Lead-free environment-friendly free-cutting zinc white copper and preparation method and application thereof

Abstract

The application discloses a lead-free environment-friendly easy-to-cut zinc white copper, and each component content of the zinc white copper includes Cu: 42-46 wt%, Ni: 12-16 wt%, Mn: 4-6 wt%, Sb: 1.0-2.2 wt%, Fe: 0.01-0.2 wt%, Sn: 0.1-0.5 wt%, and the rest is Zn and inevitable impurities; the structure of the lead-free environment-friendly easy-to-cut zinc white copper includes Mn2Sb phase, the average distribution density of the Mn2Sb phase is greater than or equal to 4000 / mm 2 , and the average distribution density of the Mn2Sb phase with a particle size greater than or equal to 5 mu m is less than or equal to 200 / mm 2 . The zinc white copper has excellent cutting performance, good cold and hot working performance and corrosion resistance under the premise of not using traditional easy-to-cut elements such as Pb, Bi, Si, P and the like, through the synergistic effect of Sb and Mn, Fe and Sn. The application further discloses a preparation method and application of the zinc white copper.

Description

Technical Field

[0001] This invention relates to a copper alloy material and its preparation method, specifically to a lead-free, environmentally friendly, free-cutting zinc-copper alloy, its preparation method, and its applications. Background Technology

[0002] Zinc-Ni-Zn cupronickel (Cu-Ni-Zn alloy) is widely used in eyeglass parts, pen manufacturing (e.g., pen tips), instruments, medical devices, zippers, keys, and the optics and watchmaking industries due to its silvery-white color, good corrosion resistance, moderate strength, and excellent machinability. However, traditional free-machining zinc-Ni-Zn alloys commonly incorporate lead to improve machinability. Lead is almost insoluble in the copper matrix, distributed as dispersed particles at grain boundaries and within grains. During cutting, it softens or melts due to frictional heat from the cutting tool, creating a "cutting effect" that helps break chips. However, lead-containing parts cause serious environmental pollution and harm human health during production and use. The United States and the European Union have successively introduced relevant laws and regulations to strictly control the lead content in parts, with the RoHS directive requiring a lead content of no more than 0.1 wt%. Therefore, developing lead-free, environmentally friendly free-machining zinc-Ni-Zn alloys has become an urgent industry need.

[0003] In recent years, research on lead-free free-machining zinc-copper alloys has made some progress both domestically and internationally. Existing technologies mainly improve machinability by adding elements such as Bi, Si, P, Sn, and Mg. For example, patent application CN101787463A discloses an environmentally friendly lead-free free-machining zinc-copper alloy with the following composition: Zn 27.0-44.0 wt%, Ni 6.0-25.0 wt%, Si 0.05-2.5 wt%, Ce 0.03-0.1 wt%, P 0.03-1.5 wt%, and the balance Cu. By adding silicon, phosphorus, and cerium to replace lead and bismuth, the machinability reaches over 70% of that of leaded brass C36000. Patent application CN110952019A discloses a free-machining zinc-copper alloy with the following composition: Cu 42.5-47.5 wt%, Ni 8.0-12.0 wt%, Mn 4.0-8.0 wt%, Bi 0.05-1.5 wt%, and the balance being Zn. The alloy utilizes the β phase to enhance its strength while improving its machinability, enabling it to achieve machinability similar to lead-zinc-copper alloys at a relatively low Bi content.

[0004] However, the aforementioned existing technologies still have the following problems: While adding Bi can improve machinability, the alloy products are prone to natural cracking after bismuth is added, and Bi is expensive, making it less competitive in the market; the content range of elements such as Si and P is wide, and the performance stability under different compositions needs further optimization, and excessive silicon content will reduce cold working performance; although adding elements such as Sn and Mg can help improve machinability, excessive addition will affect the cold and hot working performance of the alloy. More importantly, the existing methods of improving machinability by adding foreign elements to form brittle phases are often accompanied by problems such as increased raw material costs, difficulty in process control, and decreased alloy plasticity.

[0005] Therefore, there is still a lack of lead-free, environmentally friendly, free-machining zinc-copper alloys that do not rely on the addition of traditional cutting elements such as Bi, Si, and P, but instead achieve excellent cutting performance through alloy composition innovation and process control. Summary of the Invention

[0006] This invention provides a lead-free, environmentally friendly, free-machining zinc white copper. Without using traditional free-machining elements such as Pb, Bi, Si, and P, this zinc white copper achieves excellent machinability, good cold and hot working properties, and corrosion resistance through the synergistic effect of Sb with Mn, Fe, and Sn.

