Copper base alloys and terminals using the same

Abstract: A copper base alloy for terminals that is of the Cu-Ni-Sn-P or Cu-Ni-Sn-P-Zn system comprising 0.5-3.0% Ni, 0.5-2.0% Sn, 0.01-0.2% P and optimally 0.01-2.0% Zn, bal. Cu, and that has a tensile strength of at least 500 N/mm 2 , a spring limit of at least 400 N/mm 2 , a stress relaxation of no more than 10%, a conductivity of at least 30 % IACS and a bending workability in terms of the R/t ratio of no more than 2 is provided. Terminals the spring portion or the entire part of which is produced from that copper base alloy, having an initial insertion/extraction force of 1.5 N to 30 N and a resistance of no more than 3 mΩ at low voltage and low current as initial performance, with the added characteristics that the terminals will experince not more than 20% stress relaxation are also provided. The alloy is superior to the conventional bronze, phosphor bronze and Cu-Sn-Fe-P alloys for terminals in terms of tensile strength, spring limit, stress relaxation characteristics and conductivity and, hence, the terminals manufactured from those alloys have high performance and reliability than the terminals made of the conventional copper base alloys for terminals.

Description: BACKGROUND OF THE INVENTION This invention relates to copper base alloys for use in connector terminals in automobiles and other applications, as well as connector terminals that are made of those copper base alloys. In response to the recent advances in electronics technology, connector terminals for use in automobiles and other applications have increasingly been required to satisfy the need for higher packing density, smaller scale, lighter weight and higher reliability. On the other hand the constant improvement in the engine performance has led to a higher temperature in the engine room. Under these circumstance, there has risen the need that the copper base alloys for terminals that are used as conductive materials on the engine should have even higher reliability and heat resistance. However, brass that has heretofore been used as an inexpensive copper base alloy for terminals has low electrical conductivity (to take C26000 as an example, its electrical conductivity is 27% IACS); it also has problems with anti-stress relaxation characteristics, corrosion resistance and stress corrosion cracking resistance. Further, phospher bronze has high strength but its electrical conductivity (hereunder simply referred to as "conductivity") is also low (to take C52100 as an example, its conductivity is ca. 12% IACS); in addition, it has problems with anti-stress relaxation characteristics, and from an economic viewpoint (high price). Cu-Sn-Fe-P alloys have been developed with a view to solving those problems of brass and phospher bronze. For example, Cu-2.0Sn-0.1Fe-0.03P has a conductivity of 35 % IACS and is superior in strength; however, its anti-stress relaxation characteristics has not been completely satisfactory in view of its use as an alloy for terminals. US 5 322 575 A describes a copper base alloy having the features set out in the preamble of claim 1. For manufacturing highly reliable automotive terminals, it is necessary to use copper base alloys that are superior in strength, spring limits and conductivity and that will cause neither stress relaxation nor corrosion after prolonged use. However, none of the conventional copper base alloys, i.e., brass, phosphor bronze and Cu-Sn-Fe-P alloys, have satisfied those requirements. A further problem is that the terminals manufactured from the aforementioned copper base alloys reflect the characteristics of those alloys in a straightforward manner. The terminals using brass, phosphor bronze or Cu-Sn-Fe-P alloys do not satisfy the requirements for high conductivity and good anti-stress relaxation characteristics simultaneously, so they will generate heat by themselves, potentially causing various problems including oxidation, plate separation, stress relaxation, circuit voltage drop, and the softening or deformation of the housing. SUMMARY OF THE INVENTION An object, therefore, of the present invention is to provide a copper base alloy that is superior in all aspects of tensile strength, spring limits, conductivity, anti-stress relaxation characteristics and bending workability. Another object of the present invention is to provide a spring material and springs containing said copper base alloy, particularly for the use in terminals. Another object of the present invention is to provide a terminal which at least has a spring made of the above stated alloy or a terminal the whole of which, inclusive of its spring, is made of the above stated alloy formed in one piece, either terminal being superior in resistance at low voltage and low current and in anti-stress relaxation characteristics. In order to attain these objects, the present inventors conducted repeated test and research efforts on Cu-Ni-Sn-P alloys, as well as Cu-Ni-Sn-P-Zn alloys and found that characteristics satisfactory in terms of tensile strength, conductivity, anti-stress relaxation characteristics, anti-migration characteristics, as well as bending workability could be attained by selecting appropriate compositions for those alloys, and causing uniform precipitation of fine precipitate of Ni-P compound in the size of no larger than 100 nm being uniformly dispersed in the alloy. It was also found that terminals with a built-in spring that was produced from those copper base alloys or terminals that were entirely made of those copper base alloys including a spring as an integral part possessed superior characteristics. