Wrought copper-zinc alloy, semi-finished product made from a wrought copper-zinc alloy, and method for producing such a semi-finished product

Abstract

Wrought copper-zinc alloy for producing a semi-finished product with composition in wt. %: Cu: 58.0 to 63.0%, Si: 0.04 to 0.32%; P: 0.05 to 0.20%; Sn: up to 0.25%; Al: up to 0.10%; Fe: up to 0.30%; Ni: up to 0.30%, Pb: up to 0.25%; Te, Se, In: up to 0.10% each; Bi: maximum 0.009%; the remainder Zn and impurities. The alloy has a microstructure of globular α phase, β phase, and phosphide particles. The proportion of β phase in relation to the total of α and β phase is 20 vol. % and at most 70 vol. %. In an area of 21000 μm2 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 a maximum of 30 phosphide particles with an equivalent diameter of more than 2 μm.

Description

[0001] The invention relates to a wrought copper-zinc alloy for production of a semifinished product in wire, pipe or bar form, to a semifinished product produced from a wrought copper-zinc alloy, and to a process for production of such a semifinished product. A wrought copper-zinc alloy generally means a wrought material composed of a copper-zinc alloy.

[0002] Copper-zinc alloys with 3% to 5% by weight of lead have excellent machinability and additionally very good hot and cold formability. Lead-containing copper-zinc alloys are therefore used in a multitude of applications, for example for connections and components in the automotive industry, in building technology, in mechanical engineering, in electrical appliances and in electronic components, in telecommunications and as fittings in water installations.

[0003] The basis of the positive effect of lead in wrought copper-zinc alloys is that lead is in elemental form as particles in the microstructure, and these particles act as chip breakers. In the course of machining, lead is in the form of a liquid phase as a result of the significant local deformation in the workpiece and the resultant local increase in temperature. Since the lead is not able to absorb stresses in the liquid state, this leads to a concentration of stress in the load-bearing, weakened matrix and hence to easier chip breakage. In addition, lead is also incorporated into the tribological layer between material and workpiece in the course of machining and hence leads to effective lubrication and hence to a reduction in friction and wear. Moreover, because of its low solubility, lead barely makes any contribution to electrical conductivity. This is advantageous especially for materials that are used in electrical applications. Furthermore, it is known that lead in copper-zinc alloys results in distinct grain refining. This is favorable for straightness and trueness to scale of a semifinished product in rod form in particular. High trueness to scale is also required in the crimping of electronic wires. Furthermore, lead is inexpensive.

[0004] However, lead is damaging to the environment. Lead accumulates in the human body when extremely small amounts are ingested and can lead to damage to health. Therefore, the EU, the USA, China and other states have reduced the limits in copper alloys ever further, and there is a drive to replace lead-containing brass with reduced-lead or lead-free machinable copper alloys. Limits are defined in EU directives, for example the RoHS (Directive 2011 / 65 / EU), which stipulates 1000 ppm (0.1% by weight) of Pb as the upper limit. In order to ensure good machinability of the material even in the case of such low lead contents, various alloy elements are proposed as an alternative to lead.

[0005] It is known from a multitude of publications that bismuth (Bi) can be used as an alternative to lead in order to improve machinability. In order to alleviate the problem of film formation by Bi along the grain boundaries and associated proneness to stress cracking and thermal cracking, it is proposed that further elements be included in the alloy. In this regard, reference is made in particular to documents 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 since it is firstly a metal of low availability that exists only in limited volumes, and secondly leads to hot brittleness in the material cycles of the copper alloys.

[0006] In addition, document EP 2 194 150 B1 discloses copper-zinc alloys containing 0.1% to 1.5% by weight of Si, 0.03% to 0.4% by weight of Al, 0.01% to 0.36% by weight of P, 0.05% to 0.5% by weight of Sn, and 0.001% to 0.05% by weight of rare earths. Owing to the formation of an α, β and possibly γ microstructure, the alloys have good machinability. The Al fraction results in formation of aluminum phosphides. Although the γ phase and aluminum phosphides improve chip formation, they worsen the service life of the tool. Moreover, the proportion of rare earths is likely to lead to embrittlement of the microstructure. The alloys are used for castings and hot pressings.

[0007] The replacement of lead by phosphorus that forms brittle phosphides in the alloy is also described in document WO 2020 / 261 604 Al for a material with Cu at 58.5% to 63.5% by weight, Si at 0.4% to 1.0% by weight, P at 0.005% to 0.19% by weight, Pb at 0.003% to 0.25% by weight, balance: zinc and further optional elements. The addition of 0.005% to 0.19% by weight of P for formation of phosphides and of 0.4% to 1.0% by weight of Si for consolidation of the α phase and the β phase lead here to a material of good machinability. However, because of the high Si content, conductivity is reduced compared to lead-containing brass. This is firstly disadvantageous for use as electronic component; secondly, the phosphides, especially at elevated temperatures that occur on drilling for example, lose their brittleness and hence their chip-breaking function. The extent of this effect increases inversely to thermal conductivity and hence electrical conductivity of the material.

