WO2019137832A1

WO2019137832A1 - Copper-zinc alloy

Info

Publication number: WO2019137832A1
Application number: PCT/EP2019/050005
Authority: WO
Inventors: Thomas Plett; Hermann Gummert; Björn Reetz
Original assignee: Otto Fuchs - Kommanditgesellschaft -
Priority date: 2018-01-09
Filing date: 2019-01-02
Publication date: 2019-07-18
Also published as: EP3529389A1; RU2020115663A; RU2020115663A3; KR20200103709A; CN111788321A; ES2780202T3; BR112020012537A2; EP3529389B1; DE202018100075U1; US20200370147A1; JP2021509934A; JP7374904B2

Abstract

The invention relates to a copper-zinc alloy for producing electrically conductive components, for example contacts, consisting of: – Cu: 62.5 - 67% by weight, – Sn: 0.25 - 1.0% by weight, – Si: 0.015 - 0.15% by weight, – at least two silicide-forming elements from the group Mn, Fe, Ni and Al with, in each case, at most 0.15% by weight, wherein the sum of these elements does not exceed 0.6% by weight, – Pb: at most 0.1% by weight, – the rest being formed by Zn and also unavoidable impurities.

Description

Copper-zinc alloy

The invention provides a copper-zinc alloy and a copper-zinc alloy product produced from such an alloy. The invention relates to a special brass alloy. Special brass alloys are used to produce a wide variety of products. A typical application for the use of special brass alloy products are bearing parts, engine and gear parts, such as synchro rings and the like, as well as fittings, especially for drinking water applications. Brass alloy products are also used for electrical and refrigeration applications, for example, for the manufacture of connector shoes, contact terminals or the like. In refrigeration applications, the good thermal conductivity of brass alloy products is used. These brass alloys have a high copper content due to the well-known good thermal conductivity of copper and are only correspondingly low alloyed. Special brass alloys have a significantly lower thermal conductivity.

If a brass alloy should have particularly good electrically conductive properties, the Cu content should be selected to be correspondingly high. However, the electrical conductivity of such a product decreases with increasing zinc content. For this reason, special alloys having good electrical conductivity in the foreground are alloys which have a Zn content of typically not more than 5 to 10% by weight. In addition to the elements copper and zinc, one or more of the following elements are involved in the construction of special brass alloys: Al, Sn, Si, Ni, Fe and / or Pb. Each of these elements has a different influence on the properties of the special brass alloy produced from the alloy. It should be noted that one and the same alloying element, depending on its participation, is responsible for different properties with regard to the processability of the alloy and the characteristics of a special alloy produced therefrom. brass alloy product can be. The same applies to the processability of the alloy. Due to the large number of different applications of special brass alloy products, a large number of special brass alloys differing in their alloy composition are also known. These differ, for example, in terms of their strength values, their machinability, their surface workability, their thermal conductivity, their modulus of elasticity, their heat distortion temperature and the like. In most cases, the previously known special brass alloys have been developed with regard to their composition for very specific purposes.

A special brass alloy, from which special brass alloy products are to be produced for electrical applications, must not only have sufficient electrical conductivity, but, in addition, in order to be able to produce the desired products, they must have good workability and machinability, as well as sufficient strength values. With regard to processability of the alloy, it should be producible with standard processing steps so that the costs of special brass alloy products produced therefrom are not made more expensive by complicated and possibly unusual process control steps.

From DE 20 2017 103 901 U1 a special brass alloy for electrical and / or cooling technology applications has become known. This contains 58.5-62 wt.% Cu, 0.03-0.18 wt.% Pb, 0.3-1.0 wt.% Fe, 0.3-1.2 wt. Mn, 0.25-0.9% by weight Ni, 0.6-1.3% by weight Al, 0.15-0.5% by weight Cr, max. 0.1% by weight of Sn, max. 0.05 wt .-% Si with a balance of Zn plus unavoidable impurities. Although this previously known special brass alloy has sufficient thermal conductivity for the cooling technology applications provided for this purpose and sufficient electrical conductivity for many applications, it would be desirable if not only the electrical conductivity but also the extrudability and the machinability were improved could be to better produce the manufacturability of electrical components such as contacts, sockets or the like. In addition, the alloy product produced from such an alloy should have good cold workability. properties, such as good cold drawability properties, in order in this way to be able to equip the formed semi-finished product with higher strength values for the end product. A lead-free brass alloy with good machinability is known from US 2014/0234411 A1. This alloy comprises 70-83% by weight of Cu, 1-5% by weight of Si and the other matrix-active elements: 0.01-2% by weight Sn, 0.01-0.3% by weight Fe and or Co, 0.01-0.3% by weight of Ni, 0.01-0.3% by weight of Mn, balance Zn together with unavoidable impurities. In addition, the alloy may contain up to 0.1% by weight of P and the elements Ag, Al, As, Sb, Mg, Ti and Cr each contain at most 0.5% by weight.

