooling to below 300° C. within 5-15 minutes.

[0028] Furthermore, in step (3), the drawing processing rate is controlled at 8-15%.

[0029] Furthermore, in step (3), the low-temperature annealing process is as follows: the low-temperature annealing temperature is 240-300°C, the time from room temperature to annealing temperature is 30-60 minutes, the holding time is 180-360 minutes, and the temperature is cooled to 50-70°C and the time taken out of the furnace is 90-180 minutes. The alloy of the present invention is subjected to stress relief annealing after being stretched to the finished product specifications in order to eliminate the residual stress generated during the copper rod processing process and to prevent this residual stress from being superimposed on the residual stress generated during the part turning process and the assembly stress generated during the part assembly process, thereby causing stress cracking.

[0030] Furthermore, in order to avoid surface oxidation of the finished wire, the annealing atmosphere is a reducing atmosphere, and the reducing atmosphere is composed of N2 and H2, wherein the volume ratio of N2 to H2 is 3:1.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention adds appropriate amounts of Cu, Al, Ni and Sn so that the α phase occupies a larger area ratio in the structure, so that the smaller β phase can be divided into isolated particles by the α phase. The β phase is a hard and brittle phase, and the cracks of thin walls expand along the β phase channel. When the β phase is divided by the α phase and distributed in discontinuous particles, the crack encounters the soft α phase during the crack expansion process, and the energy is absorbed, so the crack stops expanding. When the average size of the β phase is controlled to be ≤15 μm, the more thoroughly the β phase is divided by the α phase, the better the effect of preventing crack expansion.

[0033] In the preparation method provided by the present invention, by controlling the extrusion temperature and extrusion speed, a larger block-shaped α phase can be obtained. By providing a suitable holding temperature and time, the interconnection of the α phase is promoted, thereby further increasing the size of the α phase. After a short holding time, strong cooling prevents the growth of the β phase, controls the average size of the β phase, and thus forms a microstructure in which the β phase is divided by the α phase and distributed in an isolated granular manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a metallographic photograph of the lead brass for thin-walled parts prepared in Example 1 of the present invention (magnified 200 times);

[0035] Figure 2 This is a metallographic photograph of the lead brass for thin-walled parts prepared in Comparative Example 1 of the present invention (magnified 200 times). DETAILED DESCRIPTION

[0036] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0037] The present invention provides 4 embodiments and 2 comparative examples, and the specific compositions are shown in Table 1.

[0038] Example 1

[0039] A lead brass hexagonal bar for thin-walled parts, with a specification of S19mm, is prepared as follows:

[0040] 1) Melting: According to the required composition, the materials are smelted in an electromagnetic induction melting furnace. After all the metals are melted and the components are tested and qualified, the copper liquid is discharged into an electromagnetic induction holding furnace for insulation. The converter temperature is: 1060-1080℃.

[0041] 2) Continuous casting: ingot specification Φ254mm, casting temperature 1000-1020℃, traction stroke 8mm, traction speed 8mm / s, traction pause time: 0.3s, reverse thrust stroke: 2mm, reverse thrust speed: 3mm / s, reverse thrust pause time: 5s, ingot sawing length 1000mm.

[0042] 3) Extrusion: The ingot is heated to 590°C in a heating furnace and then extruded on a 3150T extruder. The extrusion specification is S21mm, the extrusion flow number is 1, the extrusion ratio is 176.8, and the extrusion speed is 10.5mm / s. The extruded billet flows out of the die hole into the take-up trough. When entering the take-up reel, the surface temperature of the extruded billet is detected and controlled at 470-510°C. The cooling fans of the first five take-up reels are turned off, and the cooling fans of the 6th to 12th take-up reels are turned on. The fan flow rate is 10m 3 / h, so that the extruded billet is kept in the range of 470-510℃ for 20min.

[0043] 4) Drawing: After the S21mm extruded blank is pickled to remove the oxide scale, it is continuously stripped to S19.6mm on the drawing machine and then extended to S19mm. The processing rate is controlled at 9.4%.

