US20080181811A1

US20080181811A1 - Copper alloy for an electric connecting device

Info

Publication number: US20080181811A1
Application number: US12/076,728
Authority: US
Inventors: Kuniteru Mihara; Tatsuhiko Eguchi
Original assignee: Furukawa Electric Co Ltd
Current assignee: Furukawa Electric Co Ltd
Priority date: 2005-09-30
Filing date: 2008-03-21
Publication date: 2008-07-31
Also published as: KR100902201B1; CN101268206A; KR20080046710A; WO2007040148A1; CN101268206B

Abstract

A copper alloy for an electric connecting device, having Cr in the range from 0.1 to 1 mass %, Zn in the range from 0.1 to 5.0 mass %, and Sn in the range from 0.1 to 2.0 mass %, with the balance being inevitable impurities and Cu, wherein the copper alloy has tensile strength of 600 MPa or more, 0.2% yield strength of 560 MPa or more, electric conductivity of 40% IACS or more, and rupture time of 500 hours or more in a stress corrosion test under a load of 80% of the 0.2% yield strength.

Description

TECHNICAL FIELD

The present invention relates to a copper alloy for a connecting device set up in electric wiring.

BACKGROUND ART

Electric connecting devices have been widely used for portions of electrical connection, such as electrical outlets of electric appliances and switches of illumination. Metals are generally used for the connecting portion, and electric contact is made by permitting the metals to contact to one another. There are two kinds of such electric connecting portions: one is connection to an electric wire (copper wire) from which electricity is supplied, and the other is connection to an object to which electricity is supplied. Pure copper, excellent in electric conductance, and a copper alloy (such as C14410) in which a trace amount of Sn or Ag (≦0.2%) is added, to improve heat resistance, have been used in the contact portion.
The mechanical strength of these materials is so low. Therefore, to maintain a contact to the aforementioned object to which electricity is supplied, the connecting portion employed a structure that the contact portion was reinforced using a high mechanical strength material, such as stainless steel, as a spring material. However, since stainless steel is expensive, a high-mechanical strength copper alloy as a substitute for stainless steel has been desired.
Since a technology to make a structure in which a “receiving blade (contact plate)”, which is an electronic contact portion, and a “spring material” are integrated, has been developed for reducing cost, a high-mechanical strength material that also functions as the spring material is being desired for the copper alloy.
In electric connecting devices, electric connection is achieved by allowing metals to contact one another. However, heat generation has been a problem at the contact portion. It has been found that micro-electric discharge (glow) occurs at the contact portion, proliferation of cuprous oxide is induced by the micro-electric discharge, to increase a contact resistance, thereby resulting in heat generation.
Accordingly, copper alloys for electric connecting device have been proposed, by which glow and proliferation of cuprous oxide hardly occur, by reexamining alloy components (for example, JP-A-60-255944 (“JP-A” means unexamined published Japanese patent application)). However, the mechanical strengths of such alloys are so poor that they were not suitable as the spring material.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a copper alloy excellent in mechanical strength, electric conductivity, stress relaxation resistance, stress corrosion resistance, glow resistance, corrosion resistance, and the like.
Another object of the present invention is to provide a copper alloy suitable for electric connecting devices (electric wiring connectors), such as electrical outlets of electric appliances and switches of illumination, that is able to prevent glow from occurring and cuprous oxide from being proliferated.
The inventors of the present invention have made detailed investigations on the contact portion of electric connecting devices, and have developed a copper alloy excellent in mechanical strength, electric conductivity, stress relaxation resistance, stress corrosion resistance, and glow resistance.
The present invention provides:
(1) a copper alloy for an electric connecting device, comprising Cr in the range from 0.1 to 1 mass %, Zn in the range from 0.1 to 5.0 mass %, and Sn in the range from 0.1 to 2.0 mass %, with the balance being inevitable impurities and Cu, wherein the copper alloy has tensile strength (TS) of 600 MPa or more, 0.2% yield strength (YS) of 560 MPa or more, electric conductivity (EC) of 40% IACS or more, and rupture time of 500 hours or more in a stress corrosion test (SCC) under a load of 80% of the 0.2% yield strength;
(2) the copper alloy for an electric connecting device as described in (1), which has stress relaxation property (SR) of 50% or less, in 1,000 hours at 150° C.;
(3) the copper alloy for an electric connecting device as described in (1) or (2), comprising Si in the range from exceeding zero to 0.2 mass %; and
(4) the copper alloy for an electric connecting device as described in (1), (2), or (3), which is excellent in glow resistance.
Other and further objects, features and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of stress corrosion resistance test (SCC), which was performed in the working example; and

