Copper alloys and their uses

Abstract

Copper alloy with the following composition in wt.%: 10.6 to 18% Al, 10.5 to 14.5% Ni, optionally up to 2% Fe, optionally up to 1% Co, optionally up to 0.5% Ti, optionally up to 0.5% Mn, optionally up to 0.15% B, optionally up to 0.1% Ca, optionally up to 0.1% C, remainder copper and unavoidable impurities, characterized in that the alloy, after hot forming in the temperature range between 610 and 690 °C with a degree of deformation of at least 20%, has a tensile strength of at least 800 MPa and that nickel aluminides of the NiAl type are incorporated as precipitates in the microstructure of the alloy.

Description

[0001] The invention relates to an aluminium- and nickel-containing copper alloy and its use for sliding elements, connectors, sealing elements, tools, spring elements or filter elements.

[0002] The properties of copper alloys can be specifically tailored by adding certain elements. High alloy strength typically comes at the cost of significantly reduced electrical conductivity. Therefore, copper alloys that combine high strength with acceptable electrical conductivity are of particular interest.

[0003] German patent DE 1 558 773 discloses copper alloys containing 10 to 12 wt.% aluminum and 2 to 10 wt.% nickel, optionally with 1 to 6 wt.% iron, as well as a method for the heat treatment of such alloys. The heat treatment takes place in a temperature range between 427 and 566°C. Tensile strengths of up to 940 MPa were determined on samples containing between 4 and 5 wt.% nickel and between 4 and 5 wt.% iron. DE 1 558 773 provides no information regarding the electrical conductivity of these alloys.

[0004] Furthermore, corrosion-resistant copper alloys containing 0.1 to 11 wt.% aluminum, 0.1 to 10 wt.% nickel, 0.01 to 6 wt.% iron, 0.001 to 1.0 wt.% boron, and 0.01 to 10 wt.% manganese are known from US patent 3,901,692. Preferably, the aluminum content is 6 to 7 wt.%, the nickel content 5 to 7 wt.%, the iron content 3 to 4 wt.%, and the manganese content 5 to 10 wt.%. Optionally, 0.01 to 5 wt.% cobalt can be added to the alloy. For an alloy with 6.5 wt.% Ni, 6 wt.% Al, 3 wt.% Co, 3 wt.% Fe, and 0.2 wt.% Mn, an electrical conductivity between 15 and 20% IACS is reported. No information regarding the electrical conductivity of cobalt-free alloys is documented.

[0005] The invention is based on the objective of providing a bentonite- and tin-free copper alloy that exhibits a tensile strength of at least 700 MPa in the as-cast condition and a tensile strength of at least 800 MPa in the hot-formed condition without cold forming, with an electrical conductivity of at least 13% IACS. Furthermore, the alloy should possess sufficient ductility, be temper-resistant up to 500°C, and be machinable using conventional methods. In addition, the invention aims to specify uses for which this copper alloy is suitable.

[0006] The invention is described with respect to a copper alloy by the features of claim 1 and with respect to uses by the features of claims 5 to 10. The further referenced claims relate to advantageous embodiments and further developments of the invention.

[0007] The invention includes a copper alloy with the following composition in weight %: 10.6 to 18.0% Al, 10.5 to 14.5% Ni, optionally up to 2% Fe, optionally up to 1% Co, optionally up to 0.5% Ti, optionally up to 0.5% Mn, optionally up to 0.15% B, optionally up to 0.1% Ca, optionally up to 0.1% C, Residual copper and unavoidable impurities, with nickel aluminides of the NiAl type being incorporated as precipitates in the structure of the alloy.