[0044] 5) Low temperature annealing: annealing temperature: 270℃, time from room temperature to annealing temperature: 30min, holding time: 270min, cooling to 60℃ and taking out of the furnace: 100min, annealing atmosphere is reducing atmosphere, and the reducing atmosphere composition is: V N2 =25%, V H2 =75%.

[0045] 6) Fine straightening: Straighten on a special straightening machine for hexagonal bars. After straightening, the straightness of the copper bar reaches 0.4mm / m.

[0046] 7) Finished product inspection, packaging, and storage. Lead brass for thin-walled parts is obtained, and the microstructure is as follows Figure 1 As shown: the α phase accounts for 61.5% of the area, the average size of the α phase is 24.7 μm, the size of the β phase is 7.8 μm, and the α phase divides the β phase into isolated particles.

[0047] Example 2

[0048] A lead brass round bar for thin-walled parts, with a specification of Φ15mm, is prepared as follows:

[0049] 1) Melting: According to the required composition, the materials are smelted in an electromagnetic induction melting furnace. After all the metals are melted and the components are tested and qualified, the copper liquid is discharged into an electromagnetic induction holding furnace for insulation. The converter temperature is: 1060-1080℃.

[0050] 2) Continuous casting: ingot specification Φ195mm, casting temperature 1010-1025℃, traction stroke 9mm, traction speed 10mm / s, traction pause time: 0.2s, reverse thrust stroke: 3mm, reverse thrust speed: 2mm / s, reverse thrust pause time: 4s, ingot sawing length 800mm.

[0051] 3) Extrusion: The ingot is heated to 570°C in a heating furnace and then extruded on a 2200T extruder. The extrusion specification is Φ15.8mm, the extrusion flow number is 1, the extrusion ratio is 158.3, and the extrusion speed is 12mm / s. The extruded billet flows out of the die hole into the take-up trough. When entering the take-up reel, the surface temperature of the extruded billet is detected and controlled at 500-540°C. The cooling fans of the first four take-up reels are turned off, and the cooling fans of the 5th to 10th take-up reels are turned on. The fan flow rate is 12m 3 / h, so that the extruded billet is kept in the range of 500-540℃ for 15min.

[0052] 4) Drawing: After pickling and removing the oxide scale, the Φ15.8mm extruded blank is stretched to Φ15mm on a drawing machine, and the processing rate is controlled at 9.9%.

[0053] 5) Low temperature annealing: annealing temperature: 280℃, time from room temperature to annealing temperature: 30min, holding time: 240min, cooling to 60℃ and taking out of the furnace: 90min, annealing atmosphere is reducing atmosphere, and the reducing atmosphere composition is: V N2 =25%, V H2 =75%.

[0054] 6) Fine straightening: Straighten on a two-roller precision straightening machine. After straightening, the straightness of the copper rod reaches 0.32mm / m.

[0055] 7) Finished product inspection, packaging and warehousing.

[0056] Example 3

[0057] A lead brass round bar for thin-walled parts, with a specification of Φ9mm, is prepared as follows:

[0058] 1) Melting: According to the required composition, the materials are smelted in an electromagnetic induction melting furnace. After all the metals are melted and the components are tested and qualified, the copper liquid is discharged into an electromagnetic induction holding furnace for insulation. The converter temperature is: 1050-1080℃.

[0059] 2) Continuous casting: ingot specification Φ175mm, casting temperature 1020-1040℃, traction stroke 12mm, traction speed 10mm / s, traction pause time: 0.25s, reverse thrust stroke: 4mm, reverse thrust speed: 2mm / s, reverse thrust pause time: 2s, ingot sawing length 600mm.

[0060] 3) Extrusion: The ingot is heated to 550°C in a heating furnace and then extruded on an 1800T extruder. The extrusion specification is Φ9.7mm, the extrusion flow number is 2, the extrusion ratio is 162.7, and the extrusion speed is 12mm / s. The extruded billet flows out of the die hole into the take-up trough. When entering the take-up reel, the surface temperature of the extruded billet is detected and controlled at 430-480°C. The cooling fans of the first four take-up reels are turned off, and the cooling fans of the 5th to 8th take-up reels are turned on. The fan flow rate is 8m 3 / h, so that the extruded billet is kept in the range of 430-480℃ for 15min.

