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 wire, tube, or rod form, having the following composition by weight: Cu: 58.0-63.0%, Si: 0.04-0.32%, P: 0.05-0.20%, Sn: optionally up to 0.25%, Al: optionally up to 0.10%, Fe: optionally up to 0.30%, Ni: optionally up to 0.30%, Pb: optionally up to 0.25%, Te, Se, and In: optionally up to 0.10% each, Bi: max. 0.009%, and the balance being Zn and unavoidable impurities, with the proportion of unavoidable impurities being less than 0.2% by weight. The ratio of the weight fractions of P and Al is at least 1.0. 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 70% by volume. Si exists in both the α and β phases. 2 In this area, there are 7 to 200 phosphide particles with an equivalent diameter of 0.5 to 1 μm, 4 to 150 phosphide particles with an equivalent diameter of 1 to 2 μm, and up to 30 phosphide particles with an equivalent diameter greater than 2 μm.

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% by weight) of 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 easy to machine by forming an α structure, a β structure, and occasionally a γ structure. The Al content generates Al phosphides. The γ phase and Al phosphides improve chip formation but shorten tool life. Furthermore, the rare earths are 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, instead of lead is further described in Patent Document 7 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 remainder being 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 easier to machine. However, the high Si content reduces the electrical conductivity compared to leaded brass. This is, on the one hand, a disadvantage for applications as electronic components, and, on the other hand, particularly at elevated temperatures during drilling, the phosphides lose their brittleness and, as a result, their chip-breaking function is lost. This effect becomes more pronounced the worse the thermal conductivity of the material and, therefore, the electrical conductivity. [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, especially during drilling, good electrical conductivity, and contain as few alloying elements as possible that are of environmental concern. Furthermore, the alloy must be easily processable on an industrial scale. This requires that the alloy be easily hot-formed, e.g., by extrusion, and easily cold-formed, e.g., 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: 58.0-63.0%, Si: 0.04 to 0.32%, P: 0.05~0.20%, Sn: optional up to 0.25% Al: optionally up to 0.10%, preferably up to 0.05%; Fe: optionally up to 0.30%, preferably up to 0.10%; Ni: optional up to 0.30% Pb: optionally up to 0.25%, preferably up to 0.10%; Te, Se, In: optional, up to 0.10% each, Bi: Max 0.009% The balance includes Zn and inevitable impurities, The proportion of unavoidable impurities is less than 0.2% by weight. The ratio of the weight fractions of P and Al is at least 1.0. The alloy has a structure consisting of spherical α-phase, β-phase, and phosphide particles. The proportion of β-phase to the total of α-phase and β-phase is at least 20% by volume, preferably at least 30% by volume, at most 70% by volume, and preferably at most 50% by volume. Silicon is present in both the α-phase and the β-phase. 21000 μm 2 In this area, there are 7 to 200 phosphide particles with an equivalent diameter of 0.5 to 1 μm, 4 to 150 phosphide particles with an equivalent diameter of 1 to 2 μm, and up to 30 phosphide particles with an equivalent diameter greater than 2 μm.

[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, especially during drilling, as well as high electrical conductivity, are obtained, 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 control, especially during casting and hot forming, is 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 found that the fine β-phase in the as-cast state is favored by the addition of evenly finely dispersed copper- and / or zinc-containing phosphides. During primary crystallization of the β-phase, the residual melt is enriched with P, thereby causing the β-phase to be refined. During solidification, a eutectic mixture consisting of phosphides and the β-phase is formed. In addition to the grain refinement of the base matrix consisting 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, resulting in a finer grain in the final state. When the P content is at least 0.05 wt.%, the phosphide particles are present in the β-phase in the final state. When the P content is greater than 0.20 wt.%, the alloy's ductility is reduced.

[0014] Furthermore, a high proportion of P in combination with Si is detrimental to the electrical conductivity, so in a preferred embodiment of the invention the sum of the proportion of Si and the proportion of P is preferably at most 0.45% by weight.

