Patent Application
20090317290
The invention relates to a multicomponent copper alloy and to its use.
Wrought alloys based on copper-nickel-tin have been known for a long time. For example, U.S. Pat. No. 1,535,542 describes such an alloy in conjunction with the aim of improving the material properties with respect to corrosion resistance, ductility and formability.
U.S. Pat. No. 1,816,509 discloses a copper-nickel-tin alloy and a method for the further treatment of such alloys. After casting the alloy, the method involves a cold forming process and, in order to adjust particular material properties, a heat treatment for homogenizing and age hardening the alloy. The heat treatment leads to continuous and discontinuous precipitates with the formation of a further γ phase.
Specification DE 41 21 994 C2 discloses a further method by which a copper-nickel-tin alloy as a wrought alloy for friction-bearing element applications undergoes conventional steps of casting and forming, the γ phase being formed as continuous and discontinuous precipitates by a heat treatment after the last cold forming. The volume fraction of the γ phase which is formed depends on the process management selected for the heat treatment.
Further to this, numerous studies have been carried out in the system of copper-nickel-tin alloys (U.S. Pat. No. 4,142,918, U.S. Pat. No. 4,406,712 and WO 2005/108631 A1) in order constantly to refine the material properties. In practice, it has however been found that many property combinations, for example wear resistance and thermal stability, cannot be optimized simultaneously by the known process technology. The improvement in one material property is then obtained at the cost of another property, which is likewise important for certain application fields.
It is therefore an object of the invention to refine a multicomponent copper alloy so that both a high, mechanical wear resistance and a high thermal stability are achieved.
The invention is characterized with respect to a multicomponent copper alloy by the features of claim 1 and with respect to a use by the features of claim 13. The other dependent claims relate to advantageous configurations and refinements of the invention.
The invention provides a multicomponent copper alloy consisting of [in % by weight]:
remainder Cu and unavoidable impurities,
optionally up to 0.5% P,
optionally individually or in combination up to 1.5% Ti, Co, Cr, Al, Fe, Zn, Sb,
optionally individually or in combination up to 0.5% B, Zr, S,
optionally up to 5% Pb,
with Mn—Ni silicide phases, which have a mass ratio of the elements [w(Mn)+w(Ni)]/w(Si) in the range of from 1.8/1 to 7/1.
The invention is based on the idea of providing a multicomponent copper alloy which simultaneously offers very good wear resistance and, particularly for use as a friction-bearing element in a thermally stressed environment, excellent thermal stability. With silicon or manganese contents exceeding the specified maximum values of 3% by weight and 5% by weight, respectively, the alloy is susceptible to embrittlement which entails difficulties in the further treatment, in particular owing to edge cracks in the strip material during rolling. Addition of the elements Ti, Co, Cr and Fe leads to the formation of further silicide phases. Sb and Al may be added owing to the improvement in the low-friction properties or the corrosion resistance. The further elements B, Zr and S serve to deoxidize the melt or make a contribution to the grain refinement. The element phosphorus likewise serves for deoxidation, although it can also form phosphide phases which make an important contribution to increasing the hardness of the matrix. The element lead is relevant to the production of cast alloys, while in wrought alloys it is not present or present in very small amounts.
The Mn—Ni silicide phases according to the invention, which have a mass ratio of the elements [w(Mn)+w(Ni)]/w(Si) in the range of from 1.8/1 to 7/1, serve in particular to increase the contact area ratio in friction-bearing element applications. Particularly with somewhat increased manganese proportions, the alloy according to the invention having Mn—Ni silicide phases forms an increasingly fine grain structure which in principle leads to an advantageous increase in the elongation at break A5.
The wrought Cu—Ni—Sn alloys according to the invention are spinoidally demixing systems, which are particularly suitable as bearing materials in motor construction as a solid material and in composite friction-bearing elements. These materials have good friction and wear properties as well as good corrosion resistance. The thermal stability is also excellent.
With Ni contents of from 1 to 15% by weight and Sn contents of from 2 to 12% by weight, cold forming factors of up to 60% can be achieved for these materials. In combination with soft annealing, it is possible to produce thin strips suitable for material composites. These alloys may also be age hardened in the temperature range between 300 and 500° C. The material is thereby strengthened owing to the spinoidal demixing which takes place. Furthermore, continuous or discontinuous precipitates may be generated. This form of precipitation hardening is far superior to binary copper-based alloys.
Compared with copper-based alloys and conventional Cu—Ni—Sn alloys, the advantages achieved by the invention are in particular that the material properties can be adapted optimally to the respective task by means of rolling, homogenization annealing and age hardening. For example, a softer or harder multicomponent copper alloy may be combined by mechanical and thermal treatment in composite friction-bearing elements with harder materials, for example steel.
Advantageously, the mass fraction of the elements satisfies the following relationship: [w(Ni)−w(Mn)−w(Sn)]>0. In other words, the nickel content is greater than the tin and manganese contents together, since nickel should be contained both for the silicide formation and for the spinoidal demixing in the ideal case in the same proportions as tin. Not only are intermetallic phases thereby formed, which increase the contact area ratio in friction-bearing applications and also reduce the wear in jack connectors. In parallel with this, a hardness increase through spinoidal demixing can be achieved with respect to the matrix by a heat treatment.
In an advantageous configuration, the mass fraction of the elements may satisfy the following relationship: w(Mn)>w(Si). If the manganese content is more than the silicon content, sufficient manganese will be available for the silicide formation. Surprisingly, further grain refining is observed in the matrix when the manganese content is increased beyond the silicon content.
