Lead-free brass alloy and method for producing the same

Abstract

This invention discloses a lead-free brass alloy and its preparation method. The lead-free brass alloy comprises, by weight percentage: Cu 59-62%, Sn 0.7-1.0%, Si 0.1-0.5%, Fe 0.001-0.2%, B 0-0.01%, with the balance being Zn and unavoidable impurities. This application achieves a balance between machinability, hot and cold working plasticity, and corrosion resistance through the synergistic regulation of multiple elements: copper, tin, silicon, iron, and boron. Copper controls the α / β phase ratio to ensure sufficient α phase to maintain plasticity and stress corrosion resistance, while introducing an appropriate amount of β phase to improve chip breaking properties. Tin refines the grains, stabilizes the composite oxide film to resist dezincification corrosion, and promotes the uniform distribution of the free-machining phase, balancing toughness and machinability. Silicon and iron synergistically precipitate a dispersed hard phase, serving as a controllable microcrack source to achieve short, fragmented chips; its content is strictly controlled to prevent embrittlement. Boron optimizes the solidification structure, promotes equiaxed α phase, and further improves overall performance.

Description

Technical Field

[0001] This invention relates to the field of copper alloy technology, and more specifically, to lead-free brass alloys and their preparation methods. Background Technology

[0002] Brass products possess excellent mechanical properties, machinability, and corrosion resistance. Compared to conventional copper and copper alloys, their raw material cost is relatively low, making them widely used in various fields such as industrial manufacturing, construction, and electronics. In recent years, with the rapid development of the electronics and semiconductor industries, the demand for high-performance connector pins has been increasing year by year, while higher requirements have been placed on the overall performance of brass. Specific requirements mainly focus on four aspects: good cold formability, high machining precision, high corrosion resistance, and environmental compliance.

[0003] To achieve high cutting precision, the current mainstream technology mainly improves the properties of brass by adding lead. However, lead is an element that is harmful to human health. Considering environmental compliance, lead-free production has become the current development trend. How to achieve or approach the easy-to-machine properties of leaded brass is also a major research trend.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a lead-free brass alloy and its preparation method, which, while being lead-free, also achieves good machinability and corrosion resistance.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a lead-free brass alloy comprising, by weight percentage: Cu 59-62%, Sn 0.7-1.0%, Si 0.1-0.5%, Fe 0.001-0.2%, B 0-0.01%, balance Zn, and unavoidable impurities.

[0007] In an optional embodiment, the average grain size of the α phase in the lead-free brass alloy is ≤0.045 mm; And / or, the aspect ratio of the α-phase grains in the lead-free brass alloy is 1 to 4; And / or, the α-phase area percentage in the lead-free brass alloy is 30-65%; In an optional embodiment, the β phase area percentage in the lead-free brass alloy is 30-65%; And / or, the area percentage of the phases other than α and β in the lead-free brass alloy is <5%.

[0008] In an optional embodiment, the lead-free brass alloy includes a free-machining phase, which includes at least one of Cu5Si phase, Cu3Si phase and Fe3Si phase.

[0009] In an optional embodiment, the average size of both the Cu5Si and Cu3Si phases is ≤10 μm; And / or, the average size of the Fe3Si phase is ≤5 μm; And / or, the average grain size of the easily machinable phase is ≤4 μm; In an optional embodiment, the number of free-machining phases distributed per unit area is ≥3000 / mm. 2 .

[0010] In an optional embodiment, the lead-free brass alloy has a tensile strength ≥550MPa; And / or, the elongation of the lead-free brass alloy is ≥5%; And / or, the cutting index of the lead-free brass alloy is ≥40%; And / or, the lead-free brass alloy surface forms an oxide film upon contact with air, the oxide film comprising copper oxide and tin oxide.

[0011] Secondly, the present invention provides a method for preparing the lead-free brass alloy according to any one of the foregoing embodiments, comprising sequentially performing smelting, casting, extrusion, coil drawing, heat treatment, drawing and finished product annealing, wherein raw materials are added in the smelting step according to the composition of the lead-free brass alloy according to any one of the foregoing embodiments.