[0061] 4) Drawing: After pickling and removing the oxide scale, the Φ9.7mm extruded blank is stretched to Φ9mm on a drawing machine, and the processing rate is controlled at 13.9%.

[0062] 5) Low temperature annealing: annealing temperature: 240℃, time from room temperature to annealing temperature: 30min, holding time: 330min, cooling to 60℃ and taking out of the furnace for 60min, annealing atmosphere is reducing atmosphere, and the reducing atmosphere composition is: V N2 =25%, V H2 =75%.

[0063] 6) Fine straightening: Straighten on a two-roller precision straightening machine. After straightening, the straightness of the copper rod reaches 0.1mm / m.

[0064] 7) Finished product inspection, packaging and warehousing.

[0065] Example 4

[0066] A lead brass hexagonal bar for thin-walled parts, with a specification of S8mm, is prepared as follows:

[0067] 1) Melting: According to the required composition, the materials are smelted in an electromagnetic induction melting furnace. After all the metals are melted and the components are tested and qualified, the copper liquid is discharged into an electromagnetic induction holding furnace for insulation. The converter temperature is: 1060-1080℃.

[0068] 2) Continuous casting: ingot specification Φ160mm, casting temperature 1020-1050℃, traction stroke 12mm, traction speed 10mm / s, traction pause time: 0.4s, reverse thrust stroke: 2mm, reverse thrust speed: 3mm / s, reverse thrust pause time: 2s, ingot sawing length 550mm.

[0069] 3) Extrusion: The ingot is heated to 580°C in a heating furnace and then extruded on a 1250T extruder. The extrusion specification is S9mm, the extrusion flow number is 1, the extrusion ratio is 121.7, and the extrusion speed is 12.5mm / s. The extruded billet flows out of the die hole into the take-up trough. When entering the take-up reel, the surface temperature of the extruded billet is detected and controlled at 490-530°C. The cooling fans of the first 7 take-up reels are turned off, and the cooling fans of the 8th to 14th take-up reels are turned on. The fan flow rate is 9m 3 / h, so that the extruded billet is kept in the range of 490-530℃ for 20min.

[0070] 4) Drawing: After the S9mm extruded blank is pickled to remove the oxide scale, it is continuously stripped to S8.6mm on the drawing machine and then extended to S8mm. The processing rate is controlled at 13.5%.

[0071] 5) Low temperature annealing: annealing temperature: 300℃, time from room temperature to annealing temperature: 45min, holding time: 180min, cooling to 60℃ and taking out of the furnace for 60min, annealing atmosphere is reducing atmosphere, and the reducing atmosphere composition is: V N2 =25%, V H2 =75%.

[0072] 6) Fine straightening: Straighten on a special straightening machine for hexagonal bars. After straightening, the straightness of the copper bar reaches 0.15mm / m.

[0073] 7) Finished product inspection, packaging and warehousing.

[0074] Comparative Example 1

[0075] The commercially available CW614N S19 hexagonal copper rod was selected, and the microstructure was as follows Figure 2 As shown: the α phase accounts for 51.3% of the area, the average size of the α phase is 41.6μm, the size of the β phase is 18.8μm, the α phase and β phase are coarse, and the β phases are connected to each other.

[0076] Comparative Example 2

[0077] A CW614N S19 hexagonal copper rod with a specification of S19mm is prepared as follows:

[0078] 1) Melting: According to the required composition, the materials are smelted in an electromagnetic induction melting furnace. After all the metals are melted and the components are tested and qualified, the copper liquid is discharged into an electromagnetic induction holding furnace for insulation. The converter temperature is: 1060-1080℃.

