US20260028701A1

US20260028701A1 - 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

Info

Publication number: US20260028701A1
Application number: US19/102,478
Authority: US
Inventors: Timo Allmendinger; Daniel Bogatz; Andrea Käufler; Susanne HOLLY
Original assignee: Wieland Werke AG
Current assignee: Wieland Werke AG
Priority date: 2022-08-11
Filing date: 2023-07-20
Publication date: 2026-01-29
Also published as: DE102022002928A1; CN119585454A; MX2024015898A; CA3261007A1; EP4569148A1; KR20250047661A; US20260028700A1; WO2024032925A1; MX2024015900A; DE102022002928B4; TW202407110A; JP2025527197A; EP4569146A1; CA3261021A1; CN119630824A; JP2025527196A; WO2024032923A1

Abstract

Wrought copper-zinc alloy for producing a semi-finished product with composition in wt. %: Cu: 58.0 to 66.0%, Si: 0.15 to 1,2%, P: 0.20 to 0.38%, Sn: up to 0.5%, Al: up to 0.05%, Fe: up to 0.3%, Ni: up to 0.3%, Pb: up to 0.25%, Bi: up to 0.1%, Te, Se, In: 0.1%, B: up to 0.01%, the rest Zn and impurities. The alloy has globular a-phase, B-phase and phosphide particles. The proportion of B-phase in the sum of α-phase and β-phase is 20 vol. % and max. 60 vol. %. In an area of 21000 μm²are 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.

Description

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.
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.
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.
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%) 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.
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.
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 content results in formation of Al phosphides, which are unwanted. 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.
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. In order, however, to achieve the effect on the microstructure of grain refining caused by lead, contents of not more than 0.19% by weight of P are too small.
It is an object of the invention to provide a wrought copper-zinc alloy for production of semifinished products in wire, pipe or bar form that has excellent machinability, good mechanical properties 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.
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.
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 66.0%,
- Si: 0.15% to 1.2%,
- P: 0.20% to 0.38%,
- Sn: optionally up to 0.5%, preferably up to 0.3%,
- Al: optionally up to 0.05%,
- Fe: optionally up to 0.3%,
- Ni: optionally up to 0.3%,
- Pb: optionally up to 0.25%, preferably up to 0.10%,
- Bi: optionally up to 0.1%,
- Te, Se, In each optionally up to 0.1%,
- B: optionally up to 0.01%,
- balance: Zn and unavoidable impurities,
  where the proportion of unavoidable impurities is less than 0.2% by weight. The alloy has a microstructure composed of globular α phase, β phase and phosphide particles. The phosphide particles contain or preferably are copper-and/or zinc-containing phosphides. 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 22% by volume, and not more than 60% by volume, preferably not more than 40% by volume. Silicon is present both in the α phase and in the β phase. In an area of 21 000 μm², there are 50 to 700 phosphide particles having an equivalent diameter of 0.5 to 1 μm, 10 to 300 phosphide particles having an equivalent diameter of 1 to 2 μm, and 3 to 45 phosphide particles having an equivalent diameter of 2 to 5 μm. The proportion of the β phase and the proportions of Si, P and Pb are chosen such 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 β phase in % by volume, [Si] the proportion of silicon in % by weight, [P] the proportion of phosphorus in % by weight, and [Pb] the proportion of lead in % by weight.