[0007] This invention provides a lead-free, environmentally friendly, free-machining zinc-copper alloy, the contents of which are: Cu: 42-46wt%, Ni: 12-16wt%, Mn: 4-6wt%, Sb: 1.0-2.2wt%, Fe: 0.01-0.2wt%, Sn: 0.1-0.5wt%, with the balance being Zn and unavoidable impurities; The microstructure of the lead-free, environmentally friendly, free-machining zinc-copper alloy comprises a Mn2Sb phase, with an average distribution density of ≥4000 phases / mm². 2 Furthermore, the average distribution density of the Mn2Sb phase with a particle size greater than 5 μm is ≤200 particles / mm. 2 .

[0008] The Mn2Sb phase provided by this invention has a melting point of approximately 1235℃, belonging to a high-melting-point phase. It exhibits cohesive distribution and does not weaken grain boundaries. During hot extrusion (650-800℃), the Mn2Sb phase does not melt or coarsen, maintaining a stable brittle phase morphology. The Mn2Sb phase imparts excellent hot working properties to the alloy, significantly improving the yield. The Mn2Sb phase exhibits brittle fracture chip breaking, and its chip breaking effect is insensitive to temperature rise during machining, resulting in more stable cutting performance.

[0009] The Cu provided by this invention is the matrix element of the alloy, and its content directly affects the strength, plasticity, and corrosion resistance of the alloy. When the Cu content is low, the proportion of the plastic α phase in the alloy is too low, the material becomes more brittle, the cold working performance decreases significantly, and cracking is likely to occur. When the Cu content is too high, the proportion of the plastic α phase is too high, making it easy for chips to adhere during machining, and the hot working performance of the alloy deteriorates.

[0010] The synergistic effect of Ni, Mn, and Sn provided by this invention improves the alloy's resistance to dezincification corrosion and stress corrosion cracking, and outperforms traditional lead-zinc cupronickel in salt spray and acid corrosion tests.

[0011] The Ni and Cu provided by this invention are infinitely miscible, providing solid solution strengthening while improving the alloy's corrosion resistance and color stability. However, when the Ni content is too high, the proportion of the α-phase (plastic phase) becomes excessive, reducing the alloy's machinability. Furthermore, Ni is a high-priced element, and excessive Ni content increases costs.

[0012] The Mn content provided by this invention can improve the strength and corrosion resistance of alloys. Simultaneously, an appropriate amount of Mn reacts with Sb to form the high-melting-point brittle compound Mn₂Sb phase, which is dispersed in the matrix and acts as a chip-breaking agent. When the Mn content is too low, the alloy composition lacks sufficient Mn, and Sb reacts with Cu to form the Cu₂Sb phase, resulting in a small amount of Mn₂Sb phase. When the Mn content is too high, the alloy's plasticity deteriorates, its cold working performance decreases, and its corrosion resistance is also affected.

[0013] The Sb provided in this invention is a key environmentally friendly and easily machinable element. An appropriate amount of Sb preferentially forms the Mn2Sb phase with Mn, which is uniformly distributed at grain boundaries and within grains. During machining, this phase becomes a stress concentration source, promoting brittle fracture of the chips. Simultaneously, Sb does not dissolve in the copper matrix, avoiding excessive reduction in plasticity caused by solid solution strengthening. When the Sb content is below 1 wt%, it is insufficient to form the Mn2Sb phase, and the improvement in machinability is not significant; when it is above 2.2 wt%, hot brittleness increases significantly, making hot working prone to cracking.

[0014] Since the Cu2Sb phase is a low-melting-point phase and is distributed along the boundary, it is prone to melting and agglomeration during hot working, leading to hot brittleness and cracking. It can be seen that because the Cu2Sb phase is a softening chip-breaking type (dependent on cutting heat), its effectiveness decreases at low-speed cutting. Therefore, this invention controls the content of Mn and Sb elements, as well as the process parameters of hot extrusion and intermediate annealing in the preparation process, to form a dispersed Mn2Sb phase to replace the Cu2Sb phase, so that the alloy provided by this invention still has high chip-breaking ability at higher temperatures.

[0015] The Fe provided by this invention can refine alloy grains, improve the strength and hardness of the alloy, and enhance its cold and hot working properties. Compounds formed by iron with elements such as nickel and manganese can aid in chip breaking. When the Fe content is below 0.01%, the grain refining effect is not significant; when the Fe content is above 0.2%, a hard phase will form in the alloy, severely wearing down the cutting tool and thus reducing cutting and machining performance. Therefore, the Fe content should be controlled between 0.01% and 0.2%.

[0016] The Sn provided by this invention can improve the strength and hardness of alloys, inhibit dezincification, and enhance corrosion resistance. An appropriate amount of Sn can also stabilize the Mn₂Sb phase, making its distribution more uniform, and also affects the size of the Mn₂Sb phase. When the Sn content is below 0.1%, the effect is not significant; when the Sn content is above 0.5%, it reduces the cold working properties of the alloy and increases costs.

[0017] Pb is a harmful element. The Pb content provided by this invention is less than 0.1% of the total weight of the alloy, which meets the requirements of the RoHS directive.

