An aluminum metal material excellent in conductivity and corrosion resistance and a method for producing the same.

Abstract

To provide a material that gives electrical conductivity to an aluminum anodized oxide film and has corrosion resistance and hardness.SOLUTION: The present invention provides a material with low resistance, excellent corrosion resistance, and excellent hardness, which is suitable for practical use as an aluminum material, in which the electrical resistance is maintained at 1×10-2 Ω or less, the corrosion resistance is good, and the hardness is improved by creating a corrosion-resistant and electrically conductive film at a bottom of micropores after removing a barrier layer in which aluminum anodized oxide film is used as an insulating material, and by performing metal deposition on a thin film forming a nucleus of the metal deposition. This material can also be produced by applying two or multistep electrolysis of metal deposition.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an aluminum metal material excellent in conductivity and corrosion resistance and a method for producing the same.

Background Art

[0002] An aluminum anodic oxide film (hereinafter referred to as an alumite) was developed as an electrically insulating material, but has contributed to the development of aluminum today by improving decorative technology, corrosion resistance technology, hardness and abrasion resistance technology, etc. For example, due to decorative and corrosion resistance technologies, there are color panels for buildings, color sashes for window frames, and colorization of daily sundries. Due to hardness technology, the weight of mechanical parts that require slidability has been reduced. Due to corrosion resistance technology, exteriors outdoors, underwater cameras, etc. have been made lighter, and aluminum has been used in many fields. In the future, to further develop aluminum, in addition to the development of materials, it is necessary to break through the insulating material that is the starting point of the anodic oxide film and utilize the advantages of conductivity, magnetism, etc. + lightweight and easy to process to enter the electrical, electronic, and semiconductor fields. The development and practical application of an anodic oxide film having conductivity in addition to the conventional characteristics have been awaited. For example, an anodic oxide film has been used to deal with accidents in which an electronic circuit is damaged by a spark due to static electricity, and the magnetic field shielding effect of medium wave to extremely ultra-short wave used in smartphones, satellite broadcasts, taxi radios, etc. cannot be achieved, and plating is performed on the surface. However, heavy metals are generated during the treatment, disposal, and regeneration of the plating solution, which is a problem in terms of LCA, and a film that can cope with LCA and solve this problem is desired.

[0003] Regarding imparting conductivity to an anodic oxide film of alumite, a method of treating it in an anodic oxidation bath containing nitrate ions has been proposed (Patent Document 1). The conductivity achieved by this method is a resistance value of 10 5~6It is described as being at a level of Ω or above, having an anti-static function, and being usable for various computer-related products. However, in practical terms, it is insufficient to prevent accidents where electronic circuits are damaged by electrostatic sparks and to exhibit a magnetic field shielding effect in the medium wave to extremely ultra-short wave ranges used in smartphones, satellite broadcasts, taxi radios, etc. This document does not describe surface hardness, but in reality, it can only achieve a hardness of about HV280, which is not hard enough for the application fields of hard anodized aluminum and thus requires improvement.

[0004] The anodic oxide film of anodized aluminum consists of a porous layer and a barrier layer (non-porous layer). Anodized aluminum was initially developed as an insulating material at the Institute of Physical and Chemical Research and has come to the present. However, among the papers issued by the National Institute for Metals Research in the 1970s and 1980s as a method for hardening sulfuric acid films, it has been shown that when the barrier layer is removed and metal is deposited to the surface by electrolytic coloring technology, conductivity is confirmed. (Technical Document 1) Technical Document 1 describes that the electrolytic solution is sulfuric acid, the final voltage during film formation is rapidly decreased from 15 - 20V to around 0.05V, and after further dissolving the barrier layer after switching off, Ni electrodeposition is performed to achieve a hardness increase of about HV50 - 100. And it reports that there is electrical conductivity between the Al substrate and the film surface by a tester. However, since this film-making method completely eliminates the corrosion resistance, which is a characteristic of anodized aluminum, it is a product that cannot be used practically.

Prior Art Documents

[0005]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a manufacturing method for anodized aluminum, which has been conventionally unusable, by imparting conductivity and corrosion resistance to it and using it as a lightweight material.

Means for Solving the Problem

[0007] The present invention has a performance with an average electrical resistance measured by the four-terminal method between the film surface and the substrate of 1×10 -2 Ω or less, a corrosion resistance of RN8 or more after 336 hours of spraying in a salt spray test, and further a film cross-sectional hardness of 200 HV or more and less than 300 HV, and is a material having an anodic oxide film made of aluminum or an alloy thereof and a method for manufacturing the same.