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, 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.
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, with increasing P content, distinct grain refining of the cast microstructure of the original base matrix composed of β phase occurs. In order to achieve sufficient grain refining of the cast microstructure and the subsequent formed microstructure, the addition of at least 0.20% by weight of P is necessary. This is similar to the effect of 2% to 3% by weight of Pb on the grain refining of α-β-brass. 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 0.20% by weight, phosphide particles are present both in the α phase and in the B phase in the final state. The alloy preferably contains at least 0.22% by weight of P. In the case of a P content of more than 0.38% by weight, coarse phosphides are formed in the cast state in that individual phosphites coagulate and form long network-like forms. These coarse phosphides wet the grain boundaries, melt during hot forming and lead to cracks in the material. In addition, ductility is reduced.
However, such unwanted effects can occur even in the case of P contents of below 0.38% by weight when the cooling rate is too low in the casting of the alloy, for example in the case of casting with a stationary mold. The necessary high cooling rates are achieved, for example, in the case of continuous casting with a water-cooled mold. This achieves the effect that, in the case of a P content of 0.20% to 0.38% by weight, the phosphide particles are already in globular and finely distributed form in the cast state. Such a cast product then has good hot compressibility at a temperature of 620 to 700° C., preferably of 630 to 680° C. No cracks are formed in the material.
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 (° 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 a 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 50 to 700 phosphide particles having an equivalent diameter of 0.5 to 1 μm, 10 to 300 phosphide particles having an equivalent diameter of 1 to 2 μm, and 3 to 45 phosphide particles having an equivalent diameter of 2 to 5 μm. The 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 μm 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 80%. In addition, it is advantageous when at least 40%, preferably at least 60%, 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 or more than 5 μm will be present in the alloy. The number of phosphide particles having an equivalent diameter of more than 5 μm is at most 30%, preferably at least 15%, of the number of phosphide particles having an equivalent diameter of 2 to 5 μm.
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 alloying and incorporation of silicon into the α phase, and by means of fine distribution of phosphides in the α phase. Therefore, the Si content in the alloy must be at least 0.15% by weight. The above-described phosphide particles are particles that act as separation sites on machining and promote chip breaking. A P content of less than 0.20% by weight leads to unfavorable chips and relatively coarse grains. In addition, a small optional fraction of Pb has an advantageous effect on machinability.
The machinability of the alloy is consequently determined by the combined selection of the parameters of β phase, Si and P, and an optionally present small proportion of Pb. In the proposed wrought copper-zinc alloy, 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 22% by volume. A high proportion of the β phase has an adverse effect on cold formability. Therefore, the proportion of the β phase is not more than 60% by volume, preferably not more than 40% by volume. The Si content of the alloy is 0.15% to 1.2% by weight, the P content 0.20% to 0.38% by weight. In addition, there may also be up to 0.25% by weight of Pb, preferably up to not more than 0.10% by weight of Pb. At the same time, the proportion of the β phase and the proportions of Si, P and Pb are chosen such that the alloy meets the condition
$107. 3 78 - 2, 25255 \cdot [beta] - 64.1438 \cdot [Si] - 115.18 \cdot [P] - 30.7071 \cdot [Pb] + 0.017965 \cdot [beta] \cdot [beta] + 24.6217 \cdot [Si] \cdot [Si] + 66.7257 \cdot [P] \cdot [P] + 0.542512 \cdot [beta] \cdot [Si] + 1.36208 \cdot [beta] \cdot [P] + 43.4012 \cdot [Si] \cdot [P] < 37$
where [beta] denotes the proportion of the β phase in % by volume, [Si] the proportion of silicon in % by weight, [P] the proportion of phosphorus in % by weight, and [Pb] the proportion of lead in % by weight. This relation quantitatively describes the effect of the parameters of β B phase, Si, P and Pb on the machining properties of the alloy, and the interaction of these parameters with one another. For example, it is possible to compensate for a small proportion of β phase with a higher proportion of silicon and/or phosphorus within the scope of specification of the composition of the alloy, and vice versa.
The Cu content of the alloy is 58.0% to 66.0% 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 66.0%, the zinc content in the alloy is too small to achieve good machinability.
In addition, the composition of the alloy may preferably be chosen such that the Si/P ratio is at least 0.6, more preferably at least 0.9. In a further preferred embodiment, the composition of the alloy may be chosen such that the sum total of Si and P is at least 0.58% by weight, more preferably at least 0.64% by weight. Both the aforementioned measures contribute both independently and in combination to fulfilment of the above-described relations and hence to achievement of favorable machining properties.
The optional Sn and Al elements promote formation of the B phase. In the case of a Sn content of more than 0.5% by weight, further tin-containing phases may form, which can have an adverse effect on the properties of the alloy. The proportion of tin should preferably be not more than 0.3% by weight, more preferably not more than 0.2% by weight. In addition, aluminum forms aluminum phosphides with phosphorus. However, these are unwanted, and therefore the Al content should not exceed 0.05% by weight.
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 0.3% by weight, preferably not more than 0.1% by weight.
Nickel promotes the formation of the α phase. Moreover, nickel forms phosphides, which do not have an advantageous effect on machinability. Therefore, the proportion of nickel must be not more than 0.3% by weight, preferably not more than 0.1% by weight.
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. In amounts of not more than 0.1% by weight, Bi has no adverse effect on the alloy. Therefore, up to 0.1% by weight of Bi in the alloy is tolerated. Preferably, the proportion of Bi is less than 0.015% by weight.
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.
An optional proportion of up to 0.01% by weight of boron contributes to grain refining.
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 each be not more than 0.1% by weight, more preferably each not more than 0.05% by weight, because these elements can form phosphides that can compete with the copper-and/or zinc-containing phosphides.
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.
Advantageously, the ratio of the proportions by weight of P and the sum total of Fe and Ni may be more than 2.0, i.e. P/(Fe+Ni)>2.0. This achieves the effect that predominantly the copper- and/or zinc-containing phosphides that are favorable for machining properties are formed. The formation of iron phosphides or nickel phosphides is suppressed.
It may be particularly advantageous that the proportions of Fe and Ni add up to not more than 0.1% by weight. This restriction also inhibits the formation of iron phosphides and nickel phosphides compared to the formation of the copper- and/or zinc-containing phosphides.
In a particularly advantageous embodiment of the invention, the P content may be at least 0.26% by weight and at most 0.33% by weight. If the P content is at least 0.26% by weight, a sufficiently large amount of phosphide particles is formed, in order to achieve a particularly fine grain, a globular α phase and very good machinability. If the P content in the alloy is not more than 0.33% by weight, it is highly likely that cracking will be avoided on hot forming.
In a further embodiment of the invention, the Si content may be at most 0.35% by weight. A wrought copper-zinc alloy having this relatively low Si content is notable for high electrical conductivity. The electrical conductivity is then at least 12 MS/m.
In a further embodiment of the invention, the Si content may be at least 0.25% by weight, preferably at least 0.30% by weight. This achieves very good machinability with simultaneously good surface quality.
Especially in the case of the above-described embodiments, the Cu content may be at least 60.0% by weight and at most 61.5% by weight. An alloy having particularly advantageous properties is obtained with the following composition: Cu 60.0% to 61.5% by weight, Si 0.25% to 0.35% by weight and P 0.26% to 0.33% by weight, balance: Zn and unavoidable impurities.
In an alternative configuration of the invention, the Si content may be at least 0.50% by weight and at most 1.0% by weight. A wrought copper-zinc alloy having a Si content within this range is notable for excellent machine properties coupled with good ductility.
Advantageously, the wrought copper-tin alloy may have a hardness of at least 170 HV10, preferably at least 180 HV10.
Advantageously, the wrought copper-tin alloy may have a tensile strength R_mof at least 520 MPa, preferably at least 560 MPa.
Advantageously, the wrought copper-tin alloy may have an α grain size of at most 21 μm, preferably at most 17 μm.
Advantageously, the wrought copper-zinc alloy may have an electrical conductivity of at least 12 MS/m.
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.
A further aspect of the invention relates to a method of producing a semifinished product in wire, pipe or bar form. The process comprises the following steps:

- a) melting a copper alloy having a composition as described above,
- 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 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.,
- e) optionally cold forming.

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.
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.
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.
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 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 B phase, and the particle distribution of the phosphides. In particular, it is thus possible to improve ductility. The heat treatment may be followed by the steps of pickling and cold forming, as in the first production process.
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.
The invention is elucidated in detail by working examples.
Samples No. 1 to No. 45 were melted in an induction kiln 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 at 650° C. for 1 hour and then hot-formed. In the cooling that follows after the hot forming, the cooling rate within the temperature range between 550 and 350° C. was about 40° C. per minute.
Samples No. 1 to No. 26, after hot forming, were machined and then cold-formed with a degree of forming of 20%. Samples No. 27 to No. 45, after hot forming, were annealed for 3 hours. The annealing temperature was about 600° C. for samples No. 28 and No. 35 to No. 41, while it was about 550° C. for samples No. 27, No. 29 to 34 and No. 42 to No. 45. The annealing was followed by cooling within the temperature range between 500 and 350° C. at a cooling rate of about 25° C. per minute. Thereafter, samples No. 27 to No. 45 were machined and subsequently cold-formed with a degree of forming of 20%.
In the final state, tensile strength R_mand elongation at break were each determined from the tensile test, as were hardness (Vickers hardness HV10) and electrical conductivity. 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, 2 to 5 μm and—if present—greater than 5 μm.
Machinability was determined by means of a plane test. This was done using an insert with a contour that promotes chip breaking. The machining depth was 125 μm and the plane speed 35 m/min. During the planing operation, the bending moment that acts on the tool was measured, and this was used to determine the average bending moment. The resultant chips were visually assessed and categorised by chip form. The chip form was assigned a chip form number according to the following list:


Chip form number	Chip form

0	torn chips, helical chips
0.5	coiled chips with 1 to 2 turns
0.75	coiled chips with an arc that forms an
	angle of 270° to 360°
1	coiled chips with an arc that forms an
	angle of 180° to 270°
1.25	coiled chips with an arc that forms an
	angle of less than 180°

Chip form number 1 corresponds to the lead-containing reference alloy CuZn39Pb3 (sample No. 16).
The results of the studies 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 inventive samples. The unannealed samples No. 16 to No. 26 (table 2) and the annealed samples No. 35 to 45 (table 4) are comparative samples and are identified by (*).
Machinability of the samples was assessed using the bending moment ascertained in the planing and the shape of the chips. An average bending moment of not more than 36 Nm and chips that correspond to chip form number 1 or 1.25 were considered to be very favorable.
In addition, an attempt was made to parametrize the measured average bending moment as a function of the proportion by volume of the β phase and the proportions by weight of Si, P and Pb. The functional relationship thus ascertained can be presented as follows:
$f = 107.378 - 2, 25255 \cdot [beta] - 64.1438 \cdot [Si] - 115.18 \cdot [P] - 30.7071 \cdot [Pb] + 0.017965 \cdot [beta] \cdot [beta] + 24.6217 \cdot [Si] \cdot [Si] + 66.7257 \cdot [P] \cdot [P] + 0.542512 \cdot [beta] \cdot [Si] + 1.36208 \cdot [beta] \cdot [P] + 43.4012 \cdot [Si] \cdot [P]$
where f approximately quantifies the measured bending moment in Nm and where [beta] denotes the proportion of the β phase in % by volume, [Si] the proportion of silicon in % by weight, [P] the proportion of phosphorus in % by weight, and [Pb] the proportion of lead in % by weight. The value of f calculated by this formula is documented in the last column of tables 1 to 4. Comparison of this value f with the measured bending moment shows very good agreement between the two parameters. Inventive samples No. 1 to No. 15 and No. 27 to No. 34, all of which have a measured bending moment of less than 36 Nm, are characterized in that the value of f is less than 37.


						Other	α	β	α	Phosphides	Phosphides	Phosphides
	Cu	Zn	Si	P	Pb	elements	phase	phase	grain	0.5-1 μm	1-2 μm	2-5 μm
Sample	% by	% by	% by	% by	% by	% by	% by	% by	size	per	per	per
No.	wt.	wt.	wt.	wt.	wt.	wt.	vol.	vol.	μm	21 000 μm²	21 000 μm²	21 000 μm²

1	59.979	39.365	0.269	0.379			63	35	12	128	103	45
2	60.876	38.534	0.286	0.295			76	24	15	385	74	3
3	63.001	36.005	0.68	0.307			72	28	13	181	56	28
4	62.512	36.593	0.591	0.299			78	22	11	92	37	20
5	64.440	34.22	1.013	0.320			80	20	14	153	56	25
6	63.219	35.702	0.676	0.302	0.091		79	21	13	105	33	13
7	62.435	36.553	0.591	0.310	0.102		76	24	15	207	121	31
8	64.496	34.094	0.992	0.298	0.115		80	20	14	319	43	13
9	63.049	35.832	0.704	0.309		Fe: 0.1	78	22	14	75	21	9
						B: 0.0025
10	61.508	37.537	0.684	0.266			64	36	9	614	132	12
11	61.078	38.044	0.586	0.288			63	37	14	270	285	15
12	63.055	35.642	0.997	0.302			72	28	12	345	146	16
13	61.489	37.414	0.666	0.330	0.091		74	26	10	424	192	21
14	61.100	37.896	0.581	0.322	0.094		68	32	10	716	99	14
15	63.096	35.484	1.004	0.317	0.095		63	37	11	76	77	20