FIG. 2 is a schematic view of an apparatus for measuring glow resistance and cuprous oxide proliferation resistance, which apparatus was used in the working example.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferable embodiments of the present invention will be described in detail.
The content of Cr is restricted in the range from 0.1 to 1 mass %. This is because, although Cr is an addition element which reinforces the alloy by causing precipitation in copper, Cr of less than 0.1 mass % hardly gives a sufficient precipitation hardening effect while Cr of exceeding 1.0 mass % results in saturation of the effect and only causes unnecessary additional costs. The content of Cr is preferably 0.2 to 0.8 mass %, more preferably 6.2 to 0.5 mass %.
The content of Zn and the content of Sn are restricted in the ranges from 0.1 to 5.0 mass % and from 0.1 to 2.0 mass %, respectively, because Zn and Sn are elements that form solid solutions in copper and they remarkably enhance mechanical strength and exhibit an effect for improving stress relaxation resistance, in a solid-solution hardening process and subsequent cold-working process. On the other hand, these elements impair electric conductivity when too large amounts are added. These elements each exhibit insufficient effects when less than 0.1 mass % of these elements were added. When the amount of Zn exceeds 5.0 mass %, the alloy becomes poor not only in electric conductivity but also in stress corrosion resistance and causes large proliferation amount of cuprous oxide. When the amount of Sn exceeds 2.0 mass %, electric conductivity is affected. The content of Zn is preferably in the range from 0.13 to 4.0 mass %, and the content of Sn is preferably in the range from 0.2 to 1.5 mass %.
Si contributes to prevention of hot-working-induced cracks. While a Sn-containing alloy is known to have poor hot workability, addition of Si reduces susceptibility to hot working. However, too large amount of Si decreases electric conductivity. Therefore, the amount of Si is preferably in the range from 0.001 to 0.1 mass %.
The copper alloy for an electric connecting device of the present invention can be produced by means of a general production method involving appropriate repetition, for example, of rolling and heat-treating. Preferable production steps and conditions are as follows, although the present invention is not restricted thereto:
(1) casting is preferably conducted by a continuous casting process;
(2) hot rolling is conducted at a temperature in the range from 900 to 1050° C. (preferably 950 to 1030° C.) with a rolling ratio of 80% or more (preferably 90% or more) followed by quenching;
(3) cold rolling is conducted with a rolling ratio in the range from 60 to 98% (preferably 90 to 98%) under conventional conditions;
(4) heat treatment is conducted at a temperature in the range from 400 to 500° C. (preferably 450 to 500° C.) for 1 to 5 hours; and
(5) finish working (cold rolling) is conducted with a reduction ratio of 10 to 40%.
In the above, a heat treatment at a temperature in the range from 750 to 900° C. (preferably 800 to 900° C.) for 0.1 to 1 minutes may be conducted between (3) and (4) or in the course of (4).
The copper alloy according to the present invention has tensile strength of 600 MPa or more, preferably 600 to 700 MPa, and more preferably 600 to 650 MPa.
The copper alloy according to the present invention has 0.2% yield strength of 560 MPa or more, preferably 580 to 680 MPa, and more preferably 580 to 630 MPa.
The copper alloy according to the present invention has electric conductivity of 40% IACS or more, preferably 45 to 60% IACS, and more preferably 50 to 60% IACS.
The copper alloy according to the present invention has rupture time of 500 hours or more in a stress corrosion test, preferably 1000 hours or more, and more preferably 3000 hours or more.
Mechanical strength (tensile strength and 0.2% yield strength) is a property in conflict with electric conductivity. In the case of the alloy system according to the present invention, an increase of mechanical strength results in a reduction of electric conductivity, while an increase of electric conductivity results in a reduction of mechanical strength. Further, mechanical strength is also in conflict with bending workability. A higher mechanical strength is preferred, but a higher mechanical strength also results in a more deteriorated bending workability. In this connection, a higher electric conductivity allows the alloy to be applied to wiring devices that use high electric current. Furthermore, reliability of the alloy increases as the time until rupture becomes longer.
The present invention provides a copper alloy suitable for electric connecting device excellent in mechanical strength, electric conductivity, and stress relaxation resistance, as well as in stress corrosion resistance and glow resistance.
The present invention will be described in more detail based on the following examples, but the present invention is not intended to be limited thereto.

