Wrought copper-zinc alloy, semi-finished product formed of a wrought copper-zinc alloy and method for producing a semi-finished product of this type

Abstract

The invention relates to a wrought copper-zinc alloy for producing a wire-, tube- or strand-type semi-finished product with the following composition, in wt.%: Cu: 58.0 to 66.0 %, Si: 0.15 to 1,2 %, P: 0.20 to 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, In: each optionally up to 0.1 %, B: optionally up to 0.01 %, with the rest being Zn and unavoidable impurities, wherein the proportion of unavoidable impurities is less than 0.20 wt.%. The alloy has a structure of globular α-phase, ß-phase and phosphide particles. The proportion of ß-phase in the sum of the α-phase and ß-phase is at least 20 vol.% and max. 60 vol.%. Si is present in both the α-phase and ß-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 proportion of the ß-phase and the proportions of Si, P and Pb are selected such that the alloy fulfills the 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, wherein [Beta] represents the proportion of ß-phase in vol.%, [Si] represents the proportion of silicon in wt.%, [P] represents the proportion of phosphorus in wt.% and [Pb] represents the proportion of lead in wt.%.

Description

[0001] Description

[0002] Copper-zinc wrought alloy, semi-finished product made of a copper-zinc wrought alloy and process for producing such a semi-finished product

[0003] The invention relates to a wrought copper-zinc alloy for the production of wire-, tubular-, or rod-shaped semi-finished products, to semi-finished products made from a wrought copper-zinc alloy, and to a method for producing such a semi-finished product. A wrought copper-zinc alloy is generally understood to mean a wrought material made from a copper-zinc alloy.

[0004] Copper-zinc alloys with 3 to 5 wt.% lead are excellently machinable and also very suitable for hot and cold forming. Lead-containing copper-zinc alloys are therefore used in a wide variety of applications, for example, for connections and components in the automotive industry, building technology, mechanical engineering, electrical appliances and electronic components, telecommunications, and as fittings in water installations.

[0005] The positive effect of lead in wrought copper-zinc alloys is based on the fact that lead is present in elemental form as particles in the structure, and these particles act as chip breakers. During machining, lead is present in the liquid phase due to the strong local deformation in the workpiece and the resulting local temperature increase. Since lead cannot absorb stresses in its liquid state, this leads to a stress concentration in the load-bearing, weakened matrix and thus to easier chip breakage. In addition, lead is incorporated into the tribological layer between the material and the tool during machining, thus leading to effective lubrication and thus a reduction in friction and wear. Furthermore, due to its low solubility, lead has little effect on electrical conductivity. This is particularly advantageous for materials used in electrical applications.Furthermore, lead is known to significantly refine the grain of copper-zinc alloys. This is beneficial for the straightness and dimensional accuracy of semi-finished products, especially rod-shaped ones. High dimensional accuracy is also required when crimping electronic wires. Furthermore, lead is inexpensive.

[0006] However, lead is harmful to the environment. Even the smallest amounts of lead accumulate in the human body and can cause health problems. Therefore, the EU, the USA, China, and other countries have continually reduced the limits for copper alloys and are striving to replace lead-containing brass with lead-reduced or lead-free machinable copper alloys. Limits are set by EU directives such as RoHS (Directive 2011 / 65 / EU), which stipulates a maximum of 1000 ppm (0.1%) lead. To ensure good machinability of the material even at such low lead levels, various alloying elements are proposed as alternatives to lead.

[0007] Numerous publications disclose the use of bismuth (Bi) as an alternative to lead to improve machinability. To mitigate the problem of Bi film formation along grain boundaries and the associated susceptibility to stress cracking and hot cracking, the addition of additional elements is proposed. Reference is made in particular to publications KR 10 0 555 854 B1, KR 10 2006 096 877 A, JP 2005 290 475 A, JP 2014 122 427 A, and JP 2006 083 443 A. Nevertheless, Bi is undesirable because, on the one hand, it is a scarce, limited-abundance metal and, on the other hand, it leads to hot brittleness within the material cycles of copper materials.

[0008] Furthermore, copper-zinc alloys are known from the document EP 2 194 150 B1 which contain 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. The alloys are easy to machine due to the formation of an α, β and possibly γ microstructure. The Al content leads to the formation of undesirable Al phosphides. Although the γ-phase and Al phosphides improve chip formation, they reduce the service life of the tool. In addition, the proportion of rare earths probably leads to embrittlement of the microstructure. The alloys are used for castings and hot-pressed parts.

