Patent Application
20190062875
The present invention relates to a tin-containing copper alloy having excellent hot formability and cold formability, high resistance to abrasive wear, adhesive wear and fretting wear and improved corrosion resistance and stress relaxation resistance according to the preamble of any of claims 1 to 3, to a process for production thereof according to the preamble of claims 9 to 10, and to the use thereof according to the preamble of claims 16 to 18.
Owing to the tin alloy component, copper-tin alloys feature high-strength and hardness. Moreover, copper-tin alloys are considered to be corrosion-resistant and seawater-resistant.
This group of materials has high resistance to abrasive wear. Moreover, the copper-tin alloys ensure good sliding properties and high fatigue endurance limit, which results in excellent suitability for sliding elements and sliding surfaces in engine and vehicle construction and in mechanical engineering in general. Frequently, an addition of lead is added to the copper-tin alloys for slide bearing applications for improvement of the dry-running operation properties and machinability.
Copper-tin alloys find wide use in the electronics and telecommunications industry. They have an electrical conductivity that is frequently still adequate, and good to very good spring properties. The adjustment of the spring properties requires excellent cold formability of the materials.
In the music industry, percussion instruments are preferably produced from copper-tin alloys owing to their exceptional sound properties. The production of these cymbals requires very good hot formability of the materials. Two types of copper-tin alloys in particular, with 8% and 20% by weight of tin, are in wide use.
In the first production step, casting, the copper-tin materials, owing to their broad solidification interval, have a particularly high tendency to absorb gas with subsequent pore formation and to show segregation phenomena. The Sn-rich segregations can be eliminated only to a limited degree by a homogenization annealing operation that follows the casting process. The propensity of the copper-tin alloys to form pores and segregations increases with rising Sn content.
The element phosphorus is added to the copper-tin alloys in order to sufficiently deoxidize the melt. However, phosphorus additionally extends the solidification interval of copper-tin alloys, which results in elevated proneness to pores and segregations in this material group.
For this reason, documents DE 41 26 079 C2 and DE 197 56 815 C2, for the primary forming of copper-tin alloys, as well as the process of spray compaction, favor thin strip casting. In this way, by means of exact adjustment of the solidification rate of the melt, it is possible to produce a low-segregation preform having a fine and homogeneous distribution of the Sn-rich δ phase for the subsequent hot forming operation.
Document DE 581 507 A gives a pointer in principle as to how pure copper-tin alloys having 14% to 32% by weight of Sn and copper- and tin-present alloys having 10% to 32% by weight of Sn can be rendered hot-formable. What is proposed is heating of the alloy to a temperature of 820 to 970° C. with subsequent very slow cooling to 520° C. The duration of this cooling should be at least 5 hours. Cooling to room temperature at normal cooling rate may be followed by the hot forming of the material at 720 to 920° C.
Document DE 704 398 A gives a description of a process for producing shaped pieces from copper-tin alloys containing 6% to 14% by weight of Sn, more than 0.1% by weight of P, preferably 0.2% to 0.4% by weight of P, which may be replaced by silicon, boron or beryllium. Preferably, the copper-tin alloy contains about 91.2% by weight of Cu, about 8.5% by weight of Sn and about 0.3% P. Before final processing by cold forming or hot forming, the castings are accordingly homogenized at a temperature below 700° C. until the dissolution of the tin- and phosphorus-enriched eutectoids.
The significance of crystallization seeds for the formation of a fine-grain microstructure having a low proportion of Sn-rich segregations for the hot formability of Sn-containing copper alloys is emphasized in documents U.S. Pat. No. 2,128,955 A and DE 25 36 166 A1. Phosphidic compounds constitute the crystallization seeds, which achieves tempering of the cast structure and lowers the formation of low-melting copper-phosphorus or copper-phosphorus-tin phases to a minimum degree. This is said to give a crucial improvement in hot formability.
As a result of rising operating temperatures and pressures in modern engines, machines, installations and aggregates, a wide variety of different mechanisms of damage to the individual system elements occurs. Thus, there is an ever greater necessity, especially in the case of the design of sliding elements and plug connectors from the point of view of materials and construction, to take account not only of the types of sliding wear but also of the mechanism of damage by oscillating friction wear.
Oscillating friction wear, also called fretting in the jargon, is a kind of friction wear that occurs between oscillating contact faces. In addition to the geometry and/or volume wear of the components, the reaction with the surrounding medium results in friction corrosion. The damage to the material can distinctly lower local strength in the wear zone, especially fatigue strength. Fatigue cracks can proceed from the damaged component surface, and these lead to fatigue fracture/fatigue failure. Under friction corrosion, the fatigue strength of a component can drop well below the fatigue index of the material.
Oscillating friction wear differs considerably in its mechanism from the types of sliding wear with movement in one sense. More particularly, the effects of corrosion are particularly marked in the case of oscillating friction wear.
Document DE 10 2012 105 089 A1 describes the consequences of damage caused by oscillating friction wear of slide bearings. The operation of indenting the slide bearing into the bearing seat builds up high stress on the slide bearing, which is even further increased by the thermal expansions and by the dynamic shaft loads in modern engines. The changes in geometry of the slide bearing as a result of the excessive increase in stress enable micro-movements of the slide bearing relative to the bearing seat. The cyclical relative movements with low oscillation width at the contact faces between bearing and bearing seat lead to oscillation friction wear/friction corrosion/fretting of the backing of the slide bearing. The consequence is the initiation of cracks and ultimately the friction fatigue failure of the slide bearing.
In engines and machines, electrical plug connectors are frequently disposed in an environment in which they are subjected to mechanical oscillating vibrations. If the elements of a connection arrangement are present in different assemblies that perform relative movements to one another as a result of mechanical stresses, the result can be corresponding relative movement of the connection elements. These relative movements lead to oscillating friction wear and to friction corrosion of the contact zone of the plug connectors. Microcracks form in this contact zone, which greatly reduces the fatigue resistance of the plug connector material. Failure of the plug connector through fatigue failure can be the consequence. Moreover, owing to friction corrosion, there is a rise in the contact resistance.
To reduce these forms of damage, document DE 10 2007 010 266 B3 proposes equipping every wire connected to the plug connector with a means of strain relief by construction means, as a result of which the movements of the wire can no longer affect the plug connector.
Document DE 39 32 536 C1 contains a method by which the friction corrosion characteristics of plug connectors can be improved from a material point of view. For instance, a contact material composed of a silver, palladium or palladium/silver alloy having a content of 20% to 50% by weight of tin, indium and/or antimony has been applied to a carrier made of bronze, for example. The silver and/or palladium content ensures corrosion resistance. The oxides of tin, of indium and/or of antimony increase wear resistance. Thus, the consequences of friction corrosion can be countered.