EXAMPLES

Each copper alloy was cast into a book mold with a thickness of 30 mm, a width of 120 mm, and a length of 180 mm, at a tapping temperature of about 1200° C., using an open-air high-frequency induction furnace, at a melting temperature in the range from about 1200 to 1250° C. The thus-obtained ingot was kept at a temperature in the range from about 950 to 1000° C. for 1 hour in an open-air heating furnace, and, subsequently, was finished into a plate with a thickness of about 12 to 13 mm by hot rolling. The plate was further finished into a plate with a thickness of about 10 mm by scalping the surface of the hot-rolled plate.
The plate was repeatedly subjected to cold working and heat treatment, to produce a flat plate (strip) with a thickness of 0.5 mm. The heat treatment for precipitating Cr was conducted at a temperature in the range from 400 to 450° C. for a time period in the range from 2 to 5 hours, and the finish reduction ratio of 10 to 40%.
Commercially available plate materials with a thickness of 0.5 mm, comprised of copper alloys and non-iron materials, were purchased. The copper alloys were C2600, C2680, C5111, C5191, and C7701, and stainless steels were SUS301 and SUS304.
The tensile strength, 0.2% yield strength, electric conductivity, stress relaxation property, stress corrosion property of each of these materials were investigated.
Regarding tensile strength (TS) and 0.2% yield strength (YS), a JIS-5 test piece was cut out from each of these materials from a direction parallel to the roll direction, and the tensile strength and 0.2% yield strength were measured in accordance with JIS Z 2241.
Regarding electric conductivity (EC), a test piece with a width of 10 mm and a length of 150 mm was cut out from each of these materials from the direction parallel to the roll direction, and electric conductivity was measured in accordance with JIS H 3200, with an inter-terminal distance of 100 mm.
The stress relaxation property (SR) was tested in accordance with the Electronic Materials Manufactures' Association of Japan Standards (EMAS-3003: a stress relaxation test method by bending of a spring material) using a cantilever method. The test sample was allowed to stand in a high temperature chamber (in open air) at 150° C. while the sample was loaded with 80% of the 0.2% yield strength obtained in the tensile strength test. This measurement was repeated in a prescribed time interval up to 1000 hours.
The stress corrosion (SCC) test was conducted in accordance with an ammonia test method in JIS C8306, wherein a stress was applied by the method shown in FIG. 1. In the drawing, the reference numeral 10 denotes a test piece, the reference numeral 11 denotes a load, the reference numeral 12 denotes a silicon cap, the reference numeral 13 denotes a glass cell, and the reference numeral 14 denotes an ammonia solution. The measurement was conducted as follows. A test piece 10 with a width of 10 mm and a length of 100 mm was prepared, and, by applying a tape or mask, only an area of 10 mm (width)×10 mm (length) of the test piece was exposed to a 3 vol. % ammonia (NH₃) atmosphere. The time from after application of the load 11 until rupture of the test piece was measured. The loaded stress was 80% of the 0.2% yield strength obtained in the tensile strength test.