[0009] The replacement of lead by phosphorus, which forms brittle phosphides in the alloy, is further described in the document WO 2020 / 261604 A1 for a material with Cu from 58.5 to 63.5 wt.%, Si from 0.4 to 1.0 wt.%, P from 0.005 to

[0010] 0.19 wt.%, Pb from 0.003 to 0.25 wt.%, the remainder zinc, and other optional elements. The addition of 0.005 to 0.19 wt.% P to form phosphides and 0.4 to 1.0 wt.% Si to strengthen the α and β phases results in a material with good machinability. However, to achieve the grain refinement effect on the microstructure caused by lead, a maximum P content of 0.19 wt.% is too low.

[0011] The invention is based on the object of providing a copper-zinc wrought alloy for the production of wire-, tube-, or rod-shaped semi-finished products that exhibits excellent machinability, good mechanical properties, and the lowest possible content of environmentally harmful alloy components. Furthermore, the alloy should be readily processable on an industrial scale. This requires that it can be readily hot-formed, for example by extrusion, that it is readily cold-formed, for example by drawing or crimping, and that semi-finished products made from the alloy exhibit excellent straightness and very good dimensional stability. Furthermore, the invention is based on the object of specifying a method for producing a wire-, tube-, or rod-shaped semi-finished product from such an alloy.

[0012] The invention is represented 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 further dependent claims relate to advantageous embodiments and developments of the invention.

[0013] The invention relates to a copper-zinc wrought alloy for the production of wire, tube or rod-shaped semi-finished products with the following composition in weight %:

[0014] Cu: 58.0 to 66.0%,

[0015] Si: 0.15 to 1.2%,

[0016] P: 0.20 to 0.38%,

[0017] Sn: optionally up to 0.5%, preferably up to 0.3%

[0018] AI: optional up to 0.05%,

[0019] Fe: optional up to 0.3%,

[0020] Ni: optional up to 0.3%,

[0021] Pb: optionally up to 0.25%, preferably up to 0.10%

[0022] Bi: optional up to 0.1%,

[0023] Te, Se, In optionally up to 0.1% each

[0024] B: optionally up to 0.01%,

[0025] The remainder is Zn and unavoidable impurities, with the proportion of unavoidable impurities being less than 0.2 wt.%. The alloy has a microstructure of globular α-phase, β-phase, and phosphide particles. The phosphide particles preferably contain or are copper- and / or zinc-containing phosphides. The proportion of the β-phase in the sum of the α-phase and β-phase is at least 20 vol.%, preferably at least 22 vol.%, and at most 60 vol.%, preferably at most 40 vol.%. Silicon is present in both the α-phase and the β-phase. In an area of ​​21,000 pm 250 to 700 phosphide particles with an equivalent diameter of 0.5 to 1 pm, 10 to 300 phosphide particles with an equivalent diameter of 1 to 2 pm and 3 to 45 phosphide particles with an equivalent diameter of 2 to 5 pm are present. The proportion of the ß-phase as well as the proportions of Si, P and Pb are selected so that the alloy meets the condition

[0026] 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] denotes the proportion of the ß-phase in vol%, [Si] the proportion of silicon in weight%, [P] the proportion of phosphorus in weight% and [Pb] the proportion of lead in weight%.

[0027] The invention is based on the idea of ​​reducing the proportion of Pb in the copper-zinc alloy as much as possible without impairing the alloy's machinability. To this end, Si and P are selectively added to the alloy, and the proportion of the ß-phase is adjusted to ensure favorable machinability while maintaining the alloy's hot and cold formability and ensuring that the semi-finished product produced from the alloy exhibits excellent straightness. Furthermore, the process control, particularly during casting and hot forming, is selected to achieve the desired properties.