A crucial factor for sufficient resistance to oscillating friction wear/friction corrosion is accordingly a combination of the material properties of wear resistance, ductility and corrosion resistance.
Document DE 36 27 282 A1 describes the mechanisms of crystallization of a metallic melt. If only a small number of crystallization seeds is present or if only a small number of seeds is formed in the melt, the consequence is a coarse-grain, high-segregation and often dendritic solidified microstructure. A copper alloy having 0.1% to 25% by weight of calcium and 0.1% to 15% by weight of boron is named, which can be added to the melt of copper materials for grain refinement. In this way, the addition of crystallizers generates a homogeneous and fine-grain solidified microstructure in copper alloys.
Alloying with metalloids, for example boron, silicon and phosphorus, achieves the lowering of the relatively high base melt temperature, which is important from a processing point of view. In the coating and high-temperature materials of the Ni—Si—B and Ni—Cr—Si—B systems, particularly the boron and silicon alloy elements are considered to be responsible for the significant lowering of the melting temperature of nickel-base hard alloys, which makes it possible to use these as spontaneously flowing nickel-base hard alloys.
The lowering of the base melt temperature by the inclusion of boron in the alloy is utilized for copper-tin materials that find use as deposit welding material. For instance, document U.S. Pat. No. 3,392,017 A discloses an alloy having up to 0.4% by weight of Si, 0.02% to 0.5% by weight of B, 0.1% to 1.0% by weight of P, 4% to 25% by weight of Sn and a balance of Cu. The addition of boron and a very high content of phosphorus of not less than 0.1% by weight is said here to improve the spontaneous flow properties of the deposit welding alloy and the wettability of the substrate surface and make it unnecessary to use additional flux. A particularly high P content of 0.2% to 0.6% by weight is stipulated here, with an Si content of the alloy of 0.05% to 0.15% by weight. This underlines the primary requirement for the spontaneous flow properties of the material. With this high P content, however, the possibilities of hot formability of the alloy are highly restricted.
Document DE 102 08 635 B4 describes the processes in a diffusion soldering site in which there are intermetallic phases. By means of diffusion soldering, the intention is to bond parts having a different coefficient of thermal expansion to one another. In the event of thermomechanical stress on this soldering site or in the soldering operation itself, great stresses occur on the interfaces, which can lead to cracks particularly in the environment of the intermetallic phases. A remedy proposed is mixing of the soldering components with particles that bring about balancing of the different coefficients of expansion of the joining partners. For instance, particles of boron silicates or phosphorus silicates, owing to their advantageous coefficients of thermal expansion, can minimize thermomechanical stress in the solder bond. Moreover, spreading of the cracks already induced is hindered by these particles.
Laid-open specification DE 24 40 010 B2 emphasizes the influence of the element boron particularly on the electrical conductivity of a cast silicon alloy having 0.1% to 2.0% by weight of boron and 4% to 14% by weight of iron. In this Si-based alloy, a high-melting Si—B phase precipitates out, which is referred to as silicon boride.
The silicon borides, which are usually present in the SiB3, SiB4, SiB6 and/or SiBn modifications that are determined by the boron content, differ significantly from silicon in their properties. These silicon borides have metallic character, and are therefore electrically conductive. They have exceptionally high thermal stability and oxidation stability. The SiB6 modification which is used with preference for sintered products, owing to its very high hardness and its high abrasive wear resistance, is used in ceramics production and ceramics processing, for example.
It is an object of the invention to provide a copper-tin alloy that has excellent hot formability over the entire tin content range.
For hot forming, it is possible to use a precursor material that has been produced without the absolute necessity of performance of spray compaction or of thin belt casting by means of conventional casting methods.
The copper-tin alloy should be free of gas pores and shrinkage pores and stress cracks, and should be characterized by a microstructure having homogeneous distribution of the Sn-rich δ phase which is present according to the Sn content of the alloy. The cast state of the copper-tin alloy need not necessarily first be homogenized by means of a suitable annealing treatment in order to be able to establish adequate hot formability. Even the casting material should feature high strength, high hardness and high corrosion resistance. By means of further processing, comprising an annealing operation or a hot forming and/or cold forming operation with at least one annealing operation, a fine-grain microstructure with high strength, high hardness, high stress relaxation resistance and corrosion resistance, high electrical conductivity, and with a high degree of complex wear resistance should be established.
The invention is described with regard to a copper-tin alloy by the features of any of claims 1 to 3, with regard to a production process by the features of claims 9 to 10, and with regard to a use by the features of claims 16 to 18. The further dependent claims relate to advantageous forms and developments of the invention.
The invention includes a high-strength tin-containing copper alloy having excellent hot formability and cold formability, high resistance to abrasive wear, adhesive wear and fretting wear and improved corrosion resistance and stress relaxation resistance, consisting of (in % by weight):
In addition, the invention includes a high-strength tin-containing copper alloy having excellent hot formability and cold formability, high resistance to abrasive wear, adhesive wear and fretting wear and improved corrosion resistance and stress relaxation resistance, consisting of (in % by weight):
As a result of the homogeneous distribution of the Sn-rich δ phase in island form and/or in network form, the microstructure is free of Sn-rich segregations. Sn-rich segregations of this kind are understood to mean accumulations of the δ phase in the cast microstructure that take the form of what are called inverse block segregations and/or particle boundary segregations which cause damage to the microstructure in the form of cracks under thermal and/or mechanical stress on the casting, which can lead to fracture. The microstructure after casting is still free of gas pores and shrinkage pores and of stress cracks.
In this variant, the alloy is in the cast state.
In addition, the invention includes a high-strength tin-containing copper alloy having excellent hot formability and cold formability, high resistance to abrasive wear, adhesive wear and fretting wear and improved corrosion resistance and stress relaxation resistance, consisting of (in % by weight):
Preferably, the Sn-rich δ phase is at least 1% by volume.
In the further-processed state, the Sn-rich 5 phase is distributed homogeneously in the microstructure in the form of islands and/or a network and/or extended lines. In this variant, the alloy is in the further-processed state.
