description

Copper-nickel-zinc alloy and its use

The invention relates to a copper-nickel-zinc alloy, in their a- and ß-phase structure consisting of nickel, iron and manganese and / or nickel, cobalt and manganese mixed silicides are incorporated as spherical or ellipsoidal particles, and the use of such a copper-nickel-zinc alloy.

Alloys of copper, nickel and zinc are called nickel silver because of their silver-like colors. Commonly used alloys have between 47 and 64% by weight of copper and between 7 and 25% by weight of nickel. In turnable and drillable alloys usually up to 3 wt .-% lead are added as a chip breaker, in cast alloys even up to 9 wt .-%. The rest is zinc. As admixtures commercial nickel silver alloys may also contain 0.2 to 0.7 wt .-% manganese to reduce the Glühbrüchigkeit. Also, the manganese supplement acts deoxidizing and desulfurizing.

Nickel-silver alloys, such as CuNi12Zn24 or CuNi 8Zn20, are used in the optics industry, among others, for producing spectacle hinges. The progressive miniaturization of these products requires materials with higher strength. In addition, these products have high demands on the quality of the surface.

Nickel silver alloys are also used to make jewelry and watch parts. These products are particularly demanding on the

Quality of the surface provided. The material has already pulled in

Condition having a glossy and polished surface, which is free of defects such as grooves or voids. Furthermore, the material must be very easy to machine and, if necessary, be polished. Also, the color of the material must not change during use. Quite similar requirements apply to materials used in medical technology or for

Production of musical instruments are used.

From the document DE 1 120 151 high-strength nickel silver alloys with favorable properties in terms of castability and hot workability are known. These alloys consist of 0.01 to 5% Si, about 10 to 30% Ni, 45 to 70% Cu, 0.3 to 5% Mn, balance at least 10% zinc. Small additions of Si serve to deoxidize the alloy and improve castability. The manganese addition has the task to increase the toughness and thus the cold workability of the alloy, and it also serves the nickel savings. Alternatively, manganese can be completely replaced by aluminum and nickel partially by cobalt. The alloying of iron should be avoided as iron reduces the corrosion resistance of the alloy. With a manganese content of 1%, strength values ​​of approx. 400 MPa are achieved.

The document JP 01177327 describes easily machinable nickel silver alloys with good hot and cold workability. These alloys consist of 6 to 15% Ni, 3 to 8% Mn, 0.1 to 2.5% Pb, 31 to 47% Zn, balance Cu with unavoidable impurities. Optionally, small amounts of Fe, Co, B, Si, or P may be added to aid grain growth

Prevent warming before hot forming.

The document DE 10 2012 004 725 A1 discloses lead-containing copper-nickel-zinc alloys whose structure contains nickel, iron and manganese

and / or nickel, cobalt and manganese mixed silicides are incorporated as spherical or ellipsoidal particles. The alloys are characterized by high tensile strength, high cold workability and good machinability. The lead content of 1, 0 to 1, 5 wt .-% ensures the good machinability of the alloys. The alloys are used to produce high quality lead tips for ballpoint pens. The surface properties of the

Material is not always sufficient for applications with particularly high surface quality requirements.

The invention has for its object to provide a copper-nickel-zinc alloy with improved surface quality with high strength. The surface should already look like polished when pulled. Furthermore, the alloy should have a good machinability and excellent color fastness. Furthermore, the invention has for its object to provide a use for such a copper-nickel-zinc alloy.

The invention with respect to a copper-nickel-zinc alloy by the features of claim 1 and for use by the features of claims 4 and 5 reproduced. The other dependent claims relate to advantageous embodiments and further developments of the invention.

The invention includes a copper-nickel-zinc alloy having the following

Composition in% by weight:

Cu 46.0 to 51, 0%,

Ni 8.0 to 1 1, 0%,

Mn 0.2 to 0.6%,

Si 0.05 to 0.5%,

Fe and / or Co each up to 0.8%, wherein the sum of Fe content and twice the Co content is at least 0, 1 wt .-%,

Residual Zn as well as unavoidable impurities,

wherein nickel, iron and manganese and / or nickel, cobalt and manganese mixed silicides are incorporated as spherical or ellipsoidal particles in a structure consisting of α and β phase.

The invention is based on the consideration that the structure of nickel silver materials by alloying of silicon is varied so that silicide precipitates are formed. Silicides as intermetallic compounds have with about 800 HV a much higher hardness than the a and ß phase of the matrix structure. In principle, manganese is added to improve the cold and hot forming capacity and to increase the strength. In addition, manganese acts deoxidizing and desulfurizing. In the presence of manganese, iron and nickel, silicon forms mixed silicides of approximate composition predominantly between (Mn, Fe, Ni) 2 Si and (Mn, Fe, Ni) 3Si. Analogously, silicon forms mixed silicides of the approximate compositions (Mn, Co, Ni) x Si y in the simultaneous presence of manganese, cobalt and nickelwhere x> y. Furthermore, mixed silicides can be formed which contain both iron and cobalt in addition to manganese and nickel. The mixed silicides are finely distributed as spherical or ellipsoidal particles in the matrix structure. The mean value of the volume-equivalent diameter of the particles is 0.5 to 2 μm. The Ge-füge contains no large-scale and therefore easily out of the matrix structure out breaking silicides. This advantageous property is achieved in the alloy according to the invention in particular by the low levels of manganese and iron or cobalt. Both iron and cobalt act as nucleation sites for silicide formation, ie in the presence of iron and / or cobalt even small deviations from the thermodynamic equilibrium are sufficient, so that small precipitates arise. These excretory germs, which may also contain nickel in the present alloy composition are finely dispersed in the microstructure. They are further silicides, which now also contain manganese, preferably on. The low manganese content of the alloy limits the size of the individual silicides. Small amounts of iron and / or cobalt in

