Copper-nickel-tin alloy, method for the production thereof and use thereof

Abstract

A high-strength copper-nickel-tin alloy with excellent castability, hot workability and cold workability, high resistance to abrasive wear, adhesive wear and fretting wear and improved resistance to corrosion and stress relaxation stability, consisting of (in weight %): 2.0-10.0% Ni, 2.0-10.0% Sn, 0.01-1.5% Si, 0.002-0.45% B, 0.001-0.09% P, selectively up to a maximum of 2.0% Co, optionally also up to a maximum of 2.0% Zn, selectively up to a maximum of 0.25% Pb, the residue being copper and unavoidable impurities. The ratio Si/B of the element contents in wt. % of the elements silicon and boron is a minimum 0.4 and a maximum 8 such that the copper-nickel-tin alloy has Si-containing and B-containing phases and phases of the systems Ni—Si—B, Ni—B, Ni—P and Ni—Si, which significantly improve the processing properties and use properties of the alloy.

Claims

1. A copper-nickel-tin alloy consisting of (in % by weight): 2.0% to 10.0% Ni, 2.0% to 10.0% Sn, 0.01% to 1.5% Si, 0.002% to 0.45% B, 0.001% to 0.09% P, optionally up to a maximum of 2.0% Co, optionally up to a maximum of 2.0% Zn, optionally up to a maximum of 0.25% Pb, the balance being copper and unavoidable impurities, wherein the Si/B ratio of the element contents in % by weight of the elements silicon and boron is a minimum of 0.4 and a maximum of 8; the following microstructure constituents are present in the alloy after casting: a) a Si-containing and P-containing metallic base composition having, based on the overall microstructure, a1) up to 35% by volume of first phase constituents that can be reported by the empirical formula Cu.sub.hNi.sub.kSn.sub.m and have an (h+k)/m ratio of the element contents in atomic % of 2 to 6, a2) up to 15% by volume of second phase constituents that can be reported by the empirical formula Cu.sub.pNi.sub.rSn.sub.s and have a (p+r)/s ratio of the element contents in atomic % of 10 to 15, and a3) a balance of a solid copper solution; b) phases which, based on the overall microstructure, are present b1) at 0.01% to 10% by volume as Si-containing and B-containing phases, b2) at 1% to 15% by volume as Ni—Si borides having the empirical formula Ni.sub.xSi.sub.2B with x=4 to 6, b3) at 1% to 15% by volume as Ni borides, b4) at 1% to 5% by volume as Ni phosphides, and b5) at 1% to 5% by volume as Ni silicides in the microstructure, which are present individually and/or as addition compounds and/or mixed compounds and are ensheathed by tin and/or the first phase constituents and/or the second phase constituents; in the course of casting the Si-containing and B-containing phases in the form of silicon borides, the Ni—Si borides and the Ni borides, Ni phosphides and Ni silicides that are present individually and/or as addition compounds and/or mixed compounds constitute seeds for uniform crystallization during the solidification/cooling of the melt, such that the first phase constituents and/or the second phase constituents are distributed uniformly in the microstructure in the form of islands and/or in the form of a mesh; the Si-containing and B-containing phases that are in the form of boron silicates and/or boron phosphorus silicates, together with phosphorus silicates, assume the role of a wear-protecting and corrosion-protecting coating on semifinished materials and components of the alloy.

2. The copper-nickel-tin alloy as claimed in claim 1, wherein the elements nickel and tin are each present at 3.0% to 9.0%.

3. The copper-nickel-tin alloy as claimed in claim 1, wherein the element silicon is present at 0.05% to 0.9%.

4. The copper-nickel-tin alloy as claimed in claim 1, wherein the element boron is present at 0.01% to 0.4%.

5. The copper-nickel-tin alloy as claimed in claim 1, wherein the element phosphorus is present at 0.01% to 0.09%.

6. The copper-nickel-tin alloy as claimed in claim 1, wherein the alloy is free of lead apart from any unavoidable impurities.