[0028] A globular α-phase is a prerequisite for good straightness and dimensional stability of the semi-finished product. The α-phase forms from the β-phase after hot forming. Therefore, the β-phase must be fine-grained in the as-cast state. Surprisingly, it has been shown that with increasing P content, a significant grain refinement of the cast structure of the original basic matrix consisting of β-phase occurs. To achieve sufficient grain refinement of the cast structure and the subsequent forming structure, the addition of at least 0.20 wt.% P is necessary. This is similar to the effect of 2 to 3 wt.% Pb on the grain refinement of α-β-brass. During the primary crystallization of the β-crystallites, the residual melt becomes enriched with P, thereby leading to a subdivision of the β-phase. During solidification, a eutectic of phosphide and β-phase forms. In addition to the grain refinement of the basic matrix of ß-phase, grain refinement of the α-crystallites is observed.This grain refinement of the cast structure by P facilitates hot forming, continues into the structure after hot forming, and consequently leads to grain refinement in the final state. With a P content of at least 0.20 wt.%, phosphide particles are present in both the α-phase and the β-phase in the final state. The alloy preferably contains at least 0.22 wt.% P. With a P content of more than 0.38 wt.%, coarse phosphides form in the as-cast state, with individual phosphides coagulating to form long network-like structures. These coarse phosphides wet the grain boundaries, melt during hot forming, and lead to cracks in the material. In addition, ductility is reduced.

[0029] Such undesirable effects can, however, also occur with P contents below 0.38 wt.% if the cooling rate during casting of the alloy is too low, as is the case, for example, with a stationary mold. The necessary high cooling rates are achieved, for example, in continuous casting with a water-cooled mold. In this way, with a P content of 0.20 to 0.38 wt.%, the phosphide particles are already globular and finely distributed in the microstructure in the as-cast state. Such a cast product is then readily hot-pressable at a temperature of 620 to 700 °C, preferably 630 to 680 °C. No cracks form in the material.Furthermore, to achieve a globular α-phase, the cooling of the material after hot forming must be controlled: in a temperature range of 550 °C to 350 °C, the cooling rate must be at least 30 °C per minute (°C / min), preferably at least 40 °C per minute, and at most 60 °C per minute, preferably at most 50 °C per minute. The evenly finely distributed phosphides, which are associated with a fine-grained β-phase in the as-cast state, dissolve in the matrix during hot forming and then reform during the cooling process during hot forming. In this way, the characteristic distribution of the phosphides in the as-cast state is ultimately reflected in the microstructure in the final state. The distribution of the phosphides in the final state and the globular shape of the α-phase are therefore determined not only by the chemical composition of the alloy, but also by the process control during casting and hot forming.The characteristics of the phosphides in the final state are thus like a fingerprint left on the product by the specific process. The distribution of the phosphides in the final state can be characterized as follows: In an area of ​​21,000 pm. 250 to 700 phosphide particles with an equivalent diameter of 0.5 to 1 pm, 10 to 300 phosphide particles with an equivalent diameter of 1 to 2 pm, and 3 to 45 phosphide particles with an equivalent diameter of 2 to 5 pm are present. 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 the phosphide particles with an equivalent diameter of at least 0.5 pm have an equivalent diameter of at most 2 pm. Preferably, the proportion of phosphide particles with an equivalent diameter of 0.5 pm to 2 pm is at least 70% of the number of all phosphide particles with an equivalent diameter of at least 0.5 pm. This proportion is particularly preferably 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 pm have an equivalent diameter of at most 1 pm. It is not excluded that phosphides with an equivalent diameter of less than 0.5 pm or more than 5 pm are present in the alloy. The number of phosphide particles with an equivalent diameter of more than 5 pm is at most 30%, preferably at most 15%, of the number of phosphide particles with an equivalent diameter of 2 to 5 pm.

[0030] Brittle structural components are advantageous for the machinability of the alloy, as they act as separation points during machining and thus promote chip breaking. The ß-phase is brittle and promotes machinability. An increase in the proportion of ß-phase can be achieved by increasing the Zn content and / or by alloying with silicon, because silicon stabilizes the ß-phase. For good machinability, it has also proven advantageous to reduce the ductility of the α-phase. This is achieved by alloying and incorporating silicon into the α-phase as well as by finely distributed phosphides in the α-phase. Therefore, the Si content in the alloy must be at least 0.15 wt.%. The phosphide particles described above represent particles that act as separation points during machining and promote chip breaking. A P content of less than 0.20 wt.% leads to unfavorable chips and coarser grain.Furthermore, a small optional proportion of Pb has a beneficial effect on machinability.