[0008] It is an object of the invention to provide a wrought copper-zinc alloy for production of a semifinished product in wire, pipe or bar form that has excellent machinability, especially in the case of drilling, good electrical conductivity and a minimum content of alloy constituents of environmental concern. Moreover, the alloy is to have good processibility on an industrial scale. This requires it to have good hot formability, for example by extrusion, and good cold formability, for example by drawing or crimping, and for a semifinished product manufactured from the alloy to have excellent straightness and very good trueness to scale. It is a further object of the invention to provide a process for producing a semifinished product in wire, pipe or bar form from such an alloy.

[0009] The invention is described by the features of claim 1 with regard to a wrought copper-zinc alloy, and by the features of claim 16 with regard to a production process. The further dependent claims relate to advantageous embodiments and developments of the invention.

[0010] The invention relates to a wrought copper-zinc alloy for production of a semifinished product in wire, tube or bar form, having the following composition in % by weight:Cu:58.0% to 63.0%,Si:0.04% to 0.32%,P:0.05% to 0.20%,Sn:optionally 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:optionally up to 0.30%,Pb:optionally up to 0.25%, preferably up to 0.10%,Te, Se, Ineach optionally up to 0.10%,Bi:not more than 0.009%,balance: Zn and unavoidable impurities,

[0012] where the proportion of unavoidable impurities is less than 0.2% by weight. The ratio of the proportions by weight of P and Al is at least 1.0. The alloy has a microstructure composed of globular α phase, β phase and phosphide particles. The proportion of the β phase in the sum total of α phase and β phase is at least 20% by volume, preferably at least 30% by volume, and not more than 70% by volume, preferably not more than 50% by volume. Silicon is present both in the α phase and in the β phase. In an area of 21 000 μm2, there are 7 to 200 phosphide particles having an equivalent diameter of 0.5 to 1 μm, 4 to 150 phosphide particles having an equivalent diameter of 1 to 2 μm, and not more than 30 phosphide particles having an equivalent diameter of more than 2 μm.

[0013] The invention proceeds from the consideration of reducing the proportions of Pb in the copper-zinc alloy as far as possible without worsening the machinability of the alloy. For this purpose, Si and P are specifically added to the alloy, and the proportion of the β phase is adjusted so as to give favorable machining properties on the one hand, especially in the case of drilling, and high conductivity, and on the other hand not to worsen the hot and cold formability of the alloy, and such that the semifinished product produced from the alloy has excellent straightness. Furthermore, the process regime, especially in the casting and hot forming operations, is chosen so as to result in the desired properties.

[0014] A globular α phase is a prerequisite for good straightness and trueness to scale of the semifinished product. α phase forms from the β phase after hot forming. Therefore, the β phase must be in fine-grain form in the cast state. It has been found that, surprisingly, a fine-grain β phase in the cast state is favored by homogeneously finely distributed copper- and / or zinc-containing phosphides. In the primary crystallization of the β crystallites, the residual melt becomes enriched with P and hence leads to a subdivision of the β phase. Solidification forms a eutectic composed of phosphide and β phase. In addition to grain refining of the base matrix composed of β phase, grain refining of the a crystallites is observed. This grain refining of the cast microstructure by P facilitates hot forming, continues into the microstructure after hot forming, and consequently leads to grain refining in the final state. In the case of a P content of at least 0.05% by weight, phosphide particles are present in the β phase in the final state. In the case of a P content of more than 0.20% by weight, ductility of the alloy is low.

[0015] Moreover, a high P content in combination with Si has an adverse effect on electrical conductivity. In a preferred embodiment of the invention, therefore, the sum total of the proportions of Si and P is preferably not more than 0.45% by weight.

[0016] Furthermore, for a globular α phase, it is necessary for the material to be cooled in a controlled manner after hot forming: Within a temperature range from 550° C. to 350° C., the cooling rate has to be at least 30° C. per minute (30° C. / min), preferably at least 40° C. per minute, and at most 60° C. per minute, preferably at most 50° C. per minute. The uniformly finely distributed phosphides that accompany a fine-grain β phase in the cast state dissolve in the matrix during the hot forming and then reform during the cooling operation in the course of hot forming. In this way, the characteristic distribution of the phosphides in the cast state is ultimately mapped onto the microstructure in the final state. The distribution of the phosphides in the final state and the globular form of the α phase are therefore determined not only by the chemical composition of the alloy but also by the process regime in the casting and in the hot forming. The characteristics of the phosphides in the final state are thus like a fingerprint left on the product by the particular process regime. The distribution of the phosphides in the final state can be characterized as follows: In an area of 21 000 μm2, there are 7 to 200 phosphide particles having an equivalent diameter of 0.5 to 1 μm, 4 to 150 phosphide particles having an equivalent diameter of 1 to 2 μm, and not more than 30 phosphide particles having an equivalent diameter of more than 2 μm. The equivalent diameter of a phosphide particle means the diameter of a circle of equal area to the phosphide particle. The predominant portion of the phosphide particles having an equivalent diameter of at least 0.5 μm has an equivalent diameter of not more than 2 μm. The proportion of the phosphide particles having an equivalent diameter of 0.5 to 2 μm is preferably at least 70% of the number of all phosphide particles having an equivalent diameter of at least 0.5 μm. This proportion is more preferably at least 75%. In addition, it is advantageous when at least 30%, preferably at least 50%, of all phosphide particles having an equivalent diameter of at least 0.5 μm have an equivalent diameter of not more than 1 μm. It is not impossible that phosphides having an equivalent diameter of less than 0.5 μm will be present in the alloy.