7. A copper-nickel-tin alloy consisting of (in % by weight): 2.0% to 10.0% Ni, 2.0% to 10.0% Sn, 0.01% to 1.5% Si, 0.002% to 0.45% B, 0.001% to 0.09% P, optionally up to a maximum of 2.0% Co, optionally up to a maximum of 2.0% Zn, optionally up to a maximum of 0.25% Pb, the balance being copper and unavoidable impurities, wherein the Si/B ratio of the element contents in % by weight of the elements silicon and boron is a minimum of 0.4 and a maximum of 8; after further processing of the alloy by at least one annealing operation or by at least one hot forming operation and/or cold forming operation, as well as at least one annealing operation, the following microstructure constituents are present: A) a metallic base composition having, based on the overall microstructure, A1) up to 15% by volume of first phase constituents that can be reported by the empirical formula Cu.sub.nNi.sub.kSn.sub.m and have an (h+k)/m ratio of the element contents in atomic % of 2 to 6, A2) up to 5% by volume of second phase constituents that can be reported by the empirical formula Cu.sub.pNi.sub.rSn.sub.s and have a (p+r)/s ratio of the element contents in atomic % of 10 to 15, and A3) a balance of a solid copper solution; B) phases which, based on the overall microstructure, are present, B1) at 2% to 30% by volume as Si-containing and B-containing phases, Ni—Si borides having the empirical formula Ni.sub.xSi.sub.2B with x=4 to 6, as Ni borides, Ni phosphides and as Ni silicides in the microstructure, which are present individually and/or as addition compounds and/or mixed compounds and are ensheathed by precipitates of the (Cu, Ni)—Sn system, B2) at up to 80% by volume as continuous precipitates of the (Cu, Ni)—Sn system in the microstructure, and B3) at 2% to 30% by volume as Ni phosphides and Ni silicides in the microstructure that are present individually and/or as addition compounds and/or mixed compounds, are ensheathed by precipitates of the (Cu, Ni)—Sn system and have a size of less than 3 μm; the Si-containing and B-containing phases that are in the form of silicon borides, the Ni—Si borides and the Ni borides, Ni phosphides and Ni silicides that are present individually and/or as addition compounds and/or mixed compounds constitute seeds for static and dynamic recrystallization of the microstructure during the further processing of the alloy, which enables the establishment of a uniform and fine-grain microstructure; the Si-containing and B-containing phases that are in the form of boron silicates and/or boron phosphorus silicates, together with phosphorus silicates, assume the role of a wear-protecting and corrosion-protecting coating on semifinished materials and components of the alloy.

8. The copper-nickel-tin alloy as claimed in claim 7, wherein the elements nickel and tin are each present at 3.0% to 9.0%.

9. The copper-nickel-tin alloy as claimed in claim 7, wherein the element silicon is present at 0.05% to 0.9%.

10. The copper-nickel-tin alloy as claimed in claim 7, wherein the element boron is present at 0.01% to 0.4%.

11. The copper-nickel-tin alloy as claimed in claim 7, wherein the element phosphorus is present at 0.01% to 0.09%.

12. The copper-nickel-tin alloy as claimed in claim 7, wherein the alloy is free of lead apart from any unavoidable impurities.

Description

(1) Examples of the invention are explained in more detail below that include references to the drawings, in which: FIG. 1 and FIG. 2 show discontinuous precipitates of the (Cu, Ni)—Sn system and Ni phosphides in the microstructure of an age-hardened reference material R.

(2) FIG. 3 shows hard particles of the second class and continuous precipitates of the (Cu, Ni)—Sn system in the microstructure of working example A. FIG. 4 shows hard particles of the third class in the microstructure of working example A.

(3) FIG. 5 shows hard particles of the second class and continuous precipitates of the (Cu, Ni)—Sn system in the microstructure of working example A.

(4) FIG. 6 shows hard particles of the second class and hard particles of the third class in the microstructure of working example A.

(5) FIG. 7 shows hard particles of the second class and continuous precipitates of the (Cu, Ni)—Sn system in the microstructure of working example A.

(6) FIG. 8 shows hard particles of the second class and hard particles of the third class in the microstructure of a further-processed variant of working example A.

(7) An important working example of the invention is illustrated by Tables 1 to 10. Cast plates of the copper-nickel-tin alloy of the invention and of the reference material were produced by strand casting. The chemical composition of the casts is apparent from Table 1.

