Copper-zinc wrought alloys, semi-finished products made from copper-zinc wrought alloys, and methods for manufacturing such semi-finished products

Abstract

The present invention relates to a copper-zinc wrought alloy for producing semi-finished products in the form of wire, tube, or rod, having the following composition by weight: Cu: 58.0-66.0%, Si: 0.15-1.2%, P: 0.20-0.38%, Sn: optionally up to 0.5%, Al: optionally up to 0.05%, Fe: optionally up to 0.3%, Ni: optionally up to 0.3%, Pb: optionally up to 0.25%, Bi: optionally up to 0.1%, Te, Se, and In: optionally up to 0.1%, each up to 0.01%, B: optionally up to 0.01%, with the balance being Zn and unavoidable impurities, the proportion of which is less than 0.20% by weight. The alloy has a microstructure consisting of spherical α-phase, β-phase, and phosphide particles. The proportion of the β-phase relative to the total of the α-phase and β-phase is at least 20% by volume and at most 60% by volume. Si is present in both the α-phase and the β-phase. In an area of 21000 μm2, there are 50 to 700 phosphide particles with an equivalent diameter of 0.5 to 1 μm, 10 to 300 phosphide particles with an equivalent diameter of 1 to 2 μm, and 3 to 45 phosphide particles with an equivalent diameter of 2 to 5 μm. The proportions of beta phase and Si, P, and Pb were selected so that the alloy satisfied the following condition: 107.378 - 2.25255·[Beta] - 64.1438·[Si] - 115.18·[P] - 30.7071·[Pb] + 0.017965·[Beta]·[Beta] + 24.6217·[Si]·[Si] + 66.7257·[P]·[P] + 0.542512·[Beta]·[Si] + 1.36208·[Beta]·[P] + 43.4012·[Si]·[P] < 37, where [Beta] is the proportion of beta phase in volume percent, [Si] is the proportion of silicon in weight percent, [P] is the proportion of phosphorus in weight percent, and [Pb] is the proportion of lead in weight percent.

Description

[Technical Field]

[0001] The present invention relates to a copper-zinc wrought alloy for producing semi-finished products in the form of wire, tube or rod, a semi-finished product made of a copper-zinc wrought alloy, and a method for producing such semi-finished products. The copper-zinc wrought alloy generally refers to a wrought material made of a copper-zinc alloy. [Background technology]

[0002] Copper-zinc alloys containing 3-5% lead by weight have good machinability and are very suitable for hot and cold forming. Lead-containing copper-zinc alloys are therefore used in many applications, for example in the automotive industry, building technology, machine building, electronic equipment and components, for connections and components in telecommunications, and as fittings in plumbing.

[0003] The positive effect of lead in copper-zinc forging alloys is due to its isolated presence as fine particles in the structure, which act as chip breakers. During machining, lead exists in a liquid phase due to the strong local deformation of the workpiece and the resulting local temperature rise. Because liquid lead cannot absorb stress, stress is concentrated in the weak load-transmitting matrix, which makes chip breaking more likely. Additionally, during machining, lead is incorporated into the tribological layer between the material and the tool, resulting in effective lubrication and reduced friction and wear. Furthermore, due to its low solubility, lead has no effect on electrical conductivity. This is particularly advantageous for materials used in electrical applications. Lead in copper-zinc alloys is also known to produce significant grain refinement. This is particularly beneficial for the straightness and dimensional accuracy of rod-shaped blanks. High dimensional accuracy is also required for crimping electronic wires. Furthermore, lead is inexpensive.

[0004] However, lead is harmful to the environment. Even small amounts can accumulate in the human body if ingested, potentially causing health problems. Therefore, the EU, the United States, China, and other countries are constantly lowering the lead content limits in copper alloys and making efforts to use lead-reduced or lead-free machinable copper alloys instead of leaded brass. The upper limit is set at 1000 ppm (0.1%) Pb in EU directives, such as RoHS (Directive 2011 / 65 / EU). To ensure good machinability of materials even at such low lead contents, various alloying elements are proposed as lead replacements.

[0005] It is well known from numerous publications that bismuth (Bi) can be used as a lead substitute to improve machinability. The addition of further elements has been proposed to mitigate the formation of Bi films along grain boundaries and the associated susceptibility to stress cracking and hot tearing. References in particular to this regard include U.S. Pat. Nos. 5,611,149, 5,823, 5,914, 6,113, 6,149, 6,152, 6,162, 6,171, 6,181, 6,191, 6,192, 6,193, 6,194, 6,195, 6,196, 6,197, 6,198, 6,199, 7,199, 7,199, 7,199, 7,199, 8,199, 8,199, 9,199, 9,199, 9,199, 10,199, 10,199, 11,199, 12,199, 13,199, 14,199, 15,199, 16,199, 17,199, 18,199, 19,199, 20 ...