[0012] In an optional embodiment, the temperature of the melting step is 900-1150°C; And / or, the casting process is carried out using continuous casting or semi-continuous casting methods; And / or, the temperature of the casting step is 950~1080℃; And / or, the extrusion temperature is 650-750℃, the extrusion ratio is 200~1000:1, and the extrusion speed is 3~12mm / s; And / or, the cooling rate after extrusion is 20~500℃ / h; And / or, the processing rate of the coiled part is 5~40%.

[0013] In an optional embodiment, the temperature of the heat treatment step is 320~420℃, and the holding time is 2~8h; And / or, the drawing rate is 4~35%; And / or, the temperature of the finished product annealing step is 220~320℃, and the holding time is 3~12h.

[0014] The present invention has the following beneficial effects: This application's lead-free brass alloy achieves a unified optimization of machinability, plasticity, and corrosion resistance through multi-element synergistic design. Copper serves as the matrix, with controlled α / β phase ratios: an appropriate amount of α phase ensures cold working plasticity and resistance to stress corrosion, while a moderate amount of β phase enhances chip breaking properties. Tin significantly refines grains, stabilizes the composite oxide film to block chloride ions and inhibit dezincification corrosion, and promotes uniform distribution of the free-machining phase, balancing toughness and machinability. Silicon and iron synergistically precipitate dispersed hard phases, serving as controllable microcrack sources to achieve short, fragmented chips; their content is strictly controlled to avoid coarse, brittle phases damaging plasticity. Boron further synergistically enhances machinability and corrosion resistance by inhibiting columnar crystal growth, promoting equiaxed α phase, and optimizing the microstructure. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 Microstructure image (500x) of the lead-free brass alloy prepared in Example 1; Figure 2 Morphology and distribution of the free-machining phase of the lead-free brass alloy prepared in Example 1 (500x). Figure 3 Microstructure image (500x) of the lead-free brass alloy prepared for Comparative Example 1. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] The applicant is aware that adding bismuth can approach the machinability of leaded brass. However, bismuth increases the brittleness of brass, making it more prone to cracking during hot and cold working, which fails to meet the cold forming requirements of pin products. Furthermore, the potential health risks of bismuth have not yet been effectively verified, making it highly likely to be selected as a target with similar limitations as lead in the future. Other easily machinable elements, such as calcium and magnesium, while improving machinability to some extent, suffer from poor control over composition stability and uniformity during smelting and casting processes due to oxidation and burn-off, hindering large-scale, low-cost mass production.

[0019] Therefore, embodiments of the present invention provide a lead-free brass alloy comprising, by weight percentage: Cu 59-62%, Sn 0.7-1.0%, Si 0.1-0.5%, Fe 0.001-0.2%, B 0-0.01%, balance Zn, and unavoidable impurities.

[0020] In this application, the lead-free brass alloy contains 59-62% Cu by weight. As a matrix element, the lower limit of 59% ensures sufficient formation of the α phase (face-centered cubic structure, a solid solution of zinc dissolved in copper) to provide good cold-working plasticity. This avoids the formation of excessive brittle β phases (body-centered cubic structure, a solid solution based on the electron compound CuZn), reducing the risk of stress corrosion cracking. The upper limit of 62% Cu content ensures the formation of a certain number of easily machinable brittle β phases, thereby improving the material's machinability.

[0021] The lead-free brass alloy of this application contains Sn by weight of 0.7% to 1.0%. The addition of Sn can hinder grain boundary migration, suppress the growth of α and β phases during hot working, resulting in a denser microstructure, clearer grain boundaries, and improved overall mechanical properties. Sn also helps control the morphology of the α phase and reduce the continuity of the β phase, thereby improving cold working performance. Simultaneously, Sn promotes the formation of a dense and stable oxide film (mainly a Cu2O and SnO2 composite layer), blocks chloride ion penetration pathways, significantly reduces the dezincification corrosion rate, and improves the material's corrosion resistance. Furthermore, the addition of Sn can inhibit the segregation of the free-machining phase at grain boundaries, achieving spatial homogenization of the free-machining phase, avoiding local embrittlement, and improving the overall toughness-machinability balance of the material. The upper limit of the Sn content is controlled at 1.0% to avoid excessive addition which would increase the material's hardness and brittleness, and worsen its cold and hot working plasticity.

