A zinc-white copper alloy and preparation method thereof

Abstract

The invention discloses a zinc-white copper alloy, which comprises, by weight percentage, 48.0-53.2 wt% of Cu, 5.8-8.0 wt% of Ni, 1.0-3.0 wt% of Mn, 1.0-2.8 wt% of Pb, 0.0001-0.3 wt% of Fe, and the balance being Zn and unavoidable impurities. Twins are contained in the microstructure of a cross section of the zinc-white copper alloy, and the average width of the twins is 0.5-5 μm. The present invention can achieve a yield strength of zinc white copper of 520 MPa or greater, a tensile strength of 580 MPa or greater, a hardness of HV 155 or greater, and an elongation of 8 to 15%. The weight loss rate after corrosion for 48 hours is 0.02% or less. The alloy can be repeatedly bent 180° without breaking within 6 bends, thus meeting processing and use requirements. That is, after the alloy is stamped into a sample blank, the sample blank has no cracks on its surface and a dimensional tolerance of 0.02 mm or less. When a load of 1.0 Nm is applied to the sample blank, the deformation angle is less than 5°, and the drop test requirements are met.

Description

Technical Field

[0001] The invention belongs to the field of copper alloys, and in particular relates to a zinc-white copper alloy and a preparation method thereof. Background Art

[0002] Nickel silver boasts excellent strength and hardness, good plasticity, good corrosion resistance, and reasonable processing properties, making it widely used in precision instrument components. With the rapid development of science and technology in recent years, the demand for product applications has increased, and the performance requirements for nickel silver alloys have also become increasingly stringent. This is especially true for complex and miniaturized products like mechanical keys, which typically require multiple passes of deep drawing, stamping, and electroplating. These alloys require not only excellent stamping properties but also superior corrosion resistance and good plasticity.

[0003] In addition, due to the usage characteristics of the above-mentioned products, they are frequently plugged and unplugged, twisted, and easily dropped during use, which places extremely high demands on the strength and bending resistance of the alloy. Therefore, most of them use high-nickel-zinc-white copper alloy materials, but the high cost and strong dependence on precious metal resources seriously restrict the development of the processing industry of this type of products. At the same time, the surface quality and dimensional tolerance of the sample after stamping are very high. The surface of the alloy billet needs to be clean and burred, with high flatness and small dimensional tolerance. During stamping, since the alloy material needs to have good ductility to meet the stamping requirements, it will also cause a certain amount of plastic deformation along the stamping direction. Macroscopically, it manifests as excess burrs on the edge of the part, which makes it difficult to meet the usage requirements.

[0004] To meet these demands, there is an urgent need for alternative alloy materials that offer low precious metal content, high strength, bending and corrosion resistance, dimensional precision, and excellent stamping properties. Currently, the market simply replaces nickel with copper to reduce material production costs, without paying much attention to other material properties, particularly bending resistance and stamping properties. Therefore, a new alloy research is needed to develop alloys that meet the requirements of products such as mechanical keys. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a zinc-white copper alloy and a preparation method thereof in view of the shortcomings of the existing technology. The alloy has excellent strength, corrosion resistance, bending resistance, excellent stamping processability and other comprehensive properties, can be processed into rods, wires and flat wires, and is suitable for industries such as mechanical keys.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a zinc-white copper alloy, which has a weight percentage composition of: 48.0-53.2wt% Cu, 5.8-8.0wt% Ni, 1.0-3.0wt% Mn, 1.0-2.8wt% Pb, 0.0001-0.3wt% Fe, and the balance is Zn and inevitable impurities; the microstructure of the cross section of the zinc-white copper alloy contains twins, and the average width of the twins is 0.5-5μm.

[0007] The weight percentage of Ni in the zinc-white copper alloy of the present invention is 5.8 to 8.0 wt%. Ni, as the main alloying element, forms a continuous solid solution with Cu, has a solid solution strengthening effect, and improves the strength, hardness and corrosion resistance of the alloy. When the Ni content in the alloy is less than 5.8 wt%, the strength, hardness and corrosion resistance of the alloy are low, the elongation is increased, and its strength, bending resistance and electroplating processing cannot meet the requirements. When the Ni content exceeds 8.0 wt%, Ni, as a precious metal, has an excessively high Ni content that increases the alloy manufacturing cost and significantly deteriorates its processing performance. Therefore, the Ni content in the zinc-white copper alloy of the present invention is controlled to be 5.8 to 8.0 wt%.