In the case of the alloy variants, the invention proceeds from the consideration that a tin-containing copper alloy in the cast state and also in the further-processed state having Si-containing and B-containing phases is provided, which can be produced by means of the sandcasting, shell mold casting, precision casting, full mold casting, pressure diecasting and permanent mold casting process or with the aid of the continuous or semicontinuous strand casting process. The use of primary forming techniques, which are costly and inconvenient from a processing point of view, is possible but is not an absolute necessity for the production of the tin-containing copper alloy of the invention. For example, it is possible to dispense with the use of spray compaction. The cast formats of the tin-containing copper alloy of the invention can be hot-formed over the entire Sn content range, for example by hot rolling, extrusion or forging. Thus, the processing-related restrictions that have existed to date in the production of semifinished products and components from copper-tin alloys and that have led to the division of this group of materials into Cu—Sn kneading alloys and Cu—Sn casting alloys are largely eliminated.
The matrix of the microstructure of the tin-containing copper alloy in the cast state, with rising Sn content of the alloy, depending on the casting process, consists of increasing proportions of δ phase (Sn-rich) in otherwise a phase (Sn-deficient).
With rising Sn content of the alloy of the invention, there is not only an increase in the proportion of the δ phase in the microstructure, but also a change in the form of the arrangement of the δ phase in the microstructure. Thus, it has been found that, within the Sn content range from 4.0% to 9.0% by weight, the δ phase is distributed homogeneously in the microstructure with up to 40% by volume predominantly in island form. If the Sn content of the alloy is between 9.0% and 13.0% by weight, the island form of the δ phase present at up to 60% by volume in the microstructure is converted to the network form. This δ network is likewise distributed very homogeneously in the microstructure of the alloy. In the Sn content range from 13.0% to 17.0% by weight, the δ phase is present with up to 80% by volume virtually exclusively in the form of a homogeneous network in the microstructure. In the case of an Sn content of the alloy from 17.0% to 23.0% by weight, the proportion of the microstructure of the δ phase arranged in the form of a dense network in the microstructure is up to 98% by volume.
By means of the combined content of boron, silicon and phosphorus, various operations are activated in the melt of the alloy of the invention, which crucially alter the solidification characteristics thereof by comparison with the copper-tin and copper-tin-phosphorus alloys.
The elements boron, silicon and phosphorus assume a deoxidizing function in the melt. Thus, the formation of tin oxides in the tin-containing copper alloy is counteracted. The addition of boron and silicon makes it possible to lower the content of phosphorus without lowering the intensity of the deoxidation of the melt. Using this measure, it is possible to suppress the adverse effects of adequate deoxidation of the melt by means of a phosphorus addition. Thus, a high P content would additionally widen the solidification interval of the tin-containing copper alloy which is already very large in any case, which would result in an increase in the proneness of this material type to pores and segregations. Moreover, the result would be increased formation of the copper-phosphorus phase. This type of phase is considered to be a cause of the hot brittleness of the tin-containing copper alloys. The adverse effects of the addition of phosphorus are reduced by the limitation of the P content in the alloy of the invention to the range from 0.001% to 0.08% by weight.
The elements boron and silicon are of particular significance in the tin-containing copper alloy of the invention. Even in the melt, the phases of the Si-B systems precipitate out. These Si-B phases named as silicon borides may be present in the SiB3, SiB4, SiB6 and SiBn modifications. The symbol “n” in the latter modification is based on the fact that boron has a high solubility in the silicon lattice.
The Si-containing and B-containing phases which take the form of silicon borides are referred to hereinafter as hard particles. In the melt of the alloy of the invention, they assume the function of crystallization seeds during the solidification and cooling. As a result, it is no longer necessary to supply the melt with what are called extraneous seeds, the homogeneous distribution of which in the melt can be assured only to an inadequate degree.
The lowering of the base melt temperature particularly by the element boron and the existence of the hard particles that act as crystallization seeds lead to a crucial reduction in the size of the solidification interval of the alloy of the invention. As a result, the cast state of the invention, according to the Sn content, has a very homogeneous microstructure with a fine distribution of the δ phase in the form of homogeneously and densely arranged islands and/or in the form of a homogeneously dense network. Accumulations of the Sn-rich δ phase that take the form of what are called inverse block segregations and/or of grain boundary segregations cannot be observed in the cast microstructure of the invention.
In the melt of the alloy of the invention, the elements boron, silicon and phosphorus bring about a reduction of the metal oxides. The elements are themselves oxidized here and rise up to the surface of the castings, where, in the form of boron silicates, phosphorus silicates and/or boron phosphorus silicates, they form a protective layer that protects the castings from absorption of gas. Exceptionally smooth surfaces of the castings of the alloy of the invention have been found, which indicate the formation of such a protective layer. The microstructure of the cast state of the invention was also free of gas pores over the entire cross section of the castings.
A basic concept of the invention is the application of the effect of boron silicates and phosphorus silicates with regard to the balancing of the different coefficients of thermal expansion of the joining partners in diffusion soldering to the processes in the casting, hot forming and thermal treatment of the copper-tin materials. The broad solidification interval of these alloys results in great mechanical stresses between the Sn-deficient and Sn-rich structure regions that crystallize in an offset manner, which can lead to cracks and pores. In addition, these damage features can also occur in the course of hot forming and the high-temperature annealing operations on the copper-tin alloys owing to the different hot forming characteristics and the different coefficients of thermal expansion of the Sn-deficient and Sn-rich microstructure constituents.
The combined addition of boron, silicon and phosphorus to the tin-containing copper alloy of the invention results firstly in a homogeneous microstructure having a fine distribution of the microstructure constituents with different Sn content by means of the effect of the hard particles as crystallization seeds during the solidification of the melt. In addition to the hard particles, the boron silicates, phosphorus silicates and/or boron phosphorus silicates that form during the solidification of the melt, assure the necessary balancing of the coefficients of thermal expansion of the Sn-deficient and Sn-rich phases. In this way, the formation of pores and stress cracks between the phases having different Sn content is prevented.
Alternatively, the alloy of the invention can be subjected to further processing by annealing or by a hot forming and/or cold forming operation as well as at least one annealing operation.
The effect of the hard particles as crystallization seeds which, together with the boron silicates, phosphorus silicates and/or boron phosphorus silicates, bring about balancing of the coefficients of thermal expansion of the Sn-deficient and Sn-rich phases, was likewise observed during the operation of hot forming of the tin-containing copper alloy of the invention. In the course of hot forming, the hard particles serve as seeds for dynamic recrystallization. For this reason, the hard particles are considered to be responsible for the fact that dynamic recrystallization takes place in a favored manner in the hot forming of the alloy of the invention. This results in a further increase in the homogeneity and fine-grain structure of the microstructure.