[0018] Preferably, the mass ratio of Mn to Sb satisfies 3 ≤ M Mn / M Sb ≤6. This invention improves the strength of the alloy by controlling the mass ratio of Mn to Sb, allowing Sb to fully form the Mn2Sb phase with Mn and ensuring a small amount of excess Mn is dissolved in the alloy matrix. Furthermore, it can control the Mn content dissolved in the alloy matrix, maintaining appropriate hardness in the alloy matrix, minimizing tool heating during material cutting, and reducing tool wear.

[0019] Preferably, the average distribution density of the Mn2Sb phase is 4000-12000 phases / mm². 2 Furthermore, the average distribution density of the Mn2Sb phase with a particle size of 5-30 μm is 0-200 particles / mm. 2 .

[0020] Preferably, the average grain size of the lead-free, environmentally friendly, free-machining zinc-copper alloy is 8-20 μm.

[0021] Preferably, the lead-free environmentally friendly free-cutting zinc white copper has a tensile strength Rm≥640MPa, a yield strength Rp0.2≥510MPa, a hardness HV1≥160, and an elongation A≥3%; the relative cutting index reaches 85-100% of that of leaded brass C36000.

[0022] Preferably, the lead-free environmentally friendly free-cutting zinc white copper has the following tensile strength Rm: 640 MPa ≤ Rm ≤ 800 MPa, yield strength 510 MPa ≤ Rp0.2 ≤ 690 MPa, hardness 160 ≤ HV1 ≤ 230, and elongation A ≥ 3%; the relative cutting index reaches more than 85% of that of leaded brass C36000.

[0023] On the other hand, the present invention also provides a method for preparing lead-free, environmentally friendly, free-cutting zinc-copper alloy. The process flow of the preparation method includes: smelting → semi-continuous casting → homogenization treatment → hot extrusion → cold drawing → intermediate annealing → finished product drawing → low-temperature annealing. The raw materials are prepared and smelted according to the content of each component of the lead-free, environmentally friendly, free-cutting zinc-copper alloy described above. The hot extrusion temperature is 720-780℃, the extrusion ratio is 200-400, and the extrusion speed is 2-6mm / s.

[0024] This invention avoids the high-temperature brittleness zone and the low-temperature brittleness zone by controlling the hot extrusion temperature. The extrusion ratio provided by this invention is high, providing huge shear force at the high extrusion ratio, which mechanically breaks up the initial coarse Mn2Sb particles. The extrusion speed provided by this invention is low, which prolongs the deformation time and induces dynamic recrystallization. The broken Mn2Sb particles are pinned by the recrystallization grain boundaries and cannot re-aggregate, thus laying the foundation for obtaining a diffusely distributed Mn2Sb phase of appropriate size.

[0025] This invention achieves the control of the Mn2Sb phase through a combination of two key processes: "medium temperature-low speed-high extrusion ratio" and stepped intermediate annealing. This process first breaks down the Mn2Sb phase and then allows for its controlled precipitation, ultimately resulting in a high-density, finely distributed brittle phase and achieving an excellent balance between machinability, processing performance and mechanical properties.

[0026] Preferably, the intermediate annealing adopts a stepped annealing process, which includes a first-stage annealing and a second-stage annealing. The temperature of the first-stage annealing is 200-350℃, and the temperature of the second-stage annealing is 600-700℃.

[0027] This invention achieves a high-density, finely distributed Mn-Fe-Sn compound by controlling the temperature of the first-stage annealing to preferentially nucleate around Mn2Sb particles; and by controlling the second-stage annealing at a higher temperature to achieve in-situ precipitation of the Mn2Sb phase on these seeds (Mn-Fe-Sn compounds) during high-temperature recrystallization.

[0028] More preferably, the heating rate of the first stage annealing is 5-10℃ / min, and the holding time is 30-120min; the heating rate of the second stage annealing is 5-10℃ / min, and the holding time is 90-300min.

[0029] Preferably, the smelting process is as follows: Electrolytic copper, electrolytic nickel, zinc ingots, electrolytic manganese, antimony ingots, copper-iron master alloy, and tin ingots are weighed according to the component content of the lead-free, environmentally friendly, free-cutting zinc-copper alloy. These raw materials are then smelted in an electric furnace. The order of addition is as follows: first, copper, nickel, and the copper-iron master alloy are added, and the temperature is raised to 1150-1250℃ to melt. Then, the temperature is lowered to 950-1050℃, followed by the addition of zinc, antimony, and tin (zinc and tin are easily burned, and antimony, being low-melting-point and easily volatile, is added last). The entire smelting process is covered with charcoal to prevent the volatilization of zinc and antimony. After testing and adjusting the composition to ensure it meets the requirements, casting is prepared.

[0030] Preferably, before semi-continuous casting, the molten copper is allowed to stand at 1020-1070°C for 10-20 minutes.

