ELECTRICALLY CONDUCTIVE SPRING MATERIALS

Abstract: An electrically conductive material consisting essentially of 0.15 to 0.35% of Be, 0.3 to 1.5% of Aℓ, either one or both of Ni and Co in a total amount of 1.6 to 3.5%, in terms of weight, and the balance being Cu with inevitable impurities. The alloy may further contain at least one of Si, Sn, Zn, Fe, Mg and Ti in a total amount of 0.05 to 1.0%, in terms of weight ratio. Each of the Si, Sn, Zn, Fe, Mg and Ti is in an amount of 0.05 to 0.35%.

Description: The present invention relates to electrically conductive spring materials having excellent electric conductivity and spring properties and useful as materials for electrical parts such as connectors, switches, relays, etc. Although phosphor bronze has been used as an electrically conductive material for a long time, it has insufficient strength, electrical conductivity, bending formability, and stress relaxation property, when in use for electronic parts which have recently been made compact and required high reliability. So, Cu-Ni-Be base alloys having a nominal composition of Cu-0.4% Be-1.8% Ni have attracted public attention. However, such alloys unfavorably have high material costs and unsatisfactory stress relaxation property. Further, it is formerly known that addition of Aℓ to Cu-Ni-Be base ternary alloys is effective for improving strength. For instance, JP-A-48-103,023 discloses spring alloys containing 0.3 to 1.0% of Be, 1.0 to 3.0% of Ni, and 2.0 to 7.0% of Aℓ as fundamental ingredients. However, since such spring alloys contain not less than 2.0% of Al, they have other shortcomings in that the alloys have poor rollability and high production costs, and that electrical conductivity and bending formability deteriorate with Al. EP-A-180443 describes electroconductive spring material containing Ni, Be, Si, balance Cu. One specific example is 2.5% Ni, 0.21% Be, 0.6% Si, 0.8% Al, balance Cu. The present invention aims to solve the conventional problems mentioned above, and is intended to provide electrically conductive spring materials having excellent electrical conductivity, bending formability, stress relaxation property, and rollability as well as lower production costs as compared with conventional phosphor bronze, Cu-Ni-Be based alloys, and Cu-Ni-Al-Be base alloys. According to a first aspect of the invention, there is provided an electrically conductive material as set out in claim 1. According to a second aspect of the present invention, there is provided an electrically conductive material as set out in claim 3. In the invention, the content of Be is suppressed to a lower level of 0.15 to 0.35% as compared with the conventional alloys. This is to reduce the material cost. However, if Be is reduced, strength tends to drop due to growth of crystalline grains during solution treatment. In JP-A-48-103,023 referred to above, strength decrease due to reduction of Be down to 0.3% is tried to be complemented with a great addition amount of Aℓ in a range from 2 to 7%. Consequently, rollability becomes poorer and production costs increase. Thus, it is feared that the total cost increases, contrary to the intention. On the other hand, according to the present invention, strength reduction due to decrease in Be is complemented by relatively increasing Ni and/or Co with addition of a small amount of Aℓ. Thus, in the present invention, coarsening of crystalline grains during the solution treatment, which is promoted by the addition of Aℓ, is effectively controlled by optimizing the content of Ni and/or Co and the relative ratio between Aℓ + Be and Ni + Co, thereby improving formability. Further, when Aℓ is in a range from 0.3 to 1.5%, stress relaxation is improved, and rollability is not damaged without increasing production costs. The above combination of a small amount of Be in a range from 0.15 to 0.35%, a smaller amount of Aℓ in a range from 0.3 to 1.5% as compared with that of the conventional alloys, and 1.6 to 3.5% of Ni and/or Co in the first aspect of the present invention is first proposed by the present invention. Thus, the present invention is to provide Cu-Be base alloys having more excellent total balance as compared with that of the conventional alloys containing a greater amount of Aℓ. Further, according to the second aspect of the present invention, mechanical strength is