[0008] The zinc-white copper alloy of the present invention, as a primary element, dissolves extensively in the copper matrix, forming a broad single-phase α solid solution region. This exhibits a solid solution strengthening effect, improving the alloy's strength, hardness, and corrosion resistance. While the nickel content remains constant, increasing the zinc content transforms the alloy from a single α phase to an α+β dual-phase structure. This significantly enhances the alloy's corrosion resistance, meeting the requirements of electroplating processing, and improves its hot workability. Therefore, by controlling the zinc content, the present invention achieves an alloy with an α+β dual-phase structure, enhancing the alloy's strength, hardness, and corrosion resistance while also improving its processability. In zinc-white copper alloys with too low Zn content, the β-phase structure content is reduced or even non-existent. When the alloy is hot-extruded at high temperatures, it is prone to cracking, which increases the processing difficulty and is not conducive to the enhancement of strength, hardness and corrosion resistance. It is difficult to meet the requirements of bending resistance test, drop test and electroplating. However, if the Zn content is too high, the β-phase structure content will increase, reducing the plastic deformation ability of the alloy. At room temperature, the hard and brittle β-phase makes the alloy more difficult to stamp, reduces the formation of deformation twins, and reduces the twin strengthening effect.

[0009] Mn has a high solid solubility in Cu-Ni-Zn alloys, further enhancing the alloy's strength through solid solution strengthening. Furthermore, Mn significantly reduces the alloy's stacking fault energy, promoting twin formation within the grains and enhancing the alloy's twin strengthening effect. When a certain amount of Mn is added to the alloy, it forms MnNi compounds with Ni, which refine the grains and provide precipitation strengthening, further improving the alloy's strength, bend resistance, and corrosion resistance. The Mn content in the zinc-white copper alloy of the present invention is controlled to be between 1.0 and 3.0 wt%. On the one hand, excessive Mn content can lead to the formation of a large amount of MnNi compounds in the alloy, resulting in an overly hard alloy, making multiple machining and stamping difficult, and even increasing the risk of cracking during machining, reducing workability. On the other hand, a high Mn content can increase the β-phase content in the alloy, reducing its plastic deformation capacity, making cold working more difficult and more prone to cracking. However, when the Mn content is too low, its effect on improving the alloy's properties is limited.

[0010] The present invention improves the processability of the alloy by adding a small amount of Pb element. Pb is almost not soluble in copper, and is mainly in the form of particles and evenly distributed in the zinc-white copper alloy. Considering that Pb is mainly distributed on the grain boundaries in the form of particles, and the surface tension of liquid Pb is relatively small, the Pb content in the alloy should not be too high. On the one hand, the zinc-white copper alloy with a high Pb content has a large tendency to longitudinal cracking during annealing. On the other hand, the high content of Pb increases the tendency to aggregate. Large-area Pb particles will reduce the corrosion resistance of the alloy, and the corrosion resistance of the alloy is difficult to achieve the expected performance, resulting in the difficulty in completing the electroplating process of the alloy. A Pb content below 1.0wt% has no significant effect on improving the processing performance of the alloy, and the burrs of the sample blank after stamping increase, making it difficult to achieve the purpose of improving the processing efficiency and processing quality of the parts, and the dimensional tolerance of the parts is large. Therefore, the Pb content in the zinc-white copper alloy of the present invention is controlled at 1.0-2.8wt%, which is conducive to the effective control of the dimensional tolerance of the stamped products and meets the processing and application requirements of the alloy.