[0079] 2) Continuous casting: ingot specification Φ254mm, casting temperature 1000-1020℃, traction stroke 8mm, traction speed 8mm / s, traction pause time: 0.3s, reverse thrust stroke: 2mm, reverse thrust speed: 3mm / s, reverse thrust pause time: 5s, ingot sawing length 1000mm.

[0080] 3) Extrusion: The ingot was heated to a temperature of 710°C in a heating furnace and then extruded on a 3150T extruder with an extrusion specification of S21mm, an extrusion flow number of 1, an extrusion ratio of 56.3, and an extrusion speed of 6mm / s.

[0081] 4) Drawing: After the S21mm extruded blank is pickled to remove the oxide scale, it is extended to S20 on the drawing machine.

[0082] 5) Annealing: The S20 billet is annealed in an annealing furnace at 510°C, with a heating time of 60 min from room temperature to the annealing temperature and a holding time of 240 min.

[0083] 6) Drawing: After the S20mm blank is pickled to remove the oxide scale, it is extended to S20 on the drawing machine.

[0084] 7) Annealing: The S20 billet is annealed in an annealing furnace at a temperature of 510° C., a heating time from room temperature to the annealing temperature of 60 min, and a holding time of 240 min.

[0085] 8) Drawing: After the S20mm blank is pickled to remove the oxide scale, it is extended to S19.4 on the drawing machine.

[0086] 7) Bottom annealing: S19.4 billet is annealed in an annealing furnace, annealing temperature: 490 ° C, time from room temperature to annealing temperature: 60 minutes, holding time: 180 minutes.

[0087] 8) Finished product drawing: After pickling and removing the oxide scale, the S19.4mm blank is stretched to the finished product specification S19 on the drawing machine, with a processing rate of 6%.

[0088] 9) Fine straightening: Straighten on a special straightening machine for hexagonal bars. After straightening, the straightness of the copper bar reaches 0.4mm / m.

[0089] 10) Inspection, packaging and warehousing of finished products.

[0090] The following tests were performed on the microstructures of the obtained embodiments and comparative examples, and the results are recorded in Table 2.

[0091] The area ratio, size and morphology of the phases in the microstructure as well as the size and distribution number of Pb particles were observed under a microscope.

[0092] The following performance tests were performed on the four embodiments and two comparative examples, and the results are recorded in Table 3.

[0093] Tensile strength, yield strength Rp0.2 and elongation at break: tested in accordance with GB / T228.1-2021 "Tensile tests on metallic materials - Part 1: Room temperature test methods".

[0094] Hardness HV5: Tested according to GB / T4340.1-2009 "Vickers hardness test for metallic materials - Part 1: Test method".

[0095] The rods prepared in the four embodiments and two comparative examples were processed into parts and then tested on a machine. The test results are recorded in Table 4.

[0096] Table 1 Chemical composition of the present invention and comparative examples (wt%)

[0097]

[0098] Table 2 Microstructure of the Examples of the Invention and the Comparative Examples

[0099]

[0100]

[0101] Table 3 Mechanical properties of the embodiments of the present invention and the comparative examples

[0102]

[0103] Table 4 Assembly results of parts processed in the embodiments of the present invention and the comparative examples

[0104]

[0105] Table 1: The Fe content of Comparative Example 1 is only 0.075wt%, which is lower than the lower limit of 0.1wt% of the present invention. The Ni content is only 0.047wt%. Since the Sn content reaches 0.16wt%, the m Ni :m Al+Sn The ratio is very low, only 0.29; the ingredients of Comparative Example 2 are consistent with those of Example 1, and the purpose is to compare the influence of the process.

[0106] Table 2: The area ratio of the α phase, the average size of the α phase, the average size of the β phase, the average size of the Pb particles, and the number of Pb distribution in the examples meet the control requirements of the present invention; while Comparative Examples 1 and 2 do not meet the control requirements of the present invention, namely: the area ratio of the α phase is 55-70%, the average size of the α phase is 20-30 μm, the average size of the β phase is ≤15 μm, the Pb particle size is ≤2 μm, and the number of Pb distribution is not less than 16,000 pcs / mm 2 .