[0017] Brittle microstructure constituents are advantageous for machinability of the alloy that act as separation sites in the machining operation and hence promote chip breaking. The β phase is brittle and promotes machinability. An increase in the proportion of β phase can be achieved by an increase in the Zn content and / or by inclusion of silicon in the alloy, since silicon stabilizes the β phase. It has additionally been found to be advantageous for good machinability when the ductility of the α phase is reduced. This is possible by the inclusion and intercalation of silicon in the α phase. Therefore, the Si content in the alloy must be at least 0.04% by weight. In the case of an Si content of more than 0.32% by weight, electrical conductivity is lower than 12 MS / m and hence inadequate. A P content of at least 0.05% by weight leads to favorable swarf formation on drilling. In addition, a small optional fraction of Pb has an advantageous effect on machinability.

[0018] The Cu content of the alloy is 58.0% to 63.0% by weight. In the case of a Cu content of less than 58.0% by weight, ductility of the alloy is too low. In the case of a Cu content of more than 63.0% by weight, the zinc content in the alloy is too small to achieve good machinability.

[0019] The ratio of the proportions by weight of P and Al is at least 1.0. Aluminum forms aluminum phosphides with phosphorus. However, these are unwanted because they do not improve machinability characteristics. In order that there is a sufficient excess of P available for formation of copper- and / or zinc-containing phosphides, the ratio of the proportions by weight of P and Al must be at least 1.0 in the alloy.

[0020] The optional Sn and Al elements promote formation of the β phase. In the case of an Sn content of more than 0.20% by weight, there is a deterioration in the machinability properties of the alloy. However, this deterioration can be compensated for by heat treatment up to an Sn content of 0.25% by weight. The proportion of tin should preferably be not more than 0.20% by weight, more preferably not more than 0.10% by weight.

[0021] Aluminum forms aluminum phosphides with phosphorus. However, these are unwanted, and therefore the Al content should not exceed 0.10% by weight, preferably 0.05% by weight.

[0022] Iron leads to grain refining of the microstructure. Moreover, iron forms hard phosphides, which have an adverse effect on the service life of the tools on machining. Therefore, the proportion of iron must be not more than 0.30% by weight, preferably not more than 0.10% by weight.

[0023] Nickel promotes formation of the α phase and hence improves cold formability. Moreover, nickel forms phosphides, which do not have an advantageous effect on machinability. Therefore, the proportion of nickel must be not more than 0.30% by weight, preferably not more than 0.10% by weight.

[0024] The element Bi is present as an impurity in secondary raw materials, for example scrap. It is capable of improving the machinability of the alloy. However, proportions exceeding 0.009% by weight can have an adverse effect on hot formability. Therefore, up to 0.009% by weight of Bi in the alloy is tolerated.

[0025] The elements Te, Se and In can have an advantageous effect on the machinability of the alloy. In amounts of not more than 0.1% by weight each, they have no adverse effect on the alloy. Therefore, up to 0.1% by weight each of Te, Se and In in the alloy is tolerated.

[0026] The balance of the alloy composition consists of zinc and unavoidable impurities. In order to avoid uncontrollable influences of the impurities on the properties of the alloy, the proportion of these impurities is not more than 0.2% by weight. In particular, the proportions of Mn and Mg should preferably each be not more than 0.1% by weight, more preferably each not more than 0.07% by weight, because these elements can form phosphides that can compete with the copper- and / or zinc-containing phosphides.

[0027] In a preferred configuration of the invention, the Pb content in the alloy may be at least 0.02% by weight. Even such a small proportion of Pb improves the machining properties and has a positive effect on grain refining.

[0028] Advantageously, the P content may be not more than 0.15% by weight, more preferably not more than 0.12% by weight. This has a favorable effect on hot formability of the alloy.

[0029] In an advantageous embodiment of the invention, the P / Fe ratio may be at least 1.0. Iron forms hard iron phosphides with phosphorus. However, these are undesirable because they worsen the service life of the tools. In order that there is a sufficient excess of P in the alloy for formation of copper- and / or zinc-containing phosphides, the ratio of the proportions by weight of P and Fe should be at least 1.0.

[0030] In the context of a preferred configuration of the invention, the Fe content may be less than 0.10% by weight, and the Ni content may be not more than 0.07% by weight. This restriction inhibits the formation of iron phosphides and nickel phosphides compared to the formation of copper- and / or zinc-containing phosphides that are favorable for machining. Particularly favorable properties are achieved when the condition that the P / Fe ratio is at least 1.0 is met simultaneously. In addition, it is particularly preferable when the Fe content is not more than 0.05% by weight and / or the Ni content is not more than 0.04% by weight.

[0031] In an advantageous embodiment of the invention, the Si content may be at least 0.23% by weight. This promotes the machining properties of the alloy. In addition, a Si content of at least 0.23% by weight has a favorable effect on the surface quality of the product.

[0032] In an alternative embodiment of the invention to the latter, the Si content may be not more than 0.15% by weight, preferably not more than 0.12% by weight, more preferably not more than 0.08% by weight. Such a restriction of the Si content has a favorable effect on the electrical conductivity of the alloy.

[0033] In this alternative embodiment of the invention, the P content may advantageously be not more than 0.10% by weight. This promotes the electrical conductivity of the alloy to a particular degree.