[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 (30°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 are then newly formed during the cooling process during hot forming. Thus, 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: In an area of 21,000 μm², there are 7 to 200 phosphide particles with an equivalent diameter of 0.5 to 1 μm, 4 to 150 phosphide particles with an equivalent diameter of 1 to 2 μm, and up to 30 phosphide particles with an equivalent diameter greater than 2 μm. The equivalent diameter of a phosphide particle is understood to be the diameter of a circle having 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 75%. Furthermore, it is advantageous if at least 30%, preferably at least 50%, of all phosphide particles with an equivalent diameter of at least 0.5 μm have an equivalent diameter of at most 1 μm. It is not excluded that phosphide particles having an equivalent diameter of less than 0.5 μm may be present in the alloy.

[0016] A brittle structural component, which acts as a separation point during machining and thereby aids in chip breaking, is beneficial to the machinability of the alloy. The β phase is brittle and beneficial to 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 to good machinability. This is achieved by adding and embedding silicon in the α phase. Therefore, the Si proportion in the alloy must be at least 0.04 wt.%. If the Si proportion is greater than 0.32 wt.%, the electrical conductivity will be less than 12 MS / m and therefore insufficient. A P proportion of at least 0.05 wt.% results in favorable chip formation during drilling. Furthermore, a low optional Pb proportion also favors machinability.

[0017] The Cu content of the alloy is 58.0-63.0 wt.%. If the Cu percentage is less than 58.0 wt.%, the ductility of the alloy is too low. If the Cu percentage is greater than 63.0 wt.%, the zinc percentage of the alloy is too low to achieve good machinability.

[0018] The ratio of the weight fractions of P to Al is at least 1.0. Aluminum forms aluminum phosphides with phosphorus. However, these are undesirable because they do not improve the machining behavior. To ensure that sufficient excess P is available to form copper- and / or lead-containing phosphides, the ratio of the weight fractions of P to Al in the alloy must be at least 1.0.

[0019] The optional elements Sn and Al support the formation of the β phase. If the Sn content is greater than 0.20% by weight, the machinability of the alloy deteriorates. However, this deterioration can be compensated for by heat treatment if the Sn content is within 0.25% by weight. Preferably, the tin content should be at most 0.20% by weight, particularly preferably at most 0.10% by weight.

[0020] Aluminum forms aluminum phosphides with phosphorus, which are however undesirable, so the proportion of Al should not exceed 0.10% by weight, preferably 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 0.30% by weight, particularly preferably at most 0.10% by weight.

[0022] Nickel supports the formation of the α phase, thereby improving cold forming. Furthermore, nickel forms phosphides, which do not have a beneficial effect on machinability. Therefore, the nickel content should be at most 0.30% by weight, particularly preferably at most 0.10% by weight.

[0023] The element Bi is present as an impurity in secondary raw materials, such as scrap. It can improve the machinability of the alloy. However, a proportion greater than 0.009 wt.% Bi may adversely affect hot formability. Therefore, a maximum of 0.009 wt.% Bi is permitted in this alloy.

[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] 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 0.07% by weight each, since these elements can form phosphides that can compete with copper- and / or zinc-containing phosphides.

[0026] 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.

[0027] Advantageously, the proportion of P can be at most 0.15% by weight, particularly preferably at most 0.12% by weight, which has an advantageous effect on the hot formability of the alloy.

[0028] In advantageous embodiments of the present invention, the P / Fe ratio can be at least 1.0. Iron forms hard iron phosphides with phosphorus. However, these iron phosphides are undesirable because they reduce tool life. In order for there to be sufficient excess P in the alloy to form copper- and / or lead-containing phosphides, the ratio of the weight fractions of P to Fe must be at least 1.0.

[0029] In a preferred embodiment of the invention, the Fe content can be less than 0.10% by weight and the Ni content can be at most 0.07% by weight. This limitation suppresses the formation of iron and nickel phosphides compared to the formation of copper- and / or zinc-containing phosphides, which are advantageous for machining. Particularly advantageous properties are achieved if the P / Fe ratio is at least 1.0. Furthermore, it is particularly preferred if the Fe content is at most 0.05% by weight and / or the Ni content is at most 0.04% by weight.