[0031] Preferably, the semi-continuous casting process has a casting speed of 30-90 mm / min, a cooling water pressure of 0.2-0.5 MPa, an inlet-outlet water temperature difference of 7-20℃, and adopts a red ingot casting process. The length of the red ingot zone is controlled at 200-500 mm, and the ingot is naturally cooled to below 100℃ and then sawn into the required extrusion length.

[0032] Preferably, in semi-continuous casting, the crystallizer is equipped with an electromagnetic stirring device with a stirring frequency of 5-20 Hz and an stirring intensity of 50-200 A•t. Electromagnetic stirring can refine the as-cast microstructure and reduce component segregation.

[0033] Preferably, the homogenization treatment temperature is 650-750℃, and the holding time is 2-6 hours. This invention eliminates dendrite segregation by controlling the homogenization process.

[0034] Preferably, the cooling process for the homogenization treatment is to cool the furnace to below 100°C before unloading.

[0035] Since the Mn and Sb contents provided by this invention are both high, this invention further achieves full combination of Mn and Sb through the combined effect of three process improvement measures, reducing Sb segregation at grain boundaries and forming a low-melting-point Cu-Sb eutectic liquid phase. Specifically: (1) Strictly control the content and mass ratio of Mn and Sb to ensure that the Mn2Sb phase is preferentially formed in terms of stoichiometry; (2) Apply electromagnetic stirring during the semi-continuous casting process to refine the as-cast structure, promote the uniform distribution of Mn and Sb, and provide good initial conditions for the subsequent homogenization reaction; (3) Hold the ingot at 650-750℃ for 2-6 hours for homogenization treatment, so that the residual free Sb can fully diffuse and combine with Mn, and then slowly cool with the furnace to avoid non-equilibrium segregation caused by rapid cooling; Under the action of the above three conditions, a more diffusely distributed Mn2Sb phase is fully formed in the structure.

[0036] Preferably, the cold drawing is a multi-pass drawing, with a processing rate of 25-50% for each pass, and an intermediate annealing is performed between every two passes at a temperature of 600-700°C. This invention eliminates work hardening and restores the alloy's plasticity by controlling the intermediate annealing temperature.

[0037] More preferably, the holding time for the intermediate annealing is 2-5 hours, and the heating rate is 5-15℃ / min.

[0038] Preferably, the finished product stretching rate is 10-40%. This invention obtains zinc-copper rods or wires with the required mechanical properties and specifications by controlling the finished product stretching rate.

[0039] Preferably, the first straightening is performed before low-temperature annealing. If the finished product is a bar, straightening is required.

[0040] Preferably, the low-temperature annealing temperature is 230-320℃, and the annealing atmosphere is a reducing atmosphere to avoid oxidation of the finished product surface. This invention eliminates residual stress generated during the tensile process of the finished product by controlling the low-temperature annealing temperature.

[0041] More preferably, the time to rise from room temperature to the low-temperature annealing temperature is 30-90 minutes, and the holding time is 180-360 minutes.

[0042] Preferably, a second straightening is performed after low-temperature annealing. Low-temperature annealing will cause changes in the straightness of the bar stock, requiring straightening again.

[0043] On the other hand, the lead-free, environmentally friendly, free-cutting zinc-copper eyeglass accessories provided by this invention are used in the pen manufacturing industry, instrumentation, medical devices, zippers, keys, and the optical and watchmaking industries.

[0044] The zinc-copper alloy provided by this invention has a silvery-white color, good corrosion resistance, moderate strength and hardness, and can be processed into products such as bars, wires, and plates. It is widely used in eyeglass accessories (such as frames), pen manufacturing (such as pen tips), instruments and meters, medical devices, zippers, keys, and the optical and watchmaking industries.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows: The Mn2Sb phase provided by this invention is dispersed in the matrix. An appropriate amount of Mn2Sb phase can enable the alloy provided by this invention to have high hot working performance. Furthermore, this invention limits the distribution density of larger Mn2Sb phases to minimize the impact of large Mn2Sb phases on plasticity and prevent "chipping" during cutting.

[0046] The alloy provided by this invention has a low Pb content, which fully meets the requirements of the RoHS directive. At the same time, it does not add expensive or process-sensitive elements such as Bi, Si, and P, and the production cost is controllable. Attached Figure Description

[0047] Figure 1 This is a photograph of the chip phase distribution of zinc-copper alloy prepared in Example 1 of the present invention.

[0048] Figure 2 Photographs of copper chip morphology collected during the cutting process of zinc white copper obtained in Example 1 of the present invention (turning feed rate was 1 mm). Figure 3 Photographs of copper shavings collected during the cutting process of zinc white copper prepared in Comparative Example 1 of this invention (turning feed rate was 1 mm). Detailed Implementation

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0050] This invention provides four embodiments and five comparative examples, and the specific components are shown in Table 1.