[0006] Furthermore, Patent Document 6 discloses a copper-zinc alloy containing 0.1 to 1.5 wt% Si, 0.03 to 0.4 wt% Al, 0.01 to 0.36 wt% P, 0.05 to 0.5 wt% Sn, and 0.001 to 0.05 wt% rare earths. This alloy is easily machinable by forming an α-phase, a β-phase, and occasionally a γ-phase. The Al content generates undesirable Al phosphides. The γ-phase and Al phosphides improve chip formation but shorten tool life. Furthermore, the rare earth content is thought to lead to embrittlement of the structure. These alloys are used for cast and hot-forged parts.

[0007] The use of phosphorus, which forms brittle phosphides in the alloy, as a replacement for lead is further described in U.S. Patent No. 6,275,393 for a material containing 58.5-63.5 wt.% Cu, 0.4-1.0 wt.% Si, 0.005-0.19 wt.% P, 0.003-0.25 wt.% Pb, the balance zinc, and other optional elements. The addition of 0.005-0.19 wt.% P to form phosphides and 0.4-1.0 wt.% Si to strengthen the α and β phases leads, in this case, to a material that is easily machinable. However, the maximum P content of 0.19 wt.% is too low to achieve the grain-refining effect of lead on the structure. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent No. 10-0555854 [Patent Document 2] Korean Patent Publication No. 10-2006-096877 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-290475 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-122427 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-083443 [Patent Document 6] European Patent No. 2194150 [Patent Document 7] International Publication No. 2020 / 261604 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention is based on the problem of providing a copper-zinc wrought alloy for producing semi-finished wire, tubular, or rod-shaped products that have excellent machinability and good mechanical properties and contain as few alloying elements of environmental concern as possible. Furthermore, the alloy must be easily processable on an industrial scale. This requires that the alloy can be easily hot-formed, such as by extrusion, and easily cold-formed, such as by drawing or crimping, and that semi-finished products produced from the alloy have excellent straightness and very good dimensional stability. The present invention is also based on the problem of providing a method for producing semi-finished wire, tubular, or rod-shaped products from such an alloy. [Means for solving the problem]

[0010] The invention is described with respect to a copper-zinc wrought alloy by the features of claim 1 and with respect to a manufacturing method by the features of claim 16. The other related claims are advantageous embodiments and developments of the invention.

[0011] The present invention relates to a copper-zinc wrought alloy for producing semi-finished products in wire, tube or rod form, having the following composition in weight percent: Cu: 58.0-66.0%, Si: 0.15 to 1.2% P: 0.20~0.38%, Sn: optionally up to 0.5%, preferably up to 0.3%; Al: optional up to 0.05% Fe: optional up to 0.3% Ni: optional up to 0.3% Pb: optionally up to 0.25%, preferably up to 0.10%; Bi: optional, maximum 0.1% Te, Se, In: optional, up to 0.1% each, B: Arbitrary up to 0.01% The balance includes Zn and inevitable impurities, The proportion of unavoidable impurities is less than 0.2% by weight. The alloy has a structure consisting of spherical α-phase, β-phase, and phosphide grains. The phosphide grains preferably contain or are phosphides containing copper and / or zinc. The proportion of β-phase to the total of α-phase and β-phase is at least 20% by volume, preferably at least 22% by volume, at most 60% by volume, and preferably at most 40% by volume. Silicon is present in both the α-phase and the β-phase. 21000 μm 2 In this area, there are 50 to 700 phosphide particles with an equivalent diameter of 0.5 to 1 μm, 10 to 300 phosphide particles with an equivalent diameter of 1 to 2 μm, and 3 to 45 phosphide particles with an equivalent diameter of 2 to 5 μm. The proportion of the β phase and the proportions of Si, P, and Pb are determined so that this alloy satisfies the following conditions: 107.378-2.25255·[Beta]-64.1438·[Si]-115.18·[P]-30.7071·[Pb]+0.017965·[Beta]·[Beta]+24.62 17·[Si]·[Si]+66.7257·[P]·[P]+0.542512·[Beta]·[Si]+1.36208·[Beta]·[P]+43.4012·[Si]·[P]<37 where [Beta] is the proportion of the β phase in volume percent, [Si] is the proportion of silicon in weight percent, [P] is the proportion of phosphorus in weight percent, and [Pb] is the proportion of lead in weight percent.

[0012] The present invention is based on the idea of reducing the proportion of Pb in copper-zinc alloys as much as possible without impairing the machinability of the alloy. For this purpose, Si and P are appropriately added to the alloy, and the proportion of β phase is adjusted so that, on the one hand, favorable machinability properties result, and, on the other hand, the hot and cold forming of the alloy is not impaired, and the semi-finished products produced from the alloy have excellent straightness. Furthermore, the process controls, especially during casting and hot forming, are selected so as to result in the desired properties.