(8) Table 1 shows the chemical composition of a working example A and of a reference material R. The working example A is characterized by a Ni content of 6.0% by weight, a Sn content of 5.75% by weight, a Si content of 0.3% by weight, a B content of 0.15% by weight, a P content of 0.070% by weight, and by a balance of copper. The reference material R, a conventional copper-nickel-tin-phosphorus alloy, has a Ni content of 5.78% by weight, a Sn content of 5.75% by weight, a P content of 0.032% by weight, and a balance of copper.

(9) TABLE-US-00001 TABLE 1 Chemical composition of a working example A and of a reference material R (in percent by weight) Alloy Cu Ni Sn Si B P A Balance 6.0 5.75 0.3 0.15 0.070 R Balance 5.78 5.75 — — 0.032

(10) The microstructure of the strand-cast plates of the reference material R has gas pores, shrinkage pores, and Sn-rich segregations particularly at the grain boundaries.

(11) By contrast with the reference material R, the strand casting of the working example A, due to the effect of the crystallization seeds, has a uniformly solidified, pore-free and segregation-free microstructure.

(12) The metallic base material of the cast state of the working example A consists of a solid copper solution with, based on the overall microstructure, about 10% to 15% by volume of intercalated first phase constituents in the form of islands, which can be reported by the empirical formula Cu.sub.hNi.sub.kSn.sub.m and have a ratio (h+k)/m of the element contents in atomic % of 2 to 6. It was possible to detect the compounds CuNi.sub.14Sn.sub.23 and CuN.sub.19Sn.sub.20 with a ratio (h+k)/m of 3.4 and 4. Also, second phase constituents that can be reported by the empirical formula Cu.sub.pNi.sub.rSn.sub.s, and have a ratio (p+r)/s of the element contents in atomic % of 10 to 15, are intercalated in the form of islands in the metallic base material at about 5% to 10% by volume based on the overall microstructure. The compounds CuNi.sub.3Sn.sub.8 and CuNi.sub.4Sn.sub.7 were detected with a ratio (p+r)/s of 11.5 and 13.3. The first and second phase constituents of the metallic base material are predominantly crystallized in the region of the crystallization seeds and ensheath them.

(13) The analysis of the hard particles of the first class in the cast state of the working example A revealed the compound SiB.sub.6 as a representative of the Si-containing and B-containing phases, Ni.sub.6Si.sub.2B as a representative of the Ni—Si borides, Ni.sub.3B as a representative of the Ni borides, Ni.sub.3P as a representative of the Ni phosphides, and Ni.sub.2Si as a representative of the Ni silicides, which are present in the microstructure individually and/or as addition compounds and/or mixed compounds. In addition, these hard particles are ensheathed by tin and/or the first phase constituents and/or second phase constituents of the metallic base material.

(14) During the process of casting the working example A, a substructure formed in the primary cast grains. These subgrains in the cast microstructure of the working example A of the invention have a grain size of less than 10 μm. As a result of the subgrain structure and the hard particles precipitated in the microstructure of the working example A of the invention, the hardness HB of the cast state, at 156, is well above the hardness of 94 HB of the strand casting of the reference material R (Table 2).

(15) TABLE-US-00002 TABLE 2 Hardness HB 2.5/62.5 of the cast state and of the state of the alloys A and R that have been age-hardened at 400° C./3 h/air Strand casting Strand casting + Hardness HB 400° C./3 h/air Alloy 2.5/62.5 Hardness HB 2.5/62.5 A 156 176 R 94 145

(16) Likewise shown in Table 2 are the hardness values that have been ascertained on the strand casting of alloys A and R that has been age-hardened at 400° C. for a duration of 3 hours. The rise in hardness from 94 to 145 HB is at its greatest for the reference material R. The hardening is particularly attributable to the thermally activated formation of segregation of the Sn-rich phase in the microstructure. The tin-enriched phase constituents precipitate out in much finer form in the region of the hard particles in the microstructure of the working example A. For this reason, the rise in hardness from 156 to 176 HB is not as marked.