In the same way as after the casting, an exceptionally smooth surface of the parts was also detected after the hot forming of the castings. This observation indicates the formation of boron silicates, phosphorus silicates and/or boron phosphorus silicates, which takes place in the material during the hot forming. The silicates and hard particles, during the hot forming as well, result in balancing of the different coefficients of thermal expansion of the Sn-deficient and Sn-rich constituents. Thus, the microstructure, as after the casting operation, was free of cracks and pores after the hot forming operation as well.
The role of the hard particles as seeds for the static recrystallization was found during annealing treatment after a cold forming operation. The major function of the hard particles as seeds for static recrystallization was manifested in the lowering of the necessary recrystallization temperature that had become possible, which additionally facilitates the establishment of a fine-grain microstructure of the alloy of the invention.
As a result, during the further processing of the alloy of the invention, higher degrees of cold forming are enabled, by means of which it is possible to establish particularly high values for tensile strength Rm, yield point Rp0.2 and hardness. The level of the parameter Rp0.2 in particular is important for the sliding elements and guide elements in internal combustion engines, valves, turbochargers, gears, exhaust gas aftertreatment systems, lever systems, braking systems and joint systems, hydraulic aggregates, or in machines and installations in mechanical engineering in general. In addition, a high value of Rp0.2 is a prerequisite for the necessary spring properties of plug connectors in electronics and electrical engineering.
The Sn content of the invention varies within the limits between 4.0% and 23.0% by weight. A tin content below 4.0% by weight would result in excessively low strength values and hardness values. Moreover, the running properties under sliding stress would be inadequate. The resistance of the alloy to abrasive and adhesive wear would not meet the requirements. In the case of an Sn content exceeding 23.0% by weight, there would be a rapid deterioration in the ductility properties of the alloy of the invention, which would lower the dynamic durability of the components made from the material.
As a result of the precipitation of the hard particles, the alloy of the invention has a hard phase component which, owing to the high hardness of the silicon borides, contributes to an improvement in the material resistance to abrasive wear. Moreover, the proportion of hard particles results in improved resistance to adhesive wear since these phases show a low tendency to wear with a metallic counterpart in the event of sliding stress. They thus serve as an important wear substrate in the tin-containing copper alloy of the invention. In addition, the hard particles increase the heat resistance and stress relaxation resistance of components of the invention. This constitutes an important prerequisite for the use of the alloy of the invention, especially for sliding elements and for components, wire elements, guide elements and connection elements in electronics/electrical engineering.
The formation of boron silicates, phosphorus silicates and/or boron phosphorus silicates in the alloy of the invention leads not only to a significant reduction in the pores and cracks in the microstructure. These silicatic phases also assume the role of a wear-protective and/or corrosion-protective coating on the components.
Thus, the alloy of the invention ensures a combination of the properties of wear resistance and corrosion resistance. This combination of properties leads to a high resistance, as required, against the mechanisms of friction wear and to a high material resistance against friction corrosion. In this way, the invention is of excellent suitability for use as a sliding element and plug connectors since it has a high degree of resistance to sliding wear and oscillating friction wear, called fretting.
The effect of the hard particles as crystallization seeds and recrystallization seeds, as wear substrates and the action of the silicatic phases for the purpose of corrosion protection can only achieve a degree of industrial significance in the alloy of the invention when the silicon content is at least 0.05% by weight and the boron content at least 0.005% by weight. If, by contrast, the Si content exceeds 2.0% by weight and/or the B content 0.6% by weight, this leads to a deterioration in the casting characteristics. The excessively high content of hard particles would make the melt crucially more viscous. Moreover, the result would be reduced ductility properties of the alloy of the invention.
The Si content range within the limits from 0.05% to 1.5% by weight and especially from 0.5% by weight to 1.5% by weight is assessed as being advantageous.
For the element boron, the content from 0.01% to 0.6% by weight is considered to be advantageous. The particularly advantageous boron content has been found to be from 0.1% to 0.6% by weight.
For the assurance of a sufficient content of hard particles and of boron silicates, phosphorus silicates and/or boron phosphorus silicates, the establishment of a specific element ratio of the elements silicon and boron has been found to be important. For this reason, the Si/B ratio of the element contents (in % by weight) of the elements silicon and boron of the alloy of the invention is between 0.3 and 10. An Si/B ratio of 1 to 10 and additionally of 1 to 6 has been found to be particularly advantageous.
The precipitation of hard particles affects the viscosity of the melt of the alloy of the invention. This fact additionally emphasizes why an addition of phosphorus is indispensable. The effect of phosphorus is that the melt is sufficiently mobile in spite of the content of hard particles, which is of great significance for the castability of the invention. The phosphorus content of the alloy of the invention is 0.001% to 0.08% by weight. An advantageous P content is within the range from 0.001% to 0.05% by weight.
The sum total of the element contents of the elements silicon, boron and phosphorus is advantageously at least 0.5% by weight.
Machine processing of the semifinished products and components made of the conventional copper-tin and copper-tin-phosphorus kneading alloys, especially with an Sn content up to about 9% by weight, is possible only with great difficulty owing to inadequate machinability. Thus, particularly the occurrence of long turnings causes long machine shutdown times since the turnings first have to be removed by hand from the processing area of the machine.
In the case of the alloy of the invention, by contrast, the hard particles, in the regions of which the element tin and/or the δ phase has crystallized or precipitated out according to the Sn content of the alloy, act as a turning breaker. The short friable turnings and/or entangled turnings that thus arise facilitate machinability, and for that reason the semifinished products and components made from the alloy of the invention have better machine processibility.
In an advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
In a further advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
In a particularly advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
In the cast microstructure of these embodiments of the invention, the Sn-rich δ phase is arranged homogeneously in island form at up to 40% by volume. The element tin and/or the δ phase here is usually crystallized in the regions of the hard particles and/or ensheaths these.
The castings of these embodiments have excellent hot formability at the working temperature in the range from 600 to 880° C. As a result of the dynamic recrystallization that has taken place, promoted by the hard particles, the microstructure of the embodiments has a very fine-grain structure after the hot forming operation. This results in very good cold formability with a degree of cold forming s of more than 40%.
The hard particles precipitated within the microstructure act as recrystallization seeds in the thermal treatment of the cold-formed material state at the temperature of 200 to 880° C. with a duration of 10 minutes to 6 hours. By means of this further processing step, it is possible to establish a microstructure having a grain size up to 20 μm. The favoring of the recrystallization mechanisms by the hard particles allows lowering of the recrystallization temperature, such that it is possible to produce a microstructure having a grain size down to 10 μm. By means of a multistage manufacturing process composed of cold forming and annealing operations and/or by means of a purpose-specific lowering of the recrystallization temperature, it is even possible to set the size of the crystallites in the material microstructure to below 5 μm.