Glow resistance and cuprous oxide proliferation resistance were then evaluated. FIG. 2 shows a schematic view of an apparatus used for measuring glow resistance and cuprous oxide proliferation resistance.
Evaluation for glow resistance was performed as described below. That is, a copper wire 2 with a diameter 2 mm was attached to a holder 1 equipped with a load applier, and a sample 3 of any one of the examples according to the present invention or the comparative examples was placed on a sample holder 4. Then, the sample was brought into contact with the copper wire 2, and a current flowing between the copper wire 2 and the sample 3 was adjusted to 4 A, by means of Slidac 8 and a variable resistor 6. Then, the sample holder 4 was vibrated with a vibrator 5, and the wave form of a voltage between the copper wire 2 and the sample 3 was observed with an oscilloscope 7. When glow (micro-electric discharge) occurred between the copper wire 2 and the sample 3, it changed the wave form on the oscilloscope 7. A frequency (the number of times vibrated) applied until the occurrence of the change in wave form was utilized to evaluate glow resistance. With respect to evaluation of glow resistance, though it may vary depending on the application, when the number of vibration applied until occurrence of the change in wave form, which means occurrence of glow, is 1×10³or less, it is judged to be “poor”; when said number is more than 1×10³, it is judged to be “good”.
Evaluation for cuprous oxide proliferation resistance was performed as described below. Vibration with the vibrator 5 was stopped simultaneously with the confirmation of the occurrence of glow, and then the sample 3 was left to stand for 60 minutes. Then, the sample 3 was taken out, and then cuprous oxide formed on the surface of the sample 3 was collected, to measure the mass thereof. The mass, i.e. the proliferated amount of cuprous oxide (mg), was utilized to evaluate cuprous oxide proliferation resistance. With respect to evaluation of cuprous oxide proliferation resistance, though it may vary depending on the application, when the mount of cuprous oxide formed (mg) is 200 mg or less, it is judged to be “good”, and when said amount is more than 200 mg, it is judged to be “poor”.
The results of measurements are shown in Tables 1 to 4. In the tables, there are alloys showing plural values of mechanical strength, electric conductivity, and the like, even though they have the same components; these are test results obtained by changing the finish reduction ratios of such alloys as shown in the tables.