(17) One intention of the invention is that of maintaining the good cold formability of the conventional copper-nickel-tin alloys in spite of the introduction of hard particles. To verify the degree to which this aim is achieved, the manufacturing program 1 according to Table 3 was conducted. This manufacturing program consisted of one cycle of cold forming and annealing operations, wherein the cold rolling steps were each carried out with the maximum possible degree of cold forming.

(18) Due to the high hardness of the cast state of the working example A, it was calcined at the temperature of 740° C. for the duration of 2 hours and subsequently cooled down in an accelerated manner in water. This brought about the assimilation of the properties of the cast state of A and R with regard to strength and hardness.

(19) The degrees of cold forming ε of 60% and 91% that are achievable for the working example A underline the fact that the alloy of the invention, in spite of the content of hard particles, can achieve and even surpass the shape-changing properties of the conventional copper-nickel-tin alloy R.

(20) The thermal sensitivity of the reference material R with regard to the formation of the Sn-rich segregations was also found in the annealing between the two cold forming steps (No. 4 in Table 3). For this reason, the annealing temperature of 740° C. that was used for the intermediate annealing of the cold-rolled plate of alloy A had to be lowered to 690° C. for R.

(21) TABLE-US-00003 TABLE 3 Manufacturing program 1 for strips made from the strand-cast plates of the working example A and of the reference material R No. Manufacturing steps 1 Strand casting of plates of alloys A and R 2 Annealing the cast plate of alloy A: 740° C./2 h + water quench 3 Cold rolling: Alloy A: from 11 to 4.35 mm (ε = 60%, φ = 0.9) Alloy R: from 24.5 to 12.1 mm (ε = 50%, φ = 0.7) 4 Annealing: Alloy A: 740° C./2 h + water quench Alloy R: 690° C./2 h + water quench 5 Cold rolling: Alloy A: from 4.35 to 0.4 mm (ε = 91%, φ = 2.4) Alloy R: from 12.1 to 2.33 mm (ε = 81%, φ = 1.6) 6 Age hardening: 300° C./4 h, 400° C./3 h, 450° C./3 h + air cooling

(22) After the performance of the manufacturing program 1, the indices of the strips of materials A and R were ascertained after the last cold rolling operation and on completion of the age hardening that are listed in Table 4.

(23) It becomes clear that the strengths and hardnesses of the strips of the working example A that have been cold-rolled and age-hardened at 300° C. are higher than the respective properties of the strips of the reference material R.

(24) Favored by the high content of hard particles, over and above the temperature of about 400° C., recrystallization of the microstructure of alloy A takes place. This recrystallization leads to a drop in strengths and in hardness, and so the effect of the precipitation hardening and spinodal segregation cannot be manifested.

(25) The microstructure of the further-processed working example A, after age hardening at 450° C., includes the hard particles of the second class (labeled 3 in FIG. 3).

(26) In addition, further phases have precipitated out in the microstructure of the further-processed alloy A. These include the continuous precipitates of the (Cu, Ni)—Sn system that are labeled 4 in FIG. 3, and the hard particles of the third class.

(27) The size of the hard particles of the third class of less than 3 μm is characteristic of the further-processed alloy of the invention. For the further-processed working example A of the invention, after age hardening at 450° C., it is actually less than 1 urn (labeled 5 in FIG. 4).

(28) TABLE-US-00004 TABLE 4 Grain size, electrical conductivity and mechanical indices of the cold-rolled and age-hardened strips of the alloys A and R after undergoing the manufacturing program 1 (table 3) Age hard- Grain Electrical Hard- ening size conductivity R.sub.m R.sub.p0.2 A E ness Alloy [° C./h] [μm] [% IACS] [MPa] [MPa] [%] [GPa] HV1 A — — 11.2 964 913  3.1 117 313 300° C./ — 16.9 947 899  5.8 132 312 4 h 400° C./ .square-solid.<2 27.3 676 658 16.3 124 226 3 h 450° C./ <1 24.5 568 550 26.7 127 186 3 h R — — 10.7 838 787  7.2 120 267 300° C./ — 13.8 910 874  9.2 118 297 4 h 400° C./ — 22.0 793 735 13.6 108 264 3 h 450° C./ — 23.2 610 508 23.0 124 195 3 h .square-solid.= not yet fully recrystallized

(29) In order to reduce the effect of the cold formability and the recrystallization temperature on the properties of the individual alloys, a further manufacturing program was conducted. This manufacturing program 2 pursued the aim of processing the strand-cast plates of materials A and R by means of cold-forming and annealing operations to give strips, using identical parameters in each case for the degrees of cold forming and the annealing temperatures (Table 5).