[0013] A spherical α-phase is a prerequisite for good straightness and dimensional stability of the semifinished product. The α-phase arises from the β-phase after hot forming. Therefore, the β-phase must be fine in the as-cast state. Surprisingly, it has been shown that increasing the P content results in a significant grain refinement of the original base matrix of the β-phase in the as-cast structure. To achieve sufficient grain refinement of the as-cast and subsequently formed structures, an addition of at least 0.20 wt.% P is necessary. This effect is similar to the effect of 2–3 wt.% Pb on the grain refinement of α-β brass. During primary crystallization of the β-phase, P accumulates in the residual melt, thereby causing the refinement of the β-phase. During solidification, a eutectic mixture consisting of phosphides and the β-phase is formed. In addition to the grain refinement of the base matrix of the β-phase, grain refinement of the α-phase is also observed. This grain refinement of the as-cast structure by P facilitates hot forming and continues in the structure after hot forming, ultimately leading to a refined final structure. When the P content is at least 0.20 wt.%, the phosphide particles are present in both the α and β phases in the final state. Preferably, the alloy contains at least 0.22 wt.% P. At P contents above 0.38 wt.%, coarse phosphides occur in the as-cast state due to the solidification of individual phosphides into long networks. These coarse phosphides wet the grain boundaries and melt during hot forming, causing cracks in the material. In addition, ductility is reduced.

[0014] However, if the cooling rate during casting of the alloy is too slow, for example, during casting in a stationary mold, these undesirable effects can occur even with a P content of less than 0.38 wt. The required high cooling rate can be achieved, for example, by continuous casting in a water-cooled mold. Thus, with a P content of 0.20-0.38 wt. %, the phosphide particles are already spherical and finely dispersed in the structure in the as-cast state. Such cast products can then be easily hot-forged at temperatures between 620 and 700 °C, preferably between 630 and 680 °C, without cracks forming in the material.

[0015] Furthermore, the spherical α phase requires controlled cooling of the material after hot forming. In the temperature range of 550°C to 350°C, the cooling rate should be at least 30°C per minute (°C / min), preferably at least 40°C per minute, at most 60°C per minute, and preferably at most 50°C per minute. The uniformly finely dispersed phosphides, accompanied by the fine β phase in the as-cast state, dissolve within the matrix during hot forming and then are newly formed during the cooling process during hot forming. In this way, the characteristic phosphide distribution in the as-cast state is ultimately reflected in the final structure. Therefore, the phosphide distribution and the spherical shape of the α phase in the final state are determined not only by the alloy's chemical composition but also by the process controls during casting and hot forming. Therefore, the phosphide characteristics in the final state are like fingerprints left on the product by specific process controls. The phosphide distribution in the final state can be characterized as follows: 21000 μm 2 In this area, there are 50 to 700 phosphide particles with an equivalent diameter of 0.5 to 1 μm, 10 to 300 phosphide particles with an equivalent diameter of 1 to 2 μm, and 3 to 45 phosphide particles with an equivalent diameter of 2 to 5 μm. The equivalent diameter of a phosphide particle is understood to be the diameter of a circle with the same area as the phosphide particle. The majority of phosphide particles with an equivalent diameter of at least 0.5 μm have an equivalent diameter of at most 2 μm. Preferably, the proportion of phosphide particles with an equivalent diameter of 0.5 to 2 μm is at least 70% of the number of all phosphide particles with an equivalent diameter of at least 0.5 μm. Particularly preferably, this proportion is at least 80%. Furthermore, it is advantageous if at least 40%, preferably at least 60%, of all phosphide particles with an equivalent diameter of at least 0.5 μm have an equivalent diameter of at most 1 μm. The presence of phosphide particles having an equivalent diameter smaller than 0.5 μm or larger than 5 μm in the alloy is not excluded, provided that the number of phosphide particles having an equivalent diameter larger than 5 μm is at most 30%, preferably at most 15%, of the number of phosphide particles having an equivalent diameter between 2 and 5 μm.

[0016] A brittle structural component, which acts as a separation site during machining and thereby supports chip breaking, is beneficial to the machinability of the alloy. The β phase is brittle and favors machinability. An increase in the β phase proportion can be achieved by increasing the Zn content and / or by adding silicon, since silicon stabilizes the β phase. Furthermore, reducing the ductility of the α phase has been shown to be beneficial for good machinability. This is achieved by adding and embedding silicon in the α phase, as well as by finely dispersed phosphides in the α phase. Therefore, the Si proportion in the alloy must be at least 0.15 wt.%. These phosphide particles act as separation sites during machining and become particles favoring chip breaking. A P proportion less than 0.20 wt.% results in unfavorable chipping and coarse grains. Furthermore, a low optional Pb proportion favors machinability.