TABLE 1

[Examples]

					Finish
					reduction
Alloy	Cr	Sn	Zn	Si	ratio	TS	YS	EC	SR	SCC
No	(mass %)	(mass %)	(mass %)	(mass %)	(%)	(MPa)	(MPa)	(% IACS)	(%)	(Hr)

1	0.15	0.5	0.8	—	35	635	604	53	36	>500
2	0.2	0.25	0.5	—	40	651	619	57	41	>500
3	0.25	0.5	0.5	—	30	656	625	54	39	>500
4				—	40	708	687	52	42	>500
5	0.25	0.5	2	—	30	765	756	51	45	>500
6	0.25	0.5	4	—	35	826	831	50	48	>500
7	0.25	0.8	0.1	—	25	652	620	50	41	>500
8				—	40	704	682	49	44	>500
9	0.25	0.8	0.25	—	20	653	621	50	38	>500
10				—	35	705	683	49	41	>500
11	0.25	0.8	0.24	0.002	20	704	681	48	40	>500
12	0.25	0.8	0.25	0.01	20	709	688	44	39	>500
13	0.25	0.8	0.24	0.09	20	722	699	41	37	>500
14	0.25	0.8	0.5	—	20	650	619	50	38	>500
15				—	30	702	681	49	41	>500
16				—	40	723	719	48	44	>500
17	0.25	0.8	0.75	—	20	647	616	50	34	>500
18				—	30	699	678	48	38	>500
19	0.25	0.8	1	—	20	653	621	49	29	>500
20	0.25	0.9	0.5	—	20	653	621	49	34	>500
21				—	30	705	683	48	37	>500
22	0.25	0.9	0.7	—	30	656	624	49	31	>500
23	0.25	1	0.1	—	30	649	618	48	35	>500
24	0.25	1	0.12	0.003	30	653	612	47	37	>500
25	0.25	1	0.15	0.02	30	655	633	44	35	>500
26	0.25	1	0.12	0.09	30	667	623	41	33	>500
27	0.25	1	0.5	—	25	654	622	48	40	>500
28				—	35	707	684	46	43	>500
29				—	40	728	723	45	46	>500
30	0.25	1	1	—	25	654	622	47	37	>500
31	0.25	1.2	0.25	—	25	645	614	45	34	>500
32	0.25	1.2	1	—	25	654	623	45	39	>500
33	0.25	1.5	0.25	—	25	647	616	42	42	>500
34	0.3	0.2	0.5	—	30	655	623	57	41	>500
35	0.3	0.8	0.25	—	25	646	614	50	38	>500
36	0.3	0.8	0.5	—	25	656	624	50	42	>500
37				—	35	708	686	49	45	>500
38	0.3	0.8	1	—	25	649	618	49	40	>500
39				—	35	701	680	48	43	>500
40	0.3	0.9	0.5	—	25	645	614	49	40	>500
41				—	35	697	675	48	43	>500
42	0.3	0.9	0.8	—	25	655	622	48	38	>500
43	0.5	1	0.5	0.003	25	646	614	48	41	>500
44	0.5	1	1	0.01	35	653	622	47	37	>500
45	0.8	0.5	0.5	—	35	655	622	54	39	>500
46	0.8	1	1	0.05	25	649	618	47	42	>500

TABLE 2

[Comparative examples]

50	0.08	0.7	1	—	30	589	551	51	43	>500
51*	1.25	0.7	1	—	35	653	621	51	32	>500
52	0.25	0.05	0.04	—	35	552	525	49	55	>500
53					35	548	547	50	55	>500
54	0.25	0.09	0	—	40	550	524	65	54	>500
55					35	548	546	63	55	>500
56	0.25	0	0.09	—	40	546	519	50	55	>500
57					50	547	541	50	55	>500
58	0.25	1.6	0.2	0.02	30	651	620	32	33	>500
59					35	647	642	38	37	>500
60	0.3	1.0	0.5	0.25	30	655	644	38	36	>500
61	0.3	1.2	0.5	0.5	30	662	659	35	35	>500
62	0.25	0.5	5.5	—	25	651	619	53	35	480
63				—	30	648	641	60	38	465
64	0.25	1.6	20	—	25	684	651	22	62	25
65				—	30	679	676	21	65	22

Commercially available products

80	C1100 (Pure copper)	H	320	304	99	89	>500
		material**
81	C2600 (Brass)	EH	649	618	28	77	5
		material**
82	C2680 (Brass)	EH	649	617	28	68	8
		material
83	C5111 (Phosphor bronze)	EH	646	615	17	45	>500
		material
84	C5191 (Phosphor bronze)	EH	655	623	12	45	>500
		material
85	C7701 (Nickel silver)	EH	656	624	8	8	>500
		material
86	SUS301 (Stainless steel)	H	1211	1152	7	2	>500
		material
87	SUS304 (Stainless steel)	H	1312	1247	6	3	>500
		material

*No. 51 is a reference example
**In the above table, “H material” and “EH material” mean “H tempered material” and “EH tempered material”, respectively.