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a plate made of an ABS resin used as a jig for carrying out the migration test to accomplish the present invention. Fig. 2 is an illustrative side view of an apparatus for carrying out the migration test to accomplish the present invention. Fig. 3 is a perspective view of an example of the female terminal of the present invention made by way of trial for testing its performance. Fig. 4 is a perspective view of another example of the female terminal of the present invention made by way of trial for testing its performance. Fig. 5 is a graph showing the relationship between the contact load and the conditions for heat treatment in the case of measuring the stress relaxation characteristics of the copper base alloy for terminals of the present invention. Fig. 6 is a graph showing the relationship between the contact load and the conditions for heat treatment in the case of measuring the stress relaxation characteristics of the copper base alloy for terminals of the present invention. Fig. 7 is a graph showing the results of measurement of resistance at low voltage and low current in the tests of electrical performance of the copper base alloy for terminals of the present invention. Fig. 8 is a graph showing the results of measurement of resistance at low voltage and low current in the tests of electrical performance of the copper base alloy for terminals of the present invention. DETAILED DESCRIPTION OF THE INVENTION The present invention provides a copper base alloy for use in terminals that consists essentially, on a weight basis, of 0.5-3.0 % Ni, 0.5-2.0 % Sn, 0.010-0.20 % P, and optionally 0.01-2.0 % Zn, the balance being Cu and incidental impurities, said alloy having fine precipitates of Ni-P compound uniformly dispersed in the alloy, the crystal grain size of said alloy being 50 µm or less, the ratio of Ni to P (Ni/P) being in the range of 10-50, characterized in that the size of said fine precipitates of Ni-P compound uniformly dispersed in the alloy is no larger than 100 nm. Now, the invention will be described concretely hereinbelow. First, the synoptic reason why the specific ranges have been determined for the elements to be added to the alloys of the present invention will be explained below. (1) Ni Nickel (Ni) dissolves in the Cu matrix to provide improved strength, elasticity, heat resistance, anti-stress relaxation, anti-migration and anti-stress corrosion cracking characteristics. Further, Ni forms a compound with P, which disperses and precipitates to provide higher conductivity. If the Ni content is less than 0.5%, the desired effects will not be achieved; if the Ni content exceeds 3.0%, its effects will be saturated and its economy will be impaired. Therefore, the Ni content is specified to range from 0.5 to 3.0 wt%. (2) Sn Tin (Sn) also dissolves in the Cu matrix to provide improved strength, elasticity and corrosion resistance. If the Sn content is less than0.5%, the desired effects will not be achieved with respect to the strength and elasticity,; if the Sn content exceeds 2.0%, its effects will be saturated. Therefore, the Sn content is specified to range from 0.5 to 2.0 wt%. (3) P Phosphorus (P) not only works as a deoxidizer of the melt but also forms a compound with Ni, which disperses and precipitates to improve not only conductivity but also strength, elasticity, and anti-stress relaxation characteristics. If the P content is less than 0.005%, the desired effects will not be achieved; if the P content exceeds 0.20%, the conductivity, workability and adhesive quality of soldering or plating after the heat treatment thereof will be severely impaired even in the copresence of Ni, as well as anti-migration characteristics will be decreased. Therefore, the P content is specified to range from 0.010 to 0.2 wt%, preferably from 0.02 to 0.15 wt%. (4) Ni to P ratio In the course of preparing copper base alloys according to the present invention, part of Ni added is combined with part of P added to form a Ni-P compound, which uniformly disperses in the resulting alloy as finely powdered precipitates to provide improved conductivity as well as improved strength, elasticity and anti-stress relaxation characteristics. Therefore, the ratio of weight percentages of Ni to P (Ni/P) should preferably be limited within a specified range; preferably in the range of from 10 to 50; more preferably in the range of from 15 to 30. If the size of precipitated Ni-P compound exceeds 100 nm, contribution of the precipitate to the improvement in strength, elasticity and anti-stress relaxation characteristics and the bending workability will be impaired. Also, the life of a metal mold for pressing, which comprises a punch made of a hard alloy and a die made of a tool steel, often decreases if the alloy structure contains a large amount of Ni-P precipitate whose size exceeds 100 nm. Therefore, the size of Ni-P precipitate is specified to be 100 nm or less, more preferably 70 nm or less. (5) Auxiliary components Further, zinc (Zn), which can be added