[0017] Therefore, the machinability of the alloy is determined by the combined selection of the parameters of β phase, Si, P, and optionally a small proportion of Pb. In the proposed copper-zinc wrought alloy, the proportion of β phase relative to the sum of α and β phases is at least 20% by volume, preferably at least 22% by volume. A high proportion of β phase has a detrimental effect on cold forming. Therefore, the proportion of β phase is at most 60% by volume, preferably at most 40% by volume. The Si content of the alloy is 0.15-1.2% by weight, and the P content is 0.20-0.38% by weight. Furthermore, up to 0.25% by weight of Pb, preferably up to 0.10% by weight, can be added. In this case, the proportion of β phase and the proportions of Si, P, and Pb are determined so that the alloy satisfies the following conditions: 107.378-2.25255·[Beta]-64.1438·[Si]-115.18·[P]-30.7071·[Pb]+0.017965·[Beta]·[Beta]+24.62 17·[Si]·[Si]+66.7257·[P]·[P]+0.542512·[Beta]·[Si]+1.36208·[Beta]·[P]+43.4012·[Si]·[P]<37 where [Beta] is the percentage of beta phase in volume percent, [Si] is the percentage of silicon in weight percent, [P] is the percentage of phosphorus in weight percent, and [Pb] is the percentage of lead in weight percent. This relationship quantitatively describes the influence of the parameters beta phase, Si, P, and Pb on the machinability properties of the alloy, as well as the interactions between these parameters. For example, a small percentage of beta phase can be compensated for by a higher percentage of silicon and / or phosphorus in the alloy composition specification, and vice versa.

[0018] The Cu content of the alloy is 58.0-66.0 wt. %. If the Cu percentage is less than 58.0 wt. % the alloy has too little ductility. If the Cu percentage is greater than 66.0 wt. % the alloy has too little zinc to achieve good machinability.

[0019] Furthermore, the composition of the alloy can be preferably selected so that the Si / P ratio is at least 0.6, particularly preferably at least 0.9. In a further preferred embodiment, the composition of the alloy can be selected so that the sum of Si and P is at least 0.58% by weight, particularly preferably at least 0.64% by weight. The two measures mentioned above, both independently and in combination, contribute to meeting the aforementioned ratios and thus to achieving advantageous machinability properties.

[0020] The optional elements Sn and Al support the formation of the β phase. If the Sn content is greater than 0.5% by weight, additional tin-containing phases may occur, which may adversely affect the alloy's properties. Preferably, the tin content should be at most 0.3% by weight, particularly preferably at most 0.2% by weight. Furthermore, aluminum forms aluminum phosphides with phosphorus. However, these are undesirable, so the Al content should not exceed 0.05% by weight.

[0021] Iron leads to a refinement of the grain structure. Furthermore, iron forms hard phosphides, which adversely affect the tool life during machining. Therefore, the iron content should be at most 0.3% by weight, particularly preferably at most 0.1% by weight.

[0022] Nickel supports the formation of the α phase. In addition, nickel forms phosphides, which do not have a beneficial effect on machinability. Therefore, the nickel content should be at most 0.3% by weight, particularly preferably at most 0.1% by weight.

[0023] The element Bi is present as an impurity in secondary raw materials, e.g., scrap. It can improve the machinability of the alloy. In amounts up to a maximum of 0.1 wt.%, Bi does not have a detrimental effect on the alloy. Therefore, a maximum of 0.1 wt.% Bi is permitted in this alloy. Preferably, the Bi content is less than 0.015 wt.%.

[0024] The elements Te, Se, and In can advantageously have a beneficial effect on the machinability of the alloy. In amounts up to a maximum of 0.1% by weight each, they do not have a detrimental effect on the alloy. Therefore, a maximum of 0.1% by weight of Te, Se, and In each is permitted in this alloy.

[0025] Boron in any proportion up to 0.01 wt % contributes to grain refinement.

[0026] The remainder of the alloy composition consists of zinc and unavoidable impurities. To avoid uncontrollable influence of impurities on the properties of the alloy, the proportion of these impurities is limited to a maximum of 0.2% by weight. Preferably, the proportion of Mn and Mg should be at most 0.1% by weight each, and particularly preferably at most 0.05% by weight each, since these elements can form phosphides that can compete with copper- and / or zinc-containing phosphides.

[0027] In a preferred embodiment of the invention, the Pb content of the alloy may be at least 0.02% by weight, even such a small Pb content improving the machinability and having a positive effect on grain refinement.