Advantageously, the value of the elongation at break A5 at a temperature of 400° C. is more than 10%. The alloy according to the invention therefore exhibits ductile behavior. This is primarily attributable to grain refining. In a temperature range of from room temperature to about 400° C., the elongation at break lies at an almost constant level of 18-20%. Comparable alloys without silicide components, conversely, exhibit a pronouncedly brittle behavior. For these alloys, under the same conditions, an elongation at break value of from 8 to 15% is obtained, although this falls to a value of only 4% beyond about 300° C. This effect is analogous to the so-called strain ageing effect to be observed in long-term stored or heat treated seals. A comparable embrittling effect is also known for bronzes.
In a preferred configuration, the crystallite size of the Mn—Ni silicide phases may be from 0.1 to 100 μm. In this case there are sometimes also elongated particles in the matrix. For friction-bearing applications, such particle sizes are particularly advantageous with respect to the friction-bearing pair in question.
The alloy may advantageously contain from 0.01 to 0.06% P, finely distributed Ni phosphide phases being formed in the matrix. These phases have a hardness increasing effect for the matrix. Even with a proportion of about 100 ppm, a significant increase in the hardness can be achieved. Advantageously, the average grain size of the finely distributed Ni phosphide phases may be less than 100 nm.
In a particular configuration of the invention, the multicomponent copper alloy may contain from 0.1 to 2.5% Mn and from 0.1 to 1.5% Si. It has been found that modified Cu—Ni—Sn variants with an Si content of up to 1.5% by weight and an Mn content of up to 2.5% by weight can be manufactured with an improvement in the material properties. Further laboratory tests have likewise already been carried out in this regard, and have confirmed the limiting values.
In this way, the approach of achieving a further improvement in the wear resistance of Cu—Ni—Sn alloys by the formation of hard intermetallic phases is pursued. These further hard material phases involve manganese-nickel silicides. Cu—Ni—Sn alloys per se already exhibit very good properties with respect to the low-friction properties, corrosion resistance and relaxation or resistance at room temperature. The hard phases which are formed also reduce the susceptibility to adhesion in the mixed friction range and further increase the thermal stability and the ductility at higher temperatures.
By combining the structural components contributing to the wear resistance in conjunction with the spinoidally demixing alloy of the Cu—Ni—Sn system, surprisingly on the one hand it is possible to reduce the run-in behavior at the start of stress due to wear, and on the other hand such a Cu—Ni—Sn—Mn—Si material turns out to be just as thermally stable as well as sufficiently ductile.
The multicomponent copper alloy may advantageously contain from 0.1 to 1.6% Mn and from 0.1 to 0.7% Si. In particular, it has been established that it is in fact possible to manufacture without problems in terms of manufacturing technology with an Si content of up to 0.7% by weight and an Mn content of up to 1.6% by weight. With high silicon and manganese contents, corresponding adaptations should be carried out for the casting parameters in the context of standard precautions.
The multicomponent copper alloy may advantageously undergo at least one heat treatment at from 300 to 500° C. The material is thereby strengthened owing to the spinoidal demixing which takes place.
In a preferred configuration of the invention, the multicomponent copper alloy may undergo at least one heat treatment at from 600 to 800° C. The heat treatment in this range leads to homogenization, which makes the material more ductile.
In a particularly preferred configuration of the invention, the multicomponent copper alloy may undergo a combination of at least one solution anneal at from 600 to 800° C. and at least one age hardening at from 300 to 500° C. The material is thereby strengthened owing to the spinoidal demixing which takes place. The heat treatment in this range leads to homogenization, which makes the material softer. Owing to a homogenizing anneal and the hardening of the material during age hardening or rolling, the material properties of the multicomponent copper alloy can be adapted optimally to the respective task.
In another preferred configuration, the multicomponent copper alloy may be employed for friction-bearing elements or jack connectors.
Exemplary embodiments of the invention will be explained in more detail with the aid of the following example and the scanning electron microscope image shown in
In series of tests, blocks with various Mn—Si ratios were cast and subsequently cold-processed further. The alloy variants studied are collated in Table 1. The cast blocks were homogenized in the temperature range of between 700 and 800° C. and then milled.
Strips with thicknesses of between 2.5 and 2.85 mm were produced by a plurality of cold forming operations and intermediate anneals. The strips were cold-rolled and annealed in the temperature range of between 700 and 800° C., in order to achieve sufficient cold forming properties.
According to expectation, it was confirmed that the cold formability of the Cu—Ni—Sn alloy modified with silicides is somewhat less than in the case of a Cu—Ni—Sn alloy without further silicide phases.
Such strips may be combined in a further method step to form a firm material composite by roll-cladding methods. Cu—Ni—Sn alloys modified with suicides have a much lower coefficient of friction compared with the silicide-free variant. The alloy according to the invention is therefore suitable in particular as a primary material for use as a friction-bearing element (bushings, thrust rings, etc.) in the respective automotive field for motors, transmissions and hydraulics.
The composition of the silicides need not necessarily correspond to a predetermined stoichiometry. Depending on the process management, and in particular determined by the cooling rate, ternary intermetallic phases precipitate in the form of silicides of the (Mn,Ni)xSi type, which lie in the range between the limiting-case binary phases Mn5Si3 and Ni2Si.
The mechanical properties of strips of the multicomponent copper alloy containing silicides in the rolling-hardened state had a tensile strength Rm of 560 MPa and a yield point of 480 MPa with an elongation at break A5 of 25%. The hardness HB was about 176.
After age hardening the strips, a tensile strength Rm of 715 MPa and a yield point Rp0.2 of 630 MPa with an elongation at break A5 of 17% were found. The hardness HB was about 235.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 019 827.1 | Apr 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/003688 | 4/26/2007 | WO | 00 | 1/26/2009 |