[0008] The invention is based on the premise that by adding aluminum and nickel, a high-temperature-resistant, lightweight copper alloy with high strength, acceptable ductility, and simultaneously good electrical conductivity can be produced. For copper alloys with an aluminum content of 10.6 to 18 wt.% and a nickel content of 10.5 to 14.5%, the tensile strength in the as-cast condition is at least 700 MPa. By hot forming in the temperature range between 610 and 690°C with a degree of deformation of at least 20%, the tensile strength can be increased to at least 800 MPa. The degree of deformation is defined here as the relative reduction of the cross-sectional area. The hardness of such a material is at least 280 HV. Thus, with the copper alloy according to the invention, high strength can be achieved without cold forming. This allows it to be produced in large dimensions in the high-strength condition.The electrical conductivity in the as-cast state is approximately 12% IACS, and in the wrought alloy, i.e., after hot forming, it is at least 13% IACS. The strength of the copper alloy according to the invention can be further increased if the alloy is aged at temperatures between 300 and 600°C after the hot forming described above. Aging preferably takes place in the temperature range between 300 and 400°C and for a duration of at least 30 minutes and at most 7 hours. Depending on the exact composition, the density of the copper alloy according to the invention is between 6500 and 7000 kg / m³. 3 The alloy is very resistant to aging and can be machined conventionally with standard tools.

[0009] With an aluminum content of less than 10.6 wt.%, the tensile strength in the hot-formed condition is below 800 MPa, and in the as-cast condition significantly below 700 MPa. Preferably, the aluminum content is at least 11 wt.%. With an aluminum content of more than 18 wt.%, the electrical conductivity is less than 13% IACS.

[0010] With a nickel content of less than 10.5 wt.%, the tensile strength in the hot-formed condition is significantly below 800 MPa, and in the as-cast condition, significantly below 700 MPa. Preferably, the nickel content is at least 11 wt.%. Due to the high nickel content, the alloy possesses excellent corrosion resistance in air and seawater. With increasing nickel content, the alloy becomes more brittle and also more expensive. Therefore, the nickel content should not exceed 14.5 wt.%.

[0011] In the copper alloy according to the invention, nickel aluminides are formed with a particularly high volume fraction. These precipitates are incorporated into the microstructure, which otherwise consists of copper solid solution and a hard γ2-phase (Al₄Cu₉). The volume fraction of these nickel aluminides can be 50 vol.% or more. The precipitates are formed as a highly heat-resistant, ordered phase with the stoichiometric composition NiAl. The high precipitate fraction results in particularly high heat strength, as dislocations must bypass the precipitates. Furthermore, the high precipitate fraction provides high wear resistance and strength at room temperature.

[0012] In the copper alloy according to the invention, a microstructure with a small grain size can be achieved, if required, by adding at least one of the following elements: optionally up to 2 wt% Fe, optionally up to 1 wt% Co, optionally up to 0.5 wt% Ti, optionally up to 0.5 wt% Mn, optionally up to 0.15 wt% B, optionally up to 0.1 wt% Ca, optionally up to 0.1 wt% C, The addition of one or more of these elements inhibits the formation of coarse grains in the as-cast state. The grain refinement effect only becomes significant above a certain lower limit, which may differ for each element. As long as one of the aforementioned elements is present in the alloy in a proportion below this threshold, it is considered an impurity. However, it is also possible that the copper-aluminum-nickel alloy according to the invention contains none of the aforementioned elements.

[0013] Preferably, in the copper alloy according to the invention, the sum of the aluminum and nickel content can be at least 22.1 wt.%, particularly preferably at least 24 wt.%. Above these limits, a sufficient number of nickel aluminides are formed so that the properties of the alloy are well-developed.

[0014] Preferably, in the copper alloy according to the invention, the sum of the aluminum and nickel content may be at most 29 wt.%, and particularly preferably at most 27 wt.%. Below these limits, undesirable side effects of the alloying elements, such as embrittlement, occur only to a negligible extent.

[0015] In a preferred embodiment of the invention, the proportion of aluminum in the copper alloy according to the invention can be at least 12 wt.% and at most 16 wt.%. With an aluminum content in this range, a particularly favorable ratio of strength, wear resistance and electrical conductivity can be achieved.

[0016] Advantageously, in the copper alloy according to the invention, the nickel content can be at least 11 wt.% and at most 13 wt.%. With a nickel content in this range, a particularly favorable ratio of strength, ductility and electrical conductivity can be achieved.