[0051] Example 1: A method for preparing a φ2.3mm lead-free free-cutting zinc-copper wire is as follows: (1) Smelting: Weigh out the raw materials such as electrolytic copper, electrolytic nickel, zinc ingots, electrolytic manganese, antimony ingots, copper-iron master alloy, and tin ingots according to the above weight percentage composition, and smelt them in an electric furnace. The order of adding materials is as follows: first add copper, nickel, and copper-iron master alloy and heat to the temperature range of 1200-1250℃ to melt, then cool down to 994℃, add zinc, antimony, and tin, test and adjust the composition to meet the requirements before casting.

[0052] (2) Semi-continuous casting: The crystallizer is φ195mm. The molten copper is kept at 1040-1050℃ for 12min and then semi-continuous casting is carried out. The casting speed is 60mm / min, the cooling water pressure is 0.33MPa, the temperature difference between the inlet and outlet water is 14℃, the red ingot casting process is adopted, the length of the red ingot zone is 320mm, the electromagnetic stirring frequency of the crystallizer is 15Hz, the electromagnetic stirring intensity is 100A·t, and the ingot is naturally cooled to below 100℃ and then sawn into the required extrusion size of φ195mm×600mm.

[0053] (3) Homogenization treatment: The ingot is kept at 700℃ for 4 hours for homogenization treatment, and then cooled to 100℃-room temperature with the furnace before being taken out of the furnace.

[0054] (4) Hot extrusion: The extrusion temperature is 750℃, the number of extrusion die holes is 3, the die core specification is φ6.8mm, the extrusion ratio λ=266, the extrusion speed is set to V=5.5mm / s, and the coil is wound up.

[0055] (5) Cold stretching and annealing: After hot extrusion, the φ6.8 wire blank is butt welded and stretched to φ2.7 in 4 passes according to the process of φ6.8→φ5.4→φ4.2→φ3.3→φ2.7. The processing rate of each pass is 25-50%. Annealing is required between every two stretching passes. The intermediate annealing first heats up to 320℃ at a heating rate of 7℃ / min and holds for 45 min, and then heats up to 630℃ at a heating rate of 9℃ / min and holds for 180 min.

[0056] (6) Finished product stretching: After pickling, the annealed φ2.7 wire blank is stretched to φ2.3mm wire, with a processing rate of 27.4%.

[0057] (7) Low temperature annealing: The annealing temperature is 260℃, the time to rise from room temperature to this temperature is 45min, and the holding time is 210min.

[0058] (8) Inspection: The finished products are put into storage after passing all inspections.

[0059] Example 2: A method for preparing a φ6mm lead-free free-cutting zinc-copper rod is as follows: (1) Smelting: Weigh out the raw materials such as electrolytic copper, electrolytic nickel, zinc ingots, electrolytic manganese, antimony ingots, copper-iron master alloy, and tin ingots according to the above weight percentage composition, and smelt them in an electric furnace. The order of adding materials is as follows: first add copper, nickel, and copper-iron master alloy and heat to 1150-1200℃ to melt, then cool down to 1018℃, add zinc, antimony, and tin, test and adjust the composition to meet the requirements before casting.

[0060] (2) Semi-continuous casting: The crystallizer is φ254mm. The molten copper is allowed to stand at 1052℃ for 10 minutes, and then semi-continuous casting is carried out. The casting speed is 55mm / min, the cooling water pressure is 0.23MPa, the temperature difference between the inlet and outlet water is controlled at 11℃, and the red ingot casting process is adopted. The length of the red ingot zone is controlled at 390mm. The electromagnetic stirring frequency of the crystallizer is 10Hz, and the electromagnetic stirring intensity is 80A·t. The ingot is naturally cooled to below 100℃ and then sawn into the required extrusion size of φ254mm×550mm.

[0061] (3) Homogenization treatment: The ingot is kept at 720℃ for 3.5h for homogenization treatment, and then cooled to below 100℃ in the furnace before being taken out.

[0062] (4) Hot extrusion: The extrusion temperature is 740℃, the number of extrusion die holes is 2, the die core specification is φ10mm, the extrusion ratio is λ=322, the extrusion speed is set to V=6mm / s, and the coil is wound up.

[0063] (5) Cold stretching and annealing: After hot extrusion, the φ10 wire blank is butt welded and stretched to φ7.4 in one pass according to the φ10→φ7.4 process, with a processing rate of 45%. The φ7.4 wire blank is annealed in the middle first at a heating rate of 6℃ / min to 300℃ and held for 90 min, and then at a heating rate of 8℃ / min to 660℃ and held for 150 min.

[0064] (7) Finished product stretching: After pickling, the annealed φ7.4 wire rod is stretched into φ6mm bar stock with a processing rate of 34%.