A copper-zinc alloy as a material for electronic components is known from DE 41 20 499 C1. This prior art alloy comprises 74-82.9 wt% Cu, 1-2 wt% Si, 0.1-0.4 wt% Fe, 0.02-0.1 wt% P, 0.1-1.0% by weight of Al, balance Zn together with customary impurities.

Brass alloys, which should have good electrical conductivity, are produced with a high Cn content. The alloy according to DE 41 20 499 C1 is one such. Although this prior art brass alloy has a rather high mechanical strength and a high spring bending limit and thus a corresponding modulus of elasticity, resilient connector parts can be produced from this alloy. However, despite the high Cu content, the electrical conductivity is only between 6.0 - 7.0 MS / m.

Starting from the discussed prior art, the invention is therefore the task of proposing a special brass alloy, which is particularly suitable for the manufacture of electrically conductive components, such as contacts as parts of connectors, which is characterized by improved mechanical properties and an improved electrical conductivity. In addition, this should have a good machinability and good Kaltumformbarkeitseigenschaften. This object is achieved according to the invention by a copper-zinc alloy for the production of electrically conductive components, such as contacts, consisting of:

Cu: 62.5-67% by weight,

Sn: 0.25-1.0% by weight,

Si: 0.015 - 0.15 wt.%,

- At least two silicide-forming elements from the group Mn, Fe, Ni and Al, each with max. 0.15% by weight, the sum of these elements not exceeding 0.6% by weight,

- Pb: max. 0.1% by weight

- Remaining Zn plus unavoidable impurities.

This copper-zinc alloy is characterized by its special alloy composition. On the one hand, the Zn content of 31-37% by weight and the marked participation of the element Sn on the

Composition of the alloy with 0.5 - 1, 0 wt .-%. Thus, the main alloying elements of this alloy are the elements Cu, Zn and Sn. Due to the relatively high Zn content and the correspondingly lower Cu content, it was surprisingly found that, nevertheless, the electrical conductivity meets the requirements imposed on a product made from this alloy and even the conductivity of prior art special brass alloys, which have been used for electrically conductive applications exceeds. Si is involved in the alloy at 0.015-0.15 wt%. The Si in the alloy serves to form silicides as fine precipitates in the microstructure. The size of the silicides is typically less than 1 pm on average. If the silicides exceed a certain size, this has a detrimental effect on the polishability, coatability and / or solderability of the surface of the alloy product made of the alloy. A higher Si content can not improve the particular properties of the alloy according to the invention. Rather, this could adversely affect the desired good electrical conductivity. From the group of elements Mn, Fe, Ni and Al as silicide-forming elements, at least two elements are involved in the construction of the alloy. Together with Si, these elements form finely divided mixed silicides which have a positive effect on the abrasion resistance of the product made from the alloy. These silicides are finely distributed particles in the matrix. The proportion of these elements in the structure of the alloy is limited, to max. 0.15% by weight per element, the sum of these elements not exceeding 0.6% by weight. The elements Fe, Ni and Al are preferably involved in the construction of the alloy. Mn can be part of the alloy as a silicide-forming agent. The elements Fe, Ni and Al are preferably provided as silicide formers, which typically form mixed silicides. In one embodiment, it is provided that the Ni and Al components are each approximately the same size, while the Fe component is only 40-60% of the Ni or Al component. In a preferred embodiment, the Fe content is about 50% of the Ni or Al content. This particular composition of the silicide formers Fe, Ni and Al, together with the Si content between 0.015-0.15% by weight, does not have a significant adverse effect on the desired particularly good electrical conductivity of the product produced from the alloy. Nevertheless, these give the alloy product the desired strength values.