[0034] Moreover, in this alternative embodiment of the invention, the Cu content may be not more than 59.5% by weight. This upper limit for the Cu content gives rise to particularly favorable combinations of conductivity, machinability, mechanical properties and processibility.

[0035] In a further embodiment of the invention, the proportions of the elements Cu, Zn, Si, P and Pb may add up to at least 99.75% by weight. This ensures that the properties of the alloy are determined essentially by the alloy elements Cu, Zn, Si, P and Pb, while the effect of other elements plays only a very minor role. Alternatively or else additionally, it may be advantageous to select the composition of the alloy such that the proportions of the elements Cu, Zn, Si, P, Sn and Pb add up to at least 99.85% by weight. Because there is no formation of tin phosphides, it is less critical as alloy constituent than Fe, Ni or Al, for example.

[0036] Advantageously, the wrought copper-tin alloy may have a hardness of at least 120 HV10, preferably at least 150 HV10.

[0037] Advantageously, the wrought copper-tin alloy may have a tensile strength Rm Of at least 500 MPa, preferably at least 530 MPa.

[0038] Advantageously, the wrought copper-zinc alloy may have an electrical conductivity of at least 12.5 MS / m, preferably at least 12.7 MS / m, more preferably at least 13.0 MS / m.

[0039] An alloy having a particularly advantageous combination of properties has the following composition in % by weight: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:optionally up to a maximum of 0.10%Ni:optionally up to a maximum of 0.07%Sn:optionally up to a maximum of 0.20%Al:optionally up to 0.05%balance: zinc and unavoidable impurities, where the proportion of the unavoidable impurities is less than 0.1% by weight. The small proportion of alloy elements Si and P achieves a particularly high electrical conductivity of at least 14 MS / m, preferably at least 15 MS / m. Machinability is promoted by the Pb content of 0.04% to 0.08% by weight.

[0041] The invention further provides a semifinished product in wire, pipe or bar form, made from an above-described wrought copper-zinc alloy, and a component produced from such a semifinished product by machining and optional further processing steps. The semifinished product may also take the form of a profile.

[0042] A further aspect of the invention relates to a process of producing a semifinished product in wire, pipe or bar form. The process comprises the following steps:

[0043] a) melting a copper alloy having a composition as described above,

[0044] b) continuously casting a tubular or bolt-shaped cast format with a water-cooled mold,

[0045] c) hot pressing the cast format at a temperature of 620 to 700° C. with subsequent cooling at a cooling rate of 30 to 60° C. per minute within a temperature range from 550 to 350° C.,

[0046] d) optionally heat treatment within a temperature range from 525 to 625° C. for 1 to 5 hours with subsequent cooling at a cooling rate of 20 to 40° C. per minute within a temperature range from 500 to 350° C.,

[0047] e) optionally cold forming.

[0048] The alloy can be melted using Cu cathodes, Zn blocks, brass scrap, Cu—P prealloys and Cu—Si prealloys. The melting is preferably effected in an induction kiln. The melt is cast in a water-cooled mold to a tubular or bolt-shaped cast format.

[0049] The cast format may optionally be milled and is then hot-pressed at a temperature of 620 to 700° C. Subsequently, the hot-pressed intermediate product is cooled, where the cooling is effected within the temperature range from 550 to 350° C. at a cooling rate of 30 to 60° C. per minute, preferably 40 to 50° C. per minute. The defined cooling establishes a favorable ratio of the proportions of α phase and β phase, and a favorable particle distribution of copper- and / or zinc-containing phosphides. The hot pressing operation may optionally be preceded by a heat treatment for homogenization of the cast product.

[0050] In a first production process, the hot pressing operation may be followed, without further intermediate steps, by pickling and then a cold forming operation. In the cold forming operation, the degree of forming is preferably between 3% and 30%. What is meant here by degree of forming is the relative decrease in the cross-sectional area of the product. Because there are no further steps between the hot pressing and cold forming operations except for the pickling operation, this first production process is very favorable.

[0051] In a second production process, the hot pressing operation is followed by a heat treatment between 525 and 625° C., preferably between 550 and 600° C., for a period of 1 to 5 hours, with subsequent cooling at a cooling rate of 20 to 40° C. per minute within a temperature range from 500 to 350° C. By the choice of the conditions in the heat treatment operation in combination with the defined cooling after the heat treatment, it is possible to establish a favorable ratio of the proportions of α phase and β phase, and a favorable particle distribution of copper- and / or zinc-containing phosphides. If the aim is to increase the proportion of the β phase, the heat treatment should be effected at about 600° C. If the aim is to increase the proportion of the α phase, the heat treatment should be effected at about 550° C. By the heat treatment, it is thus possible to adjust and optimize the ratio of the proportions of α phase and β phase, and the particle distribution of the phosphides. In particular, it is thus possible to improve ductility. The heat treatment is followed by the steps of pickling and cold forming, as in the first production process.

[0052] With regard to further technical features and advantages of the process of the invention, explicit reference is hereby made to the elucidations in the context of the wrought copper-zinc alloy of the invention and to the working examples.

[0053] The invention is elucidated in detail by working examples.