[0028] Advantageously, the ratio of the weight fraction of P to the sum of Fe and Ni may be greater than 2.0, i.e., P / (Fe+Ni)>2.0, which results in the formation of mainly copper- and / or zinc-containing phosphides, which are advantageous for machinability, while the formation of iron or nickel phosphides is suppressed.

[0029] In particular, it may be advantageous for the proportion of Fe and Ni to be at most 0.1% by weight in total, as this limit also suppresses the formation of iron and nickel phosphides compared to the formation of copper- and / or zinc-containing phosphides.

[0030] In a particularly advantageous embodiment of the invention, the P content can be at least 0.26% by weight and at most 0.33% by weight. If the P content is at least 0.26% by weight, a sufficiently large number of phosphide particles are formed, thereby achieving particularly fine grains, a spherical α-phase, and very good machinability. If the P content of the alloy is at most 0.33% by weight, crack formation during hot forming is more reliably avoided.

[0031] In a further embodiment of the invention, the proportion of Si may be at most 0.35% by weight. Wrought copper-zinc alloys with a relatively low proportion of Si are characterized by a high electrical conductivity, i.e. a conductivity of at least 12 MS / m.

[0032] In a further embodiment of the invention, the proportion of Si can be at least 0.25% by weight, preferably at least 0.30% by weight, which achieves a good surface quality and at the same time very good machinability.

[0033] In particular, in the above-mentioned embodiments, the proportion of Cu can be at least 60.0% by weight and at most 61.5% by weight. An alloy with particularly advantageous properties is obtained with a composition of 60.0-61.5% by weight of copper, 0.25-0.35% by weight of silicon, 0.26-0.33% by weight of phosphorus, the balance being Zn and unavoidable impurities.

[0034] In an alternative embodiment of the invention, the Si percentage may be at least 0.50 wt. % and at most 1.0 wt. Wrought copper-zinc alloys with Si percentages in this range are characterized by excellent machinability while maintaining good ductility.

[0035] Advantageously, the copper-zinc wrought alloy may have a hardness of at least 170 HV10, preferably at least 180 HV10.

[0036] Advantageously, the copper-zinc wrought alloy may have a tensile strength Rm of at least 520 MPa, preferably at least 560 MPa.

[0037] Advantageously, the copper-zinc wrought alloy may have an alpha grain size of at most 21 μm, preferably at most 17 μm.

[0038] Advantageously, the copper-zinc wrought alloy may have an electrical conductivity of at least 12 MS / m.

[0039] The subject of the present invention is also a semi-finished product in the form of a wire, tube or rod, made of the above-mentioned copper-zinc wrought alloy, as well as components manufactured from such a semi-finished product by machining and any further processing steps, which semi-finished product may be in the form of a profile.

[0040] A further aspect of the present invention relates to a method for producing semi-finished products in the form of wires, tubes or rods, said method comprising the following steps: a) melting a copper alloy having the composition as described above; b) continuous casting of a tube or bolt type casting format with a water-cooled mold; c) hot forging the cast format at a temperature of 620-700 ° C, followed by cooling in the temperature range of 550-350 ° C at a cooling rate of 30-60 ° C per minute; d) optionally, a heat treatment in the temperature range of 525-625°C for 1-5 hours, followed by a cooling step in the temperature range of 500-350°C at a cooling rate of 20-40°C per minute; e) optionally, cold forming.

[0041] The alloys can be melted using Cu cathodes, Zn blocks, brass scrap, Cu-P master alloys, or Cu-Si master alloys. Melting is preferably carried out in an induction furnace. The melt is poured into water-cooled molds to produce tube or bolt casting formats.

[0042] This cast product can optionally be machined and then hot forged at a temperature of 620-700°C. The hot-forged intermediate product is then cooled at a rate of 30-60°C per minute, preferably 40-50°C per minute, in the temperature range of 550-350°C. This defined cooling results in an advantageous ratio of α-phase to β-phase and an advantageous particle distribution of copper and / or zinc phosphides. An optional heat treatment can be performed prior to hot forging to homogenize the cast product.

[0043] In the first manufacturing method, hot forging is followed by pickling without any further intermediate steps, followed by cold forming. In cold forming, the degree of deformation is preferably 3-30%, where the degree of deformation is understood to mean the relative reduction in the cross-sectional area of the product. This first manufacturing method is highly advantageous because no further work steps are performed between hot forging and cold forming, with the exception of the pickling process.