[0011] The solid solubility of Fe in white copper alloy is relatively low, improving the alloy's corrosion resistance and mechanical properties, particularly significantly enhancing its corrosion resistance. Furthermore, the addition of Fe significantly reduces the stacking fault energy of the α-phase matrix, enabling the formation of twins at lower temperatures. The corresponding required deformation energy storage is also lower, which facilitates the formation of twins in the α-phase. The Fe content in the alloy of the present invention is not greater than 0.3wt%, otherwise the alloy is prone to stress corrosion cracking, exacerbating corrosion. An appropriate amount of Fe improves the corrosion resistance of white copper to impact corrosion in corrosive solutions.

[0012] The microstructure of the cross section of the zinc-white copper alloy of the present invention contains twins, and the average width of the twins is 0.5 to 5 μm. Since the grain boundary of the twin is a special low-energy state grain boundary, it can effectively hinder the movement of dislocations, especially when the width of the twin layer is refined to a lower order, its strengthening effect begins to appear. A large number of twins can greatly improve the strength of the alloy without sacrificing plasticity and toughness; but as the width of the twin boundary layer decreases, the tensile plasticity and fracture toughness of the alloy increase, especially the softening ability of the alloy, which is not conducive to improving the bending resistance of the alloy, and the sample after stamping has unnecessary burrs, the dimensional tolerance becomes larger, and the stamping forming becomes worse. Therefore, the zinc-white copper alloy of the present invention introduces a twin stacking fault structure, and by controlling the width of the twin, while effectively hindering the movement of dislocations, and further improving the strength, hardness and bending resistance of the alloy, the work hardening ability of the alloy is reduced, so that the alloy has a certain tensile plasticity and the processing and stamping performance of the alloy is improved. When the average twin width is less than 0.5 μm, as the twin width decreases, the plastic deformation mechanism shifts from being dominated by dislocation-twin boundary interactions to being dominated by the movement of pre-existing dislocations within the twin lamella structure. The alloy softens, and its strength and stamping formability decrease, failing to meet product requirements. Furthermore, the twin boundaries present a strong barrier to the passage of individual dislocations. When the twin lamella is wide, dislocation pileups can form at the twin boundaries, generating stress concentration. This allows dislocations to cross the twin boundaries under relatively low external stresses, reducing the performance strengthening effect. Therefore, twins of a certain width are necessary to achieve high strength and a certain degree of plasticity.

[0013] Preferably, the Ni and Mn contents in the zinc-white copper alloy of the present invention are denoted as [Ni] and [Mn], respectively, and X = 0.5 [Ni] + 2.0 [Mn], where 5.5 ≤ X ≤ 9.0. The Ni and Mn contents in the zinc-white copper alloy of the present invention affect the strength, corrosion resistance, and bendability of the alloy to a certain extent. When the X value is less than 5.5, the strength, corrosion resistance, and bendability of the alloy are significantly lower. When the X value is greater than 9.0, a large amount of MnNi compounds are formed, the hardening rate of the alloy is higher, cracks are easily formed during sample processing and drop testing, and the yield rate is poor. On the other hand, when the Ni content is too high, the manufacturing cost of the alloy increases.

[0014] Preferably, the zinc-white copper alloy of the present invention may further include one or more of Sn, Mg, Al, Co, Bi, S, and Si in a total amount of 0.001 to 1.0 wt%. The addition of small amounts of Sn, Mg, Al, Co, Bi, S, and Si can reduce the alloy's stacking fault energy, facilitate the formation of twins, and enhance the strength and bending resistance of the zinc-white copper alloy of the present invention. Appropriate amounts of Sn, Mg, Al, Co, Bi, S, and Si improve the alloy's strength without significantly negatively impacting its workability and corrosion resistance. If the total amount of these elements exceeds 1.0 wt%, the overall performance of the alloy deteriorates.

[0015] Preferably, in the microstructure of the cross section of the zinc-white copper alloy of the present invention, the number of twins is ≥1×10 4 Pieces / mm 2 The zinc-white copper alloy of the present invention introduces a large number of twin fault structures to further strengthen the alloy. As the number of twins decreases, the twin spacing in the grains increases, which weakens the effect of the twins as a special grain boundary on the movement of dislocations. Dislocation movement is more likely to grow, thereby reducing the strength and bending resistance of the alloy. Therefore, the present invention controls the number of twins to ≥1×10 4 Pieces / mm 2 .