[0031] The machinability of the alloy is therefore determined by the combined selection of the parameters ß-phase, Si and P and an optionally present, small proportion of Pb. In the proposed copper-zinc wrought alloy, the proportion of the ß-phase in the sum of α-phase and ß-phase is at least 20 vol.%, preferably at least 22 vol.%. A high proportion of the ß-phase has a negative effect on cold formability. Therefore, the proportion of the ß-phase is at most 60 vol.%, preferably at most 40 vol.%. The Si content of the alloy is 0.15 to 1.2 wt.%, the P content 0.20 to 0.38 wt.%. Furthermore, up to 0.25 wt.% Pb, preferably up to a maximum of 0.10 wt.% Pb, can be added. The proportion of the ß-phase as well as the proportions of Si, P and Pb are selected so that the alloy meets the condition

[0032] 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] denotes the proportion of the ß-phase in vol%, [Si] the proportion of silicon in wt%, [P] the proportion of phosphorus in wt% and [Pb] the proportion of lead in wt%. This relationship quantitatively describes the influence of the ß-phase, Si, P, and Pb parameters on the machining properties of the alloy, as well as the interaction of these parameters with each other. For example, a low proportion of ß-phase can be compensated by a higher proportion of silicon and / or phosphorus within the specification of the alloy's composition, and vice versa.

[0033] The Cu content of the alloy is 58.0 to 66.0 wt.%. At a Cu content of less than 58.0 wt.%, the ductility of the alloy is too low. At a Cu content of more than 66.0 wt.%, the zinc content in the alloy is too low to achieve good machinability.

[0034] Furthermore, the composition of the alloy can preferably be selected such 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 such that the sum of Si and P is at least 0.58 wt.%, particularly preferably at least 0.64 wt.%. Both of the above-mentioned measures, both independently of one another and in combination, contribute to fulfilling the relationship described above and thus to achieving favorable machining properties. The optional elements Sn and Al support the formation of the β phase. With an Sn content of more than 0.5 wt.%, further tin-containing phases can form, which can have a negative effect on the properties of the alloy. The proportion of tin should preferably be at most 0.3 wt.%, particularly preferably at most 0.2 wt.%. Furthermore, aluminum forms aluminum phosphides with phosphorus.However, these are undesirable, which is why the Al content should not exceed 0.05 wt.%.

[0035] Iron leads to grain refinement of the microstructure. Furthermore, iron forms hard phosphides, which adversely affect the service life of tools during machining. Therefore, the iron content may not exceed 0.3 wt.%, preferably 0.1 wt.%.

[0036] Nickel supports the formation of the α-phase. Furthermore, nickel forms phosphides, which have no beneficial effect on machinability. Therefore, the nickel content may not exceed 0.3 wt.%, preferably 0.1 wt.%.

[0037] The element Bi is present as an impurity in secondary raw materials, such as scrap. It can improve the machinability of the alloy. In amounts up to 0.1 wt.%, Bi has no negative impact on the alloy. Therefore, up to 0.1 wt.% Bi is tolerated in the alloy. The Bi content is preferably less than 0.015 wt.%.

[0038] The elements Te, Se, and In can have a beneficial effect on the machinability of the alloy. In amounts up to 0.1 wt.% each, they have no negative impact on the alloy. Therefore, up to 0.1 wt.% each of Te, Se, and In is tolerated in the alloy.

[0039] An optional boron content of up to 0.01 wt.% contributes to grain refinement. The remainder of the alloy composition consists of zinc and unavoidable impurities. To avoid uncontrollable influences of impurities on the alloy's properties, the maximum content of these impurities is 0.2 wt.%. Preferably, the Mn and Mg contents should each be no more than 0.1 wt.%, and particularly preferably no more than 0.05 wt.%, because these elements can form phosphides that can compete with the copper- and / or zinc-containing phosphides.

[0040] In a preferred embodiment of the invention, the Pb content in the alloy can be at least 0.02 wt.%. Even such a low Pb content improves machining properties and has a positive effect on grain refinement.

[0041] Advantageously, the ratio of the weight fractions of P to the sum of Fe and Ni can be greater than 2.0, i.e., P / (Fe+Ni) > 2.0. This ensures that predominantly copper- and / or zinc-containing phosphides, which are favorable for machining properties, are formed. The formation of iron phosphides or nickel phosphides is suppressed.

[0042] It can be particularly advantageous if the total Fe and Ni contents do not exceed 0.1 wt.%. This restriction also inhibits the formation of iron phosphides and nickel phosphides, while the formation of copper- and / or zinc-containing phosphides is inhibited.