[0008] The method for measuring the electrical resistance of the present invention is excellent in low-resistance measurement as shown in "Figure 6". Using a DC four-terminal method (voltage drop method) resistance meter RM3548 (manufactured by Hioki Electric Co., Ltd.), electrodes 11 with gold plating on 1 cm 2 of copper are placed on the surfaces of the anodic oxide film and the substrate. This electrode consists of four electrode terminals including current source terminals ▲a▼ and ▲d▼ for supplying a constant current, and voltage detection terminals ▲b▼ and ▲c▼ for detecting the voltage drop. These are placed linearly with ▲a▼ and ▲b▼ on the substrate surface, and ▲c▼ and ▲d▼ on the film surface, with a distance of 1 cm between each electrode. The outer electrode terminals ▲a▼ and ▲d▼ are held with alligator clips, and a weight of 50 g / cm 2 is applied to the surfaces of the inner ▲b▼ and ▲c▼ electrodes, and the electrical resistance is measured from the voltage drop. The electrical resistance is measured at least twice by changing the location of the terminals by the above method to obtain the average electrical resistance. The film cross-sectional hardness is measured by the JIS-Z2244 (Vickers hardness test) method with a load of 0.098 N (10 grf) and a holding time of 15 seconds, and is a material having an anodic oxide film made of aluminum or an alloy thereof with a hardness of 200 HV or more and less than 300 HV, and a method for manufacturing the same.

[0009] The corrosion resistance test of the present invention was carried out using a neutral salt spray tester STP-90V-4 (manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS-Z2371. After 336 hours of continuous spraying, the evaluation method was carried out in accordance with JIS-H8679-1 (Evaluation method for pitting corrosion occurred on anodic oxide coatings of aluminum and aluminum alloys - Part 1: Rating number method (RN)). The rating number applies only to pitting corrosion (pits) that penetrate the coating and reach the metal substrate (surface defects such as discoloration that do not penetrate the coating and corrosion of the end faces generated on the test piece are not the objects of evaluation). The relationship between the rating number and the corrosion area ratio of pitting corrosion is shown in Table 1. The judgment criteria are carried out in accordance with JIS-H8603-5.6 (Hard anodic oxide coatings of aluminum and aluminum alloys - Corrosion resistance), but are divided as shown in Table 2 according to H8603-4: type (material of the material). One type is defined as having no pitting corrosion (RN10) after a 336-hour spray test using a neutral salt spray tester, and for materials other than one type, it is stipulated according to the agreement between the delivery parties. In the present invention, the above regulations are complied with, and the judgment criteria at 336 hours are added. In practice, after taking out from the salt spray tester, the corrosion products on the surface are physically and chemically removed, thoroughly washed with water, confirmed that there is no attachment on the surface, dried, and the size and quantity of pitting corrosion are evaluated by comparing with the rating number standard chart. The material of the present invention has electrical conductivity and a cross-sectional hardness of 200 HV or more. However, according to the description in Technical Document 1, although it has a certain degree of electrical conductivity, in terms of corrosion, it is stated that "pits occurred in the 24-hour salt spray test, and the surface was considerably covered with corrosion products at 240 hours", and there was only a material with no corrosion resistance. The material of the present invention has corrosion resistance achieving RN8 or more in the materials of one type and two types-(b).

[0010]

Table 1

[0011]

Table 2

[0012] The thickness of the anodic oxide film is measured after calibration with a calibration standard plate (plastic film) using JIS-H8680-2 (eddy current measurement method), and it is 6 to 60 μm, preferably 8 to 30 μm, particularly preferably 10 to 25 μm, forming a film with a color tone ranging from the base color to light brown to dark brown to black.

[0013] The manufacturing process of the present invention is composed of four electrolysis steps and post-treatment. The first electrolysis is for creating the base film (Figs. 1, 2). The second electrolysis is for removing the barrier layer at the bottom of the microporous film in the same or different electrolytic solution as the first electrolysis (Fig. 3). The third electrolysis is for depositing nuclei of metal salts at the bottom of the micropores (Fig. 4). The fourth electrolysis is for depositing metal salts in the pores in the same solution as the third electrolysis. (Fig. 5) Furthermore, by performing operations such as sealing as post-treatment, the average electrical resistance measured by the four-terminal method between the film surface and the base is 1×10 -2 Ω or less, the corrosion resistance is RN8 or more after 336 hours of spraying in the salt spray test, and the film cross-sectional hardness is 200 HV or more and less than 300 HV. It is a material and manufacturing method made of aluminum or its alloy that forms an anodic oxide film with a color tone ranging from the base color to light brown to dark brown to black.