[0016] Preferably, in the microstructure of the cross section of the zinc-white copper alloy of the present invention, the amount of β phase is ≥ 2×10 4 Pieces / mm 2 The β phase is distributed at grain boundaries and within the α phase. The grain size of the β phase at the grain boundaries is ≤50μm, and the grain size of the β phase within the α phase is ≤20μm. Since the amount, size, and distribution of the β phase within the matrix all affect the alloy's strengthening effect, the β phase in the zinc-white copper alloy of the present invention is distributed at the grain boundaries and within the α phase, pinning the grains and dislocations. This effectively improves the alloy's strength and bend resistance while enhancing the alloy's stamping workability. The β phase within the α phase of the zinc-white copper alloy of the present invention is relatively small. Within a certain range, the smaller the β phase particle size, the better the alloy's strength. Furthermore, the β phase is a hard phase, making it difficult for dislocations to cut during movement. Instead, they move around the β phase to form dislocation loops, which facilitates the absorption of external energy, ensuring the alloy's toughness while enhancing its bend resistance. The relatively large β phase particle size at the grain boundaries of the zinc-white copper alloy of the present invention facilitates the disruption of the matrix's continuity during stamping, improving the alloy's stamping workability and processing toughness.

[0017] Preferably, the microstructure of the cross-section of the zinc-white copper alloy of the present invention has an average grain size of ≤20 μm, with grains 1 μm or smaller accounting for more than 20% of the total grain count. The finer the grains, the higher the strength and hardness. This is because finer grains increase the total grain boundary area, resulting in more dislocation barriers and more grains with different orientations that need to be coordinated, increasing the alloy's resistance to plastic deformation. Furthermore, smaller grains increase the number of grains in the alloy structure, allowing for more frequent collisions with grains as cracks develop. This, along with changes in the direction of crack development, can control crack bifurcation, reduce the crack's development rate, and thus improve the alloy's bending resistance. Furthermore, finer grains increase the number of grains per unit volume, increasing the number of grains involved in deformation and making deformation more uniform, resulting in greater plastic deformation before fracture. Therefore, the present invention improves the strength, hardness, and bending resistance of the zinc-white copper alloy by refining the grains and controlling the grain size and the proportion of small grains.

[0018] The zinc-white copper alloy of the present invention has a yield strength of more than 520 MPa, a tensile strength of more than 580 MPa, a Vickers hardness of more than 155, and an elongation of 8-15%. The weight loss rate after corrosion for 48 hours is less than or equal to 0.02%. The alloy is repeatedly bent 180 degrees and does not break within 6 bends, meeting processing and use requirements. That is, after the alloy is stamped into a sample blank, the sample blank has no cracks on the surface and the dimensional tolerance is less than or equal to ±0.02 mm. When a load of 1.0 Nm is applied to the sample blank, the deformation angle is less than 5 degrees, and the drop test requirements are met.

[0019] The preparation method of the zinc-white copper alloy of the present invention comprises the following steps: melting and casting → hot extrusion → stretching → annealing → rolling → annealing → finished product stretching, specifically as follows:

[0020] (1) Melting and Casting: The alloy of the present invention is produced by horizontal continuous casting. The raw materials are melted in an induction furnace according to the composition of the invention alloy and the ingots are drawn from the holding furnace. The melting temperature is 1150-1250°C, and the mold casting is carried out at a casting temperature of 1040-1160°C. The ingots crystallized at this temperature are of good quality and are free of defects such as bubbles, looseness, and inclusions.

[0021] (2) Hot extrusion: In the hot extrusion process adopted by the alloy of the present invention, the extrusion temperature is 750-850°C and the extrusion ratio is above 290. Hot extrusion of the alloy of the present invention at an extrusion ratio above 290 is beneficial to completing the hot extrusion process, preventing cracks during hot extrusion and subsequent cold working, and improving stamping performance; on the other hand, it can ensure the microstructure of the alloy, meet the alloy performance requirements, and achieve the required specifications.