[0043] In a particularly advantageous embodiment of the invention, the P content can be at least 0.26 wt.% and at most 0.33 wt.%. If the P content is at least 0.26 wt.%, sufficient phosphide particles are formed to achieve a particularly fine grain, a globular α-phase, and very good machinability. If the P content in the alloy is at most 0.33 wt.%, crack formation during hot forming is more reliably avoided.

[0044] In a further embodiment of the invention, the Si content can be a maximum of 0.35 wt.%. A wrought copper-zinc alloy with this relatively low Si content is characterized by high electrical conductivity. The electrical conductivity is then at least 12 MS / m.

[0045] In a further embodiment of the invention, the Si content can be at least 0.25 wt.%, preferably at least 0.30 wt.%. This achieves very good machinability combined with good surface quality.

[0046] In particular, in the embodiments described above, the Cu content can be at least 60.0 wt.% and at most 61.5 wt.%. An alloy with particularly advantageous properties is obtained with the composition Cu 60.0 to 61.5 wt.%, Si 0.25 to 0.35 wt.%, and P 0.26 to 0.33 wt.%, the remainder being Zn and unavoidable impurities.

[0047] In an alternative embodiment of the invention, the Si content can be at least 0.50 wt.% and at most 1.0 wt.%. A copper-zinc wrought alloy with a Si content in this range is characterized by excellent machining properties while still maintaining good ductility.

[0048] Advantageously, the copper-zinc wrought alloy can have a hardness of at least 170 HV10, preferably at least 180 HV10.

[0049] Advantageously, the copper-zinc wrought alloy can have a tensile strength R m of at least 520 MPa, preferably at least 560 MPa.

[0050] Advantageously, the copper-zinc wrought alloy can have an a-grain size of at most 21 μm, preferably at most 17 μm.

[0051] Advantageously, the copper-zinc wrought alloy can have an electrical conductivity of at least 12 MS / m.

[0052] The invention further relates to a wire-, tube-, or rod-shaped semi-finished product made of a wrought copper-zinc alloy described above, as well as a component manufactured from such a semi-finished product by machining and optionally further processing steps. The semi-finished product can also be in the form of a profile.

[0053] A further aspect of the invention relates to a method for producing a wire-, tube-, or rod-shaped semi-finished product. The method comprises the following steps: a) melting a copper alloy with a composition as described above, b) continuously casting a tube- or bolt-shaped casting format using a water-cooled mold, c) hot pressing the casting format at a temperature of 620 to 700 °C followed by cooling at a cooling rate of 30 to 60 °C per minute in a temperature range of 550 to 350 °C, d) optionally heat treatment in a temperature range of 525 to 625 °C for 1 to 5 hours followed by cooling at a cooling rate of 20 to 40 °C per minute in a temperature range of 500 to 350 °C, e) optionally cold forming.

[0054] Cu cathodes, Zn ingots, brass scrap, Cu-P master alloys, and Cu-Si master alloys can be used to melt the alloy. Melting is preferably carried out in an induction furnace. The melt is poured into a tubular or billet-shaped casting format in a water-cooled mold.

[0055] The cast format can optionally be milled and then hot-pressed at a temperature of 620 to 700 °C. The hot-pressed intermediate product is then cooled, with cooling occurring in the temperature range of 550 to 350 °C at a cooling rate of 30 to 60 °C per minute, preferably 40 to 50 °C per minute. This controlled cooling process establishes a favorable ratio of the α-phase to β-phase components, as well as a favorable particle distribution of copper and / or zinc-containing phosphides. Heat treatment can optionally be performed prior to hot pressing to homogenize the cast product.

[0056] In a first manufacturing process, pickling and then cold forming can follow hot pressing without any further intermediate steps. In cold forming, the degree of deformation is preferably between 3 and 30%. The degree of deformation is defined as the relative reduction in the cross-sectional area of ​​the product. Because no further steps take place between hot pressing and cold forming, apart from the pickling process, this first manufacturing process is very advantageous.

[0057] In a second manufacturing process, hot pressing is followed by heat treatment at between 525 and 625 °C, preferably between 550 and 600 °C, for a period of 1 to 5 hours, followed by cooling at a cooling rate of 20 to 40 °C per minute within a temperature range of 500 to 350 °C. By selecting the heat treatment conditions in combination with the defined cooling after heat treatment, a favorable ratio of the proportions of α-phase and β-phase as well as a favorable particle distribution of copper and / or zinc-containing phosphides can be achieved. If an increase in the proportion of the β-phase is desired, heat treatment should be carried out at approximately 600 °C. If an increase in the proportion of the α-phase is desired, heat treatment should be carried out at approximately 550 °C.Heat treatment allows the ratio of the α-phase to β-phase, as well as the particle distribution of the phosphides, to be adjusted and optimized. In particular, ductility can be improved. After heat treatment, the pickling and cold forming steps can follow, as in the first manufacturing process.