[0030] In an advantageous embodiment of the invention, the Si proportion can be at least 0.23% by weight, which is advantageous for the machinability of the alloy. Furthermore, a Si proportion of at least 0.23% by weight has a beneficial effect on the surface quality of the product.

[0031] In an alternative embodiment of the invention, the Si content can be at most 0.15% by weight, preferably at most 0.12% by weight, particularly preferably at most 0.08% by weight, which has a beneficial effect on the electrical conductivity of the alloy.

[0032] In this alternative embodiment of the invention, the proportion of P may preferably be at most 0.10% by weight, which is particularly advantageous for the electrical conductivity of the alloy.

[0033] Furthermore, in this alternative embodiment of the invention, the Cu percentage can be at most 59.5 wt. %. This upper limit of the Cu percentage provides a particularly advantageous combination of electrical conductivity, machinability, mechanical properties, and processability.

[0034] In a further embodiment of the invention, the proportions of the elements Cu, Zn, Si, P, and Pb can total at least 99.75% by weight. This ensures that the properties of the alloy are primarily determined by the alloying elements Cu, Zn, Si, P, and Pb, with the influence of the other elements only playing a very subordinate role. Alternatively or additionally, it may be advantageous to select the composition of the alloy so that the proportions of the elements Cu, Zn, Si, P, Sn, and Pb total at least 99.85% by weight. Since tin phosphides are not formed, tin is less important as an alloying component than, for example, Fe, Ni, or Al.

[0035] Advantageously, the copper-zinc wrought alloy may have a hardness of at least 120 HV10, preferably at least 150 HV10.

[0036] Advantageously, the copper-zinc wrought alloy may have a tensile strength Rm of at least 500 MPa, preferably at least 530 MPa.

[0037] Advantageously, the copper-zinc wrought alloy may have an electrical conductivity of at least 12.5 MS / m, preferably at least 12.7 MS / m, and particularly preferably at least 13.0 MS / m.

[0038] An alloy having a particularly advantageous combination of properties has the following composition in weight percent: Cu: 58.5 to 59.0% Si: 0.04 to 0.09% P: 0.05 to 0.10% Pb: 0.04 to 0.08% Fe: optional up to 0.10% Ni: optional up to 0.07% Sn: optional up to 0.20% Al: optional up to 0.05% The balance is zinc and unavoidable impurities, the proportion of which is less than 0.1% by weight. A high electrical conductivity of at least 14 MS / m, preferably at least 15 MS / m, is achieved due to the low proportion of alloying elements Si and P. Machinability is supported by a Pb proportion of 0.04-0.08% by weight.

[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 can be 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, with the exception of the pickling process, are carried out between hot forging and cold forming.

[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 adjust the advantageous ratio of α-phase to β-phase and the 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 the heat treatment. This, in particular, improves ductility. After the heat treatment, pickling and cold forming are 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 through No. 44 were melted in an induction furnace and then poured into molds. The sample compositions are recorded in Tables 1 through 4. Sample No. 10 is the lead-containing reference alloy CuZn39Pb3. The samples were machined, homogenized for 1 hour, and then hot-formed. Samples No. 8 and No. 9 were hot-formed by pressing at 630°C, while the remaining samples were hot-formed by rolling at 650°C. The cooling rate after hot-forming was approximately 40°C per minute for the rolled samples and approximately 30°C per minute for the pressed samples, in the temperature range of 550 to 350°C.

[0048] Samples No. 1 to No. 7 and No. 10 to No. 23 were hot-formed, then machined, and subsequently cold-formed to a forming degree of 20%. Samples No. 8 and No. 9 were hot-formed, then pickled, and subsequently cold-formed to a forming degree of 7%.

[0049] Samples No. 24 to No. 44 were annealed after three hours of hot forming. The annealing temperature was approximately 550°C for No. 26, No. 27, and No. 38 to No. 41, and approximately 600°C for Samples No. 24, No. 25, No. 28 to No. 37, and No. 42 to No. 44. 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. 24 to No. 44 were then machined and subsequently cold formed to a degree of forming of 20%.