[0022] (3) Stretching: The processing rate is 25-35%. Under this cold deformation condition, the lattice distortion caused is small, the atomic dislocation degree is low, and deformation twins are easily generated. Stretching is used to form an ideal microstructure in the later stage, further achieving the effect of improving the performance of the alloy.

[0023] (4) Annealing: Annealing temperature is 600-700℃, annealing time is 180-300min. After annealing, some deformation twins disappear and new annealing twins are formed. On the one hand, it softens the alloy, which is beneficial for subsequent processing of the alloy; on the other hand, it further homogenizes the alloy structure, avoids the generation of cracks during processing, and improves processing performance.

[0024] (5) Rolling: The alloy of the present invention is cold-deformed by a rolling mill, with a deformation of 40-60%. Further deformation of the alloy through low-temperature rolling is beneficial for the production of high-density dislocations and micron-sized deformation twins. As the rolling deformation increases, the grains become finer, a larger number of twinned lamellae are produced, and the precipitate particles become smaller and more evenly distributed, thereby improving the overall performance of the alloy.

[0025] (6) Annealing: Annealing temperature is 600-700℃, and annealing time is 180-250min. This is to restore the plasticity of the alloy, reduce its deformation resistance, and further optimize the microstructure to achieve the desired performance.

[0026] (7) Finished product stretching: Finished product stretching is performed at a stretching rate of 20-35%, which can obtain samples of the required specifications and slightly improve the strength of the alloy without affecting other properties of the alloy.

[0027] In order to meet the preparation of samples with required specifications, multiple stretching and annealing can be performed before and after rolling during the preparation of the alloy using the preparation method of the present invention, wherein the processing rate of each stretching is 25-40%, the annealing temperature of each annealing is 600-750°C, and the annealing time is 180-280 minutes.

[0028] To remove surface defects and oxides for a smooth surface, a pickling step can be performed before each stretching process. Because white copper easily oxidizes, the presence of oxides, impurities, and other defects disrupts the uniformity and continuity of the alloy matrix, causing stress concentration. These defects are often the source of cracks. Pickling reduces the risk of cracking and improves yield.

[0029] Compared with the prior art, the advantages of the present invention are: the present invention adds the elements Pb, Mn, and a trace amount of Fe to the traditional zinc-white copper alloy to promote the formation of twins, and by controlling the average width of the twins to 0.5 to 5 μm, the alloy's strength and bending resistance are improved, while having little effect on stamping workability. The present invention can achieve a zinc-white copper with a yield strength of ≥520 MPa, a tensile strength of ≥580 MPa, a hardness HV ≥155, and an elongation of 8 to 15%, a weight loss rate of ≤0.02% after 48 hours of corrosion, and a 180° repeated bending within 6 bends without breaking, meeting processing and use requirements. Specifically, after the alloy is stamped into a sample, the sample has no cracks on the surface and a dimensional tolerance of ≤±0.02 mm. When loaded with a load of 1.0 Nm, the deformation angle is less than 5°, and it meets drop test requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a metallographic microstructure photograph of the cross section of the zinc-white copper alloy of Example 3. DETAILED DESCRIPTION

[0031] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0032] According to the compositions of the 10 example alloys and one comparative alloy (alloy designation: BZn10-38) in Table 1, the raw materials were respectively taken and proportioned, smelted at 1180°C, and continuously cast at a continuous casting temperature of 1050°C after melting to form ingots. Ingots were then hot extruded at 775°C and an extrusion ratio of 305 into wires with a diameter of 8.3 mm. The products were then pickled and shaved to remove surface impurities and oxides, and the extruded billets were stretched, annealed, and rolled: first, stretched at a processing rate of 27%, then annealed at 670°C for 210 min, pickled to remove surface impurities, further rolled at a deformation of 50%, and annealed at 650°C for 200 min. Finally, the sample was pickled to remove surface impurities and stretched to obtain a 1.76×7.76 mm flat wire with an elongation of 26%.

[0033] The obtained samples were evaluated for their properties under the following conditions. The test results are shown in Tables 2 and 3.