[0014] The first electrolysis of the present invention is a process for creating the base film. In an inorganic and / or organic electrolytic solution, the electrolysis methods include DC waveform, AC waveform, AC-DC superimposed waveform, pulse waveform, and PR pulse waveform. In the case of the DC waveform, the liquid temperature is 10 to 40 °C, the current density is 0.6 to 4.0 A / dm 2 , the voltage is 10 to 100 V, for 20 to 90 minutes, preferably the liquid temperature is 18 to 30 °C, the current density is 0.8 to 2.0 A / dm 2 , the voltage is 15 to 60 V, and the electrolysis time is 20 to 60 minutes. On the other hand, in the case of pulse waveform, PR pulse waveform, AC-DC superimposed waveform, and AC waveform, the average current density of the positive current in one cycle is 0.1 to 3 A / dm 2 , the average current of the negative current is 0.0 to 3 A / dm 2 , the liquid temperature is 10 to 40 °C, preferably the average current density of the positive current in one cycle is 0.6 to 2.0 A / dm 2 , the average current of the negative current is 0.0 to 2.0 A / dm 2, at a liquid temperature of 20 to 30 °C, anodic oxidation treatment is carried out using a direct current waveform, an alternating current waveform, a pulse waveform, a PR pulse waveform, alone or in combination of two or more, to form an anodic oxidation film having a color tone from the base color to a brown color tone. The overall image of the anodic oxidation film formed here is shown in Fig. 1, and its cross-section and surface view are shown in Fig. 2.

[0015] The second electrolysis is a barrier layer removal process. The method is that when the target film thickness is reached in the first electrolysis, the power supply is not turned off and held at the final voltage for 1 to 5 minutes, and then the voltage is gradually lowered to 0 V. The method is to lower the voltage from the final voltage of the first electrolysis by 1 to 10 V, hold at that voltage for 5 to 120 seconds, further lower by 1 to 15 V, hold for 5 to 120 seconds repeatedly until it reaches around 10 V, hold for 5 to 120 seconds, and then sequentially lower to 8 V, 6 V, 4 V, 2 V, 1 V, 0 V. The holding time at this time is 5 to 120 seconds, and the total time is carried out in 5 to 30 minutes. Preferably, it is lowered by 1 to 10 V and held for 10 to 120 seconds, and it is desirable to reach 0 V in 5 to 40 minutes. In this process, the barrier layer at the lower part of the micropores is removed. However, the removal of the barrier layer cannot be done in a short time. If it is too long, film dissolution will occur and it will become covered. If it is too short, the barrier layer cannot be removed and the resistance will increase, resulting in variations in the deposition of metals after the fifth electrolysis when carried out additionally, or spoiling (a phenomenon where the film is broken and the base material appears) may occur. A schematic diagram of the barrier layer removal is shown in Fig. 3.

[0016] The third electrolysis is carried out in an electrolytic solution composed of an acidic solution containing a metal salt and an additive. In the electrolytic solution, the metal salt is dissolved and used as metal ions. The liquid temperature is 10 to 40 °C, and the electrolysis is carried out with a direct current, a pulse, or a PR pulse waveform alone or in combination of two or more. The voltage is raised to 10 to 30 V in 1 to 10 seconds, and after 1 to 30 seconds, it is immediately returned to 0 V. Preferably, it reaches 10 to 25 V in 1 to 8 seconds at 15 to 30 °C, and after 5 to 20 seconds, it is immediately lowered to 0 V. When the power supply has a polarity, (the member to be treated) is set on the cathode side, and the anode side uses a carbon plate electrode for electrolysis. In this process, a metal serving as a nucleus precipitates at the bottom of the micropores of the anodic oxidation film. A schematic diagram of this is shown in Fig. 4.

[0017] The fourth electrolysis uses the same electrolyte as the third electrolysis, with the same solution temperature. The electrolysis conditions are carried out by direct current, pulse, or PR pulse waveform alone or in combination of two or more, with a current density of 0.1 to 5.0 A / dm 2 , a voltage of 2 to 30 V, a time of 2 to 30 minutes, preferably 0.2 to 1.5 A / dm 2 , 3 to 8 V, and 5 to 15 minutes. When the power supply has polarity, (the member to be processed) is set on the cathode side, and the anode side uses a carbon plate electrode for electrolysis. Before and after electrolysis, thorough water washing is performed with deionized water or pure water. In this step, metal is deposited from the micropores to the surface layer of the anodic oxide film. This schematic diagram is shown in FIG. 5.