[0022] In this application, the weight percentage of Si in the lead-free brass alloy is 0.1-0.5%. The addition of Si can form a dispersed Si-enriched phase (mainly including Cu5Si, Cu3Si, etc.), and at the same time, it synergistically forms the Fe3Si phase with trace amounts of Fe. The Si-enriched phase and the Fe3Si phase act as hard particles, preferentially initiating microcracks under cutting shear forces. The microcracks propagate rapidly along the phase interface. Due to the low interfacial bonding energy, debonding easily occurs, forming short and fragmented chips, thereby achieving an easy-to-machining effect. The upper limit of Si content is controlled at 0.5% to avoid excessive addition which would cause the Si-enriched phase (mainly including Cu5Si, Cu3Si, etc.) to become too large. If the Cu5Si phase with an average grain size greater than 10 μm is formed, it will lead to a sharp drop in plasticity, mainly manifested in the elongation easily falling below 5%, which cannot meet the good cold-pressing performance required for pin products.

[0023] In this application, the lead-free brass alloy contains 0.001~0.2% Fe by weight. The addition of Fe mainly synergizes with Si to form a body-centered cubic Fe3Si phase, which serves as a nucleation point for microcracks and improves chip breaking performance. Furthermore, Fe significantly delays the recrystallization process, increases the recrystallization temperature, and inhibits grain coarsening after hot working, resulting in a finer α+β dual-phase microstructure. This facilitates effective control of the microstructure, morphology, and distribution ratio during hot working and heat treatment. Controlling the Fe content to an upper limit of 0.2% prevents Fe3Si phase coarsening, avoiding the formation of Fe3Si phases exceeding 5 μm in size, thus ensuring good cold and hot working plasticity. It also avoids the formation of a large amount of brittle Fe-Zn phase, ensuring good stress corrosion resistance.

[0024] In this application, the weight percentage of boron (B) in the lead-free brass alloy is 0-0.01%. The main purpose of adding boron is to inhibit columnar crystal growth and promote equiaxed crystal formation. This invention primarily improves the overall material properties by controlling the microstructure morphology, size, distribution percentage, and the formation of a free-machining phase. For example, when adjusting the heat treatment process to meet the β phase area percentage requirements, the resulting α phase is easily distributed in a coarse, elongated shape. The aspect ratio of these elongated grains can reach over 5, which is detrimental to further improving machinability and corrosion resistance. Adding boron promotes the distribution of the α phase in an equiaxed crystal form, thereby achieving ideal machinability and corrosion resistance.

[0025] In an optional embodiment, the average grain size of the α phase in the lead-free brass alloy is ≤0.045mm; this is beneficial for improving the uniformity of the microstructure distribution and making the distribution of the free-machining phase more dispersed, providing a good foundation for obtaining a high number of free-machining phases per unit area.

[0026] In an optional embodiment, the aspect ratio of the α-phase grains in the lead-free brass alloy is 1 to 4; controlling the appropriate aspect ratio of the α-phase grains avoids the appearance of elongated grain morphology, which would deteriorate machinability and stress corrosion resistance.

[0027] In an optional embodiment, the α-phase area percentage in the lead-free brass alloy is 30-65%.

[0028] In an optional embodiment, the β phase area percentage in the lead-free brass alloy is 30-65%.

[0029] In an optional embodiment, the area percentage of the phases other than α and β in the lead-free brass alloy is <5%.

[0030] Controlling the appropriate area percentages of the α and β phases and reducing the ε phase is crucial for effectively balancing the material's machinability, stress corrosion resistance, and elongation plasticity. If the α phase area percentage is too low, it implies a high β phase area percentage, resulting in insufficient stress corrosion resistance and elongation plasticity. Conversely, if the β phase area percentage is too low, it implies a high α phase area percentage, leading to insufficient machinability.

[0031] In an optional embodiment, the lead-free brass alloy includes a free-machining phase, which includes at least one of Cu5Si phase, Cu3Si phase and Fe3Si phase.

[0032] In an optional embodiment, the average size of both Cu5Si and Cu3Si phases is ≤10 μm, which is beneficial for improving elongation.

