Copper alloy for corrosive conditions

Abstract

To provide a copper alloy for corrosive conditions that can retain a low value of surface electrical resistance even if the alloy surface experiences corrosion in corrosive environments with repeated wet and dry cycles, while exhibiting superior electrical contact performance.SOLUTION: A copper alloy for corrosive conditions contains Cu in an amount of 35 atom% or more, Sn and Zn each in an amount of 10 atom% or more and 30 atom% or less, and Al and Ni each in an amount of 1 atom% or more and 20 atom% or less, while having a Sn-rich phase with a Sn content of 90 atom% or more.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a copper alloy for use in corrosive environments. [Background technology]

[0002] Copper (Cu) is the main electrical contact material used for electrical wiring connectors. However, in humid environments and with rising temperatures, corrosion products with high electrical resistance, mainly consisting of Cu2O and CuO, are formed on the surface of Cu, causing the electrical resistance of the surface to rise and reducing its function as an electrical contact. For this reason, the surface of Cu is plated with gold (Au) or silver (Ag), which has excellent corrosion resistance 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 economical efficiency.

[0003] However, since it is difficult for Cu-based electrical contact materials to maintain low surface electrical resistance by suppressing corrosion and oxidation for a long period of time, improvements have been made to the Sn plating, such as a technique for forming an alloy layer of Cu and Sn on the outermost surface of electrical contact materials for connectors (see, for example, Patent Document 1), a technique for forming a Sn or Sn alloy layer on the outermost surface and forming an alloy layer containing an intermetallic compound of Cu and Sn underneath (see, for example, Patent Document 2), and a technique for forming an Ag3Sn layer on the Sn plating layer (see, for example, Patent Document 3).

[0004] 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.

[0005] On the other hand, the specific conditions for the composition and microstructure of the Cu alloy to maintain low surface electrical resistance for a long period of time have not been clarified. If the Sn plating is worn away, the Cu-based electrical contact material will be exposed, and it will be difficult to avoid a state in which it corrodes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-267418 A [Patent Document 2] JP 2011-12350 A [Patent Document 3] JP 2011-26677 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a copper alloy for use in corrosive environments, such as those where dry and wet conditions are repeated, which is capable of maintaining a low surface electrical resistance even if the alloy surface corrodes, and has excellent electrical contact properties. [Means for solving the problem]

[0008] 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 a Sn-rich phase is formed in a Cu alloy by controlling the amounts of Sn, Zn, Al, and Ni added.

[0009] Furthermore, they found that the Sn-rich phase exerts a sacrificial protection effect on the Cu-based alloy as a whole in a corrosive environment. During this process, the alloy surface is covered with corrosion products of Sn due to the sacrificial protection, but because the corrosion products of Sn (oxides, hydroxides, etc.) have excellent electrical conductivity, they found that this does not significantly increase the electrical resistance of the alloy surface.

[0010] The present invention is based on the above-mentioned new findings, and has the following gist: the copper alloy for use in a corrosive environment according to the present invention is characterized in that it contains Cu with a content of 35 atomic % or more, Sn and Zn with a content of 10 atomic % or more and 30 atomic % or less, and Al and Ni with a content of 1 atomic % or more and 20 atomic % or less, and has a Sn-rich phase with a Sn content of 90 atomic % or more.

[0011] In the copper alloy for use in a corrosive environment according to the present invention, the area ratio of the Sn-rich phase is preferably 2.0% or more. Effect of the Invention

[0012] The copper alloy for use in a corrosive environment according to the present invention can maintain a low surface electrical resistance even if the alloy surface corrodes in a corrosive environment where dry and wet cycles are repeated, 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 / communication equipment installed outdoors, automobiles, etc., for a long period of time. [Brief description of the drawings]

[0013] [Figure 1] 1 is a table showing the chemical compositions, area ratios of Sn-rich phases, surface electrical resistivities, and evaluations thereof for copper alloys for use in corrosive environments (Examples 1 to 6) according to embodiments of the present invention and comparative examples. [Diagram 2] 2 is a scanning electron microscope image (SE) of the microstructure of Example 2 shown in FIG. 1, and elemental maps of Cu, Zn, Al, Ni, and Sn by EDS (energy dispersive X-ray spectroscopy). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] 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 the Cu content is less than 35 atomic %, the corrosion resistance required for a copper alloy for use in corrosive environments cannot be obtained. For this reason, the copper alloy for use in corrosive environments according to the embodiment of the present invention contains 35 atomic % or more of Cu.

[0015] The copper alloy for use in a corrosive environment according to the embodiment of the present invention contains Cu at 35 atomic % or more, Sn and Zn at 10 atomic % or more and 30 atomic % or less, Al and Ni at 1 atomic % or more and 20 atomic % or less, and has a Sn-rich phase containing Sn at 90 atomic % or more. The area ratio of the Sn-rich phase is 0.5% or more. When Cu, Sn, Zn, Al, and Ni are within the above ranges, a microstructure having a Sn-rich phase containing Sn at 90 atomic % or more is formed. In the present invention, the microstructure having a Sn-rich phase containing Sn at 90 atomic % or more refers to a case where the area ratio of the Sn-rich phase is 0.5% or more. The area ratio here refers to the area ratio of the Sn-rich layer exposed on the alloy surface.