(30) Due to the high hardness of the cast state of the working example A, it was again calcined before the first cold rolling step at the temperature of 740° C. for the duration of 2 hours and subsequently cooled in an accelerated manner in water.

(31) TABLE-US-00005 TABLE 5 Manufacturing program 2 for strips made from the strand-cast plates of the working example A and the reference material R No. Manufacturing steps 1 Strand casting of plates of alloys A and R 2 Annealing of the cast plate of alloy A: 740° C./2 h + water quench 3 Cold rolling: from 9 to 6 mm (ε = 33%, φ = 0.4) 4 Annealing: 690° C./2 h + water quench 5 Cold rolling: from 6 to 3.5 mm (ε = 42%, φ = 0.5) 6 Annealing: 690° C./1 h + water quench 7 Cold rolling: from 3.5 to 3.0 mm (ε = 14%, φ = 0.15) 8 Age hardening: 400° C./3 h, 450° C./3 h, 500° C./ 3 h + air cooling

(32) After the last cold-rolling step to the final thickness of 3.0 mm, the strips of the working example A have the highest strength values and hardness values (Table 6).

(33) The age hardening operation at 400° C. for three hours, due to the spinodal segregation of the microstructure, the rise in the strengths R.sub.m (from 498 to 717 MPa) and R.sub.p0.2 (from 439 to 649 MPa) and in the hardness HB (from 166 to 230 MPa) was at its clearest for the alloy R. However, the microstructure of the age-hardened states of the alloy R is very inhomogeneous with a grain size between 5 and 30 μm. Moreover, the microstructure of the age-hardened states of the reference material R is marked by discontinuous precipitates of the (Cu, Ni)—Sn system (labeled 1 in FIG. 1 and FIG. 2). Also present in the microstructure of the further-processed state of the reference material R are Ni phosphides (labeled 2 in FIG. 1 and FIG. 2).

(34) By contrast, the microstructure of the age-hardened strips of the working example A of the invention is very uniform with a grain size of 2 to 8 μm. Moreover, the structure of the working example A lacks the discontinuous precipitates even after age hardening at 450° C. for three hours followed by air cooling. By contrast, the hard particles of the second class are detectable in the microstructure. These phases are labeled 3 in FIG. 5 and FIG. 6.

(35) In addition, further phases have precipitated out in the microstructure of the further processed alloy A. These include the continuous precipitates of the (Cu, Ni)—Sn system labeled 4 in FIG. 5 and the hard particles of the third class. For the further-processed working example A of the invention, the size of the hard particles of the third class after age hardening at 450° C. is even less than 1 μm (labeled 5 in FIG. 6).

(36) The strengths R.sub.m and R.sub.p0.2 of the strips of the alloy A after age hardening at 400° C./3 h/air, due to the spinodal segregation of the microstructure, assume the values of 675 and 600 MPa. Thus, R.sub.m and R.sub.p0.2 are lower than the indices of the correspondingly age-hardened state of the alloy R. Should the strength level of R be a particular requirement, it is possible to add a higher proportion of the alloy element nickel to the alloy of the invention.