[0033] In an optional embodiment, the average size of the Fe3Si phase is ≤5 μm, which is beneficial for improving cold and hot working plasticity.

[0034] In an optional embodiment, the average grain size of the easily machinable phase is ≤4 μm.

[0035] In an optional embodiment, the number of free-machining phases distributed per unit area is ≥3000 / mm. 2 .

[0036] Controlling the size and number of free-cutting phases per unit area is essential to ensure that the material has good chip-breaking ability, thereby achieving and meeting the requirements for good cutting performance.

[0037] In an optional embodiment, the lead-free brass alloy has a tensile strength ≥550MPa to ensure that the material has good machinability and avoid problems such as tool sticking, built-up edge, and difficulty in chip breaking during the cutting process due to the high plasticity and toughness of the material when the strength or hardness is too low.

[0038] In an optional embodiment, the lead-free brass alloy has an elongation of ≥5% to meet the good cold-pressing performance required for the pin product.

[0039] In an optional embodiment, the lead-free brass alloy has a cutting index of ≥40% to ensure machinability.

[0040] In an optional embodiment, the lead-free brass alloy surface is exposed to air to form an oxide film, the oxide film comprising copper oxide and tin oxide.

[0041] Secondly, the present invention provides a method for preparing the lead-free brass alloy according to any one of the foregoing embodiments, comprising sequentially performing smelting, casting, extrusion, coil drawing, heat treatment, drawing and finished product annealing, wherein raw materials are added in the smelting step according to the composition of the lead-free brass alloy according to any one of the foregoing embodiments.

[0042] In an optional embodiment, the temperature of the melting step is 900-1150℃; in order to ensure good raw material melting effect and efficiency, this application sets a lower limit of not less than 900℃; at the same time, in order to avoid excessive burning of elements such as Si and Zn and the formation of too many brittle oxide eutectic phases due to excessive temperature, resulting in unstable product composition and reduced quality of subsequent ingots, the upper limit is controlled to be not higher than 1150℃.

[0043] In an optional implementation, the casting step is carried out using continuous casting or semi-continuous casting.

[0044] In an optional embodiment, the casting temperature is 950~1080℃; to ensure good melt flowability and solidification effect during the casting process and reduce casting defects such as cold shuts, the lower limit is controlled to be no lower than 950℃. At the same time, to avoid the formation of high-melting-point SiO2 inclusions by oxygen reaction, which would significantly reduce the alloy flowability, and to avoid excessively high casting temperatures leading to rapid coarsening of β-phase grains and reduced ingot plasticity, the upper limit is controlled to be no higher than 1080℃.

[0045] In an optional embodiment, the extrusion temperature is 650-750℃. The purpose is to control the α-phase morphology to be distributed in a circular, island-like pattern and to control the α-phase proportion within a suitable range, achieving a balance between good machinability and good corrosion resistance. If the extrusion heating temperature is too low, the α-phase formed during the extrusion process will be elongated in the longitudinal section, forming a long strip-shaped microstructure. Due to its high toughness, the long strip-shaped α-phase is not easy to break during machining, thus failing to meet the machinability requirements. At the same time, a low extrusion temperature will also reduce the material's thermal deformation plasticity, resulting in insufficient and uneven recrystallization during extrusion deformation, ultimately failing to meet the uniformity requirements of the resulting microstructure. Controlling the upper limit of the extrusion heating temperature to 750℃ is preferable. If the extrusion temperature is too high, the number of precipitated α-phases will be less, resulting in a higher proportion of brittle β-phase. Although this improves machinability to some extent, the material's corrosion resistance is significantly reduced, making it prone to stress corrosion cracking and dezincification corrosion in subsequent processing and application environments, thus reducing its service life.

[0046] In an optional embodiment, the extrusion ratio is 200~1000:1; this, combined with the aforementioned extrusion temperature, effectively controls the morphology and size of the α-phase. If the extrusion ratio is too low, the hot extrusion deformation is insufficient, the α-phase grains cannot completely recrystallize and break down, and the microstructure is prone to retaining large-sized grains, which is not conducive to obtaining ideal machinability and corrosion resistance. If the extrusion ratio is too high, although it is beneficial to further refine the grains and improve the overall mechanical properties of the material, a high extrusion ratio is prone to causing cracking of the material, especially longitudinal cracks during the extrusion cycle. Therefore, in order to balance material quality and performance, the upper limit of the extrusion ratio is controlled to not exceed 1000:1.