[0050] In the final state, the tensile strength Rm and elongation at break A, hardness (Vickers hardness HV10), and electrical conductivity λ 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 grains. Dimensions were 167 μm × 126 μm (21000 μm 2 Image sections of 0.5-1 μm, 1-2 μm, and >2 μm diameter particles were selected and evaluated at 1000x magnification using the software ImageJ. This allowed for the recognition of individual particles and the determination of their equivalent diameter and area. Based on their equivalent diameter, the phosphide particles were classified into the following categories: 0.5-1 μm, 1-2 μm, and >2 μm.

[0051] Machinability was evaluated in the final state by drilling tests. The drilling tests were carried out with an instrumented drill head. The drilling tests were carried out using the following parameters: Twist drill, 5mm diameter Rotation speed: 3200U / min Feed rate: 0.04mm / U Five holes were drilled per specimen, with a new drill used for each specimen. Drilling depth 10mm

[0052] Drilling was performed along the forming direction. The torque and normal force acting on the drill bit were measured. The alloy CuZn39Pb3 in the unannealed state was used as a reference. The torque measured for each individual specimen was normalized by relating the torque measured for the reference alloy to the torque measured for the respective specimen. That is, the smaller the torque calculated for one specimen, the higher the normalized torque for this specimen. Similarly, the normal force measured for each specimen was normalized. The normalized torque M norm and the normal force F N norm The arithmetic mean of these two values was calculated from the above. Samples whose arithmetic mean was below 0.75 did not meet the prerequisites for good machinability.

[0053] The chip shapes were classified according to the German Copper Association's publication "Richtwerte fur die spanende Bearbeitung von Kupfer und Kupferlegierungen" (Reference Values for Machining Copper and Copper Alloys) (Informationsdruck i.18). Based on this, the chips were rated as good (2), fair (1) or poor (0). In particular, long, zigzag-shaped chips (Faltspane) led to an unfavorable rating.

[0054] The normalized torque and normal force calculated in the test, as well as the arithmetic mean (M+F) calculated from them, are shown at the top of the table. N ) / 2) are listed in Tables 1 to 8 together with the chip shape and the characteristic values of the tensile test and hardness measurement.

[0055] [Table 1]

[0056] [Table 2]

[0057] [Table 3]

[0058] [Table 4]

[0059] [Table 5]

[0060] [Table 6]

[0061] [Table 7]

[0062] [Table 8]

[0063] Samples No. 1 to No. 9 (Tables 1 and 2) are samples according to the present invention in the unannealed state. The volume fraction of the β phase is at least 33% and at most 46%. The α grain size is a maximum of 24 μm for the rolled samples and a maximum of 35 μm for the pressed samples. The small α grain size of Sample No. 5 is believed to be due to the alloying element Fe. The hardness is at least 160 HV10, and the tensile strength Rm is at least 520 MPa. The elongation at break is at least 10%. The electrical conductivity is at least 12.7 MS / m for all samples, and at least 13.0 MS / m for most samples. In the case of Sample No. 9, the electrical conductivity is greater than 15.5 MS / m. The normalized torque is in the range of 0.85 to 1.08. The normalized force is in the range of 0.45 to 0.7. The arithmetic mean of the normalized torque and normal force is always at least 0.75. Chip shape was always rated as good (2) or fair (1).

[0064] Samples 10 to 23 (Tables 3 and 4) are comparison samples in the unannealed state. Reference sample 10 contains 3.3 wt.% lead and exhibits very good machinability. Sample 11 also exhibits good machinability, but contains 2.0 wt.% lead. Samples 12 and 16 contain no lead and no other alloying elements and exhibit very poor machinability.

[0065] Samples No. 13 and No. 17 contain only 0.27 wt.% Si in addition to Cu and Zn. Although the force acting on the drill is within the allowable range, the chip shape is poor, which is thought to be due to a lack of phosphide particles acting as chip breakers. Sample No. 14 has higher Cu and Si contents than Sample No. 13. The force acting on the drill is not within the allowable range, and the chip shape is poor. Furthermore, the conductivity is low.