[0058] With regard to further technical features and advantages of the method according to the invention, reference is hereby explicitly made to the explanations in connection with the copper-zinc wrought alloy according to the invention and to the exemplary embodiments.

[0059] The invention is explained in more detail using exemplary embodiments.

[0060] Samples No. 1 to No. 45 were melted in an induction furnace and then cast. The composition of the samples is documented in Tables 1 to 4. Sample No. 16 represents the lead-containing reference alloy CuZn39Pb3. The samples were milled, homogenized for 1 hour at 650 °C, and then hot-formed. During cooling after hot-forming, the cooling rate was approximately 40 °C per minute in the temperature range between 550 and 350 °C.

[0061] Samples No. 1 to No. 26 were milled after hot forming and then cold formed to a deformation degree of 20%. Samples No. 27 to No. 45 were annealed for 3 hours after hot forming. The annealing temperature for samples No. 28 and No. 35 to No. 41 was approximately 600°C, while for samples No. 27, Nos. 29 to 34, and No. 42 to No. 45, it was approximately 550°C. After annealing, cooling took place in the temperature range between 500 and 350°C at a cooling rate of approximately 25°C per minute. Samples No. 27 to No. 45 were then milled and then cold formed to a deformation degree of 20%.

[0062] At the final state, the tensile strength R mand the elongation at break from the tensile test, the hardness (Vickers hardness HV10), and the electrical conductivity were determined. The longitudinal sections of the samples were examined by light microscopy. The area fractions of the α-phase and β-phase corresponding to the volume fractions, as well as the α-grain size, were determined. For the quantitative determination of the size distribution of the phosphide particles, the light microscopy images of the unetched samples were used. Image sections measuring 167 pm x 126 pm (corresponding to an area of ​​21,000 pm) were used. 2 ) and analyzed at 1000x magnification using the ImageJ software. This made it possible to identify individual particles and determine their equivalent diameter and area. The phosphide particles were classified based on their equivalent diameter into the categories 0.5 to 1 pm, 1 to 2 pm, 2 to 5 pm, and - if present - larger than 5 pm.

[0063] Machinability was determined using a planing test. An indexable insert with a contour that favors chip breaking was used. 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, and the mean value of the bending moment was determined. The resulting chips were visually assessed and categorized according to chip shape. A chip shape number was assigned to each chip shape according to the following list:

[0064] The chip break index of 1 corresponds to the lead-containing reference alloy CuZn39Pb3 (sample no. 16). The test results are documented in Tables 1 to 4. The unannealed samples no. 1 to no. 15 (Table 1) and the annealed samples no. 27 to 34 (Table 3) are samples according to the invention. The unannealed samples no. 16 to no. 26 (Table 2) and the annealed samples no. 35 to no. 45 (Table 4) are comparison samples and are marked with (*).

[0065] The machinability of the specimens was assessed based on the bending moment measured during planing and the shape of the chips. An average bending moment of no more than 36 Nm and chips corresponding to a chip shape number of 1 or 1.25 were considered very favorable.

[0066] Furthermore, an attempt was made to parameterize the measured mean bending moment as a function of the volume fraction of the ß-phase as well as the weight fractions of Si, P and Pb. The functional relationship determined in this way can be represented as follows: 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 approximately quantifies the measured bending moment in Nm and where [Beta] denotes the proportion of the ß-phase in vol.%, [Si] the proportion of silicon in weight%, [P] the proportion of phosphorus in weight% and [Pb] the proportion of lead in weight%. The value of f calculated according to this formula is documented in the last column of Tables 1 to 4. A comparison of this value f with the measured bending moment shows very good agreement between the two values. The inventive samples Nos. 1 to No. 15 and Nos. 27 to No.34, all of which have a measured bending moment of less than 36 Nm, are characterized by the value of f being less than 37.

