EP3781719B1 - Copper-zinc-nickel-manganese alloy - Google Patents

Description

The invention relates to a high-strength copper-zinc-nickel-manganese alloy.

Copper-zinc alloys containing between 8 and 20% by weight nickel are known as "German silver". Due to the high nickel content, they are very resistant to corrosion and have a high level of strength. Most German silver alloys contain small amounts of manganese. Particularly high-strength German silver alloys are CuNi18Zn20 and CuNi18Zn19Pb1. They have tensile strengths of up to 1000 MPa. Both alloys contain less than 1% by weight of manganese. The CuNi12Zn38Mn5Pb2 alloy contains a significantly larger proportion of manganese at around 5% by weight. Materials made from this alloy can have a tensile strength of 650 MPa.

The pamphlet JP2005 325413 discloses a copper alloy containing 40.0 to 50.0% Cu, 5.0 to 20.0% Ni, 1.0 to 10.0% Mn, 0.5 to 3.0% Bi and 2.0 to 6. 0% Sn. In particular, an alloy with the composition 49.2% Cu, 19.7% Ni, 9.96% Mn, 2.94% Bi, 5.99% Sn, balance Zn and impurities is disclosed.

From the pamphlet FR897484 It is known that manganese can replace nickel in nickel silver alloys. The manganese-containing German silver alloys proposed there contain at least as much manganese as nickel. Tensile strengths of up to 630 MPa can be achieved with these alloys, and up to 710 MPa with the addition of 1.5% by weight of iron.

The object of the invention is to provide a copper alloy with high strength, hardness, ductility, wear resistance, corrosion resistance and with good antimicrobial and antifouling properties. It should be possible to produce semi-finished products from the alloy using standard process steps on an industrial scale. In particular, high degrees of cold forming should be achievable without intermediate annealing in order to keep production costs low.

The invention is represented by the features of claim 1. The further dependent claims relate to advantageous developments and refinements of the invention.

• Zn: 17 bis 20,5 %,
• Ni: 17 bis 23 %,
• Mn: 8 bis 11,5 %,
• wahlweise noch bis zu 4 % Cr,
• wahlweise noch bis zu 5,5 % Fe,
• wahlweise noch bis zu 0,5 % Ti,
• wahlweise noch bis zu 0,15 % B,
• wahlweise noch bis zu 0,1 % Ca,
• wahlweise noch bis zu 1,0 % Pb

Rest Kupfer sowie unvermeidbare Verunreinigungen, wobei der Anteil an Kupfer mindestens 45 Gew.-% beträgt, das Verhältnis des Anteils an Ni zum Anteil an Mn mindestens 1,7 beträgt und wobei die Legierung ein Gefüge aufweist, in das Ausscheidungen vom Typ MnNi und MnNi₂ eingelagert sind.The invention relates to a copper alloy with the following composition (in % by weight):

• Zn: 17 to 20.5%,
• Ni: 17 to 23%,
• Mn: 8 to 11.5%,
• optionally up to 4% Cr,
• optionally up to 5.5% Fe,
• optionally up to 0.5% Ti,
• optionally up to 0.15% B,
• optionally up to 0.1% Ca,
• optionally up to 1.0% Pb

The remainder is copper and unavoidable impurities, the proportion of copper being at least 45% by weight, the ratio of the proportion of Ni to the proportion of Mn being at least 1.7 and the alloy having a microstructure in which precipitates of the MnNi and MnNi type ₂ are stored.

The invention is based on the consideration that by alloying certain amounts of zinc, nickel and manganese to copper, an alloy with is formed with an exceptional property profile.

The proportion of zinc in the alloy is at least 17% by weight and at most 20.5% by weight. Zinc, as a cost-effective element, should be present in the alloy in as large a proportion as possible. However, a zinc content of more than 20.5% by weight leads to a significant deterioration in ductility as well as to a Deterioration of corrosion resistance.

The proportion of nickel in the alloy is at least 17% by weight and at most 23% by weight. Nickel provides the alloy with high strength and good corrosion resistance. The alloy must therefore contain at least 17% by weight, preferably at least 18% by weight, of nickel. For reasons of cost, the alloy should contain no more than 23% by weight, preferably no more than 21% by weight, of nickel.

The proportion of manganese in the alloy is at least 8% by weight and at most 11.5% by weight. In the presence of nickel, manganese can form manganese- and nickel-containing precipitates of the MnNi ₂ and MnNi types. This effect only occurs clearly from a manganese content of approximately 8% by weight. From a manganese content of 8 wt. With manganese contents above 11.5% by weight, an increase in the formation of cracks during hot forming can be observed. The manganese content should therefore not exceed 11.5% by weight. The manganese content is preferably at least 9% by weight. The manganese content is preferably at most 11% by weight.