TABLE 1

inventive samples, unannealed

						Other
	Cu	Zn	Si	P	Pb	elements			Elongation	El.		Chip form
Sample	% by	% by	% by	% by	% by	% by	Hardness	R_m	at break	conductivity	Torque	number	f
No.	wt.	wt.	wt.	wt.	wt.	wt.	HV10	MPa	%	MS/m	Nm	—	—

1	59.977	39.363	0.269	0.383			191	565	6.8	12.43	33.6	1.25	28.6
2	60.876	38.534	0.286	0.295			185	564	10.2	12.06	35.7	1	36.2
3	63.001	36.005	0.68	0.307			189	593	10.9	9.54	31.0	1.25	28.2
4	62.512	36.593	0.591	0.299			190	581	10.9	10.02	31.5	1.25	32.4
5	64.440	34.22	1.013	0.320			196	597	9.9	8.37	32.9	1.25	33.6
6	63.219	35.702	0.676	0.302	0.091		195	593	12.6	9.43	29.0	1	29.6
7	62.435	36.553	0.591	0.310	0.102		180	580	10.3	10.03	28.2	1	27.7
8	64.496	34.094	0.992	0.298	0.115		197	601	12.1	8.23	27.4	1	29.9
9	63.049	35.832	0.704	0.309		Fe: 0.1	190	598	11.9	9.46	32.3	1.25	31.4
						B: 0.0025
10	61.508	37.537	0.684	0.266			194	602	7.2	10.07	25.6	1.25	25.6
11	61.078	38.044	0.586	0.288			183	584	7.6	10.55	26.1	1	25.5
12	63.055	35.642	0.997	0.302			203	619	9.4	8.6	25.4	1	29.9
13	61.489	37.414	0.666	0.330	0.091		189	598	4.7	9.98	25.2	1	26.2
14	61.100	37.896	0.581	0.322	0.094		192	574	4.8	10.43	24.9	1	23.9
15	63.096	35.484	1.004	0.317	0.095		200	618	7.7	8.57	24.5	1.25	26.3

						Other	α	β	α	Phosphides	Phosphides	Phosphides
	Cu	Zn	Si	P	Pb	elements	phase	phase	grain	0.5-1 um	1-2 μm	2-5 μm
Sample	% by	% by	% by	% by	% by	% by	% by	% by	size	per	per	per
No.	wt.	wt.	wt.	wt.	wt.	wt.	vol.	vol.	μm	21 000 μm²	21 000 μm²	21 000 μm²

16 (*)	57.644	39.004			3.348		70	30	17
17 (*)	59.519	40.165					59	41	21
18 (*)	60.854	38.868	0.269				65	35	23
19 (*)	60.774	38.888	0.281	0.051			68	32	19	33	8
20 (*)	60.922	38.69	0.277	0.102			67	33	20	195	79
21 (*)	62.404	37.056	0.53				73	27	25
22 (*)	62.296	37.015	0.579	0.102			71	29	22	94	103	2
23 (*)	59.761	39.993		0.241			75	25	15	18	15
24 (*)	58.791	40.909		0.294			73	27	11	33	27	6
25 (*)	62.910	35.755	0.68	0.648			79	21	14	340	118	79
26 (*)	61.886	36.765	0.697	0.644			79	21	17	266	196	53

TABLE 2

Comparative samples, unannealed

						Other
	Cu	Zn	Si	P	Pb	elements			Elongation	El.		Chip form
Sample	% by	% by	% by	% by	% by	% by	Hardness	R_m	at break	conductivity	Torque	number	f
No.	wt.	wt.	wt.	wt.	wt.	wt.	HV10	MPa	%	MS/m	Nm	—	—