[0065] (8) φ6mm bars are straightened on a two-roll straightener.

[0066] (9) Low temperature annealing: The annealing temperature is 270℃, the time to rise from room temperature to this temperature is 60min, and the holding time is 240min.

[0067] (9) Inspection: The finished products are put into storage after passing all inspections.

[0068] Example 3: A method for preparing a φ1.6mm lead-free free-cutting zinc-copper wire is as follows: (1) Smelting: Weigh out the raw materials such as electrolytic copper, electrolytic nickel, zinc ingots, electrolytic manganese, antimony ingots, copper-iron master alloy, and tin ingots according to the above weight percentage composition, and smelt them in an electric furnace. The order of adding materials is as follows: first add copper, nickel, and copper-iron master alloy and heat to the temperature range of 1180-1220℃ to melt, then cool down to 1010℃, add zinc, antimony, and tin, test and adjust the composition to meet the requirements before casting.

[0069] (2) Semi-continuous casting: The crystallizer is φ145mm. The molten copper is kept at 1032-1044℃ for 16min and then semi-continuous casting is carried out. The casting speed is 70mm / min, the cooling water pressure is 0.30MPa, the temperature difference between the inlet and outlet water is 17℃, and the red ingot casting process is adopted. The length of the red ingot zone is 260mm. The electromagnetic stirring frequency of the crystallizer is 10Hz and the electromagnetic stirring intensity is 60A·t. The ingot is naturally cooled to below 100℃ and then sawn into the required extrusion size of φ145mm×500mm.

[0070] (3) Homogenization treatment: The ingot is kept at 680℃ for 4 hours for homogenization treatment, and then cooled to below 100℃ in the furnace before being taken out.

[0071] (4) Hot extrusion: The extrusion temperature is 730℃, the number of extrusion die holes is 3, the die core specification is φ5mm, the extrusion ratio is λ=280, the extrusion speed is set to V=4.5mm / s, and the coil is wound up.

[0072] (5) Cold stretching and annealing: After hot extrusion, the φ5 wire blank is butt welded and stretched to φ1.85 in 4 passes according to the process of φ5→φ4→φ3.1→φ2.4→φ1.85. The processing rate of each pass is 25-50%. Annealing is required between every two stretching passes. The intermediate annealing first heats up to 250℃ at a heating rate of 5℃ / min and holds for 30 min, and then heats up to 620℃ at a heating rate of 12℃ / min and holds for 210 min.

[0073] (6) Finished product stretching: After pickling, the annealed φ1.85 wire blank is stretched to φ1.6mm wire, with a processing rate of 25.2%.

[0074] (7) Low temperature annealing: The annealing temperature is 240℃, the time to rise from room temperature to this temperature is 45min, and the holding time is 240min.

[0075] (8) Inspection: The finished products are put into storage after passing all inspections.

[0076] Example 4: A method for preparing a φ4mm lead-free free-cutting zinc white copper rod is as follows: (1) Smelting: Weigh out the raw materials such as electrolytic copper, electrolytic nickel, zinc ingots, electrolytic manganese, antimony ingots, copper-iron master alloy, and tin ingots according to the above weight percentage composition, and smelt them in an electric furnace. The order of adding materials is as follows: first add copper, nickel, and copper-iron master alloy and heat to 1160-1210℃ to melt, then cool down to 1022℃, add zinc, antimony, and tin, test and adjust the composition to meet the requirements before casting.

[0077] (2) Semi-continuous casting: The crystallizer is φ175mm. The molten copper is allowed to stand at 1050℃ for 13 minutes, and then semi-continuous casting is carried out. The casting speed is 65mm / min, the cooling water pressure is 0.26MPa, the temperature difference between the inlet and outlet water is controlled at 14.2℃, and the red ingot casting process is adopted. The length of the red ingot zone is controlled at 410mm. The electromagnetic stirring frequency of the crystallizer is 15Hz, and the electromagnetic stirring intensity is 90A·t. The ingot is naturally cooled to below 100℃ and then sawn into the required extrusion size of φ195mm×600mm.

[0078] (3) Homogenization treatment: The ingot is kept at 750℃ for 3 hours for homogenization treatment, and then cooled to below 100℃ in the furnace before being taken out.

[0079] (4) Hot extrusion: The extrusion temperature is 755℃, the number of extrusion die holes is 3, the die core specification is φ7mm, the extrusion ratio is λ=208, the extrusion speed is set to V=5.8mm / s, and the coil is wound up.

[0080] (5) Cold stretching and annealing: After hot extrusion, the φ7 wire blank is butt welded and stretched to φ4.6 in two passes according to the process of φ7→φ5.5→φ4.6. The processing rate of each pass is 25-50%. Annealing is required between each two stretching passes. The intermediate annealing first heats up to 300℃ at a heating rate of 6℃ / min and holds for 30 min, and then heats up to 640℃ at a heating rate of 14℃ / min and holds for 210 min.