[0016] If the amounts of Cu, Sn, Zn, Al, and Ni are outside the above ranges, the formation of an Sn-rich phase becomes insufficient, making it impossible to maintain a low surface electrical resistance during corrosion.

[0017] Sn, Zn, Al, and Ni are elements that dissolve in Cu, although each has a limited concentration range. Sn improves the malleability of the Cu alloy in a solid solution state. Zn improves the machinability and punchability in a solid solution state. Al and Ni are elements that improve the corrosion resistance of the Cu alloy in a solid solution state. In addition, Al and Ni are elements that have excellent corrosion resistance as single metals, and can be expected to improve the corrosion resistance of not only Cu alloys but also by alloying them. Therefore, in the copper alloy for corrosive environments according to the embodiment of the present invention, Sn, Zn, Al, and Ni contribute to improving various properties, including corrosion resistance, in phases other than the Sn-rich phase.

[0018] Incidentally, Sn is a less noble metal than Cu. Therefore, the Sn-rich phase exerts a sacrificial anticorrosive effect in a corrosive environment on the entire alloy mainly composed of Cu. With the sacrificial anticorrosion, the corrosion products of Sn cover the alloy surface, but since the corrosion products of Sn (oxides, etc.) have excellent electrical conductivity, they do not significantly increase the electrical resistance of the alloy surface. However, in the sacrificial anticorrosion effect, it is not preferable that metals other than Sn are dissolved to form corrosion products, since the electrical resistance of the corrosion products increases. Therefore, the copper alloy for use in a corrosive environment according to the embodiment of the present invention, which has excellent electrical contact characteristics, needs to be an Sn-rich phase containing 90 atomic % or more of Sn. When the Sn concentration in the Sn-rich phase is less than 90 atomic %, the electrical resistance of the corrosion products generated becomes high.

[0019] From the viewpoint of improving corrosion resistance, it is preferable that the amount of Sn-rich phase containing 90 atomic % or more of Sn is large. When it is necessary to maintain low surface resistance for a long period of time in a severe corrosive environment, it is desirable that the area ratio of the Sn-rich phase containing 90 atomic % or more of Sn is 2.0% or more. The area ratio here refers to the area ratio of the Sn-rich layer exposed on the alloy surface.

[0020] Since the copper alloy for use in a corrosive environment according to the embodiment of the present invention contains Sn, Zn, Al, and Ni, in addition to the Sn-rich phase containing 90 atomic % or more of Sn, a phase consisting of a specific combination of these metal elements may be generated. For example, a Ni-Al phase in which Ni is the main component and Al is solid-dissolved, a Cu-Sn-Zn phase or a Cu-Zn-Sn phase in which Cu is the main component and Sn and Zn are solid-dissolved, etc. may be generated. Here, the Cu-Sn-Zn phase means that the concentration of Sn is higher than that of Zn, and the Cu-Zn-Sn phase means that the concentration of Zn is higher than that of Sn.

[0021] The copper alloy for use in a corrosive environment according to the embodiment of the present invention is required to have a Sn-rich phase containing 90 atomic % or more of Sn, and the type and composition of other phases are not specified.

[0022] 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

[0023] Copper alloys for corrosive environments, whose chemical compositions are 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 particle size of 1 μm.

[0024] 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 2 and an element map by EDS (energy dispersive X-ray analysis).

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] Figure 1 shows the surface electrical resistance of each test piece and its evaluation. The surface electrical resistance was evaluated based on the degree of increase in resistivity before and after the wet-dry cycle test. 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 as × (bad).

[0030] As shown in Fig. 1, it was found that the increase in resistivity during the wet-dry cycle test was smaller in the alloys of Examples 1 to 6 than in Comparative Examples 1 to 5. In particular, when the element concentration of any one of Cu, Sn, Zn, Al, and Ni is outside the range of the copper alloy for use in a corrosive environment according to the embodiment of the present invention, the area ratio of the Sn-rich phase containing 90 atomic % or more of Sn becomes less than 0.5%, and it is found that the surface electrical resistance increases significantly during the corrosion test. In addition, Comparative Example 5 is an example of pure copper, and it is found that the increase in resistivity is extremely large compared to the alloys obtained in Examples 1 to 6. [Industrial Applicability]

[0031] Possible applications of the copper alloy for use in corrosive environments 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 % or more; Sn and Zn each having a content of 10 atomic % or more and 30 atomic % or less, Contains Al and Ni, each of which has a content of 1 atomic % or more and 20 atomic % or less, The Sn content is 90 atomic % or more. A copper alloy for use in corrosive environments.

2. The copper alloy for use in a corrosive environment according to claim 1, characterized in that the area ratio of the Sn-rich phase is 2.0% or more.

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