16 (*)	57.644	39.004			3.348						22.0	1
17 (*)	59.519	40.165					156	492	22.3	16.78	64.9	0	45.2
18 (*)	60.854	38.868	0.269				173	525	20.4	13.58	35.2	0.5	40.2
19 (*)	60.774	38.888	0.281	0.051			167	540	17	13.12	33.6	0.75	39.6
20 (*)	60.922	38.69	0.277	0.102			167	531	14.6	12.73	35.4	1	36.4
21 (*)	62.404	37.056	0.53				174	538	16.2	11.4	36.5	0.5	40.3
22 (*)	62.296	37.015	0.579	0.102			174	560	10.6	10.7	33.2	1	32.9
23 (*)	59.761	39.993		0.241			163	515	17.9	15.08	49.9	1.25	46.6
24 (*)	58.791	40.909		0.294			174	527	12.1	15.74	39.0	1.25	42.4
25 (*)	62.910	35.755	0.68	0.648			200	593	7.2	9.22	31.5	1.25	34.6
26 (*)	61.886	36.765	0.697	0.644			192	606	4.6	9.42	26.2	1.25	34.6

						Other	α	β	α	Phosphides	Phosphides	Phosphides
	Cu	Zn	Si	P	Pb	elements	phase	phase	grain	0.5-1 μm	1-2 μm	2-5 μm
Sample	% by	% by	% by	% by	% by	% by	% by	% by	size	per	per	per
No.	wt.	wt.	wt.	wt.	wt.	wt.	vol.	vol.	μm	21 000 μm²	21 000 μm²	21 000 μm²

27	59.977	39.363	0.269	0.383			62	38	15	105	106	44
28	60.876	38.534	0.286	0.295			61	39	21	73	47	45
29	61.508	37.537	0.684	0.266			73	27	11	318	62	15
30	61.078	38.044	0.586	0.288			77	23	12	207	112	21
31	63.055	35.642	0.997	0.302			74	26	16	211	106	28
32	61.489	37.414	0.666	0.33	0.091		69	31	11	238	103	20
33	61.1	37.896	0.581	0.322	0.094		74	26	13	162	96	29
34	63.096	35.484	1.004	0.317	0.095		78	22	14	93	38	17

TABLE 3

inventive samples, annealed

						Other
	Cu	Zn	Si	P	Pb	elements			Elongation	El.		Chip form
Sample	% by	% by	% by	% by	% by	% by	Hardness	R_m	at break	conductivity	Torque	number	f
No.	wt.	wt.	wt.	wt.	wt.	wt.	HV10	MPa	%	MS/m	Nm	—	—

27	59.977	39.363	0.269	0.383			173	555	15	12.45	32.3	1.25	27.8
28	60.876	38.534	0.286	0.295			172	526	13.4	12.06	34.0	1	27.7
29	61.508	37.537	0.684	0.266			189	597	10.3	10.81	30.3	1.25	29.1
30	61.078	38.044	0.586	0.288			183	573	10.9	11.19	30.7	1	32.0
31	63.055	35.642	0.997	0.302			194	600	10.5	9.15	28.8	1	30.6
32	61.489	37.414	0.666	0.33	0.091		189	578	5.2	10.64	27.9	1	24.2
33	61.1	37.896	0.581	0.322	0.094		189	574	7.7	11.15	28.0	1	26.7
34	63.096	35.484	1.004	0.317	0.095		194	604	8.1	9.07	27.3	1.25	29.5

						Other	α	β	α	Phosphides	Phosphides	Phosphides
	Cu	Zn	Si	P	Pb	elements	phase	phase	grain	0.5-1 μm	1-2 μm	2-5 μm
Sample	% by	% by	% by	% by	% by	% by	% by	% by	size	per	per	per
No.	wt.	wt.	wt.	wt.	wt.	wt.	vol.	vol.	μm	21 000 μm²	21 000 μm²	21 000 μm²

35 (*)	60.854	38.868	0.269				70	30	31
36 (*)	60.774	38.888	0.281	0.051			64	36	31	22	15
37 (*)	60.922	38.69	0.277	0.102			69	31	39	23	38	18
38 (*)	62.404	37.056	0.53				69	31	38
39 (*)	62.296	37.015	0.579	0.102			65	35	33	20	27	24
40 (*)	59.761	39.993		0.241			70	30	22	23	32	44
41 (*)	58.791	40.909		0.294			63	37	23	20	25	58
42 (*)	63.001	36.005	0.68	0.307			82	18	15	96	110	66
43 (*)	62.512	36.593	0.591	0.299			81	19	17	167	96	32
44 (*)	64.44	34.22	1.013	0.32			82	18	20	117	99	53
45 (*)	62.91	35.755	0.68	0.648			91	9	17	201	190	66

TABLE 4

Comparative samples, annealed

Other

Cu

Zn

Si

P

Pb

elements

Elongation

El.