[0047] In an optional implementation, the extrusion speed is 3~12 mm / s.

[0048] In an optional embodiment, the cooling rate after extrusion is 20~500℃ / h. The above extrusion process parameters directly affect the microstructure of the material. Furthermore, due to the high temperature after extrusion, the extruded billet will undergo certain phase and microstructure changes during the cooling process. Therefore, it is necessary to strictly control the appropriate cooling rate. If the cooling rate is too high, the β phase will not have enough time to transform into the α phase after high-temperature extrusion, resulting in a higher proportion of the β phase and reduced corrosion resistance of the material. If the cooling rate is too low, it will hinder production efficiency and significantly increase production time and costs.

[0049] In an optional implementation, the coil drawing rate is 5-40%, which reduces the diameter of the extruded billet, increases dislocation energy storage, and provides the driving force for recovery and recrystallization in subsequent heat treatment processes. At the same time, this drawing rate also promotes the dispersed distribution of the free-machining phase, further improving machinability. Controlling the drawing rate to an upper limit of 40% aims to avoid the risk of material cracking or fracture due to excessive drawing. It should be noted that pickling can be performed before coil drawing. Pickling aims to remove oxide scale, oil, and impurities from the metal surface before coil drawing, improving surface finish and lubrication adhesion.

[0050] In an optional embodiment, the heat treatment step is performed at a temperature of 320~420℃ for 2~8 hours. The heat treatment step softens the billet after extrusion, ensuring the plasticity required for subsequent drawing. It also further refines the microstructure, improving the uniformity of grain size, morphology, and phase area percentage. Due to temperature losses during the extrusion process, slight differences exist in the microstructure and characteristics of the extruded head, middle, and tail billets. The heat treatment step further reduces these differences and promotes uniformity. A lower temperature of 320℃ is controlled to achieve basic softening and ensure normal plasticity for subsequent drawing. An upper temperature of 420℃ is controlled to prevent excessive precipitation of the α-phase and growth of the easily machinable phase, which would deteriorate the material's machinability.

[0051] In optional embodiments, the drawing rate is 4-35%. Drawing further work-hardens the material, refines the grains, and promotes the dispersed distribution of the free-machining phase, achieving good machinability. If the drawing rate is too low, the material has high plasticity and a small number of free-machining phases per unit area, making the material prone to tool sticking and chip breaking during machining, and the machinability cannot meet the requirements. If the drawing rate is too high, the material has more dislocations, and crack initiation is easily generated at grain boundaries or where the free-machining phase is distributed, causing drawing cracks or fractures, and the material's stress corrosion resistance also cannot meet the requirements. It should be noted that pickling can be performed before drawing. Pickling aims to remove oxide scale, oil, and impurities from the metal surface before drawing, improve surface finish and lubrication adhesion, and prevent die wear, surface scratches, or fractures during drawing.

[0052] In an optional embodiment, the annealing temperature of the finished product is 220~320℃, and the holding time is 3~12h. The purpose is to eliminate tensile stress and further improve the plasticity of the material without significantly reducing its mechanical properties, thereby improving its cold pressing deformation performance. The upper limit of the temperature is controlled at 320℃ to avoid a significant decrease in material strength due to excessively high temperature, while excessively high plasticity is detrimental to machinability.

[0053] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0054] Example 1 This embodiment provides a method for preparing a lead-free brass alloy, specifically including the following steps: 1) Smelting: Proportion according to the composition requirements in Table 1, add the raw materials to the smelting furnace in sequence for heating and melting, and control the smelting temperature to 980℃.

[0055] 2) Casting: Ingots are produced using a semi-continuous casting method at a casting temperature of 970℃.

[0056] 3) Extrusion: The ingot is heated and held at 660℃. After the ingot reaches the required temperature, it is hot extruded at an extrusion ratio of 432:1, an extrusion speed of 10mm / s, and a cooling rate of 200℃ / h after extrusion.