[0067]

[0068] Table 1: Samples according to the invention, unannealed

[0069]

[0070] Table 1 (continued): samples according to the invention, unannealed

[0071]

[0072] Table 2: Reference samples, unannealed

[0073]

[0074] Table 2 (continued): Reference samples, unannealed

[0075]

[0076] Table 3: Samples according to the invention, annealed

[0077]

[0078] Table 3 (continued): samples according to the invention, annealed

[0079]

[0080] Table 4: Comparison samples, annealed

[0081]

[0082] Table 4 (continued): Reference samples, annealed

[0083] Samples No. 1 to No. 15 (Table 1) are samples according to the invention in the unannealed state. The volume fraction of the ß-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 R m at least 560 MPa. The elongation at break is at least 4.7%. The measured maximum bending moment is 35.7 Nm. The shape of the chips corresponds to a chip break number of 1 or 1.25 in all specimens.

[0084] Samples No. 16 to No. 26 (Table 2) are comparison samples in the unannealed state. Reference sample No. 16 contains 3.3 wt% lead and exhibits very good machining properties. Sample No. 17 shows that, without lead and without other alloying elements, the machining properties are very poor.

[0085] Sample No. 18 contains, in addition to Cu and Zn, only 0.27 wt.% Si. The bending moment is good, but the chip shape is poor, which can be attributed to the lack of phosphide particles as chip breakers. The same can be observed for sample No. 21, which contains 0.53 wt.% Si. Samples Nos. 19, 20, and 22 contain 0.05 to 0.1 wt.% phosphorus, which has a positive effect on the chip shape and, at least in the case of sample No. 19 and sample No. 22, also on the bending moment. However, for samples Nos. 19 and 20, the hardness and tensile strength R m significantly below the values ​​of samples No. 1 to No. 15. Sample No. 22, with a Si content of 0.58 wt.%, shows only slightly improved hardness and tensile strength. Furthermore, samples No. 18 to No. 22 have a significantly larger a-grain size of 19 to 25 pm than samples No. 1 to No. 15. The coarser a-grain leads to disadvantages in straightness and dimensional stability.

[0086] The silicon-free samples No. 23 and No. 24, with a P content of 0.24 and 0.29 wt.%, respectively, produce excellent chip formation, but the bending moment is at a high level. Samples No. 25 and No. 26, each with a P content of 0.65 wt.%, exhibit excellent machining properties. However, due to the high P content, they are prone to cracking during hot forming. Furthermore, low elongation at room temperature is the result. The high P content results in a large number of phosphide particles with an equivalent diameter of 2 to 5 μm. This indicates poor hot formability and brittle material behavior at room temperature when the alloy is in an area of ​​21,000 μm. 2 more than 45 phosphide particles with an equivalent diameter of 2 to 5 pm.

[0087] The samples demonstrate that silicon leads to a reduction in bending moment and that phosphorus promotes chip breaking. The combination of both elements leads to good machining properties and a small a-grain size.

[0088] Samples No. 27 to No. 34 (Table 3) are inventive samples in the annealed state. The volume fraction of the ß-phase is at least 22% and at most 39%. For sample No. 28, the α-grain size is 21 μm. This can be attributed to the annealing temperature of 600 °C. For the remaining samples, which were annealed at 550 °C, the α-grain size is a maximum of 16 μm. Compared to samples No. 1 to No. 15, samples No. 27 to No. 34 have a slightly lower hardness of at least 170 HV10 and a slightly lower tensile strength R mof at least 520 HV10. Annealing, on the other hand, improved the elongation at fracture. Consequently, a more ductile material condition can be achieved. The bending moment and chip shape are very good to excellent.

[0089] Samples No. 35 to No. 45 (Table 4) are comparison samples in the annealed condition. Samples No. 35 and No. 38, which contain silicon but are free of phosphorus, are characterized by an unfavorably high bending moment and poor chip formation. Samples No. 36, 37, and 39, with a low P content, exhibit significantly improved machining properties compared to samples No. 19, 20, and 22, but their hardness and tensile strength are unsatisfactory. Furthermore, samples No. 25 to No. 39 have a significantly larger a-grain size of 31 to 39 pm than samples No. 1 to No. 15. The coarser a-grain leads to disadvantages in straightness and dimensional stability.