Chip form

Sample

% by

Hardness

R_m

at break

conductivity

Torque

number

f

No.

wt.

HV10

MPa

%

MS/m

Nm

—

35 (*)	60.854	38.868	0.269		150	489	21.5	13.7	38.6	0	44.9
36 (*)	60.774	38.888	0.281	0.051	161	511	17.7	13.13	35.9	0.75	36.4
37 (*)	60.922	38.69	0.277	0.102	163	515	15.6	12.67	35.1	1	38.1
38 (*)	62.404	37.056	0.53		164	510	20.6	11.51	42.9	0.5	36.6
39 (*)	62.296	37.015	0.579	0.102	156	531	12.7	10.71	32.7	1	29.0
40 (*)	59.761	39.993		0.241	150	475	19.1	14.8	39.7	1	41.9
41 (*)	58.791	40.909		0.294	169	501	17.6	15.6	39.3	1	35.3
42 (*)	63.001	36.005	0.68	0.307	168	540	15.2	10.17	39.3	0.5	34.6
43 (*)	62.512	36.593	0.591	0.299	170	536	15	10.75	39.8	0.5	34.8
44 (*)	64.44	34.22	1.013	0.32	183	557	10.7	8.75	39.4	0.5	34.7
45 (*)	62.91	35.755	0.68	0.648	181	531	8.9	10.21	44.5	1	40.1

Samples No. 1 to No. 15 (table 1) are inventive samples in the unannealed state. The proportion by volume of the β phase is at least 20% and at most 38%. α grain size is not more than 15 μm. Hardness is at least 180 HV10, and tensile strength R_mat least 560 MPa. Elongation at break is at least 4.7%. The measured bending moment is not more than 35.7 Nm. The form of the chips for all samples corresponds to chip form number 1 or 1.25.
Samples No. 16 to No. 26 (table 2) are comparative samples in the unannealed state. The reference sample No. 16 contains 3.3% by weight of lead and shows very good machining properties. Sample No. 17 shows that machining properties are very poor without lead and without further alloy elements.
Sample No. 18, aside from Cu and Zn, contains only 0.27% by weight of Si. The bending moment is good, but the chip form is poor, which can be attributed to the absence of phosphide particles as chip breakers. The same finding is made for sample No. 21, containing 0.53% by weight of Si. Samples No. 19, 20 and 22 have 0.05% to 0.1% by weight of phosphorus, which has a favourable effect on chip form and, at least in the case of sample No. 19 and in the case of sample No. 22, on bending moment as well. In the case of samples No. 19 and 20, however, hardness and tensile strength R_mare well below the values for samples No. 1 to No. 15. Sample No. 22 having an Si content of 0.58% by weight shows only slightly improved hardness and tensile strength. In addition, samples No. 18 to No. 22 show a much greater α grain size at 19 to 25 μm than samples No. 1 to No. 15. The coarser α grain leads to drawbacks in terms of straightness and trueness to scale.
The silicon-free samples No. 23 and No. 24, with a P content of 0.24% and 0.29% by weight, give an excellent chip form, but the bending moment is at a high level. Samples No. 25 and No. 26, each with a P content of 0.65% by weight, show excellent machining properties. Because of the high P content, however, they have a tendency to crack in the course of hot forming. Furthermore, this results in low elongation at break at room temperature. The high P content is reflected in a large number of phosphide particles having an equivalent diameter of 2 to 5 μm. It is thus a sign of poor hot formability and additionally of brittle material characteristics at room temperature if the alloy, in an area of 21 000 μm², has more than 45 phosphide particles having an equivalent diameter of 2 to 5 μm.
The samples document that silicon leads to a reduction in the bending moment and that phosphorus promotes chip breaking. The combination of the two elements leads overall to good machining properties and to a small α grain size.
Samples No. 27 to No. 34 (table 3) are inventive samples in the annealed state. The proportion by volume of the B phase is at least 22% and at most 39%. In the case of sample No. 28, α grain size is 21 μm. This can be attributed to the annealing temperature of 600° C. In the case of the other samples that were annealed at 550° C., α grain size is not more than 16 μm. Compared to samples No. 1 to No. 15, samples No. 27 to No. 34 have a somewhat lower hardness of at least 170 HV10 and a somewhat lower tensile strength R_mof at least 520 HV10. By contrast, annealing improved elongation at break. Consequently, a more ductile material state can be established. Bending moment and chip form are very good to excellent.
Samples No. 35 to No. 45 (table 4) are comparative samples in the annealed state. The silicon-containing but phosphorus-free samples No. 35 and No. 38 are characterized by an unfavorably high bending moment and poor chip form. Samples No. 36, 37 and 39 having a small P content have a distinct improvement in machine properties compared to samples No. 19, 20 and 22, but hardness and tensile strength are unsatisfactory. In addition, samples No. 25 to No. 39 show a much greater α grain size at 31 to 39 μm than samples No. 1 to No. 15. The coarser α grain leads to drawbacks in terms of straightness and trueness to scale.
The phosphorus-containing but silicon-free samples No. 40 and 41 give a very good chip form, but bending moment is an unfavorably high-level. The annealed samples No. 42, 43 and 44, which correspond to the unannealed samples No. 3, 4 and 5 in terms of composition, show a higher bending moment and poorer chip form than the unannealed variants. The annealing reduced the proportion by volume of the β phase to values below 20% and shifted the distribution of the phosphide particles toward coarser particles. These two effects together lead to a deterioration in machining properties. Sample No. 45 having a P content of 0.65% by weight is characterized by a high bending moment. This is caused by a very small proportion of β phase of only 9% by volume. Moreover, the sample has a very high density of phosphides having an equivalent diameter of 2 to 5 μm.
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 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%,