[0054] Samples No. 1 to No. 44 were melted in an induction kiln and then cast. The composition of the samples is documented in tables 1 to 4. Sample No. 10 represents the lead-containing reference alloy CuZn39Pb3. The samples were milled, homogenized for 1 hour and then hot-formed. Samples No. 8 and No. 9 were hot-formed by pressing at 630° C., the other samples by rolling at 650° C. In the course of cooling after hot forming, the cooling rate within the temperature range between 550 and 350° C. was about 40° C. per minute for the rolled samples and about 30° C. per minute for the pressed samples.

[0055] Samples No. 1 to No. 7 and No. 10 to No. 23, after hot forming, were milled and then cold-formed with a degree of forming of 20%. Samples No. 8 and No. 9, after hot forming, were pickled and then cold-formed with a degree of forming of 7%.

[0056] Samples No. 24 to No. 44, after hot forming, were annealed for 3 hours. The annealing temperature was about 550° C. for samples No. 26, No. 27 and No. 38 to No. 41, while it was about 600° C. for samples No. 24, No. 25, No. 28 to No. 37 and No. 42 to No. 44. The annealing was followed by cooling within the temperature range between 50° and 350° C. at a cooling rate of about 25° C. per minute. Thereafter, samples No. 24 to No. 44 were milled and subsequently cold-formed with a degree of forming of 20%.

[0057] In the final state, tensile strength Rm and elongation at break A were each determined from the tensile test, as were hardness (Vickers hardness HV10) and electrical conductivity A. The longitudinal sections of the samples were examined by light microscopy. The area proportions of the α phase and of the β phase corresponding to the proportions by volume, and the α grain size were determined therefrom. The light microscope images of the unetched samples were used for quantitative determination of the size distribution of the phosphide particles. Image details of dimensions 167 μm×126 μm (corresponding to an area of 21 000 μm2) were chosen, and these were evaluated in 1000-fold magnification by means of the ImageJ software. In this way, it was possible to discern individual particles and to determine the equivalent diameters thereof and the area thereof. The phosphide particles were classified by their equivalent diameter into the categories of 0.5 to 1 μm, 1 to 2 μm, and greater than 2 μm.

[0058] Machinability was assessed in the final state by drilling tests. The drilling tests were conducted with an instrumented drill head. The drilling tests were conducted with the following parameters:

[0059] spiral drill, diameter 5 mm

[0060] speed 3200 rpm

[0061] advance rate 0.04 mm / rev

[0062] 5 bores per sample, using a new drill for each sample

[0063] drilling depth 10 mm

[0064] The bores were made longitudinally to the forming direction. The torque acting on the drill blade and the normal force were measured. The reference used was the CuZn39Pb3 alloy in the unannealed state. The torque measured on the individual samples was normalized by expressing the torque measured on the reference alloy relative to the torque measured on each respective sample. In other words, the lower the torque ascertained on a sample, the greater the normalized torque for that sample. The measured normal force for each sample was normalized in an analogous manner. The normalized torque Mnorm and the normalized normal force FNnorm were used to ascertain the arithmetic average for these two parameters. Samples where the arithmetic average thus calculated is below 0.75 do not meet the prerequisites for good machinability.

[0065] The swarf form was classified in accordance with the document “Richtwerte für die spanende Bearbeitung von Kupfer und Kupferlegierungen” [Guidelines for the Machining of Copper and Copper Alloys], information sheet i.18, published by the Deutsche Kupferinstitut [German Copper Institute]. On that basis, the swarf was rated good (2), average (1) or poor (0). In particular, long swarf turnings led to an unfavorable assessment.