[0044] In the second manufacturing method, hot forging is followed by a heat treatment at a temperature in the range of 525-625°C, preferably 550-600°C, for 1-5 hours, followed by cooling at a temperature in the range of 500-350°C at a cooling rate of 20-40°C per minute. By selecting the heat treatment conditions in combination with the defined cooling after the heat treatment, it is possible to achieve an advantageous ratio of α-phase to β-phase and an advantageous particle distribution of copper and / or zinc phosphides. To increase the proportion of β-phase, heat treatment should be performed at approximately 600°C. To increase the proportion of α-phase, heat treatment should be performed at approximately 550°C. Thus, the ratio of α-phase to β-phase and the particle distribution of phosphides can be adjusted and optimized by heat treatment. This, in particular, improves ductility. After the heat treatment, pickling and cold forming can be performed, as in the first manufacturing method. DETAILED DESCRIPTION OF THE INVENTION

[0045] Further technical features and advantages of the method according to the invention will now be explicitly given in the description and examples relating to the copper-zinc wrought alloy according to the invention.

[0046] The present invention will now be described in detail with reference to examples.

[0047] Samples No. 1 to No. 45 were melted in an induction furnace and then poured into molds. The sample compositions are recorded in Tables 1 to 4. Sample No. 16 is the lead-containing reference alloy CuZn39Pb3. The samples were machined, homogenized at 650°C for 1 hour, and then hot-formed. The cooling rate after hot-forming was approximately 40°C per minute in the temperature range of 550 to 350°C.

[0048] Samples No. 1 to No. 26 were hot-formed, then machined, and subsequently cold-formed to a forming ratio of 20%. Samples No. 27 to No. 45 were annealed after three hours of hot forming. The annealing temperature was approximately 600°C for No. 28 and No. 35 to No. 41, and approximately 550°C for Samples No. 27, No. 29 to No. 34, and No. 42 to No. 45. After annealing, the samples were cooled at a rate of approximately 25°C per minute in the temperature range of 500 to 350°C. Samples No. 27 to No. 45 were then machined, and subsequently cold-formed to a forming ratio of 20%.

[0049] In the final state, the tensile strength Rm and elongation at break, hardness (Vickers hardness HV10), and electrical conductivity were determined from tensile tests, respectively. The longitudinal sections of the samples were examined by optical microscopy. Subsequently, the area fractions of the α and β phases corresponding to the volume fractions as well as the α grain size were calculated. Optical micrographs of unetched samples were used to quantitatively determine the size distribution of the phosphide particles. The dimensions were 167 μm × 126 μm (21000 μm 2 Image sections of 0.5-1 μm, 1-2 μm, 2-5 μm, and >5 μm (if present) were selected and evaluated at 1000x magnification using the software ImageJ. In this way, individual particles could be recognized and their equivalent diameters and areas determined. Based on their equivalent diameters, phosphide particles were classified into the following categories: 0.5-1 μm, 1-2 μm, 2-5 μm, and >5 μm (if present).

[0050] The machinability was determined by planing tests. Here, a contoured indexable insert was used, which favors chip breaking. The depth of cut was 125 μm and the planing speed was 35 m / min. During the planing process, the bending moment acting on the tool was measured, from which the mean bending moment value was determined. The corresponding chips were optically evaluated and classified with regard to chip shape. The chip shapes were assigned a chip shape number according to the following list:

[0051] [Table 1]

[0052] Chip shape number 1 corresponds to the lead-containing reference alloy CuZn39Pb3 (sample No. 16).

[0053] The test results are recorded in Tables 2 to 9. Unannealed Samples Nos. 1 to 15 (Tables 2 and 3) and annealed Samples Nos. 27 to 34 (Tables 4 and 5) are samples according to the invention. Unannealed Samples Nos. 16 to 26 (Tables 6 and 7) and annealed Samples Nos. 35 to 45 (Tables 8 and 9) are comparative samples and are marked with an (*).

[0054] The bending moment and chip shape calculated during planing were used to evaluate the machinability of the samples. Chips with an average bending moment of 36 Nm or less and chip shape numbers of 1 or 1.25 were rated as very favorable.

[0055] Furthermore, we attempted to parameterize the measured average bending moment as a function of the volume fraction of the β phase and the weight fractions of Si, P, and Pb. The functional relationships calculated in this way can be shown as follows:

[0056] f=107.378-2.25255 [Beta]-64.1438 [Si]-115.18 [P]-30.7071 [Pb]+0.017965 [Beta] [Beta]+24 .6217·[Si]·[Si]+66.7257·[P]·[P]+0.542512·[Beta]·[Si]+1.36208·[Beta]·[P]+43.4012·[Si]·[P] where f is an approximate quantification of the measured bending moment in Nm, [Beta] is the percentage of β phase in volume percent, [Si] is the percentage of silicon in weight percent, [P] is the percentage of phosphorus in weight percent, and [Pb] is the percentage of lead in weight percent. The values of f calculated according to this formula are recorded in the last column of Tables 1-4. A comparison of this value of f with the measured bending moment shows excellent agreement between the two magnitudes. Samples No. 1-15 and No. 27-34 according to the present invention are characterized by measured bending moments all less than 36 Nm and values of f less than 37.