[0066] Sample No. 15 has a slightly higher Si content and 0.1 wt% P added compared to Sample No. 14. This reduces the force acting on the drill and improves chip shape somewhat. However, the elongation at break and electrical conductivity are low. Sample No. 15 has a similar P content and β-phase volume fraction to Sample No. 1, but a higher Si content. While the force acting on the drill is similarly good, Sample No. 15 has unfavorable chip shape and poor electrical conductivity.

[0067] Sample No. 18 differs from sample No. 17 in that it contains 0.38 wt% P, which mainly leads to a clear improvement in chip shape, but the elongation at break is very small.

[0068] Sample No. 19 contains 0.11 wt% P in addition to Cu and Zn. This is beneficial for chip shape, but the force acting on the drill is not satisfactory. In Sample No. 22, the P content is increased to 0.29 wt% compared to Sample No. 19, resulting in a deterioration in normal force.

[0069] Sample No. 20 differs from sample No. 15 mainly in that it has a slightly lower P content, which leads to improved elongation at break, but the high Si content means that the electrical conductivity is not at the required level.

[0070] Sample No. 21 contains 0.22 wt.% Sn in addition to 0.27 wt.% Si and 0.06 wt.% P. Compared to sample No. 2, which does not contain tin, the addition of tin results in a moderate deterioration in the force acting on the drill. Most of the phosphide particles are only observed to be between 0.5 and 1 μm in diameter. The electrical conductivity is not affected at all by the 0.22 wt.% Sn.

[0071] Sample No. 23 contains 0.29 wt% Si and 0.30 wt% P. As with sample No. 18, the chip shape is good, but the elongation at break, electrical conductivity, and drilling force are not satisfactory.

[0072] Samples No. 24 to No. 31 (Tables 5 and 6) are samples according to the present invention in the annealed state. Samples No. 26 and No. 27 were annealed at 550°C, and the other samples in Table 3 were annealed at 600°C. The volume fraction of the β phase is at least 31% and at most 49%. The α grain size is in the range of 25 to 40 μm, with Samples No. 26 and No. 27 having the smallest grain size. The hardness is at least 160 HV10, and the tensile strength Rm is at least 510 MPa. The elongation at break is at least 11.5%. The electrical conductivity is at least 12.7 MS / m for all samples, and at least 13.0 MS / m for the majority of samples. The normalized torque is in the range of 0.79 to 1.03. The normal force is in the range of 0.56 to 0.71. The arithmetic mean of the normalized torque and normalized normal force is always at least 0.75. The chip shape rating is always good (2) or fair (1). In the case of sample No. 31, which corresponds in composition to the unannealed sample No. 21, annealing allowed for a significant improvement in the forces acting during drilling and in the chip shape. Furthermore, it can be seen that annealing shifted the center of gravity of the phosphide particle distribution towards larger particles.

[0073] Samples No. 32 to No. 44 (Tables 7 and 8) are comparative samples in the annealed state. The lead-containing samples No. 32 and No. 33 show good machining properties in the annealed state. Samples No. 34 (annealed at 600°C) and No. 38 (annealed at 550°C), which contain only Cu and Zn, are characterized by poor drilling properties even in the annealed state.

[0074] Samples 35 and 36, containing silicon but no phosphorus and annealed at 600°C, generate torque during drilling that is more than twice the torque calculated for reference sample 10. The higher silicon content in sample 36 improves chip shape but reduces electrical conductivity. Sample 39, containing silicon but no phosphorus and annealed at 550°C, has a better drilling force than samples 35 and 36. This is likely due to the significantly higher proportion of β phase. However, the chip shape is poor.

[0075] Sample No. 37, which contains 0.58 wt. % Si and 0.10 wt. % P and is annealed at 600°C, has better drilling properties than sample No. 15, despite having the same composition in the unannealed state. However, due to the high proportion of Si, its electrical conductivity is insufficient.