The mechanical properties of some embodiments are representative of the entire range of alloy compositions and of the manufacturing parameters. The results of the study of corresponding working examples and those that are outlined hereinafter illustrate that it is possible to achieve values for tensile strength Rm of more than 700 to 800 MPa, values for yield point Rp0.2 of more than 600 to 700 MPa. At the same time, the ductility properties of the embodiments are at a very high level. This fact is expressed by the high values for elongation at break A5.
In an advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
In a further advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
In a particularly advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
The microstructure of these embodiments of the invention is characterized by a content of the δ phase of up to 60% by volume, this phase type being distributed homogeneously in the microstructure in island form and network form. Again, the element tin and/or the δ phase here is usually crystallized in the regions hard particles and/or ensheaths these.
The castings of these embodiments have excellent hot formability at the working temperature in the range from 600 to 880° C.
As a result of the dynamic recrystallization that has taken place, promoted by the hard particles, the microstructure of the embodiments has a very fine-grain structure after the hot forming operation. This results in very good cold formability, which can be further improved by accelerated cooling after hot forming under air or in water and/or by an annealing treatment after the hot forming operation at the temperature of 200 to 880° C. with a duration of 10 minutes to 6 hours. After the operating step of hot forming, the microstructure feature of the crystallization of the element tin and/or of the δ phase in the regions of the hard particles and/or the ensheathing of these hard particles with the element tin and/or the δ phase is more completely manifested with regard to the cast state.
The hard particles precipitated within the microstructure act as recrystallization seeds in the thermal treatment of the cold-formed material state at the temperature of 200 to 880° C. with a duration of 10 minutes to 6 hours. By means of this further processing step, it is possible to establish a finer-grain microstructure. The favoring of the recrystallization mechanisms by the hard particles allows lowering of the recrystallization temperature, such that it is possible to produce a microstructure having a further-reduced grain size. By means of a multistage manufacturing operation composed of cold forming and annealing operations, it is possible to further optimize the fine-grain structure of the microstructure.
In an advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
In a further advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
In a particularly advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
The δ phase in the cast microstructure of these embodiments of the invention is in the form of a homogeneously arranged network at up to 80% by volume. The element tin and/or the δ phase here is usually crystallized in the regions of the hard particles and/or ensheaths these.
The castings of these embodiments likewise have excellent hot formability at the working temperature in the range from 600 to 880° C. Specifically within this content range for the alloy element tin from 13.0% to 17.0% by weight, the conventional copper-tin alloys are hot-formable only with very great difficulty without the occurrence of heat cracks and heat fractures.
As a result of the dynamic recrystallization that has taken place, promoted by the hard particles, the microstructure of the embodiments has a very fine-grain structure after the hot forming operation. This gives rise to very good cold formability, which can be further improved with the performance of accelerated cooling of the semifinished products under air or in water after the hot forming and/or by an annealing treatment after the hot forming operation at the temperature of 200 to 880° C. with a duration of 10 minutes to 6 hours. After the operating step of hot forming, the microstructure feature of the crystallization of the element tin and/or of the δ phase in the regions of the hard particles and/or of the ensheathing of these hard particles with the element tin and/or the δ phase is more complete with regard to the cast state.
The hard particles precipitated within the microstructure act as recrystallization seeds in the thermal treatment of the cold-formed material state at the temperature of 200 to 880° C. with a duration of 10 minutes to 6 hours. By means of this further processing step, it is possible to establish a microstructure having a grain size of up to 30 μm. The favoring of the recrystallization mechanisms by the hard particles allows lowering of the recrystallization temperature, such that it is possible to produce a microstructure having a grain size of up to 15 μm. The network-like arrangement of the δ phase in the microstructure is conserved.
By means of a multistage manufacturing operation composed of cold forming and annealing operations and/or a purpose-specific lowering of the recrystallization temperature, it is even possible to adjust the size of the crystallites in the material microstructure to below 5 μm.
In an advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
In a further advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
In a particularly advantageous embodiment of the invention, the tin-containing copper alloy may consist of (in % by weight):
A very dense network of the δ phase in a homogeneous arrangement with up to 98% by volume in the cast microstructure is a feature of the embodiments of the invention. The element tin and/or the δ phase usually crystallizes here in the regions of the hard particles and/or ensheaths these.
As a result of the homogeneity of the dense δ phase, the castings of these embodiments likewise have excellent hot formability at the working temperature in the range from 600 to 880° C.
During the adhesive wear stress on a component made of the tin-containing copper alloy of the invention, the alloy element tin makes a particular contribution to the formation of what is called a tribological layer between the friction partners. Particularly under mixed friction conditions, this mechanism is important when the dry-running properties of a material come increasingly to the forefront. The tribological layer leads to a decrease in size of the purely metallic contact area between the friction partners, which prevents welding or seizing of the elements.
Owing to the increase in efficiency of modern engines, machines and aggregates, ever higher operating pressures and operating temperatures are occurring. This is to be observed particularly in the newly developed internal combustion engines where the aim is ever more complete combustion of the fuel. In addition to the elevated temperatures within the chamber of the internal combustion engines, there is also the evolution of heat that occurs during the operation of the slide bearing systems. Owing to the high temperatures in bearing operation, in the parts made of the alloy of the invention, similarly to the case of the casting operation and the hot forming operation, there is formation of boron silicates, phosphorus silicates and/or boron phosphorus silicates. These compounds strengthen the tribological layer, which results in enhanced adhesive wear resistance of the sliding elements made of the alloy of the invention.
Even during the casting operation of the invention, there is precipitation of the hard particles in the microstructure. These hard phases protect the material from the consequences of abrasive wear stress, i.e. from removal of material by scoring wear. In addition, the hard particles have a low tendency to welding with the metallic friction partner, and therefore, together with the tribological layer of complex structure, they assure high adhesive wear resistance of the invention.
As well as their function as wear substrates, the hard particles have higher thermal stability of the microstructure of the copper alloy of the invention. This results in high heat resistance and an improvement in the stability of the material against stress relaxation.
