Highly corrosion-resistant copper alloy

Abstract

To provide a highly corrosion-resistant copper alloy that exhibits high corrosion resistance in corrosive environments with repeated wet and dry cycles, can retain a low value of surface electrical resistance, and delivers superior electrical contact performance.SOLUTION: A highly corrosion-resistant copper alloy contains Cu in an amount of 35 atom% or more, Sn in an amount of 30 atom% or more, Ni in an amount of 15 atom% or more, and Zn and Al, each in an amount of 1 atom% or more and 10 atom% or less. The copper alloy also includes a Sn-Cu-Ni phase and a Cu-Sn phase. The Sn-Cu-Ni phase contains 50 atom% or more of Sn, 15 atom% or more of Cu, and 15 atom% or more of Ni. The Cu-Sn phase contains 65 atom% or more of Cu and 5 atom% or more of Sn.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a highly corrosion resistant copper alloy. [Background technology]

[0002] Copper (Cu) is the main electrical contact material used in connectors for electrical wiring. However, when the material is repeatedly wet and dry under relatively high temperature conditions, the surface of the Cu corrodes, producing corrosion products with high electrical resistance, mainly consisting of Cu2O and CuO. This increases the electrical resistance of the surface, reducing its functionality as an electrical contact. For this reason, the Cu surface is plated with gold (Au) or silver (Ag), which have excellent corrosion and oxidation resistance. However, because precious metal plating is expensive, tin (Sn), which is inexpensive and relatively corrosion resistant, is used for industrial equipment such as automobiles, which require cost-effectiveness.

[0003] However, due to the need for weight reduction and resource saving in automobiles and other transportation equipment, there is a demand to make the thickness of Sn plating as thin as possible. Sn is a relatively soft metal, so when used in automotive connectors, it is necessary to assume that the Sn plating layer may be worn down and lost due to sliding caused by vibration, etc. With the realization and spread of electric vehicles and autonomous driving, poor contact in connectors may lead to serious accidents, and it is necessary to avoid this.

[0004] On the other hand, the specific conditions for the composition and microstructure of Cu alloys to maintain low surface electrical resistance for a long period of time have not been clarified, and when the Sn plating disappears, the Cu-based electrical contact material is exposed, and it is difficult to avoid a state in which it corrodes itself. In this context, there is a demand for highly corrosion-resistant copper alloys that maintain low surface electrical resistance even in corrosive environments and have excellent electrical contact properties.

[0005] Meanwhile, attempts have been made to improve the corrosion resistance of Cu by adding alloy elements. For example, aluminum bronze (Cu-6~12%Al-1.5~6%Fe-5%Ni), brass (Cu-40%Zn), phosphor bronze (Cu-4~10%Sn), cupro-nickel (Cu-10~30%Ni), and nickel silver (Cu-5~35%Ni-15~35%Zn) are used in corrosive environments. However, although these have excellent corrosion resistance, corrosion products are generated on the surface in a corrosive environment, increasing the electrical resistance of the surface, making them unsuitable as electrical contact materials for connectors.

[0006] Therefore, a technique has been disclosed for connectors such as charging sockets for electric vehicles in which a Cu alloy surface is coated with Sn or an Sn alloy, and then heat-treated to form a Cu-Sn intermetallic compound (Cu3Sn, Cu4Sn, etc.) on the surface (see, for example, Patent Document 1). However, Sn is an electrochemically less noble metal than Cu, and has poorer corrosion resistance than Cu, which is a noble metal. For this reason, the corrosion resistance of the Cu-Sn alloy is not very high.