[0057] 4) Coil drawing: The extruded billet is pickled and then coiled, with a coil drawing rate of 32%.

[0058] 5) Heat treatment: The billet after being drawn into a coil is heat treated at a temperature of 360℃ for 5 hours.

[0059] 6) Drawing: The heat-treated billet is pickled and then drawn to the finished product specifications. The drawing rate is 20%, and a finished product with a diameter of φ5mm is obtained.

[0060] 7) Finished product annealing: The drawn finished product is subjected to low-temperature annealing treatment at 250℃ for 6 hours. The microstructure and free-machining phase morphology and distribution of the resulting lead-free brass alloy are shown in the figure. Figure 1-2 As shown.

[0061] Table 1. Components of each embodiment and comparative example, in wt%

[0062] Example 2 This embodiment provides a method for preparing a lead-free brass alloy, specifically including the following steps: 1) Smelting: Proportion according to the composition requirements in Table 1. Add the raw materials to the smelting furnace in sequence for heating and melting, and control the smelting temperature to 1000℃.

[0063] 2) Casting: Ingots are produced using a semi-continuous casting method at a casting temperature of 990℃.

[0064] 3) Extrusion: The ingot is heated and held at 670℃. After the ingot reaches the required temperature, it is hot extruded at an extrusion ratio of 432:1, an extrusion speed of 9mm / s, and a cooling rate of 200℃ / h after extrusion.

[0065] 4) Coil drawing: The extruded billet is pickled and then coiled, with a coil drawing rate of 32%.

[0066] 5) Heat treatment: The billet after being drawn into a coil is heat treated at a temperature of 370℃ for 5 hours.

[0067] 6) Drawing: The heat-treated billet is pickled and then drawn to the finished product specifications. The drawing rate is 20%, and a finished product with a diameter of φ5mm is obtained.

[0068] 7) Finished product annealing: The drawn finished product is subjected to low-temperature annealing treatment at a temperature of 250℃ for 6 hours.

[0069] Example 3 This embodiment provides a method for preparing a lead-free brass alloy, specifically including the following steps: 1) Melting: Proportion the raw materials according to the requirements in Table 1, and add them sequentially to the melting furnace for heating and melting. Control the melting temperature at 1030℃.

[0070] 2) Casting: Ingots are produced using a semi-continuous casting method at a casting temperature of 1010℃.

[0071] 3) Extrusion: The ingot is heated and held at 700℃. After the ingot reaches the required temperature, it is hot extruded at an extrusion ratio of 661:1, an extrusion speed of 7mm / s, and a cooling rate of 230℃ / h after extrusion.

[0072] 4) Coil drawing: The extruded billet is pickled and then coiled, with a coil drawing rate of 33%.

[0073] 5) Heat treatment: The blank after being drawn is heat treated at a temperature of 380℃ for 4 hours to obtain a finished product with a diameter of φ4mm.

[0074] 6) Drawing: The heat-treated billet is pickled and then drawn to the finished product specifications. The drawing rate is 20%.

[0075] 7) Finished product annealing: The drawn finished product is subjected to low-temperature annealing treatment at a temperature of 280℃ for 4 hours.

[0076] Example 4 This embodiment provides a method for preparing a lead-free brass alloy, specifically including the following steps: 1) Smelting: Proportion the raw materials according to the requirements in Table 1, and add them sequentially to the smelting furnace for heating and melting. Control the smelting temperature at 1120℃.

[0077] 2) Casting: Ingots are produced using a semi-continuous casting method at a casting temperature of 1050℃.

[0078] 3) Extrusion: The ingot is heated and held at 735℃. After the ingot reaches the required temperature, it is hot extruded at an extrusion ratio of 661:1, an extrusion speed of 5mm / s, and a cooling rate of 230℃ / h after extrusion.

[0079] 4) Coil drawing: The extruded billet is pickled and then coiled, with a coil drawing rate of 33%.

[0080] 5) Heat treatment: The billet after being drawn is heat treated at a temperature of 410℃ for 3.5 hours.