further improved by adding at least one element selected from the group consisting of Sn, Zn, Fe, Mg and Ti to the alloy composition of the first aspect. No effect is obtained if each of the elements is less than 0.05%. In contrast, if each of them exceeds 0.35% or if the total amount is more than 1.0%, the effect is not only saturated, but also electrical conductivity is lowered. For a better understanding of the invention, reference is made to the attached drawings, wherein: Fig. 1 is a graph showing the relationship between the content of Aℓ and that of Ni +Co; and Fig. 2 is a graph showing the relationship between the content of Be and that of Ni + Co. First, the reasons for the limitation of the respective ingredients of the alloys according to the present invention will be explained below. In the following, "%" means "% by weight" unless otherwise specified. If Be is less than 0.15%, strength is lowered due to decreased precipitation hardenability, and coarsening of crystalline grains cannot be prevented during solution treatment. In contrast, if Be is more than 0.35%, the costs of the materials cannot be reduced. Thus, Be is set in a range from 0.15 to 0.35%. Aℓ is an important element to complement strength reduction due to the decreased amount of Be and particularly to improve stress relaxation property. If Aℓ is less than 0.3%, its effect is not remarkable. In contrast, if it is more than 1.5%, electrical conductivity is extremely reduced and production costs become higher due to reduced rollability. Thus, Aℓ is set in a range from 0.3 to 1.5%, preferably from 0.4 to 1.1%. When Aℓ is added in an amount from 0.3 to 1.5%, castability of the alloys, separability of slag, oxidation resistance, etc. are greatly improved, and the production cost is reduced. If the total amount of Ni and Co is less than 1.6%, the crystalline grains cannot be prevented from becoming coarse during the solution treatment due to reduced Be and added Aℓ. Consequently, strength, elongation, or formability cannot be improved. On the other hand, if the total amount of Ni and Co is more than 3.5%, there arise problems in that strength is reduced, electrical conductivity becomes lower, and castability and hot processability of the materials are damaged. Thus, the total amount of Ni and Co is set in a range from 1.6 to 3.5%, preferably from 2.0 to 2.7%. The relationships between the total amount of Ni and Co and the content of Aℓ or the content of Be have been examined in detail. As a result, it was found that the most preferable characteristics can be obtained when they satisfy the following inequalities (1) and (2) in terms of weight percents. (1.75 + 0.5 × Aℓ content) ≦ (Ni content + Co content) ≦ (2.75 + 0.5 × Aℓ content) (1) (2.4 - 2 × Be content) ≦ (Ni content + Co content) ≦ (3.6 - 2 × Be content) (2) These relationships are shown as shadowed portions in the graphs of Figs. 1 and 2, respectively. In order to offset the influences such as coarsening of the crystalline grains due to increased Aℓ during the solution treatment, as is seen from Figs. 1 and 2, the content of (Ni + Co) must be increased with increase in Aℓ. Further, when the content of Be decreases, that of (Ni + Co) must be increased. Next, the second aspect of the present invention will be explained. In the second aspect of the present invention, mechanical strength is improved by further adding at least one element selected from the group consisting of Sn, Zn, Fe, Mg and Ti to the alloy composition in the first aspect of the present invention. If each of the elements is less than 0.05%, no effect is recognized. On the other hand, if each of them is more than 0.35% or if the total content thereof is more than 1.0%, the effect is not only saturated, but also electrical conductivity is lowered. The alloys according to the first and second aspects of the present invention have equivalent or more excellent spring characteristics as compared with spring phosphor bronze, have particularly excellent stress relaxation property, electrical conductivity, and formability, and are excellent in terms of costs. Next, characteristic values of the alloys according to the present invention will be given with reference to the following specific examples below. Experiment 1 : Alloy Nos. 1-14 (Nos. 1-8: alloys of the first aspect of the present invention, Nos. 9-13: alloys