as an auxiliary component, has the ability to further improve the adhesive quality of a plating layer to the surface of a copper base alloy, when heat treated after plating. However, if the Zn content is up to 0.01%, the above-mentioned effects will not be achieved; if the Zn content exceeds 2.0%, its effects will be saturated. Therefore, the Zn content within the range of 0.01 - 2.0 wt% is preferred. Next, we describe about the characteristics of terminals according to the present invention. The terms "insertion force" and "extraction force" herein used for connector terminals represent, respectively, the "force required to insert a male terminal into a female terminal" and the "force required to break the male terminal away from the female terminal". Thus, the insertion force should preferably be small and the extraction force should preferably be large. If the insertion force is unduly large, the male terminal cannot be readily inserted into the female terminal. This causes a particular problem with circuits of high packing density because routine assembling operations cannot be accomplished efficiently if the number of terminals to be connected increases. On the other hand, if the extraction force is too weak, separation occurs due to the vibration or an oxide film will easily form and the contact resistance is too unstable to insure satisfactory electrical reliability for connectors. Under the circumstances, the initial insertion/extraction force of the terminal is desirably from 1.5N to 30N and, to this end, the terminal material to be used must have a tensile strength of at least 500 N/mm 2 , a spring limit of at least 400 N/mm 2 and, from a view point of good moldability of terminals, a value of R/t of 2 or less. In order to obtain better bending workability, it is important that the crystal grain size is 50 µm or less, more preferably 25 µm or less. The initial resistance at low voltage and low current is desirably small, preferably not more than 3 mΩ. The value of contact electric resistance is dependent primarily on how much the contact load on the coupling will decrease due to heat cycles. However, the stress relaxation caused by spontaneous heat generation from the material as well as the stress relaxation caused by the effects of temperature in the automobile's engine room or around the exhaust system will also reduce the contact load, which eventually leads to a higher contact electric resistance. To avoid this problem, the terminal material itself must not undergo stress relaxation greater than 10% upon standing at 150°C for 1,000 hours, and it is also required to have a tensile strength of at least 500 N/mm 2 , a spring limit of at least 400 N/mm 2 , an electric conductivity of at least 30 % IACS and a stress relaxation after working into a spring of no more than 20%. The following example is provided for the purpose of further illustrating the present invention. Example 1 The measurement of tensile strength, conductivity and spring limit were in accordance with JIS Z 2241, JIS H 0505 and JIS H 3130, respectively. The bending workability of each sheet was evaluated by a 90° W bend test, in which according to CES-M0002-6 the sample was subjected to 90°W bend with a tool of R=0.1 mm and the surface state of the center ridge was evaluated by the following criteria: × , cracking occurred; Δ, wrinkles occurred; ○, good results. The bending axis was set to be parallel to the rolling direction. In a stress relaxation test, the test piece was bent in an arched way such that a stress of 400 N/mm 2 would develop in the central part and the residual bend that remained after holding at 150°C for 1,000 hours was calculated as "stress relaxation" by the following formula: stress relaxation(%)={(L 1 -L 2 )/(L 1 -L 0 ))X100 where L o : the length of the tool (mm); L 1 : the initial length of the sample (mm) L 2 : the horizontal distance between the ends of the sample after the test (mm) The migration test was conducted in the following way: A plate as shown in Fig. 1 (1: ABS resin; 2: opening) made of ABS resin (2 mm(t) X 16 mm(w) X 72 mm(1)) and having in the central area thereof a circular opening was sandwiched by a pair of test pieces (each 0.2 mm(t) X 5 mm(w) X 80 mm(1)) and the resulting assembly was joined together by winding around it at both upper and lower portions with separate pieces of Teflon tape. Then, the fixed assembly was held in a testing vessel filled with tap water as shown in Fig. 2 (3: Teflon tape; 4: test piece; 5: tap water; 6: testing vessel; 7: ammeter; 8: DC power source). The migration characteristics of each test piece was evaluated by measuring maximum leakage current after 8 hours' application of 14 V DC voltage. Alloys having the compositions shown in Table 4 were melted in a high-frequency melting furnace and hot-rolled at 850°C to a thickness of 5.0 mm. The surface of each slab was scalped to a thickness of 4.8 mm and by subsequent repetition of cold-rolling operations and heat treatments, sheets having a thickness of 0.2 mm with a final reduction ratio of 67% were obtained. In the course of executing these operations, conditions of heat treatments (age-precipitation) were varied in order to vary the sizes of precipitates and the crystal grain diameters thereof. As regards precipitates, an average diameter of the largest 10 precipitate