[0066] The normalized torques and normal forces ascertained in the experiments and the arithmetic average calculated therefrom, identified in the table headings as (M+FN) / 2, are listed in tables 1 to 4 together with the swarf forms and the indices from the tensile test and the hardness measurement.TABLE 1inventive samples, unannealedαβPhosphidesPhosphidesPhosphidesCuZnSiPPbOtherphasephaseα grain0.5-1 μm1-2 μm>2 μmSample% by% by% by% by% byelements% by% bysizeperperperNo.wt.wt.wt.wt.wt.% by wt.vol.vol.μm21 000 μm221 000 μm221 000 μm2160.9238.690.2770.10267332019579259.8939.780.2740.0515446242110359.9839.610.2980.10262381845371459.6839.790.2720.1330.118613915102411559.8239.590.2840.104Fe: 0.19559411359348660.0939.490.2840.057Mn: 0.0686238205512760.5938.850.2690.1540.125673322132663859.2740.2180.370.140.00259413519711958.6241.090.0810.0910.065446321887CuZnSiPPbOther(M +SwarfSample% by% by% by% by% byelementsHardnessRmAλMnormFNnormFN) / 2formNo.wt.wt.wt.wt.wt.% by wt.HV10MPa%MS / m————160.9238.690.2770.10216753114.612.730.910.670.792259.8939.780.2740.0511975731413.470.960.540.751359.9839.610.2980.10217658310.313.001.000.640.822459.6839.790.2720.1330.11817555014.412.961.080.470.782559.8239.590.2840.104Fe: 0.19517456114.913.620.910.650.781660.0939.490.2840.057Mn: 0.06817955815.213.330.850.650.752760.5938.850.2690.1540.12517153611.812.740.950.560.762859.2740.220.370.140.00216355913.912.950.860.640.751-2958.6241.090.0810.0910.0616852116.715.710.880.630.761-2TABLE 2Comparative samples, unannealedαβPhosphidesPhosphidesPhosphidesCuZnSiPPbOtherphasephaseα grain0.5-1 μm1-2 μm>2 μmSample% by% by% by% by% byelements% by% bysizeperperperNo.wt.wt.wt.wt.wt.% by wt.vol.vol.μm21 000 μm221 000 μm221 000 μm21057.6439.003.3587030171157.6340.322.0476337191259.5240.175941211360.8538.870.2696535231462.437.060.537327251562.337.020.5790.1027129229410321658.9641.036238161759.8539.870.2726040171859.9839.360.2690.383633512128103471958.7541.130.109633725768222061.3338.030.5520.075623821504732159.9339.530.2720.056Sn: 0.2155347125132258.7940.910.294732711332762360.8838.530.2860.295762415385743CuZnSiPPbOther(M +SwarfSample% by% by% by% by% byelementsHardnessRmAλMnormFNnormFN) / 2formNo.wt.wt.wt.wt.wt.% by wt.HV10MPa%MS / m————1057.6439.003.35816148915.816.291.001.001.0021157.6340.322.04715550121.816.91.140.610.8821259.5240.1715649222.316.780.340.540.4401360.8538.870.26917352520.413.580.950.620.7901462.437.060.5317453816.211.40.830.440.6401562.337.020.5790.10217456010.610.70.910.620.7711658.9641.031615152517.280.770.370.5701759.8539.870.27217955621140.870.680.7801859.9839.360.2690.3831915656.812.430.930.560.7521958.7541.130.10917251915.816.310.850.580.7222061.3338.030.5520.07517455816.911.230.780.630.711-22159.9339.530.2720.056Sn: 0.2151805621213.230.850.510.6812258.7940.910.29417452712.115.740.850.370.6112360.8838.530.2860.29518556410.212.060.800.600.702TABLE 3inventive samples, annealedαβPhosphidesPhosphidesPhosphidesCuZnSiPPbOtherphasephaseα grain0.5-1 μm1-2 μm>2 μmSample% by% by% by% by% byelements% by% bysizeperperperNo.wt.wt.wt.wt.wt.% by wt.vol.vol.μm21 000 μm221 000 μm221 000 μm22460.77438.8880.2810.051643631221502560.92238.690.2770.1026931392338182659.88639.7810.2740.051554528301802759.98439.610.2980.1025941262332152859.68439.7870.2720.1330.1186238334830182959.8239.590.2840.104Fe: 0.195564432172193060.0939.490.2840.057Mn: 0.06851493328133159.9339.530.2720.056Sn: 0.2155446323817CuZnSiPPbOther(M +SwarfSample% by% by% by% by% byelementsHardnessRmAλMnormFNnormFN) / 2formNo.wt.wt.wt.wt.wt.% by wt.HV10MPa%MS / m————2460.77438.8880.2810.05116151117.713.130.950.580.7722560.92238.690.2770.10216351515.612.721.000.570.7922659.88639.7810.2740.05119054112.613.41.030.660.8522759.98439.610.2980.10217455716.212.991.000.610.8122859.68439.7870.2720.1330.11817253612.413.030.950.610.7822959.8239.590.2840.104Fe: 0.19517055118.113.660.790.710.7513060.0939.490.2840.057Mn: 0.06817154914.113.481.000.560.7813159.9339.530.2720.056Sn: 0.21516355111.613.20.930.620.782TABLE 4Comparative samples, annealedαβPhosphidesPhosphidesPhosphidesCuZnSiPPbOtherphasephaseα grain0.5-1 μm1-2 μm>2 μmSample% by% by% by% by% byelements% by% bysizeperperperNo.wt.wt.wt.wt.wt.% by wt.vol.vol.μm21 000 um221 000 μm221 000 μm23257.6439.003.3586634323357.6340.322.0476139293459.5240.176337393560.8538.870.2697030313662.437.060.536931383762.337.020.5790.1026535332027243858.9641.036634193959.8539.870.2725941244059.9839.360.2690.383623815105106504158.7541.130.109604029395714261.3338.030.5520.075594137172474358.7940.910.2946337232025594460.8838.530.2860.295613921734748CuZnSiPPbOther(M +SwarfSample% by% by% by% by% byelementsHardnessRmAλMnormFNnormFN) / 2formNo.wt.wt.wt.wt.wt.% by wt.HV10MPa%MS / m————3257.6439.003.3581484344.416.31.110.911.0123357.6340.322.0471514463.516.771.210.801.0123459.5240.1715746825.816.970.220.500.3603560.8538.870.26915048921.513.70.430.830.6303662.437.060.5316451020.611.510.450.770.6113762.337.020.5790.10215653112.710.711.030.680.8613858.9641.0315548924.616.960.780.670.7303959.8539.870.2721715361913.950.980.690.8404059.9839.360.2690.3831735551512.451.000.620.8124158.7541.130.1091585181816.160.850.620.7424261.3338.030.5520.07517153713.611.280.800.710.7614358.7940.910.29416950117.615.60.580.490.5414460.8838.530.2860.29517252613.412.061.050.700.881-2Samples No. 1 to No. 9 (table 1) are inventive samples in the unannealed state. The proportion by volume of the β phase is at least 33% and at most 46%. The α grain size for the rolled samples is at most 24 μm, and for the pressed samples at most 35 μm. The low α grain size of sample No. 5 can be attributed to the alloy element Fe. Hardness is at least 160 HV10, and tensile strength Rm at least 520 MPa. Elongation at break is at least 10%. Electrical conductivity for all samples is at least 12.7 MS / m, and for most of the samples at least 13.0 MS / m. For sample No. 9, electrical conductivity is more than 15.5 MS / m. Normalized torque is between 0.85 and 1.08. Normalized normal force is between 0.45 and 0.7. The arithmetic average of normalized torque and normalized normal force is always at least 0.75. The swarf form was always assessed as good (2) or average (1).Samples No. 10 to No. 23 (table 2) are comparative samples in the unannealed state. The reference sample No. 10 contains 3.3% by weight of lead and shows very good machining properties. Good machining properties are also shown by sample No. 11, containing 2.0% by weight of lead. Samples No. 12 and No. 16 document that the machining properties are very poor without lead and without further alloy elements.Samples No. 13 and No. 17, aside from Cu and Zn, contain only 0.27% by weight of Si.