[0018] The fifth electrolysis that can be additionally performed after the fourth electrolysis, or further multi-stage electrolysis, is carried out in an acidic solution containing a metal salt different from that of the third and fourth electrolyses, at a solution temperature of 10 to 60 °C. The electrolysis uses direct current, pulse, or PR pulse waveform, with a current density of 0.1 to 5.0 A / dm 2 , or a voltage of 3 to 8 V and an electrolysis time of 2 to 30 minutes, preferably 0.2 to 3.0 A / dm 2 , 3 to 8 V, and 5 to 20 minutes. When the power supply has polarity, (the member to be processed) is set on the cathode side, and the anode side uses a carbon plate electrode for electrolysis. Before and after electrolysis, thorough water washing is performed with deionized water or pure water. In this step, metal is deposited from the micropores to the surface layer of the anodic oxide film. Also, the metal salts used in the fourth and fifth electrolyses or multi-stage electrolysis may be different combinations.

[0019] The electrolytes used in the first and second electrolyses of the present invention are preferably a single or mixed system mainly composed of aliphatic or aromatic sulfonic acid and / or carboxylic acid-based organic acids. Alternatively, an inorganic acid and / or an organic acid different from the above-mentioned mainly used organic acid, or an electrolyte with additives added as required, or a sulfuric acid-based inorganic acid system, with one or more of the above-mentioned organic acids added to the additives. The main liquid concentration of these is preferably 0.1 to 4.5 mol / L.

[0020] The electrolytic solution used for the third electrolysis, the fourth electrolysis, the fifth electrolysis, or multi-stage electrolysis consists of an acidic solution containing a metal salt and an additive. The metal salt is used in a state of soluble metal ions. Representative acidic solutions mainly include sulfuric acid compounds and oxalic acid compounds. As additives, carboxylic acid-based organic acids, boric acid, etc. are added to the solution. As the metal salt compounds to be added, compounds of gold, silver, copper, platinum, tin, cobalt, nickel, iron, tungsten, molybdenum, chromium, zinc, palladium, zirconium, rhodium, ruthenium, vanadium, titanium, manganese, etc. are used. Tin or zinc is most preferred to maintain the excellent corrosion resistance of the anodic oxide film of the obtained material.

[0021] The fourth, fifth, or multi-stage electrolysis method is very similar to the electrolytic coloring method of anodized aluminum. However, for the deposits in the micropores in electrolytic coloring, according to "Electrolytic Coloring Mechanism of Aluminum Anodic Oxide Film by Anodic Stripping Method" in Surface Technology, Vol40, No12, 1989, "In nickel-based baths and cobalt-based baths... metal ions precipitate as hydroxides... while in copper-based baths and tin-based baths... it is considered that the precipitates formed as hydroxides or oxides are mixed in the pores... 4. Introduction... It was found that the forms of the deposits in the film pores can be classified into three types: simple metal, simple metal oxide (hydrate), and a mixture of metal and metal oxide (hydrate).". Thus, the micropores in electrolytic coloring are composed of a mixture of metal, hydroxide, or oxide. The average electrical resistance between the film surface and the substrate by the four-terminal method is, for example, about 1×10 4~5 Ω for tin electrolytic coloring and 1×10 1~2 Ω for nickel. On the other hand, in the present invention, since metal precipitates in the micropores, the average electrical resistance between the substrate and the film is 1×10 -2 Ω or less. Also, in electrolytic coloring during the electrolysis operation, an electrolytic voltage of 10 - 25V is usually used, but the electrolytic voltage of the present invention is 2 - 8V for electrolysis. "

[0022] In the present invention, anodic oxide films in the color range from the substrate color to light brown to dark brown to black are formed even on films with a thickness of 6 to 60 μm, particularly 10 to 30 μm. However, this black film is not colored with dyes or pigments, etc., but is formed by metal deposition through the fourth or fifth electrolysis or a multi-step electrolysis method.