[0057] [Table 2]

[0058] [Table 3]

[0059] [Table 4]

[0060] [Table 5]

[0061] [Table 6]

[0062] [Table 7]

[0063] [Table 8]

[0064] [Table 9]

[0065] Samples No. 1 to No. 15 (Tables 2 and 3) are samples according to the invention in the unannealed state. The volume fraction of the β phase is at least 20% and at most 38%. The α grain size is at most 15 μm. The hardness is at least 180 HV10, and the tensile strength Rm is at least 560 MPa. The elongation at break is at least 4.7%. The measured bending moment is at most 35.7 Nm. The chip shape corresponds to chip shape number 1 or 1.25 in all samples.

[0066] Samples 16 to 26 (Tables 4 and 5) are comparison samples in the unannealed state. Reference sample 16 contains 3.3 wt.% lead and exhibits very good machinability. Sample 17 contains no lead and no other alloying elements and exhibits very poor machinability.

[0067] Sample No. 18 contains only 0.27 wt% Si in addition to Cu and Zn. Although the bending moment is good, the poor chip shape is likely due to a lack of phosphide particles acting as chip breakers. The same can be seen for Sample No. 21, which contains 0.53 wt% Si. Samples Nos. 19, 20, and 22 contain 0.05–0.1 wt% phosphorus, which favors chip shape and, at least for Samples No. 19 and No. 22, favors bending moment. However, the hardness and tensile strength (Rm) of Samples No. 19 and No. 20 are significantly lower than those of Samples No. 1–15. Sample No. 22, with a Si content of 0.58 wt%, only shows slight improvements in hardness and tensile strength. Furthermore, Samples No. 18–No. 22, with α grain sizes of 19–25 μm, have significantly larger α grain sizes than Samples Nos. 1–15. Larger alpha grains are detrimental to straightness and dimensional stability.

[0068] Silicon-free samples No. 23 and No. 24, containing 0.24 and 0.29 wt.% P, were found to exhibit excellent chip shape, but exhibited high bending moments. Samples No. 25 and No. 26, containing 0.65 wt.% P, respectively, exhibited excellent machinability. However, the high P content made these samples prone to cracking during hot forming. Furthermore, this resulted in low elongation at break at room temperature. The high P content was reflected in the high number of phosphide particles with an equivalent diameter of 2 to 5 μm. Therefore, if an alloy contained more than 45 phosphide particles with an equivalent diameter of 2 to 5 μm per 21,000 μm2, the hot formability was poor, and the material's behavior at room temperature became brittle.

[0069] These samples show that silicon leads to a reduction in bending moment, while phosphorus is beneficial for chip breaking. Overall, the combination of the two elements results in good machining properties and small alpha grain size.

[0070] Samples No. 27 to No. 34 (Tables 6 and 7) are samples according to the present invention in the annealed state. The volume fraction of the β phase is at least 22% and at most 39%. In Sample No. 28, the α grain size is 21 μm. This is believed to be due to the annealing temperature of 600°C. In the other samples annealed at 550°C, the α grain size is at most 16 μm. Samples No. 27 to No. 34 have slightly lower hardness (at least 170 HV10) and slightly lower tensile strength Rm (at least 520 HV10) than Samples No. 1 to No. 15. Conversely, the elongation at break is improved by annealing. As a result, the ductility of the material can be adjusted. The bending moment and chip shape are very good to excellent.

[0071] Samples No. 35 to No. 45 (Tables 8 and 9) are comparative samples in the annealed state. Samples No. 35 and No. 38, which contain silicon but no phosphorus, are characterized by unfavorably high bending moments and poor chip shape. Samples No. 36, 37, and 39, which contain low P content, have significantly improved machinability compared to Samples No. 19, 20, and 22, but their hardness and tensile strength are insufficient. Furthermore, Samples No. 25 to No. 39, with sizes ranging from 31 to 39 μm, have significantly larger α grain sizes than Samples No. 1 to 15. Larger α grains are detrimental to straightness and dimensional stability.

[0072] Samples No. 40 and No. 41, containing phosphorus but no silicon, exhibit very good chip shape, but undesirably high bending moments. Annealed samples No. 42, 43, and 44, which are identical in composition to unannealed samples No. 3, 4, and 5, exhibit higher bending moments and worse chip shape than their unannealed counterparts. Annealing reduces the volume fraction of the β phase to below 20% and shifts the phosphide particle distribution toward larger particles. These two effects combine to result in poor machinability. Sample No. 45, containing 0.65 wt.% P, is characterized by a high bending moment. This is due to the very low β phase fraction of only 9 vol.%. Furthermore, this sample exhibits a very high density of phosphides with an equivalent diameter of 2–5 μm.