[0007] In order to improve the corrosion resistance of Cu, it is presumed that it is suitable to add Sn, Zn, Ni, and Al in an appropriate composition, which have a composition range in which they dissolve in Cu. However, specific conditions regarding the composition and microstructure of such Cu alloys have not been clarified. In particular, the technology to maintain not only high corrosion resistance but also low surface electrical resistance required for electrical contact materials for connectors in electrical wiring is unclear. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 10-25562 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly corrosion-resistant copper alloy which exhibits high corrosion resistance in a corrosive environment where drying and wetting are repeated, can maintain a low surface electrical resistance, and has excellent electrical contact properties. [Means for solving the problem]

[0010] The present inventors have completed the present invention through various experimental studies in order to overcome the limitations of the conventional techniques and solve the unsolved problems described above. In particular, they have found that when the amounts of Sn, Zn, Al, and Ni added to a Cu alloy are controlled, a Sn-Cu-Ni phase containing 50 atomic % or more of Sn and 15 atomic % or more of Cu and Ni, and a Cu-Sn phase containing 65 atomic % or more of Cu and 5 atomic % or more of Sn are formed.

[0011] Furthermore, it was found that the Cu alloy composed of these two phases exhibited very little corrosion weight loss in a wet-dry cycle test, and that the surface electrical resistance did not increase significantly as a result of the wet-dry cycle test.

[0012] The present invention is based on the above-mentioned new findings, and has the following gist: the highly corrosion-resistant copper alloy according to the present invention has Cu with a content of 35 atomic % or more, Sn with a content of 30 atomic % or more, Ni with a content of 15 atomic % or more, and Zn and Al with a content of 1 atomic % or more and 10 atomic % or less, and has a Sn-Cu-Ni phase and a Cu-Sn phase, the Sn-Cu-Ni phase contains 50 atomic % or more Sn, 15 atomic % or more Cu and 15 atomic % or more Ni, and the Cu-Sn phase contains 65 atomic % or more Cu and 5 atomic % or more Sn.

[0013] In the highly corrosion-resistant copper alloy according to the present invention, the Sn-Cu-Ni phase preferably has an Sn content of 60 atomic % or more. Effect of the Invention

[0014] The highly corrosion-resistant copper alloy according to the present invention exhibits high corrosion resistance in a corrosive environment where drying and wetting are repeated, and is capable of maintaining a low surface electrical resistance and has excellent electrical contact properties. Therefore, according to the present invention, it is possible to dramatically reduce contact failures in connectors of electrical wiring in electrical and communication equipment installed outdoors, automobiles, etc., for a long period of time. [Brief description of the drawings]

[0015] [Figure 1] 1 is a table showing chemical compositions of highly corrosion-resistant copper alloys according to embodiments of the present invention (Examples 1 to 6) and comparative examples, as well as the compositions and area ratios of Sn—Cu—Ni phases and Cu—Sn phases. [Diagram 2] 2 is a scanning electron microscope image (SE) of the microstructure of Example 6 shown in FIG. 1, and elemental maps of Cu, Zn, Al, Ni, and Sn by EDS (energy dispersive X-ray spectroscopy). [Diagram 3] 2 is a table showing the corrosion resistance (average corrosion depth) and surface electrical resistance of the examples and comparative examples shown in FIG. 1, as well as their evaluation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described. Cu is a metal with relatively high corrosion resistance and low electrical resistance. It also has excellent workability, Sn plating property, and solderability. For this reason, it is an essential element for copper alloys for use in corrosive environments. However, if Cu is less than 35 atomic %, the corrosion resistance required for a copper alloy for use in a corrosive environment cannot be obtained. For this reason, the highly corrosion-resistant copper alloy according to the embodiment of the present invention contains Cu at 35 atomic % or more.

[0017] A highly corrosion-resistant copper alloy according to an embodiment of the present invention contains 35 atomic % or more of Cu, 30 atomic % or more of Sn, 15 atomic % or more of Ni, and 1 atomic % or more and 10 atomic % or less of Zn and Al, and has a Sn-Cu-Ni phase containing 50 atomic % or more of Sn and 15 atomic % or more of Cu and Ni, and a Cu-Sn phase containing 65 atomic % or more of Cu and 5 atomic % or more of Sn.

[0018] When Cu, Sn, Zn, Al, and Ni are within the above-mentioned ranges, a microstructure is formed having a Sn-Cu-Ni phase containing 50 atomic % or more of Sn and 15 atomic % or more each of Cu and Ni, and a Cu-Sn phase containing 65 atomic % or more of Cu and 5 atomic % or more of Sn.