[0023] The organic acids preferably used in the first electrolysis and the second electrolysis in the present invention are aliphatic or aromatic sulfonic acids and / or carboxylic acid systems, either alone or in combination. Specifically, oxalic acid, malonic acid, succinic acid, malic acid, maleic acid, citric acid, tartaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, etc. In the case of sulfonic acid systems, sulfosalicylic acid, sulfophthalic acid, sulfoacetic acid, etc. These can be used alone or in combination of two or more, or sulfuric acid is used as the main component of the inorganic acid system and the above organic acids are used as additives to form the electrolytic solution during anodization. The concentration of these solutions is preferably 0.1 to 4.5 mol / L. The electrolysis method is a DC waveform with a solution temperature of 10 to 40°C and a current density of 0.6 to 4.0 A / dm 2 2, for 20 to 90 minutes, preferably with a solution temperature of 18 to 30°C and a current density of 0.8 to 2.0 A / dm 2 2, and the electrolysis time is 20 to 60 minutes, or a pulse waveform, PR pulse waveform, or AC waveform, with an average current density of the positive current of 0.1 to 3 A / dm in one cycle 2 2, and the average current of the negative current is 0.1 to 3 A / dm 2 2, with a solution temperature of 10 to 40°C, preferably with an average current density of the positive current of 0.6 to 2.0 A / dm in one cycle 2 2, and the average current of the negative current is 0.0 to 3.0 A / dm 2 2, with a solution temperature of 20 to 30°C, using a single or a combination of two or more of DC waveform, AC waveform, pulse waveform, and PR pulse waveform of current or voltage waveforms for anodization at a solution temperature of 10 to 40°C to produce an anodic oxide film with a thickness of 6 to 50 μm.

[0024] The current density in the commonly used DC electrolysis refers to the amount of electricity (A·s) divided by the electrolysis time (s) and the surface area of the object to be treated (dm 2The value obtained by dividing by 2 is referred to. In direct current constant current electrolysis (usually called direct current electrolysis), since there is no current change over time with respect to the object to be treated, the current density and the average current density are used as synonyms, and the unit is A / dm 2 . However, in the case of pulse, PR pulse waveforms, etc., a "positive current", "0 (time when current does not flow)", or "negative current" with reversed polarity flows over time. Therefore, the average current density in the waveform needs to be expressed as the value obtained by dividing the electrical quantity (A·s) of each of the positive current part and the negative current part by the electrolysis time and the surface area of the object to be treated in one cycle (cycle) of the current waveform, as the positive current average current density and the negative current average current density. As an example, in the case of a PR waveform, when electrolyzing an object to be treated with an electrolysis area of 2 dm 2 , if one cycle of the waveform is 10 seconds, the positive current of 2 A flows for 4 seconds and then the negative current of 1 A flows for 6 seconds, the average current density of the positive current and the negative current are 0.4 A / dm 2 and 0.3 A / dm 2 respectively. When only the positive current is used, the average current density of the negative current is 0.0 A / dm

[0025] Those that can be added as additives to an electrolytic solution mainly composed of an organic acid are one or more compounds of an inorganic acid type or an organic acid type. Additives for an electrolytic solution mainly composed of an inorganic acid are also one or more compounds of an inorganic acid type or an organic acid type. As the organic acid type compounds, they are the aliphatic or aromatic sulfonic acids and / or carboxylic acid type compounds described above, but those different from the organic acids used in the electrolytic solution mainly composed of an organic acid are used as additives. In addition, alcohol type compounds such as ethylene glycol, diethylene glycol, and glycerin can also be used as solvents, and the amount thereof is up to 60%, and these alcohol type compounds can also be used as part of the solvent together with water. As the inorganic acid type compounds, boric acid, silicic acid, hydrofluoric acid, sulfuric acid, phosphoric acid, nitric acid or their salts, pyrophosphoric acid, sulfamic acid or their salts, or one or more of fluoride salts, bifluoride salts, permanganate salts, etc. can be used. The usage amount of these additives is preferably less than the usage amount of the organic acid mainly used in the electrolytic solution, and the liquid concentration is 0.001 to 0.9 mol / L.

[0026] In addition, the anodic oxidation film of the present invention has excellent corrosion resistance and at the same time has a hardness of 200 HV or more and less than 300 HV in the Vickers hardness test. Furthermore, it simultaneously has an excellent characteristic that the electromagnetic field characteristics are equivalent to those of the aluminum substrate at 500 KHz to 1000 MHz in the electromagnetic wave shielding effect.