[0081] 6) Drawing: The heat-treated billet is pickled and then drawn to the finished product specifications. The drawing rate is 20%, and the finished product with a diameter of φ4mm is obtained.

[0082] 7) Finished product annealing: The drawn finished product is subjected to low-temperature annealing treatment at a temperature of 280℃ for 4 hours.

[0083] Comparative Example 1 This comparative example provides a method for preparing a lead-free brass alloy, specifically including the following steps: 1) Smelting: Proportion according to the composition requirements in Table 1, add the raw materials to the smelting furnace in sequence for heating and melting, and control the smelting temperature at 1000℃.

[0084] 2) Casting: The production is carried out by iron mold casting. After the raw material melts and reaches the temperature required for smelting, it is held at the temperature for 20 minutes, and then the molten copper is directly poured into the iron mold.

[0085] 3) Extrusion: The ingot is heated and then extruded. The extrusion heating temperature is 650℃, the heating time is 2h, the extrusion strain percentage is 71%, and the extrusion ratio is 13:1.

[0086] 4) Finished product stretching: The extruded billet is pickled and then stretched, with a stretching rate of 14%.

[0087] The microstructure of the lead-free brass alloy prepared in Comparative Example 1 is shown in the figure below. Figure 3 As shown.

[0088] Comparative Example 2 This comparative example provides a method for preparing a lead-free brass alloy, which differs from Comparative Example 1 only in its composition, as shown in Table 1.

[0089] Comparative Example 3 This comparative example provides a method for preparing a lead-free brass alloy, which differs from Example 1 only in the extrusion temperature, which is 620°C.

[0090] Comparative Example 4 This comparative example provides a method for preparing a lead-free brass alloy, which differs from Example 1 only in the extrusion temperature, which is 800°C.

[0091] Comparative Example 5 This comparative example provides a method for preparing a lead-free brass alloy, which differs from Example 1 only in the annealing temperature of the finished product, which is 160°C.

[0092] The microstructure and mechanical properties of the lead-free brass alloys prepared in the above embodiments and comparative examples were tested. The test results are shown in Table 2. The test methods are as follows: Tensile strength and elongation: Refer to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Tensile testing at room temperature".

[0093] Microscopic properties: Performed according to YS / T 449-2002 "Inspection Methods for Microstructure of Copper and Copper Alloy Castings and Processed Products". Area percentage and area distribution number refer to the total area or number of target phases identified in the selected test area using image processing software, and calculated based on the area of ​​the corresponding phase, within a 500x magnified image of the microstructure.

[0094] Table 2. Performance test results of copper alloy products from the examples

[0095] Note: The easily machinable phases in Examples 1-4 include Cu5Si phase, Cu3Si phase and Fe3Si phase; ε phase refers to all phases except α and β.

[0096] The processing properties and corrosion resistance of the lead-free brass alloys prepared in the above embodiments and comparative examples were tested. The test results are shown in Table 3. The test methods are as follows: Ammonia fumigation test: The test shall be conducted in accordance with GB / T 10567.2-2007 "Method for testing residual stress of copper and copper alloy processed materials - ammonia fumigation test".

[0097] Cutting index: The cutting performance test method in Appendix B of YS-T 647-2007 "Copper-Zinc-Bismuth-Tellulose Alloy Rods" is used for evaluation. The cutting index of C36000 (HPb63-3) is set to 100%.

[0098] Table 3. Test Results of Terminal Applications in Examples and Comparative Examples

[0099] According to Tables 2 and 3: 1) The elongation of Comparative Examples 1-2 is significantly lower than that of the Example, which cannot meet the requirements of cold pressing of the pin products.

[0100] 2) Comparative Examples 1-2 have lower extrusion ratios, resulting in insufficient grain and machinable phase fragmentation, larger overall size, and lower distribution number per unit area. Therefore, their machinability is inferior to that of the Examples.

[0101] 3) The α phase area ratio of comparative examples 1-2 is relatively high, and the morphology is continuously distributed. The uniformity of the microstructure and properties is not as good as that of the examples. These factors result in greater cutting resistance and less chip breaking during the cutting process compared to the examples, thus resulting in lower cutting performance.