[0019] The Sn-Cu-Ni phase is a phase that exhibits high corrosion resistance and low surface electrical resistance even after a corrosion test. In order to exhibit this characteristic, it is necessary to contain 50 atomic % or more of Sn and 15 atomic % or more each of Cu and Ni. This phase exhibits relatively high corrosion resistance, which is an effect of Ni. If Ni is less than 15 atomic %, the corrosion resistance decreases. If Cu is less than 50 atomic %, it is difficult to exhibit low surface electrical resistance even after a corrosion test. Similarly, if Sn is less than 15 atomic %, it is difficult to exhibit low surface electrical resistance even after a corrosion test.

[0020] The Cu-Sn phase also exhibits high corrosion resistance and low surface electrical resistance even after a corrosion test. In order to exhibit this characteristic, it is necessary to contain 65 atomic % or more of Cu and 5 atomic % or more of Sn. If the Cu concentration is less than 65 atomic %, the corrosion resistance decreases. If the Sn concentration is less than 5 atomic %, it is not possible to exhibit low surface electrical resistance even after a corrosion test.

[0021] The highly corrosion-resistant copper alloy according to the embodiment of the present invention is not limited in the ratio of the Sn-Cu-Ni phase and the Cu-Sn phase produced or in the overall alloy, but it is necessary that the alloy has the Sn-Cu-Ni phase and the Cu-Sn phase. With regard to the area of ​​the phases, it is preferable that the Sn-Cu-Ni phase is 50% or more, and the Cu-Sn phase is 10% or more and 50% or less. This is because the Cu-Sn phase and the Sn-Cu-Ni phase exert different actions.

[0022] That is, the Cu-Sn phase has a lower corrosion resistance than the Sn-Cu-Ni phase, but is excellent in maintaining the surface electrical resistance at a low value after the corrosion test. Conversely, the Sn-Cu-Ni phase has a higher corrosion resistance than the Cu-Sn phase, but is inferior in maintaining the surface electrical resistance at a low value after the corrosion test. In order to ensure a balance between corrosion resistance and surface electrical resistance, it is preferable that the Sn-Cu-Ni phase is 50% or more and the Cu-Sn phase is 10% to 50%. In addition to these two phases, a Ni-Al phase with an area ratio of 10% or less may be generated, and the highly corrosion-resistant copper alloy of the embodiment of the present invention does not exclude such generation, but it is preferable that the alloy is formed from two phases, the Sn-Cu-Ni phase and the Cu-Sn phase.

[0023] As described above, the Sn-Cu-Ni phase has higher corrosion resistance than the Cu-Sn phase, but is inferior in maintaining the surface electrical resistance at a low value after the corrosion test. However, if it is desired to control the surface electrical resistance to a particularly low value, it is desirable for the Sn concentration in the Sn-Cu-Ni phase to be 60 atomic % or more. Sn has the effect of maintaining the surface electrical resistance of the Sn-Cu-Ni phase, and therefore the entire Cu alloy surface, at a low value after the corrosion test.

[0024] Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the description of the examples. EXAMPLES

[0025] Highly corrosion-resistant copper alloys with the chemical compositions shown in Figure 1 were prepared by vacuum induction melting. Alloys of each composition were placed in a vacuum heat treatment furnace, heated to 500°C over 1 hour, and subjected to homogenizing heat treatment at 500°C for 5 hours. They were then immediately placed in ice water (stirred at 5°C or less) for rapid cooling. The ice water was stirred so that the cooling rate was 900°C / min or more. After that, each alloy was cut to a thickness of 5 mm, width of 15 mm, and length of 25 mm, and mirror-polished to prepare test pieces. For mirror polishing, the front, back, and end faces of the cut alloys were polished using diamond paste with a grain size of 1 μm.

[0026] The microstructure of each test piece was observed by an optical microscope, and the composition of each phase was analyzed by a scanning electron microscope and energy dispersive X-ray analysis. The average composition of the entire test piece was quantified by fluorescent X-ray analysis. The area ratio of the Sn-rich phase was calculated for a field of view of 1 mm x 1 mm. Note that FIG. 2 shows a scanning electron microscope image of the microstructure of the test piece of Example 6 and an element map by EDS (energy dispersive X-ray analysis).