[0017] In a particularly advantageous embodiment of the copper alloy according to the invention, the aluminum content can be at least 12 wt.%, particularly preferably at least 13 wt.%, and at most 16 wt.%, and the nickel content at least 11 wt.% and at most 13 wt.%. A wrought copper alloy of this composition can achieve a tensile strength of over 1000 MPa with an electrical conductivity of at least 15% IACS without cold working. Alloys of this composition are also particularly heat-resistant. A noticeable decrease in tensile strength is only observed after a heat treatment of 6 hours at 600°C. A noticeable decrease here means a decrease of more than 10%.

[0018] Furthermore, in the copper alloy according to the invention, it can be advantageous for the ratio of aluminum content (in wt.%) to nickel content (in wt.%) to be at least 0.95 and at most 1.28. If the aluminum and nickel content are in this ratio to each other, then particularly favorable conditions exist for the formation of the advantageous nickel aluminides. Aluminum present in stoichiometric excess is either incorporated into the matrix of the alloy or forms the wear-resistant, but brittle, Al4Cu9 phase.

[0019] Another aspect of the invention includes the use of the copper alloy according to the invention for plain bearings. Due to the high volume fraction of NiAl precipitates, the copper alloy according to the invention exhibits high heat resistance and high wear resistance. These properties are advantageous for plain bearings. Plain bearings made of the copper alloy according to the invention can also be operated under overload, in dry running conditions, or at temperatures above 200°C without damage occurring.

[0020] Another aspect of the invention involves the use of the copper alloy according to the invention for connectors. For use in connectors, a material must exhibit a special combination of strength, electrical conductivity, and resistance to stress relaxation. The strength of the copper alloy according to the invention is at a very high level for copper materials. With a minimum value of 13% IACS, the electrical conductivity of the copper alloy according to the invention is at a level sufficient for connectors. The high heat resistance and high softening temperature of the copper alloy according to the invention result in good resistance to stress relaxation.

[0021] Another aspect of the invention includes the use of the copper alloy according to the invention for sealing elements. Examples include cylinder head gaskets and contact rings. Sealing elements must be wear-resistant and resistant to oxidation and creep, even at high temperatures. The copper alloy according to the invention fulfills these requirements in an outstanding manner due to its composition and properties.

[0022] Another aspect of the invention includes the use of the copper alloy according to the invention for tools. Tools must exhibit high hardness and high wear resistance, even at elevated temperatures. The copper alloy according to the invention is therefore particularly well suited as a material for tools. Drill rods are another possible application for the copper alloy according to the invention.

[0023] Another aspect of the invention involves the use of the copper alloy according to the invention for spring elements. Springs must exhibit high resilience and be resistant to relaxation. Resilience is the ability of a material to return to its original state after significant elastic deformation. A material with high resilience is able to store and release a large amount of energy in elastic form. The copper alloy according to the invention exhibits a high yield strength under tensile stress and a high compression strength under compressive stress. Plastic deformation does not occur up to these limits. Consequently, a spring element made of the copper alloy according to the invention can store a large amount of energy elastically. The low density of 6500 to 7000 kg / m³ 3 This enables the construction of relatively lightweight spring elements.

[0024] Another aspect of the invention includes the use of the copper alloy according to the invention for filter elements, in particular antimicrobial filter elements. Antimicrobial filters must be able to ensure the flow of liquid or air while simultaneously mechanically blocking bacteria and most viruses. For this purpose, channels with a penetration width of 20 to 50 nm are required. A structure with such channels can be produced by subjecting the copper alloy according to the invention to an etching treatment in its as-cast state. The etching treatment removes the copper solid solution from the microstructure, leaving the NiAl precipitates in a lamellar form. Between adjacent lamellae, channels with a penetration width of approximately 20 to 50 nm are formed by the removal of the copper solid solution.Such a structure represents an effective mechanical barrier against all types of bacteria and approximately 80% of all known viruses.

[0025] The invention is explained in more detail using exemplary embodiments.