[0076] In samples No. 40 and No. 41, which are comparable in composition to samples No. 18 or No. 19 but annealed at 550°C, the annealing improved the drill force, and in particular, sample No. 40 showed a clear improvement in ductility. However, sample No. 40 has low electrical conductivity due to its high proportion of Si and P. In the case of sample No. 41, the lack of Si cannot be compensated for by annealing until the drilling force reaches an acceptable level.

[0077] Sample No. 42, which has an Si content of 0.55% by weight and a P content of 0.075% by weight, has too low conductivity due to the high Si content.

[0078] Samples No. 43 and No. 44 correspond in composition to unannealed samples No. 22 and No. 23, but a clear improvement in ductility was achieved by annealing at 600 °C. Sample No. 43 does not have satisfactory machinability even after annealing. Sample No. 44 has a P content of 0.3 wt.% in combination with a Si content of 0.29 wt.%, resulting in a low electrical conductivity.

[0079] Samples No. 1 through No. 44 demonstrate that alloys with favorable combinations of properties can be produced by appropriately selecting the elements Si and P. Si reduces the forces acting on the drill, thereby improving machinability. However, Si percentages greater than 0.32 wt.% result in decreased electrical conductivity. P percentages between 0.05 and 0.2 wt.% are favorable for chip shape. Higher P percentages, in combination with Si, lead to poor ductility and electrical conductivity. Alloys with these favorable combinations of properties can be produced without annealing. Subsequent annealing, particularly at 550°C to 600°C, by appropriately setting the β-phase fraction and phosphide particles, can improve machinability for a significant number of element combinations.

[0080] 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 63.0%, Si: 0.04-0.32%, P: 0.05-0.20%, Sn: optionally up to 0.25%; Al: optional up to 0.10%; Fe: optional up to 0.30%; Ni: optional up to 0.30%; Pb: optionally up to 0.25%; Te, Se, In: optional, up to 0.10% each; Bi: max 0.009%, The balance includes Zn and inevitable impurities, the proportion of the inevitable impurities is less than 0.2% by weight, the ratio of the weight fractions of P and Al is at least 1.0; 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 70% by volume; Si is present in both the α phase and the β phase, 21000 μm ２ in an area containing 7 to 200 phosphide grains having an equivalent diameter of 0.5 to 1 μm, 4 to 150 phosphide grains having an equivalent diameter of 1 to 2 μm, and up to 30 phosphide grains having an equivalent diameter greater than 2 μm.

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

3. A copper-zinc wrought alloy according to any one of claims 1 to 2, characterized in that the proportion of P is at most 0.15% by weight.

4. A copper-zinc wrought alloy according to any one of claims 1 to 3, characterized in that the P / Fe ratio is at least 1.

0.

5. 5. A copper-zinc wrought alloy according to claim 1, wherein the proportion of Fe is less than 0.10% by weight and the proportion of Ni is at most 0.07% 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 least 0.23% by weight.

7. A copper-zinc wrought alloy according to any one of claims 1 to 5, characterized in that the proportion of Si is at most 0.15% by weight.

8. 8. A copper-zinc wrought alloy according to claim 7, characterized in that the proportion of P is at most 0.10% by weight.

9. A copper-zinc wrought alloy according to claim 7 or 8, characterized in that the proportion of Cu is at most 59.5% by weight.

10. A copper-zinc wrought alloy according to any one of claims 1 to 9, characterized in that the proportions of the elements Cu, Zn, Si, P, Pb total at least 99.75% by weight.

11. A copper-zinc wrought alloy according to any one of claims 1 to 10, characterized in that the alloy has a hardness of at least 120 HV10, preferably at least 150 HV10.

12. A copper-zinc wrought alloy according to any one of claims 1 to 11, characterised in that the alloy has a tensile strength Rm of at least 500 MPa, preferably at least 530 MPa.

13. A copper-zinc wrought alloy according to any one of claims 1 to 12, characterized in that the alloy has an electrical conductivity of at least 12.5 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 10; 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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