particles determined by transmission electron microscopy, wherein the specimen being observed at three phases at the magnification of 50,000X, was shown as the size of the precipitate. Crystal grain diameters were evaluated according to JIS H 0501. Then, with respect to the above mentioned materials, the tensile strength, elongation and spring limit were measured; at the same time, the bending workability and stress relaxation characteristics were investigated. The results are shown in Table 4 in comparison with one another. As shown by the above results, all the alloy sample Nos. 27 - 34 prepared in accordance with the present invention had a tensile strength of no less than 500 N/mm 2 , a spring limit of no less than 400 N/mm 2 and a conductivity of no less than 30% IACS, and their bending workability was also satisfactory. In addition, these samples had superior stress relaxation characteristics of no less than 10% as well as superior anti-migration characteristics. In contrast, the alloy sample Nos. 35 - 42 prepared in accordance with the conventional method which comprises precipitates whose size exceeds 100 nm or whose crystal grain size exceeds 50 µm, showed decreased bending workability and they were inferior to the alloy of the present invention in any other characteristic properties inclusive of tensile strength, spring limit, anti-stress relaxation characteristics, and anti-migration characteristics. The copper base alloy of the present invention for use in terminals is superior in tensile strength, spring limit, electric conductivity, anti-stress relaxation characteristics, anti-migration characteristics and bending workability. In addition, a terminal which is constructed by the alloy of the present invention and which has a spring in it is superior in the resistance at low voltage and low current as well as stress relaxation characteristics, and therefore the alloy has a remarkable advantage from a view point of industry. That is, according to the present invention, there is provided a copper base alloy for use in a terminal which has an electric conductivity of as high as at least 30% IACS and also has both high tensile strength and high spring limit as well as superior stress relaxation characteristics of not higher than 10%. There is further provided a terminal which has contained in its structure a spring made of the alloy of the present invention or a terminal wholly made of the alloy of the present invention inclusive of its spring, the terminal having proper initial properties inclusive of a proper insertion power in the range of 1.5 - 30 N, a proper resistance at low voltage and low current of no more than 3 mℓ and a proper stress relaxation characteristics of no more than 20%.

Claims: A copper base alloy for use in terminals that consists essentially, on a weight basis, of 0.5-3.0 % Ni, 0.5-2.0 % Sn, 0.010-0.20 % P, and optionally 0.01-2.0 % Zn, the balance being Cu and incidental impurities, said alloy having fine precipitates of Ni-P compound uniformly dispersed in the alloy, the crystal grain size of said alloy being 50 µm or less, the ratio of Ni to P (Ni/P) being in the range of 10-50, characterized in that the size of said fine precipitates of Ni-P compound uniformly dispersed in the alloy is no larger than 100 nm. A copper base alloy according to claim 1, characterized in that said alloy satisfies all of the following three requirements: (a) the crystal grain size of the alloy is 25 µm or less, (b) the ratio of Ni to P ((Ni/P) is in the range of 15-30, and (c) the size of said fine precipitates of Ni-P compound uniformly dispersed in the alloy is no larger than 70 nm. The copper base alloy for use in terminals according to claim 1 or claim 2, said alloy having a tensile strength of at least 500 N/mm 2 , a spring limit of at least 400 N/mm 2 , a stress relaxation of no more than 10 %, a conductivity of at least 30 % IACS and a bending workability given in terms of the ratio of R to t (R/t) of no more than 2; where R is a bend radius and t is a thickness of the specimen. A terminal with a built-in spring that is produced from a spring material or a terminal that is entirely made of said spring material including a spring as an integral part, said spring material being produced by melting a copper base alloy according to any one of claims 1, 2 and 3, said alloy being worked, after melting, by at least one of cold rolling and hot rolling. The terminal according to claim 4 for use as a connector terminal in automobiles and other applications. A process for preparing a copper base alloy according to claim 1, claim 2 or claim 3 comprising: melting a composition consisting essentially, on a weight basis, of 0.5-3.0 % Ni, 0.5-2.0 % Sn, 0.010-0.20 % P, and optionally 0.01-2.0 % Zn, the balance being Cu and incidental impurities, hot-rolling the molten composition to obtain a sheet, and carrying out repeated cold-rolling operations and heat treatments, wherein the conditions of heat treatments are varied in order to vary the sizes of precipitates and the crystal grain diameter thereof.

Inventors: ENDO TAKAYOSHI, HANA YOSHIAKE, SUGAWARA AKIRA, ENDO, TAKAYOSHI, HANA, YOSHIAKE, SUGAWARA, AKIRA
Applicants: DOWA MINING CO, YAZAKI CORP, DOWA MINING CO., LTD., YAZAKI CORPORATION
Application year: 1998
Main classification: C22C9
IPC codes: H01R13, C22F1, C22C9