[0081] (7) Finished product stretching: After pickling, the annealed φ4.6 wire rod is stretched into φ4mm bar stock, with a processing rate of 24.4%.

[0082] (8) φ4mm bars are straightened on a two-roll straightener.

[0083] (9) Low temperature annealing: The annealing temperature is 280℃, the time to rise from room temperature to this temperature is 60min, and the holding time is 240min.

[0084] (9) Inspection: The finished products are put into storage after passing all inspections.

[0085] Example 5: A method for preparing a φ2.3mm lead-free free-cutting zinc-copper wire is as follows: (1) Smelting: Weigh out the raw materials such as electrolytic copper, electrolytic nickel, zinc ingots, electrolytic manganese, antimony ingots, copper-iron master alloy, and tin ingots according to the above weight percentage composition, and smelt them in an electric furnace. The order of adding materials is as follows: first add copper, nickel, and copper-iron master alloy and heat to the temperature range of 1200-1250℃ to melt, then cool down to 994℃, add zinc, antimony, and tin, test and adjust the composition to meet the requirements before casting.

[0086] (2) Semi-continuous casting: The crystallizer is φ195mm. The molten copper is kept at 1040-1050℃ for 12min and then semi-continuous casting is carried out. The casting speed is 60mm / min, the cooling water pressure is 0.33MPa, the temperature difference between the inlet and outlet water is 14℃, the red ingot casting process is adopted, the length of the red ingot zone is 320mm, the electromagnetic stirring frequency of the crystallizer is 15Hz, the electromagnetic stirring intensity is 100A·t, and the ingot is naturally cooled to below 100℃ and then sawn into the required extrusion size of φ195mm×600mm.

[0087] (3) Homogenization treatment: The ingot is kept at 700℃ for 4 hours for homogenization treatment, and then cooled to below 100℃ in the furnace before being taken out.

[0088] (4) Hot extrusion: The extrusion temperature is 750℃, the number of extrusion die holes is 3, the die core specification is φ6.8mm, the extrusion ratio λ=266, the extrusion speed is set to V=5.5mm / s, and the coil is wound up.

[0089] (5) Cold stretching and annealing: After hot extrusion, the φ6.8 wire blank is butt welded and stretched to φ2.7 in 4 passes according to the process of φ6.8→φ5.4→φ4.2→φ3.3→φ2.7. The processing rate of each pass is 25-50%. Annealing is required between every two stretching passes. The intermediate annealing first heats up to 320℃ at a heating rate of 7℃ / min and holds for 45 min, and then heats up to 630℃ at a heating rate of 9℃ / min and holds for 180 min.

[0090] (6) Finished product stretching: After pickling, the annealed φ2.7 wire blank is stretched to φ2.3mm wire, with a processing rate of 27.4%.

[0091] (7) Low temperature annealing: The annealing temperature is 260℃, the time to rise from room temperature to this temperature is 45min, and the holding time is 210min.

[0092] (8) Inspection: The finished products are put into storage after passing all inspections.

[0093] The difference between Example 5 and Example 1 is that the content of Sb element is different in the chemical composition of Example 5, and M... Mn / M Sb Does not satisfy 3≤M Mn / M Sb For relationships ≤6, the rest are consistent with Implementation 1, see Table 1 for details.

[0094] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not contain Sb in its chemical composition. Because Comparative Example 1 does not contain Sb, it has better mechanical properties but poorer machinability.

[0095] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not contain Fe or Sn elements in its chemical composition. Due to the lack of Fe and Sn, its mechanical properties and machinability are poor.

[0096] The difference between Comparative Example 3 and Example 1 is that the chemical composition is the same, and the extrusion speed of the ingot in Comparative Example 3 is 12 mm / s. Everything else is the same. However, due to the excessively high extrusion speed in Comparative Example 3, the Mn2Sb particles are larger in size, fewer in number, and have poorer machinability.

[0097] The difference between Comparative Example 4 and Example 1 is that the chemical composition is the same, but the extrusion ratio in Comparative Example 4 is less than 200, while the extrusion ratio is 54, and the rest are the same. Due to the lower extrusion ratio, the Mn2Sb phase particles are larger, the precipitated phase size is larger, and the machinability is poorer.

[0098] The difference between Comparative Example 5 and Example 1 is that the chemical composition is the same, and in the preparation process, Comparative Example 5 did not use a stepped heating method for intermediate annealing, but the rest is the same. The intermediate annealing temperature is 630°C and the holding time is 180 min.

[0099] The mechanical properties, metallographic structure, and machinability of the bars or wires prepared in the five examples and five comparative examples were tested: Metallographic observation: For the 5 example products and 5 comparative products prepared, samples were taken and observed under a metallographic microscope, and the metallographic structure was measured using metallographic analysis software. The results are recorded in Table 2.