In the cast variant and the further-processed variant of the alloy of the invention, the following optional elements may be present:
The element zinc may be added to the tin-containing copper alloy of the invention with a content from 0.1% to 2.0% by weight. It was found that the alloy element zinc, depending on the Sn content of the alloy, increases the proportion of Sn-rich phases in the invention, which results in an increase in strength and hardness. However, it was not possible to find any pointers that addition of zinc has a positive effect on the homogeneity of the microstructure and on the further decrease in the content of pores and cracks in the microstructure. It is obvious that the influence of the combined alloy content of boron, silicon and phosphorus in this regard is predominant. Below 0.1% by weight of Zn, no strength- and hardness-enhancing effect was observed. In the case of Zn contents above 2.0% by weight, the toughness properties of the alloy were lowered to a lower level. Moreover, there was a deterioration in the corrosion resistance of the tin-containing copper alloy of the invention. Advantageously, a zinc content in the range from 0.5% to 1.5% by weight can be added to the invention.
For a further improvement in the mechanical material properties of strength and hardness and in stress relaxation resistance at elevated temperatures, the alloy elements iron and magnesium can be added individually or in combination.
The alloy of the invention may contain 0.01% to 0.6% by weight of iron. In the microstructure, therefore, there is up to 10% by volume of Fe borides, Fe phosphides and Fe silicides and/or Fe-rich particles. In addition, in the microstructure, there is formation of addition compounds and/or mixed compounds of the Fe-containing phases and of the Si-containing and B-containing phases. These phases and compounds contribute to an increase in strength, in hardness, in heat resistance, in stress relaxation resistance, in electrical conductivity, and to an improvement in the resistance to abrasive and adhesive wear stress on the alloy. In the case of an Fe content below 0.01% by weight, this improvement in properties is not achieved. If the Fe content exceeds 0.6% by weight, there is the risk of cluster formation of the iron in the microstructure. This would be associated with a crucial deterioration in the processing properties and the use properties.
In addition, the element magnesium may be added to the alloy of the invention from 0.01% to 0.5% by weight. In this case, in the microstructure, up to 15% by volume of Mg borides, Mg phosphides and Cu—Mg phases and Cu—Sn—Mg phases are present. In addition, in the microstructure, there is formation of addition compounds and/or mixed compounds of the Mg-containing phases and of the Si-containing and B-containing phases. These phases and compounds likewise contribute to an increase in strength, in hardness, in heat resistance, in stress relaxation resistance, in electrical conductivity, and to an improvement in the resistance to abrasive and adhesive wear stress on the alloy. In the case of an Mg content below 0.01% by weight, this improvement in properties is not achieved. If the Mg content exceeds 0.5% by weight, there is a deterioration in the castability of the alloy in particular. Moreover, the excessively high content of Mg-containing compounds would worsen the toughness properties of the alloy of the invention to a crucial degree.
The tin-containing copper alloy may or may not include small proportions of lead. Lead contents that are still just acceptable and above the contamination limit here are up to a maximum of 0.25% by weight. In a particularly preferred advantageous embodiment of the invention, the tin-containing copper alloy is free of lead apart from any unavoidable impurities. In this connection, lead contents up to a maximum of 0.1% by weight of Pb are contemplated.
A particular advantage of the invention is considered to be the substantial freedom of the microstructure from gas pores and shrinkage pores, craters, segregations and cracks in the cast state. This results in the particular suitability of the alloy of the invention as an antiwear layer which is melted, for example, onto a main body made of steel. The alloy composition of the invention can suppress the formation of open porosity in particular in the melting process, which increases the compressive strength of the sliding layer.
A further particular advantage of the invention is the elimination of the absolute necessity of performing a specific primary forming technique, for example that of spray compaction or of thin strip casting, for provision of a homogeneous, substantially pore-free and segregation-free microstructure. For the establishment of such a microstructure, it is possible to use conventional casting methods for the primary forming operation of the alloy of the invention. Thus, one aspect of the invention includes a process for producing end products or components in near-end-product form from the tin-containing copper alloy of the invention with the aid of the sandcasting process, shell mold casting process, precision casting process, full mold casting process, pressure diecasting process or lost foam process.
Moreover, one aspect of the invention includes a process for producing strips, sheets, plates, bolts, round wires, profile wires, round bars, profile bars, hollow bars, pipes and profiles from a tin-containing copper alloy of the invention with the aid of the permanent mold casting process or the continuous or semicontinuous strand casting process.
It is remarkable that, after the permanent mold casting or strand casting of the formats from the alloy of the invention, there is also no need to conduct any complex forging processes and/or indentation processes at elevated temperature in order to weld, i.e. to close, pores and cracks in the material.
Moreover, in the invention, for assurance of sufficient hot formability, it is no longer absolutely necessary to more finely distribute the Sn-rich δ phase, which is present according to the Sn content, in the microstructure or to dissolve it by homogenization annealing or solution annealing, and hence to eliminate it. The δ phase which is in any case homogeneously and finely distributed in the cast microstructure of the alloy of the invention with an appropriate Sn content assumes an essential function for the use properties of the alloy.
In a preferred configuration of the invention, the further processing of the cast state may include the performance of at least one hot forming operation within the temperature range from 600 to 880° C.
Advantageously, the semifinished products and components after the hot forming can be cooled down using calmed or accelerated air or with water.
Advantageously, at least one annealing treatment of the cast state and/or of the hot-formed state of the invention can be conducted within the temperature range from 200 to 880° C. with the duration of 10 minutes to 6 hours, or alternatively with cooling using calmed or accelerated air or with water.
One aspect of the invention relates to an advantageous method of further processing of the cast state or of the hot-formed state or of the annealed cast state or of the annealed hot-formed state, which comprises the performance of at least one cold forming operation.
Preferably, at least one annealing treatment of the cold-formed state of the invention can be conducted within the temperature range from 200 to 880° C. with the duration of 10 minutes to 6 hours.
Advantageously, a stress relief annealing/age annealing operation can be conducted within the temperature range from 200 to 650° C. with the duration of 0.5 to 6 hours.
The matrix of the homogeneous microstructure of the invention consists of ductile α phase with, according to the Sn content of the alloy, of proportions of the δ phase. By virtue of its high strength and hardness, the δ phase leads to high resistance of the alloy to abrasive wear. Moreover, the δ phase, owing to its high Sn content, which results in its tendency to form a tribological layer, increases the resistance of the material to adhesive wear. The hard particles are intercalated in the metallic base material. In further executions of the invention, there are additionally Fe- and/or Mg-containing phases in the metallic base material.
This heterogeneous microstructure consisting of a metallic base material composed of α and δ phase, in which precipitates of high hardness are intercalated, imparts an excellent combination of properties to the subject matter of the invention. The following should be mentioned in this connection: high strength values and hardness values with simultaneously good toughness, excellent hot formability, adequate cold formability, high thermal stability of the microstructure with resulting high heat resistance and high stress relaxation resistance, adequate electrical conductivity for many applications, high corrosion resistance and high resistance to the wear mechanisms of abrasion, adhesion, surface breakup and to oscillating friction wear, called fretting.