[0026] Table 1 shows a compilation of alloy samples Nos. 1 to 8. For each sample, the alloy composition in wt.%, the hardness, the electrical conductivity, and the tensile strength are given. With the exception of sample No. 6, which is only available in the as-cast condition, the samples are in the state immediately after hot forming in the temperature range between 600 and 800°C and a degree of deformation of 20%. Samples Nos. 1 to 6 are reference samples; samples Nos. 7 and 8 have a composition according to the invention. Sample No. Al in wt.% Ni in wt.% Cu and impurities hardness Electrical conductivity in IACS Tensile strength R m in MPa 1 5,7 6,9 rest 201 HV 11,7% 401 2 6,5 7,9 rest 234 HV 13,3% 422 3 7,6 8,9 rest 248 HV 13,4% 661 4 8,6 9,8 rest 246 HV 13,5% 717 5 10,7 10,1 rest 271 HV 12,7% 820 6 9,2 17,9 rest 250 HV 8,0% - 7 11,1 11,2 rest 280 HV 14,1% 830 8 13,9 12,1 rest 300 HV 14,8% 1000 Table 1: Alloy samples No. 1 to 8

[0027] Samples 1 to 4 have a comparatively low proportion of aluminum and / or nickel. The tensile strength of these samples increases with increasing proportions of aluminum and nickel, remaining well below 750 MPa. The electrical conductivity of samples 2 to 4 is at the same level. Sample 5 exhibits increased tensile strength and hardness compared to samples 2 to 4, but its electrical conductivity is reduced. Sample 6 has a very high nickel content of 17.9 wt.%. Its hardness is approximately the same as that of samples 3 and 4, but its electrical conductivity is low at 8% IACS.

[0028] Samples Nos. 7 and 8 according to the invention exhibit unexpectedly good properties. Comparing sample No. 7 with sample No. 5, it can be observed that the increased proportions of aluminum and, in particular, nickel further increased the strength, but surprisingly, the electrical conductivity also increased. The increase in electrical conductivity in sample No. 7 was not expected based on the properties of samples Nos. 1 to 6. The best results were achieved with sample No. 8. With approximately 14 wt% aluminum and 12 wt% nickel, a tensile strength of approximately 1000 MPa was achieved in the hot-rolled condition. The electrical conductivity, at almost 15% IACS, is the highest of all the samples tested. The electrical conductivity of sample No. 8 could be further increased to almost 16% IACS by an annealing treatment of 3 hours at 330°C.

[0029] Sample No. 8 contains a total of 26 wt% of the alloying elements Al and Ni. Sample No. 6 contains a total of approximately 27 wt% of the alloying elements Al and Ni. Both samples thus have approximately the same total weight fraction of alloying elements. However, the properties of Sample No. 8 are significantly better than those of Sample No. 6. This shows that the alloying elements Al and Ni must be selected in a specific ratio to each other. In Sample No. 8, the ratio of the weight fractions of Al and Ni is approximately 1.15. Alloys with favorable properties are obtained when the ratio of Al to Ni is at least 0.95 and at most 1.28. QUOTES INCLUDED IN THE DESCRIPTION

[0030] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0031] DE 1558773 [0003, 0003] US 3901692

[0004]

Claims

[1] Copper alloy with the following composition in wt.%: 10.6 to 18% Al, 10.5 to 14.5% Ni, optionally up to 2% Fe, optionally up to 1% Co, optionally up to 0.5% Ti, optionally up to 0.5% Mn, optionally up to 0.15% B, optionally up to 0.1% Ca, optionally up to 0.1% C, Residual copper and unavoidable impurities, characterized by that nickel aluminides of the NiAl type are embedded as precipitates in the microstructure of the alloy. [2] Copper alloy according to claim 1, characterized by that the proportion of aluminium is at least 12 wt.% and at most 16 wt.%. [3] Copper alloy according to claim 1 or 2, characterized by that the proportion of nickel is at least 11% by weight and at most 13% by weight. [4] Copper alloy according to any one of claims 1 to 3, characterized bythat the ratio of aluminium content in wt.% to nickel content in wt.% is at least 0.95 and at most 1.

28. [5] Use of a copper alloy according to any of the preceding claims for sliding elements. [6] Use of a copper alloy according to any of the preceding claims for connectors. [7] Use of a copper alloy according to any of the preceding claims for sealing elements. [8] Use of a copper alloy according to any of the preceding claims for tools. [9] Use of a copper alloy according to any of the preceding claims for spring elements. [10] Use of a copper alloy according to any of the preceding claims for filter elements.