[0102] 4) The embodiments effectively controlled the size and morphology of the α phase, while also reasonably controlling the proportion of the β phase to avoid excessive embrittlement of the material, achieving a balance between reasonable machinability and corrosion resistance. Furthermore, through reasonable process design, the residual stress inside the material was kept within a low range, and no cracking occurred after ammonia fumigation testing. The overall corrosion resistance performance was superior to comparative examples 1-2.

[0103] 5) Due to the lower extrusion temperature, Comparative Example 3 exhibits a large number of elongated (length-to-width ratio much greater than 4) α-phase structures. At the same time, the proportion of α-phase also increases due to the lower temperature, reducing the number of easily machinable phases in the material. Furthermore, the elongated α-phase is not conducive to chip breaking during machining. Therefore, the cutting performance of Comparative Example 3 is inferior to that of the Example.

[0104] 6) In Comparative Example 4, due to the higher extrusion temperature, the number of brittle β phases was higher and the number of soft and tough α phases was lower, which further improved the machinability, but significantly reduced the corrosion resistance.

[0105] 7) Comparative Example 5 has a lower annealing temperature, resulting in higher residual stress inside the material, lower elongation, and inferior stress corrosion resistance and cold working formability compared to the Example.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lead-free brass alloy, characterized in that, It comprises, by weight percentage, Cu 59-62%, Sn 0.7-1.0%, Si 0.1-0.5%, Fe 0.001-0.2%, B 0-0.01%, with the balance being Zn and unavoidable impurities.

2. The lead-free brass alloy according to claim 1, characterized in that, The average grain size of the α phase in the lead-free brass alloy is ≤0.045 mm; And / or, the aspect ratio of the α-phase grains in the lead-free brass alloy is 1 to 4; And / or, the α phase area percentage in the lead-free brass alloy is 30-65%.

3. The lead-free brass alloy according to claim 1, characterized in that, The β phase area percentage in the lead-free brass alloy is 30-65%; And / or, the area percentage of the phases other than α and β in the lead-free brass alloy is <5%.

4. The lead-free brass alloy according to claim 1, characterized in that, The lead-free brass alloy includes a free-machining phase, which includes at least one of Cu5Si phase, Cu3Si phase and Fe3Si phase.

5. The lead-free brass alloy according to claim 4, characterized in that, The average size of both Cu5Si and Cu3Si phases is ≤10 μm; And / or, the average size of the Fe3Si phase is ≤5 μm; And / or, the average grain size of the easily machinable phase is ≤4μm.

6. The lead-free brass alloy according to claim 4, characterized in that, The number of free-machining phases per unit area is ≥3000 / mm². 2 .

7. The lead-free brass alloy according to claim 1, characterized in that, The lead-free brass alloy has a tensile strength ≥550MPa; And / or, the elongation of the lead-free brass alloy is ≥5%; And / or, the cutting index of the lead-free brass alloy is ≥40%; And / or, the lead-free brass alloy surface forms an oxide film upon contact with air, the oxide film comprising copper oxide and tin oxide.

8. A method for preparing the lead-free brass alloy according to any one of claims 1-7, characterized in that, The process includes sequential smelting, casting, extrusion, coil drawing, heat treatment, drawing and finished product annealing, wherein raw materials are added in the smelting step according to the composition of the lead-free brass alloy as described in any one of claims 1-7.

9. The method for preparing the lead-free brass alloy according to claim 8, characterized in that, The temperature for the smelting step is 900-1150℃; And / or, the casting process is carried out using continuous casting or semi-continuous casting methods; And / or, the temperature of the casting step is 950~1080℃; And / or, the extrusion temperature is 650-750℃, the extrusion ratio is 200~1000:1, and the extrusion speed is 3~12mm / s; And / or, the cooling rate after extrusion is 20~500℃ / h; And / or, the processing rate of the coiled part is 5~40%.

10. The method for preparing the lead-free brass alloy according to claim 8, characterized in that, The temperature for the heat treatment step is 320~420℃, and the holding time is 2~8h; And / or, the drawing rate is 4~35%; And / or, the temperature of the finished product annealing step is 220~320℃, and the holding time is 3~12h.

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