Unexpectedly and surprisingly, this alloy or an alloy product produced from this alloy has shown that this not only has a particularly fine grain (typically 10-100 pm), but is also very readily extrudable or hotformable, and can be readily cold worked by cold working and has a good machinability and yet has a very good electrical conductivity of more than 12 MS / m (20% IACS) for special brasses of the type in question. This is also confined to the relatively high Sn content with simultaneously limited proportions of the silicide-forming elements.

In general, the prevailing teaching was that brass alloys which should have good machinability must not have a copper content of less than 70% by weight (see, for example, US 2014/0234411 A1). In this respect, it was surprising to find that despite the low copper content, the alloy according to the invention or the product produced therefrom is very easy to machine. What is of interest for electrical applications of a special brass alloy product made from this alloy is its particular good galvanic coatability. In some applications, such products are coated with a particularly highly conductive metal layer, ie a coating whose electrical conductivity clearly exceeds that of the product made from the brass alloy. Such a metal layer is typically applied galvanically. This not only requires a certain conductivity of the special brass alloy product, but, above all, that a subsequently applied galvanic coating adheres to it permanently and uniformly over the surface. This is justified, in particular, in the uniform fine-grained com- pound arising in the case of this special brass alloy. This is the case with products made from this alloy. A coating of the brass alloy product can also serve for wear protection. Furthermore, coatings can be used to improve certain properties of the brass alloy product on the surface, such as better solderability, such as for attaching contacts, thermal insulation for thermal protection of the special brass alloy product or as a primer layer for a further coating. In addition, the modulus of elasticity of a product made from this alloy is sufficiently high. Therefore, this brass alloy can also be used to produce products with resilient properties, such as plug shoes as contacts. With an E-modulus of more than 100 to 120 GPa, this is in the size range of the E-modules, which are known from low-alloyed copper-zinc binary alloys, such as these typically for electrical applications in which it sometimes to be applied spring force, are used.

With this brass alloy can produce alloy products, which have an electrical conductivity of more than 12 MS / m (20% IACS). This achieves electrical conductivity values which are generally higher than for other special brass alloys with a Zn content of 30% by weight or more and which are sufficient for many applications. This is combined with strength values for alloy products made from this alloy, which are otherwise known only from special brass alloys specially designed for this purpose. However, they do not then have the further positive properties of this alloy or of a product produced therefrom.

Not insignificant for the special brass alloy product produced from this special brass alloy, especially in electrical applications, is its good solderability.

A special feature of this copper-zinc alloy is its simple chemical structure due to the small number of elements involved in the construction of the alloy. This also includes that the alloy is Cr-free. The alloy is also typically Pb-free, with a Pb content of max. 0.1 wt .-% is allowed. It can not always be avoided that small quantities of Pb are introduced into the alloy as a result of carry-over or the use of recycled material. Within the permitted range, Pb does not adversely affect the above-described positive properties of this copper-zinc alloy. With a maximum permitted content of 0.1% by weight of Pb, this alloy is still considered Pb-free. Furthermore, the use of elements such as P, S, Be, Te and others is dispensed with - elements that are often used in addition to Cr in other special brass alloys for achieving certain strength or processing properties. This, too, justifies the surprising result that the above-described positive properties of a product made from the alloy occur, even though the alloy is composed of only a few elements, provided that the elements participate in the stated proportions of the alloy. The use of only a small number of elements in the structure of the alloy simplifies the production process. Danger of elemental dragging on other alloys is avoided in commercial production because the elements involved in assembly of the alloy are standard features of any special brass alloy.

The particularly good machinability of an alloy product produced from this alloy can be specified with an index of 60-70 and in a specific embodiment of more than 80. The copper-zinc alloy according to the invention preferably has the following composition:

Cu: 64-66% by weight,

Sn: 0.3-0.7 wt%,

- Si: 0.03 - 0.1 wt .-%, with which alloy composition, the positive properties of the alloy are further improved. According to one embodiment, the Sn and Si content is further limited, as is the proportion of the silicide-forming elements. Such an alloy is composed as follows:

Cu: 64.5-66% by weight,

Sn: 0.4-0.6 wt%,

Si: 0.03-0.08 wt%,

- At least two silicide-forming elements from the group Mn, Fe, Ni and Al, each with max. 0.1% by weight, the sum of these elements not exceeding 0.4% by weight,

Pb: max. 0.1% by weight,

- Remaining Zn plus unavoidable impurities.