[0100] Mechanical property testing: Tensile strength Rm, yield strength Rp0.2 and elongation after fracture A were tested according to GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1: Test method at room temperature", and the results are recorded in Table 3.

[0101] Cutting performance testing: The cutting performance index is used to reflect the cutting performance. The cutting force is calculated by the cutting force tester and compared with that of leaded brass C36000. The relative cutting performance index is calculated according to the formula: Cutting performance index = (C36000 cutting force / Example alloy cutting force) × 100%. The closer the value is to 100, the closer the cutting performance of the example alloy is to the best cutting performance of C36000. Specific data are shown in Table 4.

[0102] Table 1 Chemical composition of the examples and comparative examples Table 2. Microstructure of the embodiments and comparative examples of the present invention Table 3 Mechanical properties of embodiments and comparative examples of the present invention As shown in Tables 2 and 3, the Mn2Sb phase of the zinc-copper alloys prepared in Examples 1-5 is dispersed in the matrix, with suitable size, and has good mechanical and machinability.

[0103] like Figure 1 As shown, the brittle chip phase Mn2Sb of the zinc-copper alloy prepared in Example 1 has a small overall size, uniform distribution, and a small number of 5μm-sized chips.

[0104] like Figure 2 As shown, the zinc-copper alloy scraps obtained in Example 1 are in fragment form, with no shreds appearing.

[0105] like Figure 3 As shown, the zinc-copper alloy shavings obtained in Comparative Example 1 are fragmented, C-shaped, and curled.

Claims

1. A lead-free, environmentally friendly, free-machining zinc-copper alloy, characterized in that, Its component content Includes: Cu: 42-46wt%, Ni: 12-16wt%, Mn: 4-6wt%, Sb: 1.0-2.2wt%, Fe: 0.01-0.2wt%, Sn: 0.1-0.5wt%, balance Zn and unavoidable impurities; The microstructure of the lead-free, environmentally friendly, free-machining zinc-copper alloy comprises a Mn2Sb phase, with an average distribution density of ≥4000 phases / mm². 2 Furthermore, the average distribution density of Mn2Sb phase with a particle size greater than 5 μm is ≤200 particles / mm. 2 .

2. The lead-free, environmentally friendly, free-machining zinc-copper alloy according to claim 1, characterized in that, The mass ratio of Mn to Sb satisfies 3 ≤ M Mn / M Sb ≤6.

3. The lead-free, environmentally friendly, free-machining zinc-copper alloy according to claim 1, characterized in that, The average grain size of the lead-free, environmentally friendly, free-machining zinc-copper alloy is 8-20 μm.

4. A method for preparing lead-free, environmentally friendly, free-machining zinc-copper according to any one of claims 1-3, characterized in that, The process flow of the preparation method includes: melting → semi-continuous casting → homogenization treatment → hot extrusion → cold stretching → intermediate annealing → finished product stretching → low temperature annealing. The raw materials are prepared and smelted according to the content of each component of the lead-free, environmentally friendly, free-cutting zinc-copper alloy described above; The hot extrusion temperature is 720-780℃, the extrusion ratio is 200-400, and the extrusion speed is 2-6mm / s.

5. The method for preparing lead-free, environmentally friendly, free-machining zinc-copper alloy according to claim 4, characterized in that, The intermediate annealing adopts a stepped annealing process, which includes a first-stage annealing and a second-stage annealing. The temperature of the first-stage annealing is 200-350℃, and the temperature of the second-stage annealing is 600-700℃.

6. The method for preparing lead-free, environmentally friendly, free-machining zinc-copper alloy according to claim 4, characterized in that, The heating rate for the first stage of annealing is 5-10℃ / min, and the holding time is 30-120 min; the heating rate for the second stage of annealing is 5-10℃ / min, and the holding time is 90-300 min.

7. The method for preparing lead-free, environmentally friendly, free-machining zinc-copper alloy according to claim 4, characterized in that, In semi-continuous casting, the crystallizer is equipped with an electromagnetic stirring device with a stirring frequency of 5-20 Hz and an electromagnetic stirring intensity of 50-200 A•t.

8. The method for preparing lead-free, environmentally friendly, free-machining zinc-copper alloy according to claim 4 or 7, characterized in that, The homogenization treatment is carried out at a temperature of 650-750℃ for 2-6 hours.

9. The method for preparing lead-free, environmentally friendly, free-machining zinc-copper alloy according to claim 4, characterized in that, The cold drawing is a multi-pass drawing, with a processing rate of 25-50% for each pass. Intermediate annealing is performed between every two passes, and the intermediate annealing temperature is 600-700℃.

10. The application of lead-free, environmentally friendly, free-cutting zinc-copper alloy according to any one of claims 1-3 in eyeglass accessories, pen manufacturing, instrumentation, medical devices, zippers, keys, and the optical and watchmaking industries.

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