(37) TABLE-US-00006 TABLE 6 Grain size, electrical conductivity and mechanical indices of the cold-rolled and age-hardened strips of the alloys A and R after undergoing the manufacturing program 2 (Table 5) Age Hard- hard- Grain Electrical ness ening size conductivity R.sub.m R.sub.p0.2 A E HBW Alloy [° C./h] [μm] [% IACS] [MPa] [MPa] [%] [GPa] 1/30 A — — 12.2 551 497 25.6 115 184 400° C./ 2-8 15.7 675 600 20.1 130 216 3 h 450° C./ 2-8 17.2 657 525 20.8 117 208 3 h 500° C./ 2-8 17.0 605 439 23.6 120 187 3 h R — — 11.2 498 439 27.9 104 166 400° C./ .square-solid. 15.2 717 649 17.8 132 230 3 h 5-30 450° C./ .square-solid. 17.0 705 591 20.6 121 219 3 h 5-30 500° C./ .square-solid. 18.6 628 420 24.6 118 190 3 h 5-20 .square-solid. = inhomogeneous

(38) The next step included the testing of the hot formability of the strand casting of the alloys A and R. For this purpose, the cast plates were hot-rolled at the temperature of 720° C. (Table 7). For the further processing steps of cold forming and intermediate annealing, the parameters of manufacturing program 2 were adopted.

(39) TABLE-US-00007 TABLE 7 Manufacturing program 3 for strips made from the strand-cast plates of the working example A and of the reference material R No. Manufacturing steps 1 Strand casting of plates of alloys A and R 2 Hot rolling at 720° C. + water quench 3 Cold rolling of alloy A: from 9 to 6 mm (ε = 33%, φ = 0.4) 4 Annealing of alloy A: 690° C./2 h + water quench 5 Cold rolling of alloy A: from 6 to 3.5 mm (ε = 42%, φ = 0.5) 6 Annealing of alloy A: 690° C./1 h + water quench 7 Cold rolling of alloy A: from 3.5 to 3.0 mm (ε = 14%, φ = 0.15) 8 Age hardening of alloy A: 400° C./3 h, 450° C./3 h + air cooling

(40) During the hot rolling of the cast plates of the reference alloy R, deep heat cracks formed even after a few passes, which led to failure of the plates through fracture.

(41) By contrast, the cast plates of the working example A of the invention were hot-rollable without damage and could be manufactured to the final thickness of 3.0 mm after multiple cold rolling processes and calcination processes. The properties of the age-hardened strips (Table 8) correspond largely to those of the strips that have been produced without hot forming by the manufacturing program 2 (Table 6).

(42) Also comparable is the microstructure of the strips made from the working example A of the alloy of the invention that were manufactured without and with a hot forming step. Thus, FIG. 7 and FIG. 8 show the uniform structure of the strips made from the working example A that were produced with a hot forming stage and a subsequent age hardening operation at 400° C./3 h/air cooling. In FIG. 7 and FIG. 8, the hard particles of the second class, labeled 3, are again apparent.

(43) In addition, FIG. 7 shows the continuous precipitates of the (Cu, Ni)—Sn system, labeled 4, and the hard particles of the third class. In the microstructure of the further-processed variant of the working example A, the hard particles of the third class actually assume a size of less than 1 μm (labeled 5 in FIG. 8).

(44) The analysis of the hard particles of the second and third class in this further-processed state of the working example A again revealed the compound SiB.sub.6 as a representative of the Si-containing and B-containing phases, Ni.sub.6Si.sub.2B as a representative of the Ni—Si borides, Ni.sub.3B as a representative of the Ni borides, Ni.sub.3P as a representative of the Ni phosphides, and Ni.sub.2Si as a representative of the Ni silicides, which are present individually and/or as addition compounds and/or mixed compounds in the microstructure. In addition, these hard particles are ensheathed by precipitates of the (Cu, Ni)—Sn system.

(45) TABLE-US-00008 TABLE 8 Grain size, electrical conductivity and mechanical indices of the cold-rolled and age-hardened strips of the alloy A after undergoing the manufacturing program 3 (Table 7) Age Hard- hard- Grain Electrical ness ening size conductivity R.sub.m R.sub.p0.2 A E HBW Alloy [° C./h] [μm] [% IACS] [MPa] [MPa] [%] [GPa] 1/30 A — — 12.4 545 500 23.9 105 181 400° C./ 3-10 15.7 671 607 21.3 128 213 3 h 450° C./ 3-10 17.1 652 527 22.1 127 202 3 h

(46) In the construction of installations, devices, engines and machinery, components having relatively high dimensions are required for numerous applications. For example, this is often the case in the field of slide bearings. The production of the corresponding components requires a precursor material of appropriately large dimensions. Therefore, due to the limited producibility of infinitely large castings, it is necessary to establish the required material properties if at all possible by means of small degrees of cold forming as well.