The preferred Zn content is between 32 and 36 wt .-%.

The invention is described below with reference to an exemplary embodiment in comparison to three comparative alloys. The alloy according to the invention was prepared from two samples - the samples A and B - in addition to three comparative alloys and extruded. The composition of the tested alloys is shown in the following table:

(In% by weight) In the above table, the comparative alloys are Alloy 1, Alloy 2 and Alloy 3. When extruded, the alloy according to the invention has the following strength values according to Samples A and B:

0.2% proof strength: 100 N / mm ² ,

Tensile strength: approx. 300 N / mm ² ,

Elongation at break: approx. 55%,

Hardness: 70 HB 2.5 / 62.5 The good cold-drawing ability and concomitant work hardening with the result of introducing increased strength values into the alloy product can be achieved in the cold-drawn state of the extrusion rod in a first step with 20% reduction in cross-section and in a second step with a 35% reduction in cross-section (see in this regard also FIGS. 1 to 5):

Strength values of the cold-drawn rod with 20% reduction in cross-section:

- 0.2% proof stress: approx. 310 N / mm ² '

Tensile strength: approx. 390 N / mm ² ,

- Elongation at break: approx. 25%,

- Hardness: approx. 120 HB 2.5 / 62.5.

Strength values of the cold drawn rod with 35% reduction in cross section: - 0.2% proof stress: approx. 400 N / mm ² ,

- Tensile strength: approx. 450 N / mm ² ·

- Elongation at break: 12%,

- Hardness: 143 HB 2.5 / 62.5.

The microstructure of the alloy according to the invention has at room temperature predominantly a-phase in the matrix. At hot-stamping temperatures there is a sufficient proportion of β-phase. The grain structure is small at room temperature with a mean grain size of 10 to 100 pm. The silicides are finely distributed as fine precipitates that form from the press heat.

The properties of the alloy samples A and B according to the invention at room temperature in comparison to the three comparative alloys are shown in the following table for a respectively partially solidified state, as is customary for the production of connectors:

This comparison shows that the alloy according to the invention has particularly good properties in the parameters relevant for electrical applications. This is also associated with a particularly high modulus of elasticity and very good strength values. That's why Above all, this alloy is also required for the manufacture of electrical contact elements that have material-elastic properties.

Investigations on casting samples of the alloy samples A and B according to the invention show that the β-mixed crystal fraction with 12-15% and a remainder of a-mixed crystal fraction is quite low. The proportion of intermetallic phases is less than 1%. The high a-phase content already during casting has a positive effect on subsequent cold forming steps. In the case of a desired hot forming, it will be endeavored to keep the β-phase fraction somewhat higher.

By extruding the ß-share has reduced to less than 2%. The density is 8.58 g / cm ³ . The electrical conductivity in the extruded state of these samples is 13.8 MS / m (23.8% IACS). These samples have a hardness of about 80 HB 2.5 / 62.5.

When performing a stress corrosion cracking test in accordance with DIN 59016 Part 1 no stress cracks have occurred. This means that in the pressing state no, at least no significant residual stresses in the structure is present. This result fits in well with the high homogeneity of the microstructure and the small grain, which has been confirmed by micrographs. The special structure of such an alloy product with its predominant a-phase is responsible for the good electrical conductivity already described. In addition, due to the homogeneous structure, not only are the mechanical properties in different directions the same, but also the electrical conductivity.

The electrical conductivity can be improved by performing a subsequent annealing step, which is preferably carried out between 380 ° C and 500 ° C for about 3 hours. Preferably, the annealing is carried out at temperatures between 440 ° C and 470 ° C for 3 hours. During this annealing, fine precipitates are removed, as these impede the electrical conductivity. After annealing, an electrical conductivity of about 14.2 MS / m was measured on Samples A and B. Of particular advantage of the alloy according to the invention is also their particularly good cold workability. The semifinished products produced therefrom can also be cold formed several times without intermediate annealing, for example stretched or bent, in order to allow the component to achieve particularly high strength values as a result of the cold work hardening that occurs therewith.