Combination with a small amount of manganese are therefore the prerequisite for the formation of mixed silicides. The minimum amount of iron or cobalt is defined by the fact that the sum of the iron content and twice the cobalt content is at least 0.1 wt .-%.

Surprisingly, it has been found that the copper-nickel-zinc alloy according to the invention has an excellent surface quality. Already in the drawn state, the surface of the material is very smooth, silvery shiny and free of visible defects. The surface looks like it's already polished. Thus, the surface of a semi-finished product produced by a forming process, such as a drawing or rolling process from an alloy according to the invention in many cases already meets the quality requirements of the final product. Further processing to improve the surface is no longer necessary. The average roughness Ra of the surface of such a semi-finished product is typically at most 0.2 μm. The average roughness Ra is determined over a measuring length of at least 4 mm.

The surface quality of the copper-nickel-zinc alloy according to the invention is at least as good as the materials previously used in the optics industry. However, the strength of the copper-nickel-zinc alloy according to the invention is significantly higher than that of the materials used hitherto. This increase in strength allows the components to be made smaller and more filigree and thus meet the current design requirements. The tensile strength of the copper-nickel-zinc alloy according to the invention is between 700 and 900 MPa, depending on the degree of deformation of the material. In the hard state, it is at least 800 MPa.

Workpieces made of a copper-nickel-zinc alloy according to the invention are characterized by a very high-quality surface and an attractive appearance, so that this alloy for the production of jewelry and watch parts

are suitable. Furthermore, workpieces of a copper-nickel-zinc alloy according to the invention can be polished very well, whereby the visual impression of the workpiece can be further improved if necessary and the value of the product can be increased. Furthermore, the surface of the copper-nickel-zinc alloy according to the invention is readily coatable because of its excellent flatness.

In particular, the surface quality of a copper-nickel-zinc alloy according to the invention is significantly better than that of lead-containing copper-nickel-zinc alloys of similar composition. In a copper-nickel-zinc alloy according to the invention small amounts of lead of up to 0.1 wt .-% may be contained in the impurities, which are neither matrix effective nor have an influence on the formation of Mischsilicide. Preferably, the lead content of a copper-nickel-zinc alloy according to the invention is at most 0.05 wt .-%. A copper-nickel-zinc alloy according to the invention is particularly preferably lead-free.

Another advantage of a copper-nickel-zinc alloy according to the invention is its high zinc content of about 40 wt .-%. This makes the material cheaper than, for example, the nickel silver alloys CuNi12Zn24 or

CuNi18Zn20.

Moreover, a copper-nickel-zinc alloy according to the invention has a good machinability. The alloy can be well formed both warm and cold. The manufacturing costs of semi-finished products and end products are thereby reduced. In particular, the copper-nickel-zinc alloy according to the invention has a very good machinability, although it contains at most very small amounts of lead. Even at Pb levels well below the threshold of unavoidable impurities, a copper-nickel-zinc alloy of the invention is readily machinable. The reason for the good machinability of the alloy are the finely divided mixed silicides, which act as chip breakers.

Advantageously, either the Fe content or the Co content can be at least 0.1% by weight. This favors the formation finely distributed

Mischsilicide.

In a preferred embodiment of the invention, the copper-nickel-zinc alloy according to the invention may have the following composition [in% by weight]:

Cu 47.5 to 49.5%,

Ni 8.0 to 10.0%,

Mn 0.2 to 0.6%,

Si 0.05 to 0.4%,

Fe 0.2 to 0.8%,

optionally up to 0.8% Co

Rest Zn as well as unavoidable impurities.

In this composition, nickel-, iron- and manganese-containing mixed silicides may be incorporated as spherical or ellipsoidal particles in a microstructure consisting of α and β phases. By selectively alloying iron, very fine mixed silicides are formed, which have an advantageous effect on the surface quality of the material.

In an alternative advantageous embodiment of the invention, the copper-nickel-zinc alloy according to the invention may have the following composition [in% by weight]:

Cu 47.5 to 49.5%,

Ni 8.0 to 10.0%,

Mn 0.2 to 0.6%,

Si 0.05 to 0.4%,

Co 0.1 to 0.8%,

optionally up to 0.8% Fe,

Rest Zn as well as unavoidable impurities.