of the second aspect of the present invention) and Comparative alloys Nos. 1-10 having respective compositions given in Table 1 were each melt and cast in a high frequency wave induction furnace, hot forged, hot rolled, and repeatedly annealed and rolled, thereby obtaining alloy sheets of 0.34 mm in thickness. Next, each of them was heated at 930°C for 5 minutes and cooled in water as a final solution treatment, rolled at a draft of 40%, and aged at 450°C for 2 hours. Then, various characteristics were measured. Results are shown in Table 2. Comparative Example 10 was an alloy having a nominal composition of Cu-0.4% Be-1.8%Ni, and Comparative alloy No. 11 was a commercially available spring phosphor bronze. The stress relaxation property was determined by applying a maximum bending stress of 400 MPa (40 kgf/mm²) to a test piece, releasing a bending load by maintaining it at 200°C for 100 hours, measuring a perpetually deformed amount, and converting the deformed amount to a stress residual percentage. The bending formability was evaluated by the ratio of R/t in which R and t were the minimum radium causing no cracks when the test piece was bent, and the thickness of the test piece, respectively. The above characteristics were examined with respect to a longitudinal direction and a transverse direction to a rolling direction. Experiment 2 Specimens having a thickness of 0.22 mm were obtained by processing each of the alloy Nos. 1-13 and Comparative alloy Nos. 1-10 in the same manner as in Experiment 1. Next, specimens was subjected to the final solution treatment at 930°C for 5 minutes, rolling at a draft of 10%, and ageing at 450°C for 2 hours thereby obtaining. Then, various characteristics were measured. Results are shown in Table 3. Evaluations were carried out in the same manner as in Experiment 1. Experiment 3 Specimens having a thickness of 2.0 mm in thickness was obtained by processing Example alloy Nos. 1-13 and Comparative alloy Nos. 1-10 in Table 1 in the same manner as in Experiment 1. Next, specimens was subjected to the final solution treatment at 930°C for 5 hours, rolling at a draft of 90%, and ageing at 400°C for 4 hours. Then, various characteristics were measured. Results are shown in Table 4. As is clear from the characteristic values in the above Examples, according to the present invention, as compared with the conventional Cu-Ni-Be base alloy in Comparative alloy No. 10, the Be content is decreased to reduce the material cost, and stress relaxation property is improved while strength is maintained at the same level. Further, as compared with the spring phosphor bronze in Comparative alloy No. 11, the alloys according to the present invention have more excellent stress relaxation property, electrical conductivity and formability. As mentioned above, the electrically conductive spring materials according to the present invention have more excellent total balance among various characteristics and cost performances.

Claims: An electrically conductive material consisting by weight of 0.15 to 0.35% of Be, 0.3 to 1.5% of Al, either one or both of Ni and Co in a total amount of 1.6 to 3.5%, the balance being Cu and unavoidable impurities. An electrically conductive material according to claim 1, wherein the following inequalities are satisfied, the contents being expressed in weight percent: (1.75 + 0.5 x Al content) ≦ (Ni content + Co content) ≦ (2.75 + 0.5 x Al content), (2.4 - 2 x Be content) ≦ (Ni content + Co content) ≦ (3.6 - 2 x Be content). An electrically conductive spring material consisting by weight of 0.15 to 0.35% of Be, 0.3 to 1.5% of Al, either one or both of Ni and Co in a total amount of 1.6 to 3.5%, at least one of Sn, Zn, Fe, Mg and Ti in a total amount of 0.05 to 1.0% with the amount of each among Sn, Zn, Fe, Mg and Ti present being 0.05 to 0.35%, the balance being Cu and unavoidable impurities. An electrically conductive spring material according to claim 3, wherein the following inequalities are satisfied, the contents being expressed in weight percent: (1.75 + 0.5 x Al content) ≦ (Ni content + Co content) ≦ (2.75 + 0.5 x Al content), (2.4 - 2 x Be content) ≦ (Ni content + Co content) ≦ (3.6 - 2 x Be content).

Inventors: IWADACHI, TAKAHARU
Applicants: NGK INSULATORS, LTD.
Application year: 1988
Main classification: H01B1
IPC codes: H01R13, H01B1, C22C9, H01H1