The ratio of the proportion of nickel to the proportion of manganese is at least 1.7, so that precipitations of the MnNi ₂ and MnNi type can be formed. These precipitates are embedded in the structure of the alloy.

The copper content in the alloy should be at least 45% by weight. The copper content largely determines the antimicrobial properties of the alloy. The copper content should therefore be at least 45% by weight, preferably at least 48% by weight.

Optionally, up to 2% by weight of chromium can be added to the alloy. Chromium forms an additional species of precipitates alongside the MnNi and MnNi ₂ precipitates. Chromium thus contributes to a further increase in strength. Preferably, at least 0.2% by weight of chromium should be added to the alloy in order to achieve a significant effect.

Optionally, up to 5.5% by weight of iron can be added to the alloy. Iron forms an additional type of precipitation in addition to the MnNi and MnNi ₂ precipitations. Iron thus contributes to a further increase in strength. Preferably, at least 0.2% by weight of iron should be added to the alloy in order to achieve a significant effect.

The optional elements Ti, B and Ca result in grain refinement of the structure. The optional element Pb improves the machinability of the material. It must be taken into account that Pb impairs hot workability, so that hot work is not carried out if Pb is significantly alloyed with it.

The alloy is free of beryllium and rare earth elements.

The particular advantage of the invention is that the special selection of the proportions of the elements zinc, nickel and manganese forms an alloy which, as a wrought material, has a special profile of properties. It features an excellent combination of strength, ductility, deep drawability, corrosion resistance and spring properties. It has excellent antimicrobial and anti-fouling properties. Materials with a tensile strength of at least 1100 MPa and/or a yield strength of at least 1000 MPa can be produced by precipitation hardening.

The alloy can either be hot worked after a cast shape has been cast without solution annealing, or the cast shape can be cold worked immediately without hot work. In the first variant of the process, after the alloy has been cast and cooled, hot forming is carried out at temperatures between 650 °C and 850 °C. The alloy is then cold-formed, with a degree of forming of up to 99% being achievable. A degree of deformation of at least 90% is preferred. The degree of deformation is understood here to mean the relative decrease in the cross section of the workpiece. After cold working, the alloy is heat treated at a temperature between 310°C and 500°C for a time between 10 minutes and 30 hours. As a result, precipitations of the MnNi ₂ and MnNi types are formed in the structure of the material. The precipitates increase the strength of the material considerably. The greater the degree of deformation from the previous cold forming, the higher the strength of the material after heat treatment. If the alloy is cold-formed with a degree of deformation of at least 95%, then after heat treatment the material has a tensile strength R _m of up to 1350 MPa and a yield point R _p0.2 of up to 1300 MPa. The hardness of such a material is up to 460 HV10. With a degree of deformation of 90%, the material has a tensile strength R _m of up to 1260 MPa and a yield point R _p0.2 of up to 1200 MPa with an elongation at break of 2.1% after heat treatment. For the production of such high-strength materials, the temperature for the heat treatment is preferably between 330 and 370.degree. The duration of the heat treatment is between 2 and 30 hours.

Softer states with a tensile strength of around 700 MPa and an elongation at break of 30% can also be achieved by choosing an annealing temperature above 450 °C and a heat treatment duration of less than one hour.

Studies show that cracks occur during hot forming if the Alloy containing more than 12% by weight manganese. During hot rolling, the cracks form from the lateral edges of the rolled strip. The usable width of the strip is thus significantly reduced. Furthermore, it can be assumed that micro-cracks will also appear in the areas of the strip where no cracks can be seen with the naked eye. In order to avoid the formation of such cracks, the manganese content of the alloy must not exceed 11.5% by weight.

The manganese content must therefore be set within a narrowly defined range so that, on the one hand, the advantages of precipitation formation can be used and, on the other hand, crack formation during hot forming is avoided. The alloy according to the invention is therefore a particularly advantageous choice. In particular, the proportions of zinc and manganese in the alloy are adjusted in such a way that the alloy can still be hot-formed without any problems and also allows a high degree of cold-forming.

In the second, alternative process variant, the alloy is processed without hot forming. For this purpose, the cast state of the alloy is cold-formed. A total degree of deformation of up to 90% can be achieved. After cold forming with a total degree of forming of at least 80%, the material has a tensile strength R _m of 850 MPa and a yield point R _p0.2 of 835 MPa. The elongation at break is 3% and the hardness is 276 HV10. A tensile strength of more than 900 MPa can be achieved by cold forming with a degree of forming of 90%.