In this composition, nickel-, cobalt- and manganese-containing mixed silicides may be incorporated as spherical or ellipsoidal particles in a microstructure consisting of α and β phases. The deliberate alloying of cobalt produces mixed silicides which have an advantageous effect on the strength of the material with simultaneously good surface quality.

Another aspect of the invention includes the use of an alloy according to the invention for the production of consumer goods with high demands on the surface quality such as jewelry, watch parts, spectacle hinges, musical instruments or devices for medical technology. Due to the excellent surface quality of workpieces made of an alloy according to the invention, this is particularly suitable for the production of jewelry, watch parts and musical instruments. Also advantageous in these applications is the high color stability of the alloy. The color fastness follows from the high corrosion resistance of the alloy. Devices used in medical technology must be easy to clean. The smoother the surface of the equipment, the easier it is to remove unwanted substances.

Glasses hinges.

Another aspect of the invention includes the use of an alloy according to the invention for the production of keys, locks, connectors or lead tips for ballpoint pens. In the production of commodities such as keys or locks come the advantageous

Properties of a copper-nickel-zinc alloy according to the invention with regard to workability, namely good formability and good machinability, for

Carry. The same applies to the use of a copper-nickel-zinc alloy according to the invention as connectors, which are made of a profile, a rod or a tube by machining. When used as a lead tip for ballpoint moreover, the good corrosion resistance of the copper-nickel-zinc alloy according to the invention has an advantageous effect.

The invention will be explained in more detail with reference to an embodiment.

An inventive copper-nickel-zinc alloy, as well as three comparative alloys were melted and cast to bolts. From the bolts were by means of hot pressing and cold forming wires and rods with a

Outer diameter made of 4 mm. Table 1 shows the composition of the individual alloys in% by weight.

Table 1: Composition of the individual alloys in% by weight

Roughness measurements were made on the drawn wires. The following characteristic values ​​were determined over a measuring length of 4 mm in each case longitudinally and transversely to the drawing direction:

Ra mean roughness

Rz average roughness

Rmax maximum roughness

Rt Total height of the profile

Table 2 compares the values ​​obtained on the samples.

Table 2: Roughness measurements, data in μηη

The measured values ​​documented in Table 2 show that the surface of the inventive alloy has the lowest roughness or roughness depth in seven out of eight measured values. The inventive alloy thus has the best surface quality in the drawn state. In particular, the measured values ​​determined on the inventive alloy are always lower than the measured values ​​determined on the lead-containing comparative samples 1 and 3.

Cutting tests were carried out on the four samples. For this purpose, an axially parallel central bore with an inner diameter of 2 mm was introduced into the wires. The alloy according to the invention and the two lead-containing

Comparative Samples 1 and 3 could be machined without problems. The drill chips were fine. The lead-free Comparative Sample 2 became very hot in the drill trial and the drill broke off during the trial.

Samples of an alloy according to the invention having a composition according to Table 1 were documented in Table 3 as mechanical

Properties determined:

un ra erc knife, mm aa

Table 3: Mechanical properties of an alloy according to the invention

The experiments show that a copper-nickel-zinc alloy according to the invention advantageously combines properties that are not found in this combination in the prior art alloys.

claims

Copper-nickel-zinc alloy with the following composition [in

Wt .-%]:

Cu 46.0 to 51, 0%,

Ni 8.0 to 11, 0%,

Mn 0.2 to 0.6%,

Si 0.05 to 0.5%,

Fe and / or Co in each case up to 0.8%,

wherein the sum of Fe content and twice the Co content is at least 0.1%,

Residual Zn as well as unavoidable impurities,

wherein in an a- and ß-phase microstructure consisting of nickel, iron and manganese and / or nickel, cobalt and manganese-containing

Mixed silicides are incorporated as spherical or elliptical particles.

Copper-nickel-zinc alloy according to claim 1 with the following

Composition [in% by weight]:

Cu 47.5 to 49.5%,

Ni 8.0 to 10.0%,

Mn 0.2 to 0.6%,

Si 0.05 to 0.4%,

Fe 0.2 to 0.8%,

optionally up to 0.8% Co,

Residual Zn as well as unavoidable impurities,

wherein nickel, iron and manganese mixed silicides are incorporated as spherical or ellipsoidal particles in a structure consisting of α and β phase.

3. copper-nickel-zinc alloy according to claim 1 with the following composition [in wt.%]:

Cu 47.5 to 49.5%,

Ni 8.0 to 10.0%,

Mn 0.2 to 0.6%,

Si 0.05 to 0.4%,

Co 0.1 to 0.8%,

optionally up to 0.8% Fe,

Residual Zn as well as unavoidable impurities,

wherein in a structure consisting of α and β phase, mixed silicides containing nickel, cobalt and manganese are incorporated as spherical or ellipsoidal particles.

Use of a copper-nickel-zinc alloy according to one of

Claims 1 to 3 for the production of consumer goods with high

Requirements for the surface quality.

Use of a copper-nickel-zinc alloy according to one of

Claims 1 to 3 for the production of keys, locks,

Connectors or lead tips for ballpoint pens.