[0034] The room temperature tensile test is carried out in accordance with GB / T 228.1-2010 Metallic materials tensile tests Part 1: Room temperature test methods on an electronic universal mechanical properties testing machine to test strength and elongation.

[0035] The microhardness HV value is tested on a digital Vickers hardness tester in accordance with GB-T 4340.1-2009 Metallic materials Vickers hardness test Part 1: Test method.

[0036] The corrosion resistance test is carried out in a neutral salt spray with a pH value of 7 for 48 hours in accordance with the NSS test of GB / T 10125-2021 "Artificial atmosphere corrosion test salt spray test".

[0037] Grain size, β phase, twin size and quantity test The sample organization was observed using a metallographic microscope, and the average grain size, quantity and proportion of the phases were calculated based on the results. The calculation results are shown in Table 3. The metallographic microstructure photo of the cross section of the zinc-white copper alloy of Example 3 is shown in Table 3. Figure 1 .

[0038] Deformation angle: After stamping the alloy into a sample with a size of 1.76*7.76mm, it is loaded with a load of 1.0Nm and the permanent deformation angle is measured. The deformation angle is qualified if it is less than 5°.

[0039] Drop test: After the alloy with a size of 1.76*7.76mm is punched into a sample, it is judged as qualified if the sample does not break, bend or other conditions that affect normal use after being dropped from a height of 1m 100 times or more, and is indicated by "○"; otherwise, it is judged as unqualified and is indicated by "×".

[0040] The bending test is carried out in accordance with GB / T238-2013 "Metallic Wire Repeated Bending Test Method" by repeatedly bending 180° on a motorized bending test machine until it breaks, and the number of bends at the time of fracture is determined.

[0041] Table 1

[0042]

[0043] Table 2

[0044]

[0045] Table 3

[0046]

[0047] Note: The B value is the percentage of grains with a grain size of less than 1μm in the total number of grains.

Claims

1. A zinc-white copper alloy, characterized in that: The zinc-white copper alloy comprises, by weight percentage, 48.0-53.2 wt% of Cu, 5.8-8.0 wt% of Ni, 1.0-3.0 wt% of Mn, 1.0-2.8 wt% of Pb, 0.0001-0.3 wt% of Fe, and the remainder being Zn and unavoidable impurities. The microstructure of the cross section of the zinc-white copper alloy contains twins, and the average width of the twins is 0.5-5 μm. The number of β phases is ≥2×10 4 Pieces / mm 2 The β phase is distributed at the grain boundaries and within the α phase, wherein the grain size of the β phase at the grain boundaries is ≤50μm, and the grain size of the β phase within the α phase is ≤20μm.

2. A zinc-white copper alloy according to claim 1, characterized in that: The contents of Ni and Mn in the weight percentage composition of the zinc-white copper alloy are respectively denoted as [Ni] and [Mn], and X=0.5[Ni]+2.0[Mn], then 5.5≤X≤9.

0.

3. The zinc-white copper alloy according to claim 1, characterized in that: The weight percentage composition of the zinc-white copper alloy also includes one or more elements of Sn, Mg, Al, Co, Bi, S, and Si in a total amount of 0.001-1.0 wt%.

4. The zinc-white copper alloy according to claim 1, characterized in that: In the microstructure of the cross section of the zinc-white copper alloy, the number of twins is ≥1×10 4 Pieces / mm 2 .

5. The zinc-white copper alloy according to claim 1, characterized in that: In the microstructure of the cross section of the zinc-white copper alloy, the average grain size is ≤20 μm, and the number of grains below 1 μm accounts for more than 20% of the total number of grains.

6. The zinc-white copper alloy according to any one of claims 1 to 5, characterized in that The zinc-white copper alloy can be bent repeatedly by 180 degrees without breaking within 6 bends.

7. The method for preparing the zinc-white copper alloy according to any one of claims 1 to 6, characterized in that: The following steps are involved: Casting → hot extrusion → stretching → annealing → rolling → annealing → finished product stretching, among which the deformation of rolling is 40~60%.

8. The method for preparing zinc-white copper alloy according to claim 7, characterized in that: The temperature of hot extrusion is 750~850℃, and the extrusion ratio is ≥290.

Images