[0027] Each test piece was subjected to a wet-dry cycle test using artificial seawater adjusted to pH 8.2, and the surface electrical resistance was measured by the four-probe method before and after the test.

[0028] This wet and dry cycle test simulates atmospheric corrosion caused by sea salt particles and is used to evaluate the durability of corrosion resistance in coastal areas.

[0029] The wet-dry cycle test was carried out using a thermo-hygrostat, in which each test piece was repeatedly immersed in artificial seawater (25°C) for 3.5 hours and then dried for 30 minutes in an environment of 25°C and 30% RH. The immersion time in the artificial seawater was set to 1 hour 20 minutes until the entire test piece was immersed, 50 minutes for the entire test piece to be immersed, and 1 hour 20 minutes for the entire test piece to come out of the artificial seawater. The combination of immersion in artificial seawater and drying constituted one cycle, and 20 cycles of wet-dry cycle test were performed.

[0030] The four-terminal method used a probe with rhodium-plated terminals arranged in a line at intervals of 2.0 mm, and measured the electrical resistance by pressing the probe against the test piece with a constant force of 100 gf.

[0031] Figure 3 shows the corrosion resistance (average erosion depth) and surface electrical resistance of each test piece, as well as their evaluation. Corrosion resistance was evaluated based on the average erosion depth before and after the wet-dry cycle test. 3 g of chromium trioxide (VI) and 12 mL of sulfuric acid were dissolved in pure water to make a total of 100 mL, and each test piece after the wet-dry cycle test was immersed in a 25°C solution for 10 seconds to remove the corrosion products, and the average erosion depth was calculated from the change in mass before and after the test and the surface area of ​​the test piece. Average erosion depths of 1 μm or less were rated as ◎ (very good), those between 1 μm and 3 μm or less were rated as ○ (good), and those exceeding 3 μm were rated as × (poor).

[0032] The electrical resistance of the surface was evaluated based on the degree of increase in resistivity before and after repeated wet-dry tests. Compared to the resistivity in the mirror-polished state, an increase of one digit or less was rated as ◎ (very good), an increase of two digits or less was rated as ○ (good), and an increase of more than two digits was rated × (bad).

[0033] As shown in Fig. 3, it was found that the alloys of Examples 1 to 6 had better corrosion resistance than those of Comparative Examples 1 to 5, and also showed a slight increase in resistivity following the wet-dry cycle test. In particular, when the element concentration of any one of Cu, Sn, Zn, Al, and Ni is outside the range of the highly corrosion-resistant copper alloy of the embodiment of the present invention, the Sn-Cu-Ni phase and the Cu-Sn phase are not formed (see Fig. 1), and not only is the corrosion resistance rating reduced, but the surface electrical resistance increases significantly following the corrosion test. In addition, Comparative Example 5 is an example of pure copper, but it is found that it has low corrosion resistance and a very large increase in resistivity compared to the alloys of Examples 1 to 6. [Industrial Applicability]

[0034] Possible applications of the highly corrosion-resistant copper alloy according to the present invention include contact materials for electrical wiring connectors in automobiles and materials for electrical contacts in outdoor electrical equipment.

Claims

1. Cu with a content of 35 atomic percent or more; Sn having a content of 30 atomic % or more; Ni content of 15 atomic percent or more; Contains Zn and Al, each of which has a content of 1 atomic % or more and 10 atomic % or less, It has a Sn-Cu-Ni phase and a Cu-Sn phase, The Sn-Cu-Ni phase contains 50 atomic % or more of Sn, 15 atomic % or more of Cu, and 15 atomic % or more of Ni; The Cu-Sn phase contains 65 atomic % or more of Cu and 5 atomic % or more of Sn. A highly corrosion-resistant copper alloy.

2. 2. The highly corrosion-resistant copper alloy according to claim 1, wherein the Sn--Cu--Ni phase has an Sn content of 60 atomic % or more.

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