[0073] Alloys having the aforementioned compositions can also be used as casting alloys for cast parts.

Claims

1. 1. A copper-zinc wrought alloy for producing semi-finished products in wire, tube or rod form, having the following composition in weight percent: Cu: 58.0 to 66.0%, Si: 0.15-1.2%, P: 0.20-0.38%, Sn: optionally up to 0.5%; Al: optionally up to 0.05%; Fe: optional up to 0.3%; Ni: optional up to 0.3%; Pb: optionally up to 0.25%; Bi: optional up to 0.1% Te, Se, In: optional, up to 0.1% each; B: optional up to 0.01%; The balance includes Zn and inevitable impurities, the proportion of the inevitable impurities is less than 0.20% by weight, The alloy has a structure consisting of spherical α-phase, β-phase, and phosphide particles, and the ratio of the β-phase to the total of the α-phase and the β-phase is at least 20% by volume and at most 60% by volume; Si is present in both the α phase and the β phase, 21000 μm ２ in an area of the particle, there are 50 to 700 phosphide particles having an equivalent diameter of 0.5 to 1 μm, 10 to 300 phosphide particles having an equivalent diameter of 1 to 2 μm, and 3 to 45 phosphide particles having an equivalent diameter of 2 to 5 μm; The proportion of the β phase and the proportions of Si, P, and Pb are such that the alloy satisfies the following conditions: 107.378-2.25255・[Beta]-64.1438・[Si]-115.18・[P]-30.7071・[Pb]+0.017965・[Beta]・[Beta]+24.62 17・[Si]・[Si]+66.7257・[P]・[P]+0.542512・[Beta]・[Si]+1.36208・[Beta]・[P]+43.4012・[Si]・[P]<37 wherein [Beta] represents the proportion of the β phase in volume percent, [Si] represents the proportion of silicon in weight percent, [P] represents the proportion of phosphorus in weight percent, and [Pb] represents the proportion of lead in weight percent.

2. 2. The copper-zinc wrought alloy according to claim 1, wherein the Pb proportion is at least 0.02% by weight.

3. 3. The copper-zinc wrought alloy according to claim 1, wherein the weight fraction ratio of P to the sum of Fe and Ni is greater than 2.

0.

4. 4. A copper-zinc wrought alloy according to claim 1, wherein the proportion of Fe and Ni is at most 0.1% by weight in total.

5. A copper-zinc wrought alloy according to any one of claims 1 to 4, characterized in that the proportion of P is at least 0.26% by weight and at most 0.33% by weight.

6. A copper-zinc wrought alloy according to any one of claims 1 to 5, characterized in that the proportion of Si is at most 0.35% by weight.

7. A copper-zinc wrought alloy according to any one of claims 1 to 6, characterized in that the proportion of Si is at least 0.25% by weight.

8. 8. A copper-zinc wrought alloy according to claim 6 or 7, characterized in that the proportion of Cu is at least 60.0% by weight and at most 61.5% by weight.

9. A copper-zinc wrought alloy according to any one of claims 1 to 5, characterized in that the proportion of Si is at least 0.50% by weight and at most 1.0% by weight.

10. A copper-zinc wrought alloy according to any one of claims 1 to 9, characterized in that the alloy has a hardness of at least 170 HV10.

11. A copper-zinc wrought alloy according to any one of claims 1 to 10, characterized in that the alloy has a tensile strength Rm of at least 520 MPa.

12. A copper-zinc wrought alloy according to any one of the preceding claims, characterized in that the alloy has an alpha grain size of at most 21 μm.

13. A copper-zinc wrought alloy according to any one of claims 6 to 8, characterized in that the alloy has an electrical conductivity of at least 12 MS / m.

14. A semi-finished product in the form of a wire, tube or rod, made from the copper-zinc wrought alloy of any one of claims 1 to 13.

15. Component manufactured from a semi-finished product according to claim 14 by machining and optional further processing steps.

16. 15. A method for producing a wire, tube or rod semi-finished product according to claim 14, comprising the following steps: a) melting a copper alloy having a composition according to any one of claims 1 to 9; b) continuous casting of a tube or bolt type casting format with a water-cooled mold; c) hot forging the cast format at a temperature of 620-700°C, followed by cooling at a rate of 30-60°C per minute in the temperature range of 550-350°C; d) optionally, heat treatment in the temperature range of 525-625°C for 1-5 hours, followed by cooling in the temperature range of 500-350°C at a cooling rate of 20-40°C per minute; e) Optionally, cold forming A method including:

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