[0070] The forces acting on the drill are within the acceptable range, but the swarf form is poor, which can be attributed to the lack of phosphide particles as chip breakers. In the case of sample No. 14, the Cu content and the Si content were increased compared to sample No. 13. The forces acting on the drill are not within the acceptable range and the swarf form is poor. Moreover, electrical conductivity is low.

[0071] In the case of sample No. 15, the Si content has been increased slightly compared to sample No. 14, and 0.1% by weight of P has been included in the alloy. The forces acting on the drill were thus reduced, and the swarf form was somewhat improved. However, elongation at break and electrical conductivity are low. Sample No. 15, by comparison with sample No. 1, shows a higher Si content with a similar P content and a similar proportion by volume of the β phase. The forces acting on the drill are similarly good, but the swarf form for sample No. 15 is less favorable and conductivity is poorer.

[0072] Sample No. 18 differs from sample No. 17 by 0.38% by weight of P. This essentially leads to a distinct improvement in swarf form. However, elongation at break is very low.

[0073] Sample No. 19, aside from Cu and Zn, contains only 0.11% by weight of P. Although this favors the swarf form, the forces acting on the drill are unsatisfactory. In the case of sample No. 22, by comparison with sample No. 19, the proportion of P was increased to 0.29% by weight, with consequent worsening of the normal force.

[0074] Sample No. 20 differs from sample No. 15 essentially by a somewhat smaller P content. This leads to an improvement in elongation at break. But electrical conductivity is not at the desired level owing to the high Si content.

[0075] Sample No. 21, as well as 0.27% by weight of Si and 0.06% by weight of P, also contains 0.22% by weight of Sn. By comparison with sample No. 2, which contains no tin, the inclusion of tin in the alloy leads to moderate worsening of the forces acting on the drill. Almost exclusively phosphide particles having a diameter of 0.5 to 1 μm are observed. Electrical conductivity is barely affected by 0.22% by weight of Sn.

[0076] Sample No. 23 contains 0.29% by weight of Si and 0.30% by weight of P. Similarly to sample No. 18, the swarf form is good, but elongation at break, conductivity and the forces acting in the course of drilling are unsatisfactory.

[0077] Samples No. 24 to No. 31 (table 3) are inventive samples in the annealed state. Samples No. 26 and No. 27 were annealed at 550° C., while the other samples in table 3 were annealed at 600° C. The proportion by volume of the β phase is at least 31% and at most 49%. α grain size is between 25 and 40 μm, with samples No. 26 and No. 27 having the smallest grain size. Hardness is at least 160 HV10, and tensile strength Rm at least 510 MPa. Elongation at break is at least 11.5%. Electrical conductivity for all samples is at least 12.7 MS / m, and for most of the samples at least 13.0 MS / m. Normalized torque is between 0.79 and 1.03. Normalized normal force is between 0.56 and 0.71. The arithmetic average of normalized torque and normalized normal force is always at least 0.75. The swarf form was always assessed as good (2) or average (1). In the case of sample No. 31, which corresponds to the unannealed sample No. 21 in terms of its composition, annealing achieved a significant improvement of the forces acting on drilling and the swarf form. In addition, it can be stated that the annealing moved the center of the distribution of the phosphide particles toward larger particles.

[0078] Samples No. 32 to No. 44 (table 4) are comparative samples in the annealed state. The lead-containing samples No. 32 and No. 33 show good machining properties in the annealed state. The solely Cu- and Zn-containing samples No. 34 (annealed at 600° C.) and No. 38 (annealed at 550° C.), in the annealed state too, are characterized by poor properties on drilling.

[0079] The silicon-containing but phosphorus-free samples No. 35 and No. 36, which were annealed at 600° C., give a torque on drilling that is more than twice as high as the torque ascertained on reference sample No. 10. The greater Si content in the case of sample No. 36 does improve the swarf form, but reduces electrical conductivity. The silicon-containing but phosphorus-free sample No. 39 that was annealed at 550° C. has more favorable forces on drilling than samples No. 35 and No. 36. This can be attributed to the much higher proportion of β phase. However, the swarf form is poor.

[0080] Sample No. 37, which contains 0.58% by weight of Si and 0.10% by weight of P and was annealed at 600° C., has more favorable properties on drilling than sample No. 15 with the same composition in the unannealed state, but electrical conductivity is unsatisfactory owing to the high proportion of Si.