Owing to the homogeneous and fine-grain microstructure with substantial freedom from pores, freedom from cracks and freedom from segregations and the content of hard particles, the alloy of the invention, even in the cast state, has a high degree of strength, hardness, ductility, complex wear resistance and corrosion resistance. For this reason, the alloy of the invention, even in the cast state, has a wide spectrum of use.
The result is the particular suitability of the alloy of the invention as an antiwear layer which is melted, for example, onto a main body made of steel. In this regard, it should be emphasized that the treatment temperatures for quenched and tempered steels (hardening 820 to 860° C., annealing 540 to 660° C.; DIN EN 10083-1) are within the heat treatment range of the invention. This means that, after the melting of the tin-containing copper alloy onto a main body made of quenched and tempered steel, the mechanical properties of the two composite partners can be optimized in just one treatment step. A further advantage is that, in the melting operation, the formation of open porosity is suppressed, which increases the compressive strength of the antiwear layer.
Apart from melting, there are also further useful joining methods. In this connection, composite production by means of forging, soldering or welding would also be conceivable, with the optional performance of at least one annealing operation within the temperature range from 200 to 880° C. It is likewise possible to produce, for example, bearing composite shells or bearing composite bushings by roll cladding, inductive or conductive roll cladding or by laser roll cladding.
Even the cast formats in strip form, sheet form, plate form, bolt form, wire form, rod form, tube form or profile form can be used to produce sliding elements and guide elements in internal combustion engines, valves, turbochargers, gears, exhaust gas aftertreatment systems, lever systems, braking systems and joint systems, hydraulic aggregates, or in machines and installations in mechanical engineering in general. By means of further processing of the cast state, it is possible to produce semifinished products and components having complicated geometry and enhanced mechanical properties and optimized wear properties for these end uses. This takes account of the elevated component demands under dynamic stress.
A further aspect of the invention includes use of the tin-containing copper alloy of the invention for components, wire elements, guiding elements and connecting elements in electronics/electrical engineering.
By virtue of the excellent strength properties and the wear resistance and corrosion resistance of the tin-containing copper alloy of the invention, there is a further possible use. Thus, the invention is suitable for the metallic articles in constructions for the breeding of seawater-dwelling organisms (aquaculture). A further aspect of the invention includes use of the tin-containing copper alloy of the invention for propellers, wings, marine propellers and hubs for shipbuilding, for housings of water pumps, oil pumps and fuel pumps, for guide wheels, runner wheels and paddle wheels for pumps and water turbines, for gears, worm gears, helical gears and for forcing nuts and spindle nuts, and for pipes, seals and connection bolts in the maritime and chemical industry.
For the use of the alloy of the invention for production of percussion instruments, the material is of great significance. Especially cymbals of high quality are manufactured from tin-containing copper alloys by means of hot forming and at least one annealing operation before they are converted to the final shape, usually by means of a bell or shell. Subsequently, the symbols are annealed once again before the material-removing final processing thereof. The production of the various variants of the cymbal, for example ride cymbals, hi-hats, crash cymbals, china cymbals, splash cymbals and effect cymbals, accordingly requires particularly advantageous hot formability of the material, which is assured by the alloy of the invention. Within the range limits of the chemical composition of the invention, different microstructure components for the δ phase and for the hard particles can be set within a very wide range. In this way, it is possible even from an alloy point of view to affect the sound characteristics of the cymbals.
Further important working examples of the invention are elucidated in tables 1 to 11. Cast blocks of the tin-containing copper alloy of the invention were produced by permanent mold casting. The chemical composition of the castings is apparent from tab. 1 and 3.
Tab. 1 shows the chemical composition of alloy variants 1 and 2. These materials are characterized by an Sn content of 7% by weight, a P content of 0.015% by weight and by a different element ratio of the elements silicon and boron, and a balance of copper.
After the casting, the microstructure of working examples 1 and 2 is shaped by a very homogeneous, mostly island-like distribution of a comparatively small proportion of the δ phase (about 15 to 20% by volume) and of the hard particles. The microstructure of the cast state of alloy 1 is shown in
The hardness of these types of alloy is 105 HB for alloy 1 and 98 HB for alloy 2 (tab. 2).
Tab. 3 shows the chemical composition of a further alloy variant 3. This material contains, as well as about 15% by weight of Sn and 0.024% by weight of P, the further elements Si (0.77% by weight) and boron (0.20% by weight).
One characteristic feature of the invention is that the microstructure in the cast state, with rising Sn content of the alloy, depending on the casting/cooling operation, consists of increasing proportions of δ phase. The arrangement of this Sn-rich δ phase is transformed from a finely distributed island form, with increasing Sn content of the alloy, to a dense network form. In the cast microstructure of alloy type 3, the S phase is present with a distinctly higher content (up to about 70% by volume). This microstructure is shown in
The increase in hardness of the material with rising Sn content is expressed by the distinctly higher value of 190 HB of alloy 3 (tab. 4).
One aspect of the invention relates to a process for production of strips, sheets, plates, bolts, wires, bars, profile bars, hollow bars, pipes and profiles from the tin-containing copper alloy of the invention with the aid of the permanent mold casting process or the continuous or semicontinuous strand casting process.
The alloy of the invention can additionally be subjected to further processing. This firstly enables the production of particular and often complicated geometries. Secondly, in this way, the demand for an improvement in the complex operating properties of the materials, particularly for wear-stressed components and for components and connection elements in electronics/electrical engineering is met, since there is a significant increase in stress on the system elements in the corresponding machines, engines, gears, aggregates, constructions and installations. In the course of this further processing, a significant improvement in the toughness properties and/or a significant increase in tensile strength R., yield point Rp0.2 and hardness is achieved.
Owing to the excellent hot formability of the alloy of the invention, the further processing of the cast state can advantageously include the performance of at least one hot forming operation within the temperature range from 600 to 880° C. By means of hot rolling, it is possible to produce plates, sheets and strips. Extrusion enables the manufacture of wires, rods, tubes and profiles. Finally, forging processes are suitable for producing near-end-shape components with complicated geometry in some cases.
A further advantageous means of further processing the cast state or the hot-formed state or the annealed cast state or the annealed hot-formed state comprises the performance of at least one cold forming operation. In particular, this process step significantly increases the material indices Rm, Rp0.2 and the hardness. This is important for applications where there is mechanical stress and/or intense abrasive and/or adhesive wear stress on the components. In addition, the spring properties of the components made of the alloy of the invention are significantly improved as a result of a cold forming operation.