Materials made from the alloy according to the invention are very resistant to fatigue, oil corrosion and low wear. They are therefore suitable for use in plain bearings, tools, relays and watch parts. Furthermore, such materials have good spring properties. Due to their high resilience, they can store a lot of energy elastically. Therefore, the alloy according to the invention is well suited for springs and spring elements. the The combination of cold formability, corrosion resistance and spring properties makes the alloy according to the invention the preferred material for frames and hinges of spectacles.

In a preferred embodiment of the invention, the ratio of the proportion of Ni to the proportion of Mn can be at most 2.3. If the ratio Ni/Mn is chosen in this way, then there are particularly favorable conditions for the formation of precipitates of the stoichiometry MnNi. When the Ni/Mn ratio is greater than 2.3, precipitates of stoichiometry MnNi ₂ are increasingly formed since the excess of Ni is larger. MnNi-type precipitates cause a greater increase in strength than MnNi ₂ -type precipitates. Therefore, it is preferable that the ratio Ni/Mn is 2.3 or less.

Advantageously, the ratio of the proportion of Ni to the proportion of Mn can be at least 1.8, particularly preferably at least 1.9. The manganese content influences the elongation at break of the alloy and the formation of cracks during hot forming. The more manganese bound by nickel in precipitations, the greater the elongation at break and the lower the risk of cracking during hot forming. It is therefore favorable if at least 1.8 times, preferably at least 1.9 times, as much nickel as manganese is present in the alloy.

Furthermore, the resistance to surface corrosion deteriorates with increasing manganese content. It is therefore advantageous for applications that are highly relevant to corrosion if the Mn content does not exceed 10% by weight.

In an advantageous embodiment of the invention, the Zn content can be at most 19.5% by weight. Limiting the Zn content further reduces the risk of alloy embrittlement. When the Zn content is 19.5 wt% or less, the alloy is very ductile and can be very good for both cold and hot forming.

The alloy according to the invention advantageously has a structure with an α-phase matrix. Up to 2% by volume of β-phase can be embedded in this α-phase matrix. Furthermore, the precipitates of the MnNi and MnNi ₂ types are embedded in the α-phase matrix. The almost pure α-phase matrix of the alloy enables high cold workability. The proportion of the β-phase is so small that it hardly affects the cold formability. In a particularly preferred embodiment of the invention, the alpha-phase matrix of the structure is free of beta-phase. The microstructure therefore consists only of the α-phase with precipitates of the MnNi and MnNi ₂ types embedded in it. This can be achieved through a special selection of the alloying elements, in particular the zinc content.

Fig. 1

ein Diagramm, in dem die Härte der Legierung gegen den Mangan-Anteil aufgetragen ist.

Fig. 2

ein Diagramm, in dem Zugfestigkeit, Streckgrenze und Bruchdehnung der Legierung vor der Ausscheidungsglühung gegen den Mangan-Anteil aufgetragen sind.

Fig. 3

ein Diagramm, in dem die Zugfestigkeit und Streckgrenze der Legierung nach der Ausscheidungsglühung gegen den Mangan-Anteil aufgetragen sind.

The invention is explained in more detail using exemplary embodiments. Show it:

1

a diagram in which the hardness of the alloy is plotted against the manganese content.

2

Figure 12 is a plot of alloy tensile strength, yield strength and elongation at break versus manganese content prior to precipitation annealing.

3

Figure 12 is a graph of alloy tensile strength and yield strength versus manganese content after precipitation annealing.

Samples having the composition shown in Table 1 were prepared. Table 1: Composition of the samples in % by weight. Samples 1, 2, 4 and 5 are comparative samples. sample 1 sample 2 sample 3 sample 4 sample 5 Cu 55% 52.5% 50% 47.5% 45% Zn 20% 20% 20% 20% 20% no 20% 20% 20% 20% 20% Mn 5% 7.5% 10% 12.5% 15% cracking no no no Yes Yes

In the samples, the proportions of zinc and nickel were each kept constant at 20% by weight. The manganese content was varied from 5% to 15% by weight. The proportion of copper decreased accordingly from 55% by weight to 45% by weight. The unavoidable impurities were less than 0.1% by weight.

The samples were melted and cast. After solidification, the ingots were hot-rolled at 775 °C. In the last line of the table, crack formation during hot rolling is documented. After hot rolling, the specimens were cold rolled with a true deformation of 90%. Hardness, tensile strength, yield point and elongation at break were measured on the samples in this state.