[0107] Table 3: The mechanical properties of the comparative example and the embodiment all meet the requirements, namely: tensile strength Rm≥430Mpa, yield strength Rp0.2≥250Mpa, elongation at break A≥10%, and hardness HV5≥120.

[0108] Table 4: When assembling parts made of rods in the example, cracks appeared in the thin-walled parts, while cracks appeared in the comparative example.

[0109] The data in Tables 1-4 show that when the mechanical properties of the material meet the requirements, the problem of cracking in thin-walled parts during component assembly cannot be solved without special regulation of the Ni, Sn, and Al content in the chemical composition, the area ratio of the α phase in the microstructure, the average size of the α phase, the average size of the β phase, the average size of the Pb particles, and the amount of Pb distribution.

Claims

1. A lead brass for thin-walled parts, characterized in that: The composition by mass percentage is Cu: 57.0-59.0wt%, Fe: 0.1-0.3wt%, Al≤0.05wt%, Ni≤0.3wt%, Sn≤0.3wt%, Pb: 2.5-3.0wt%, impurities <0.2wt%, and the balance is Zn; The structure of the lead brass for thin-walled parts includes α phase, β phase and Pb particles, the average size of the α phase is 20-30 μm, the average size of the β phase is ≤15 μm, and the β phase is divided into isolated particles by the α phase; When Al+Sn≥0.02wt%, the mass ratio of Ni to Al+Sn is m Ni :m Al+Sn ≥5.

6.

2. The lead brass for thin-walled parts according to claim 1, characterized in that: The area proportion of the α phase is 55-70%.

3. The lead brass for thin-walled parts according to claim 1, characterized in that: The Pb particle size is ≤2μm, and the Pb distribution quantity is not less than 16000pcs / mm 2 .

4. A method for preparing lead brass for thin-walled parts according to any one of claims 1 to 3, characterized in that: include: (1) Mixing, smelting and continuously casting the lead brass for thin-walled parts according to the mass percentage of each component as described in any one of claims 1 to 3 to obtain an ingot; (2) Extruding the ingot obtained in step (1), the billet obtained after extrusion is kept at 420-540°C for 15-30 minutes and then cooled to obtain an extruded billet, wherein the extrusion process is as follows: the extrusion temperature is 540-600°C, and the extrusion speed is 8-14 mm / s: (3) The extruded billet obtained in step (2) is subjected to drawing, low-temperature annealing and fine straightening to obtain lead brass for thin-walled parts.

5. The method for preparing lead brass for thin-walled parts according to claim 4, characterized in that: In step (1), the molten copper obtained by smelting is continuously cast, and the continuous casting process is as follows: the casting temperature is 990-1050°C, the traction stroke is 3-15mm, the traction speed is 5-20mm / s, the traction pause time is 0.1-0.6s, the reverse thrust stroke is 0.5-5mm, the reverse thrust speed is 1-5mm / s, and the reverse thrust pause time is 1-8s.

6. The method for preparing lead brass for thin-walled parts according to claim 4, characterized in that: The extrusion process is as follows: extrusion temperature is 540-600° C., then extrusion is performed on a 1250-3150T extruder, the extrusion flow number is 1-2, the extrusion ratio is 100-200, and the extrusion speed is 8-14 mm / s.

7. The method for preparing lead brass for thin-walled parts according to claim 4, characterized in that: In step (2), the cooling process is: cooling to below 300° C. within 5-15 minutes.

8. The method for preparing lead brass for thin-walled parts according to claim 4, characterized in that: In step (3), the drawing processing rate is controlled at 8-15%.

9. The method for preparing lead brass for thin-walled parts according to claim 4, characterized in that: In step (3), the low-temperature annealing process is as follows: the low-temperature annealing temperature is 240-300°C, the time from room temperature to annealing temperature is 30-60 minutes, the heat preservation time is 180-360 minutes, and the temperature is cooled to 50-70°C and taken out of the oven for 90-180 minutes.

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