[0081] In the case of samples No. 40 and No. 41, which were annealed at 550° C. and correspond in terms of composition to samples No. 18 and No. 19 respectively, by virtue of the annealing, an improvement in the forces acting on the drill was found and, especially in the case of sample No. 40, also a distinct improvement in ductility. However, sample No. 40 has low electrical conductivity because of the high proportions of Si and P. In the case of sample No. 41, the absence of Si cannot be compensated for by the annealing to such an extent that the forces on drilling are at an acceptable level.

[0082] Sample No. 42 with an Si content of 0.55% by weight and a P content of 0.075% by weight has too low an electrical conductivity owing to the high Si content.

[0083] In the case of samples No. 43 and No. 44, which correspond to the unannealed samples No. 22 and No. 23 in terms of their composition, annealing at 600° C. achieved a distinct improvement in ductility. Sample No. 43 has unsatisfactory machining properties even after annealing. In the case of sample No. 44, the P content of 0.3% by weight in combination with the Si content of 0.29% by weight leads to low electrical conductivity.

[0084] Samples No. 1 to No. 44 document that it is possible by a specific selection of the elements Si and P to produce alloys that have a favorable combination of properties. Si reduces the forces acting on the drill and hence improves the machining properties. However, an Si content of more than 0.32% by weight reduces electrical conductivity. A P content of 0.05% to 0.2% by weight promotes chip formation. A higher proportion of P in combination with Si leads to a deterioration in ductility and electrical conductivity. Alloys having a favorable combination of these properties can be produced even without annealing. By annealing between 550° C. and 600° C. in particular, for some element combinations, the machining properties can be subsequently improved by controlled adjustment of the β phase content and the phosphide particles.

[0085] Alloys having an above-described composition can also be used as casting alloys for castings.

Claims

1. A wrought copper-zinc alloy for production of a semifinished product in wire, tube or bar form, having the following composition in % by weight:Cu:58.0% to 63.0%,Si:0.04% to 0.32%,P:0.05% to 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, Ineach optionally up to 0.10%,Bi:not more than 0.009%,balance:Zn and unavoidable impurities,where the proportion of unavoidable impurities is less than 0.2% by weight,where the ratio of the proportions by weight of P and Al is at least 1.0,where the alloy has a microstructure composed of globular α phase, β phase and phosphide particles, and the proportion of the β phase in the sum total of α phase and β phase is at least 20% by volume and at most 70% by volume,where Si is present both in the α phase and in the β phase,where, in an area of 21 000 μm2, there are 7 to 200 phosphide particles having an equivalent diameter of 0.5 to 1 μm, 4 to 150 phosphide particles having an equivalent diameter of 1 to 2 μm, and not more than 30 phosphide particles having an equivalent diameter of more than 2 μm.

2. The wrought copper-zinc alloy as claimed in claim 1, wherein the Pb content is at least 0.02% by weight.

3. The wrought copper-zinc alloy as claimed in claim 1, wherein the P content is not more than 0.15% by weight.

4. The wrought copper-zinc alloy as claimed in claim 1, wherein the P / Fe ratio is at least 1.0.

5. The wrought copper-zinc alloy as claimed in claim 1, wherein the Fe content is less than 0.10% by weight and the Ni content is not more than 0.07% by weight.

6. The wrought copper-zinc alloy as claimed in claim 1, wherein the Si content is at least 0.23% by weight.

7. The wrought copper-zinc alloy as claimed in claim 1, wherein the Si content is not more than 0.15% by weight.

8. The wrought copper-zinc alloy as claimed in claim 7, wherein the P content is not more than 0.10% by weight.

9. The wrought copper-zinc alloy as claimed in claim 7, wherein the Cu content is not more than 59.5% by weight.

10. The wrought copper-zinc alloy as claimed in claim 1,wherein the proportions of the elements Cu, Zn, Si, P and Pb add up to at least 99.75% by weight.

11. The wrought copper-zinc alloy as claimed in claim 1,wherein the alloy has a hardness of at least 120 HV10.

12. The wrought copper-zinc alloy as claimed in claim 1,wherein the alloy has a tensile strength Rm of at least 500 MPa.

13. The wrought copper-zinc alloy as claimed in claim 1,wherein the alloy has an electrical conductivity of at least 12.5 MS / m.

14. A semifinished product in wire, pipe or bar form, made from a wrought copper-zinc alloy as claimed in claim 1.

15. A component produced by machining and optional further processing steps from a semifinished product as claimed in claim 14.

16. A process for producing a semifinished product in wire, pipe or bar form, wherein the process comprises the following steps:a) melting a copper alloy having a composition as claimed in claim 1,b) continuously casting a tubular or bolt-shaped cast format with a water-cooled mold,c) hot pressing the cast format at a temperature of 620 to 700° C. with subsequent cooling at a cooling rate of 30 to 60° C. per minute within a temperature range from 550 to 350° C.,d) optionally, heat treating within a temperature range from 525 to 625° C. for 1 to 5 hours with subsequent cooling at a cooling rate of 20 to 40° C. per minute within a temperature range from 500 to 350° C., ande) optionally, cold forming.

17. The wrought copper-zinc alloy as claimed in claim 11, wherein the alloy has a hardness of at least 150 HV10.

18. The wrought copper-zinc alloy as claimed in claim 12, wherein the alloy has a tensile strength Rm of at least 530 MPa.