The accompanying FIGS. 1 to 5 show diagrams from which the mechanical strength properties of the alloy according to the invention are established with reference to sample A with increasing elongation of the sample body. In each case the strain on the starting surface or initial length of the sample body is plotted on the x-axis.

FIG. 1 shows the development of the 0.2% proof stress of the specimen with increasing elongation, up to a total elongation of 60%. The 0.2% proof stress increases with increasing elongation of the specimen. The same behavior can be observed in the tensile strength. The elongation performed as cold working results in an increase in tensile strength of more than 100% when the specimen has been stretched over 50%. An increase in the yield ratio is also observed with increasing elongation of the specimen.

The elongation at break is of particular interest to the claimed alloy. Despite elongation even in areas of over 50% and thus despite strong deformation, the elongation at break does not fall below a value of 10%

With the increasing elongation of the sample body, the hardness increases due to the concomitant cold deformation, namely up to about 180 HB 2.5 / 62.5.

These diagrams illustrate the particularly good cold workability properties of a product made from the inventive alloy.

Claims

claims

1. Copper-zinc alloy for producing electrically conductive components, such as contacts, consisting of:

Cu: 62.5-67% by weight,

Sn: 0.25-1.0% by weight,

Si: 0.015 - 0.15 wt.%,

- At least two silicide-forming elements from the group Mn, Fe, Ni and Al, each with max. 0.15 wt .-%, wherein the

Sum of these elements does not exceed 0.6% by weight, Pb: max. 0.1% by weight,

- Remaining Zn plus unavoidable impurities.

2. copper-zinc alloy according to claim 1 with

Cu: 64 to 66.5% by weight,

Sn: 0.3-0.7 wt%,

Si: 0.03-0.1 wt%.

3. copper-zinc alloy according to claim 2 with

Cu: 64.5-66% by weight,

Sn: 0.4-0.6 wt%,

Si: 0.03-0.8% by weight,

- At least two silicide-forming elements from the group Mn, Fe, Ni and Al, each with max. 0.1 wt .-%, wherein the

Sum of these elements does not exceed 0.4% by weight,

- Remaining Zn plus unavoidable impurities.

4. copper-zinc alloy according to one of claims 1 to 3, characterized in that the alloy contains Zn 32-36 wt .-%.

5. copper-zinc alloy according to one of claims 1 to 4, characterized in that of the silicide-forming elements in the alloy Fe, Ni and Al are contained, wherein the proportions of Ni and Al are each about the same and the Fe 40% to 60% of the Ni or Al content.

6. copper-zinc alloy according to claim 5, characterized in that the Ni and Al content in each case 0.04 to 0.1 wt .-% and the Fe 0.02 to 0.05 wt .-% is ,

7. copper-zinc alloy according to claim 6, characterized in that the Ni content and the Al content in each case 0.06 to 0.08 wt .-% and the Fe content 0.03 to 0.04 wt. -% is.

8. Copper-zinc alloy according to one of claims 1 to 7, characterized in that the alloy is Cr-free.

9. copper-zinc alloy product, made of a copper-zinc alloy according to any one of claims 1 to 8, characterized in that the matrix contains at room temperature predominantly a-phase.

10. copper-zinc alloy product according to claim 9, characterized in that the mean grain size of the structure is between 10 and 100 pm.

11. copper-zinc alloy product according to claim 9 or 10, characterized in that its electrical conductivity is at least 12 MS / m (20% IACS).

A copper-zinc alloy product according to any one of claims 9 to 11, characterized in that the product is cold-worked from a slab by drawing it having a cross-sectional reduction of about 20% and having the following strength values:

- 0.2% proof stress: -ca. 310 Take ² ·

Tensile strength: approx. 390 N / mm ² ,

- Elongation at break: approx. 25%,

Hardness: approx. 120 HB 2.5 / 62.5.

13. copper-zinc alloy product according to one of claims 9 to 11, characterized in that the product of a semifinished product is cold-worked by drawing it with a cross-sectional reduction of about 35% and has the following strength values:

- 0.2% proof stress: approx. 400 Nmm ² ,

- Tensile strength: approx. 450 N / mm ² ·

- Elongation at break: 12%,

Hardness: -143 HB 2.5 / 62.5.