After cold rolling, the samples were annealed at 320°C for 12 hours. After annealing, hardness, tensile strength, yield point and elongation at break were also measured.

1 shows a graph of alloy hardness versus manganese content. The lower row of measurement points represents the measurement values for the condition immediately after cold rolling, i.e. without annealing, while the upper points in the diagram represent the measurement values after annealing represent. Without annealing, the alloy shows a steady increase in hardness from 270 to 290 HV10 with increasing manganese content. The hardness of the alloy increases significantly as a result of the annealing. The increase in hardness is about 50 HV10 at 5 and 7.5 wt%, while at a manganese content of at least 10 wt% the increase in hardness is more than 80 HV10. The increase in hardness as a result of precipitation annealing is significantly more pronounced with a manganese content of more than 7.5% by weight than with smaller manganese proportions. In order to increase the hardness of the material to at least 350 HV10, approximately 9% by weight of manganese is required. A hardness of 350 HV10 and more is advantageous for plain bearings, for example. The alloy is therefore able to replace Cu-Be alloys as a plain bearing material.

2 Figure 12 shows a plot of tensile strength, yield strength and elongation at break versus manganese content of the alloy before heat treatment. Tensile strength values are represented by filled circles, yield strength values by open squares. Tensile strength and yield point refer to the left axis of the diagram. Elongation at break values are represented by the open triangles and refer to the right axis of the graph. From 5 to 10 wt% manganese there is a moderate increase in tensile strength and yield strength. Between 10 and 12.5 wt% manganese, the tensile strength and yield point decrease somewhat. At 15% by weight of manganese, values are measured for the tensile strength and the yield point that are slightly above the level of the values at 10% by weight. The elongation at break decreases slightly between 5 and 10% by weight of manganese, but drops significantly from 3% to around 1% at higher manganese contents.

3 Figure 12 shows a graph of tensile strength and yield strength versus manganese content of the alloy after heat treatment. Tensile strength values are represented by filled circles, the values the yield point by open squares. From 5 to 10% by weight of manganese, there is a significant increase in tensile strength and yield point. In particular, the yield point in this area increases from below 900 MPa to 1200 MPa. Between 10 and 12.5 wt% manganese, the tensile strength and yield point decrease somewhat. At 15% by weight manganese, values are measured for the tensile strength and the yield point which are on the same level as the values at 10% by weight.

A comparison of the values of 2 and 3 shows that for a manganese content above 7.5% by weight, the effect of strengthening by annealing is particularly large. At 10 wt% manganese, annealing increased tensile strength and yield strength each by nearly 300 MPa, while at 5 wt% manganese, annealing increased tensile strength and yield strength by only about 130 MPa was hardly changed.

The test results show that with a manganese content of around 10% by weight, there are very favorable conditions in the alloy. On the one hand, the tensile strength and yield point are at a maximum, on the other hand, the alloy does not yet tend to crack.

Claims (6)

1. Copper alloy having the following composition (in % by weight):

   Zn: 17 to 20.5%,

   Ni: 17 to 23%,

   Mn: 8 to 11.5%,

   optionally also up to 4% Cr,

   optionally also up to 5.5% Fe,

   optionally also up to 0.5% Ti,

   optionally also up to 0.15% B,

   optionally also up to 0.1% Ca,

   optionally also up to 1.0% Pb,

   the balance being copper and inevitable impurities, wherein

   the proportion of copper is at least 45% by weight,

   the ratio of the proportion of Ni to the proportion of Mn is at least 1.7 and wherein the alloy has a structure in which precipitations of the type MnNi and MnNi₂ are embedded.
2. Copper alloy according to claim 1, characterised in that the ratio of the proportion of Ni to the proportion of Mn is a maximum of 2.3.
3. Copper alloy according to claim 1 or claim 2, characterised in that the ratio of the proportion of Ni to the proportion of Mn is at least 1.8, preferably at least 1.9.
4. Copper alloy according to any one of claims 1 to 3, characterised in that the Zn proportion is a maximum of 19.5% by weight.
5. Copper alloy according to any one of claims 1 to 4, characterised in that the alloy has a structure having an α-phase matrix having a proportion of embedded β-phase of a maximum of 2% by volume and wherein the precipitations of the type MnNi and MnNi₂ are embedded in the α-phase matrix.
6. Copper alloy according to claim 5, characterised in that the α-phase matrix of the structure is free from β-phase.

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