(47) Table 9 lists the process steps that are used in the course of the manufacturing program 4. The manufacturing operation was effected with one cycle of cold forming and annealing operations. Due to the temperature sensitivity ascertained in the conventional strand casting of the reference material R and of comparatively high strength and hardness of the cast state of the working example A, only the cast plates of the alloy A were calcined prior to the first cold rolling operation at 740° C.

(48) The first cold rolling operation on the cast plaque of the alloy R and on the annealed cast plaque of the alloy A was implemented with a degree of forming s of 16%. An annealing operation at 690° C. was followed by a cold rolling operation with ε of 12%. Finally, age hardening of the strips took place at the temperatures of 350° C., 400° C. and 450° C.

(49) TABLE-US-00009 TABLE 9 Manufacturing program 4 No. Manufacturing steps 1 Strand casting of plates of alloys A and R 2 Annealing of the cast plate of alloy A: 740° C./2 h + water quench 3 Cold rolling: from 9 to 7.6 mm (ε = 16%, φ = 0.17) 4 Annealing: 690° C./2 h + water quench 5 Cold rolling: from 7.6 to 6.7 mm (ε = 12%, φ = 0.126) 6 Age hardening: 350° C./3 h, 400° C./3 h, 450° C./3 h + air cooling

(50) The low degree of cold forming in the first cold rolling step of ε=16%, together with the subsequent annealing operation at 690° C., was insufficient to eliminate the dendritic and coarse-grain microstructure of the reference material R. Moreover, this thermomechanical treatment enhanced the coverage of the grain boundaries of the alloy R with Sn-rich segregations.

(51) Across the dendritic structure and across the grain boundaries of R covered by Sn-rich segregations, cracks running from the surface deep into the interior of the strip formed during the second cold rolling step.

(52) The crack-free and homogeneous microstructure of the strips of the working example A is characterized by the arrangement of the hard particles of the second and third class. As was already the case after the preceding manufacturing programs, the hard particles of the third class have a size of less than 1 μm, even after the manufacturing program 4.

(53) The resulting properties of the strips after the last cold rolling operation and after the age hardening operation are shown in Table 10. Due to the high density of cracks, it was not possible to take undamaged tensile samples from the strips of the alloy R. Thus, it was possible to undertake only the metallographic analysis and the measurement of hardness on these strips.

(54) The working example A has a high degree of age hardenability which is manifested by interaction of the mechanisms of precipitation hardening and spinodal segregation of the microstructure. Thus, there is a rise in the indices R.sub.m and R.sub.p0.2 as a result of age hardening at 400° C. from 517 to 639 MPa and from 481 to 568 MPa.

(55) TABLE-US-00010 TABLE 10 Grain size, electrical conductivity and mechanical indices of the cold-rolled and age-hardened strips of the alloys A and R after undergoing the manufacturing program 4 (Table 9) Age Hard- hard- Grain Electrical ness ening size conductivity R.sub.m R.sub.p0.2 A E HBW Alloy [° C./h] [μm] [% IACS] [MPa] [MPa] [%] [GPa] 1/30 A — — 12.1 517 481 20.6 104 186 350° C./ 15-20 13.9 613 536 24.3 110 207 3 h 400° C./ 20 14.9 639 568 20.3 126 217 3 h 450° C./ 20 16.3 623 484 19.4 114 202 3 h R — .square-solid.— Not possible due to formation 175 350° C./ .square-solid.— of cracks! 242 3 h 400° C./ .square-solid.— 229 3 h 450° C./ .square-solid.— 217 3 h .square-solid.= dendritic, with Sn-rich segregations

(56) As a result, it can be stated that, by means of the variation of the chemical composition, the degrees of forming for the cold forming operation(s), and the variation in the age hardening conditions, it is possible to adjust the degree of precipitation hardening and the degree of spinodal segregation of the microstructure of the invention to the required material properties. In this way, it is possible to bring the strength, hardness, ductility and electrical conductivity of the alloy of the invention into line with the field of use envisaged.