[0090] The phosphorus-containing but silicon-free samples No. 40 and No. 41 produce very good chip formation, but the bending moment is at an unfavorably high level. The annealed samples No. 42, 43, and 44, which correspond in composition to the unannealed samples No. 3, 4, and 5, exhibit a higher bending moment and poorer chip formation than the unannealed variants. Annealing reduced the volume fraction of the ß-phase to values ​​below 20% and shifted the distribution of the phosphide particles toward larger particles. These two effects together lead to a deterioration in the machining properties. Sample No. 45, with a P content of 0.65 wt.%, is characterized by a high bending moment. The reason for this is a very low ß-phase content of only 9 vol.%. Furthermore, this sample exhibits a very high density of phosphides with an equivalent diameter of 2 to 5 μm.

[0091] Alloys with a composition described above can also be used as casting alloys for castings.

Claims

Patent claims Copper-zinc wrought alloy for the production of wire, tube or rod-shaped semi-finished products with the following composition in weight %: Cu: 58.0 to 66.0%, Si: 0.15 to 1.2%, P: 0.20 to 0.38%, Sn: optional up to 0.5%, AI: optional up to 0.05%, Fe: optional up to 0.3%, Ni: optional up to 0.3%, Pb: optional up to 0.25%, Bi: optional up to 0.1%, Te, Se, In: optionally up to 0.1% each B: optionally up to 0.01%, Balance Zn and unavoidable impurities, with the proportion of unavoidable impurities being less than 0.20 wt.%, wherein the alloy has a structure of globular a-phase, ß-phase and phosphide particles and the proportion of the ß-phase in the sum of a-phase and ß-phase is at least 20 vol-% and at most 60 vol-%, wherein Si is present in both the a-phase and the ß-phase, wherein in an area of ​​21000 pm 2 50 to 700 phosphide particles with an equivalent diameter of 0.5 to 1 pm, 10 to 300 phosphide particles with an equivalent diameter of 1 to 2 pm and 3 to 45 Phosphide particles with an equivalent diameter of 2 to 5 pm are present, and the proportion of the ß-phase as well as the proportions of Si, P and Pb are selected so that the alloy meets the 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] denotes the proportion of the ß-phase in vol. %, [Si] the proportion of silicon in weight %, [P] the proportion of phosphorus in weight % and [Pb] the proportion of lead in weight %. Copper-zinc wrought alloy according to claim 1, characterized in that the Pb proportion is at least 0.02 wt. %. Copper-zinc wrought alloy according to claim 1 or 2, characterized in that the ratio of the weight proportions of P and the sum of Fe and Ni is more than 2.

0. Copper-zinc wrought alloy according to one of claims 1 to 3, characterized in that the proportions of Fe and Ni in total amount to at most 0.1 wt. %. A wrought copper-zinc alloy according to any one of claims 1 to 4, characterized in that the P content is at least 0.26 wt.% and at most 0.33 wt.%. A wrought copper-zinc alloy according to any one of claims 1 to 5, characterized in that the Si content is at most 0.35 wt.%.Copper-zinc wrought alloy according to one of claims 1 to 6, characterized in that the Si content is at least 0.25 wt.%. Copper-zinc wrought alloy according to claim 6 or 7, characterized in that the Cu content is at least 60.0 wt.% and at most 61.5 wt.%. Copper-zinc wrought alloy according to one of claims 1 to 5, characterized in that the Si content is at least 0.50 wt.% and at most 1.0 wt.%. Copper-zinc wrought alloy according to one of the preceding claims, characterized in that the alloy has a hardness of at least 170 HV10. Copper-zinc wrought alloy according to one of the preceding claims, characterized in that the alloy has a tensile strength R mof at least 520 MPa. A copper-zinc wrought alloy according to any one of the preceding claims, characterized in that the alloy has an a-grain size of at most 21 pm. 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. A wire-, tubular-, or rod-shaped semi-finished product made of a copper-zinc wrought alloy according to any one of the preceding claims. A component produced by machining and optional further processing steps from a semi-finished product according to claim 14. A method for producing a wire-, tube-, or rod-shaped semi-finished product according to claim 14, wherein the method comprises the following steps: a) melting a copper alloy having a composition according to one of claims 1 to 9, b) continuous casting of a tube- or bolt-shaped casting format using a water-cooled mold, c) hot pressing the casting format at a temperature of 620 to 700 °C with subsequent cooling at a cooling rate of 30 to 60 °C per minute in a temperature range of 550 to 350 °C, d) optionally heat treatment in a temperature range of 525 to 625 °C for 1 to 5 hours with subsequent cooling at a cooling rate of 20 to 40 °C per minute in a temperature range of 500 to 350 °C, e) optionally cold forming.

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