From the results shown in Tables 1 and 2, the followings are understood.
First, the comparative examples were evaluated as follows.
No. 50 was poor in mechanical strength, due to a small content of Cr.
No. 51 exhibited properties not different from those of the examples. However, addition of Cr in an excess amount results in saturation of its effects and only results in an increased cost; thus not suited for practical use.
Nos. 52 to 57, which contained Sn and Zn in small amounts, were poor in mechanical strength and were remarkably poor in stress relaxation resistance giving values exceeding 50%.
Nos. 58 and 59 were poor in electric conductivity.
Nos. 60 and 61 were poor in electric conductivity.
Nos. 62 to 65 were poor in stress corrosion resistance, due to a large content of Zn.
Among the commercially available alloys, No. 80 was poor in electric conductivity and further poor in evaluation items other than stress corrosion cracking. The brasses of Nos. 81 and 82 were poor in electric conductivity and stress corrosion resistance. The phosphor bronzes of Nos. 83 and 84, the nickel silver of No. 85, and Nos. 86 and 87 were poor in electric conductivity.
In contrast, examples Nos. 1 to 46 obtained the copper alloys for electric connecting device excellent in all the properties, such as tensile strength (TS), 0.2% yield strength (YS), electric conductivity (EC), stress corrosion resistance (SCC), and stress relaxation resistance (SR).
The results of the glow resistance test, and the amount of generated cuprous oxide as a result of the test are shown in Tables 3 and 4.

TABLE 3

		Amount
	Numbers until	of
	occurrence of	cuprous
Alloy	glow discharge	oxide
No.	(×10³times)	(mg)

1	18	19
2	25	40
3	20	45
4	14	68
5	26	86
6	21	94
7	15	14
8	23	31
9	16	56
10	21	93
11	21	53
12	21	15
13	14	3
14	25	38
15	21	93
16	18	55
17	25	86
18	20	56
19	18	10
20	25	45
21	23	100
22	24	99
23	14	70
24	24	2
25	22	21
26	21	46
27	24	77
28	20	9
29	20	82
30	20	64
31	17	35
32	25	118
33	23	108
34	25	95
35	16	41
36	13	26
37	21	30
38	18	49
39	19	109
40	15	5
41	23	57
42	23	109
43	21	51
44	20	55
45	19	49
46	24	98

TABLE 4

		Amount
	Numbers until	of
	occurrence of	cuprous
Alloy	glow discharge	oxide
No.	(×10³times)	(mg)

50	11	40
51	19	33
52	17	49
53	25	79
54	20	19
55	18	22
56	20	84
57	27	119
58	18	39
59	25	38
60	23	42
61	19	22
62	16	35
63	24	90
64	14	46
65	17	86
80	17	9
81	19	451
82	29	428
83	23	272
84	17	212
85	21	119
86	20	222
87	20	269

As is apparent from the results shown in Tables 3 and 4, the alloys according to the present invention had excellent glow properties.
Further, by considering the results shown in Tables 1 to 4 synthetically, the alloys according to the present invention satisfied respective required properties, and thus were excellent as alloy for electric connecting devices.

INDUSTRIAL APPLICABILITY

The copper alloy of the present invention has high mechanical strength and high electrical conductivity and is excellent in stress relaxation resistance and corrosion resistance, and thus the alloy is suitable as the copper alloy for electric connecting device.
Having described our invention as related to the present embodiments, it is our intention that the invention not be limited by any of the details of the description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

Claims

1. A copper alloy for an electric connecting device, comprising Cr in the range from 0.1 to 1 mass %, Zn in the range from 0.1 to 5.0 mass %, and Sn in the range from 0.1 to 2.0 mass %, with the balance being inevitable impurities and Cu, wherein the copper alloy has tensile strength of 600 MPa or more, 0.2% yield strength of 560 MPa or more, electric conductivity of 40% IACS or more, and rupture time of 500 hours or more in a stress corrosion test under a load of 80% of the 0.2% yield strength.

2. The copper alloy for an electric connecting device as claimed in claim 1, which has stress relaxation property of 50% or less, in 1,000 hours at 150° C.

3. The copper alloy for an electric connecting device as claimed in claim 1, comprising Si in the range from exceeding zero to 0.2 mass %.

4. The copper alloy for an electric connecting device as claimed in claim 2, which is excellent in glow resistance.