balance: Zn and unavoidable impurities,

where the proportion of unavoidable impurities is less than 0.20% by weight,

where the alloy has a microstructure composed of globular a 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 60% 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 50 to 700 phosphide particles having an equivalent diameter of 0.5 to 1 μm, 10 to 300 phosphide particles having an equivalent diameter of 1 to 2 μm, and 3 to 45 phosphide particles having an equivalent diameter of 2 to 5 μm, and where the proportion of the β phase and the proportions of Si, P and Pb are chosen such 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 β phase in % by volume, [Si] the proportion of silicon in % by weight, [P] the proportion of phosphorus in % by weight, and [Pb] the proportion of lead in % by weight.

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 ratio of the proportions by weight of P and the sum total of Fe and Ni is more than 2.0.

4. The wrought copper-zinc alloy as claimed in claim 1, wherein the proportions of Fe and Ni add up to not more than 0.1% by weight.

5. The wrought copper-zinc alloy as claimed in claim 1, wherein the P content is at least 0.26% by weight and at most 0.33% by weight.

6. The wrought copper-zinc alloy as claimed in claim 1, wherein Si content is not more than 0.35% by weight.

7. The wrought copper-zinc alloy as claimed in claim 1, wherein the Si content is at least 0.25% by weight.

8. The wrought copper-zinc alloy as claimed in claim 6, wherein the Cu content is at least 60.0% by weight and not more than 61.5% by weight.

9. The wrought copper-zinc alloy as claimed in claim 1, wherein the Si content is at least 0.50% by weight and at most 1.0% by weight.

10. The wrought copper-zinc alloy as claimed in claim 1, wherein the alloy has a hardness of at least 170 HV10.

11. The wrought copper-zinc alloy as claimed in claim 1, wherein the alloy has a tensile strength R_mof at least 520 MPa.

12. The wrought copper-zinc alloy as claimed in claim 1, wherein the alloy has an α grain size of not more than 21 μm.

13. The wrought copper-zinc alloy as claimed in claim 6, wherein the alloy has an electrical conductivity of at least 12 MS/m.

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

e) optionally, cold forming.