For corresponding recrystallization of the microstructure of the invention after a cold forming operation, it is possible to conduct at least one annealing treatment within a temperature range from 200 to 880° C. with the duration of 10 minutes to 6 hours. The very fine-grain structure that thus forms is an important prerequisite for establishing the combination of properties of high-strength and hardness and of sufficient toughness of the material.
For lowering of the residual stresses of the components, it is advantageously additionally possible to conduct a stress relief/age annealing operation within a temperature range from 200 to 650° C. with the duration of 0.5 to 6 hours.
For the fields of use having particularly severe complex component stress, it is possible to choose a further processing operation comprising at least one cold forming operation or the combination of at least one hot forming operation and at least one cold forming operation in conjunction with at least one annealing operation within a temperature range from 200 to 800° C. with the duration of 10 minutes to 6 hours and leads to a recrystallized microstructure of the alloy of the invention. The fine-grain structure of the alloy established in this way assures a combination of high strength, high hardness and good toughness properties. In addition, for lowering of the residual stresses of the components, a stress relief annealing treatment within the temperature range from 200 to 650° C. with the duration of 0.5 to 6 hours is possible.
For manufacture of semifinished products in strip form from working examples 1 and 2 (tab. 1), three different production sequences were selected. They differ primarily in the number of cold forming/annealing cycles and in the level of the degrees of cold forming and annealing temperatures employed (tab. 5).
After the permanent mold casting and the hot rolling, the corresponding blocks or semifinished products are characterized by an exceptionally smooth surface. As a result of the dynamic recrystallization of the microstructure that has taken place during the hot rolling operation, the hot-formed state of both alloy variants 1 and 2 has excellent cold formability. Thus, it was possible to cold-roll the hot-rolled plates without cracking with a cold-forming of about 70%.
In the course of manufacture 1, the cold-rolled strips were annealed at the temperature of 280° C. with a duration of 2 h. The indices of the strips thus subjected to stress relief are apparent from tab. 6. In spite of high strength and hardness values, the strips of both alloys have extremely good toughness properties as measured by the high values for elongation at break A5.
An indication of the importance of the Si/B element ratio of the elements silicon and boron is given by the comparison of the individual data for the strips made from alloys 1 and 2. Owing to the higher Si/B ratio of alloy 1 of about 2.5, the boron silicates, phosphorus silicates and/or boron phosphorus silicates are formed to an enhanced degree during the casting and during the thermal and thermomechanical production steps. For this reason, in various tests, the superiority of alloy 1 with regard to the corrosion resistance by comparison with alloy 2 was established. In addition, the values for Rm and Rp0.2 of the strips made from alloy 1 are at a much higher level. As a result of the lower Si/B ratio at about 0.5, a higher Si content was bound in the hard particles in the microstructure of alloy 2. This results particularly in a higher electrical conductivity and increased elongation at break A5, which results in better ductility of the alloy 2. Even the results from the manufacture 1 suggest that the properties can be matched exactly to the respective fields of use with a variation of the chemical composition of the invention.
In the course of manufacture 2, the strips of alloy variants 1 and 2, after the first cold rolling operation, were annealed at 680° C. for 3 hours. This was followed by the cold rolling of the strips with a cold-forming ϵ of about 60%. To complete the manufacture, the strips were subjected to thermal stress relief at different temperatures between 280 and 400° C. The indices of the resulting material states are listed in tab. 7.
In the same way as after manufacture 1, the states of working example 1 show the higher strength values, whereas working example 2 features higher values for electrical conductivity and for elongation at break A5. Furthermore, it can be inferred from tab. 7 that the microstructure of the strips subjected to stress relief at 280° C. include deformation features, and therefore no value can be reported for grain size. At about 340° C., the recrystallization of the microstructure sets in, which leads to a significant drop in strengths and in the hardness.
For this reason, in the course of manufacture 3, the annealing temperature after the first cold forming operation was lowered to 450° C. The annealing operation at this temperature for three hours was followed by the cold rolling of the strips with the cold-forming ϵ of about 30%. The final stress relief annealing for two hours at temperatures between 240 and 360° C. led to the indices shown in tab. 8.
The microstructure with 500-fold magnification of the final state of the strip of working example 1 that has been subjected to stress relief annealing at 240° C./2 h is shown in
The results point to a completely recrystallized microstructure having exceptionally high values for strength and hardness. Nevertheless, the high values for elongation at break A5 indicate the excellent ductility of the material states. After manufacture 3 as well, the strength values of the states of alloy 1 are above those of alloy 2. By contrast, the states of alloy 2 offer advantages with regard to elongation at break A5 and electrical conductivity.
The strips of working example 3 of the invention, the chemical composition of which can be found in tab. 3, were produced by the manufacturing program shown in tab. 9. The hot rolling of the permanent mold casting formats was effected at the temperature of 750° C. with subsequent cooling using calmed air in water. The advantage of accelerated cooling of the hot-formed semifinished product in water is manifested in the form of better cold formability. For instance, the hot-rolled strip that has been quenched in water can subsequently be cold-rolled with a cold-forming ϵ of 24%. By contrast, the strip that has been cooled under air after hot rolling permits only cold rolling with a cold-forming ϵ of about 5%.
The grain size and hardness of the cold-rolled state and of the cold-rolled and annealed state are shown in tab. 10. As a result of the annealing treatment, the microstructure properties balance out at a high level with rising annealing temperatures.
The microstructure of strip 3-A was finally heat-treated with the parameters Of 500° C./3 h+air and 600° C./3 h+air and is shown in
The strip 3-B was subjected to further processing with multiple cold rolling/annealing cycles. The indices of the final states that have been subjected to stress relaxation at different temperatures are listed in tab. 11.
With each cycle that consists of a cold rolling step and an annealing treatment, the microstructure of working example 3 of the invention is continually stretched in a linear manner. The linear arrangement of the very high 5 component, resulting from the high Sn content of the alloy, leads to high hardness values close to 300 HV1. At the same time, there is an increase in the brittle character of the alloy, which is expressed by the very low values for elongation at A11.3.
As a result, it can be concluded that the alloy of the invention has excellent castability and hot formability over the entire Sn content range from 4% to 23% Sn. Cold formability is also at a high level. However, there is naturally a deterioration in the ductility of the invention with rising Sn content owing to the rising 5 component of the microstructure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 002 618.9 | Mar 2016 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/000190 | 2/10/2017 | WO | 00 |