[0027] The measurement of the electromagnetic wave shielding effect of the film of the present invention was carried out by the KEC method at the KEC Kansai Electronic Industry Promotion Center, Test Business Department from 100 KHz to 1000 MHz (1 GHz) for electrolysis and magnetic field measurement. As a guaranteed value, there is 30 db or more at 500 KHz to 1000 MHz (1 GHz), which is the same value as the aluminum substrate and has a shielding effect equivalent to the limit value of aluminum. As a result, it has heat resistance and corrosion resistance, so it is difficult to be corroded, the shielding effect is maintained stably over a long period of time, and it is also difficult to be damaged, and it also plays a role as a material with good heat absorption and radiation, and is considered as an unprecedented material.

[0028] Electromagnetic waves are waves (fluctuations) formed by changes in the electric and magnetic fields in space. Light and radio waves are a type of electromagnetic wave. Generally, those with wavelengths longer than infrared rays (more than mm) are called radio waves, those up to about 1 μm are infrared rays, those from 0.7 to 0.3 μm are visible light, those even shorter up to several nm are called ultraviolet rays, and those from 10 nm to 1 pm are roughly classified as X-rays. Also, electromagnetic waves have both wave and particle properties. They exhibit various wave properties such as scattering, reflection, refraction, and interference depending on the wavelength, while microscopically, they can be counted as particles. The radio waves used in the present invention are roughly classified into long waves (LF), medium waves (MF), short waves (HF), very high frequency waves (VHF), ultra-high frequency waves (UHF), centimeter waves (SHF), millimeter waves (EHF), and sub-millimeter waves. Among these, in the range of 500 KHz to 1000 MHz (1 GHz) of medium waves to ultra-high frequency waves, the purpose is to shield the wavelength range used mainly for mobile phones, smartphones, TVs, taxi radios, aircraft phones, AM radios, FM broadcasts, ships, international broadcasts, beacons for ships and aircraft, etc.

[0029] In recent years, mobile phones have become smartphones, and many devices such as robots and drones communicate wirelessly, filling the surroundings with electronic devices. The electromagnetic compatibility (EMC countermeasures) of receiving necessary electromagnetic waves and eliminating (shielding) unnecessary electromagnetic waves has been increasing. Also, in addition to noise countermeasures between devices, there are actually many people who are concerned about the effects on the human body such as electromagnetic hypersensitivity. Here, generally, electromagnetic shielding is called RF and targets frequencies from about 300 Hz to 3 THz. The basis of electromagnetic shielding is to improve the shielding performance from reflection loss, absorption loss, or multiple reflection loss which is a combination of them. Reflection loss is the loss (attenuation) caused by the reflection of electromagnetic waves on the shield surface when they are incident on and transmitted through the shield material. Absorption loss is that when electromagnetic waves are incident on the shield material, they are absorbed as induced currents inside the shield material. Multiple reflection loss is to stack multiple shield materials in a laminate. When electromagnetic waves penetrate inside the shield material, some are reflected, some are transmitted, and they propagate to the next shield material, repeating reflection, penetration, and transmission again to attenuate and enhance the shielding effect.

[0030] The electromagnetic shielding effect is expressed in decibels (dB). It is a unit that relatively represents how much the electromagnetic wave is attenuated before and after shielding, and is derived from the following calculation formula. Decibel (dB) = 20Log 10 (E0 / E1 E0: Electric field strength (V / m) when there is no shielding material E1: Electrolytic strength (V / m) transmitted through the shielding material The relationship between decibels, shielding rate, and attenuation rate is shown in Table 3. Typical methods for evaluating the performance of electromagnetic shielding materials are the "KEC method" developed by the Kansai Electronic Industry Center and the "Advantest method" developed by Advantest Corporation.

[0031]

Table 3

Advantages of the Invention

[0032] The anodic oxide film of aluminum was originally developed as an insulating material. After years of improvement, it has become today's anodic oxide film, which has undoubtedly contributed to the development of aluminum. However, due to the recent progress of semiconductors, the mounting density has increased significantly, and along with this, the miniaturization of electronic devices has advanced rapidly. As a result, the space that was not a problem conventionally has been extremely narrowed, and sparks generated by static electricity have occurred, leading to serious damage to electronic devices. To solve this problem, a film that is a conductor and can satisfy LCA and always discharges static electricity to the ground without accumulating it on the surface has been required. At this time, the anodic oxide film of the present invention has been developed as an excellent film that has conductivity, corrosion resistance, electromagnetic shielding effect, and antistatic effect. By combining these, it is expected to be used for further miniaturization of electronic devices, the shielding effect of 5G in communication, and charging of smartphones, etc.

Best Mode for Carrying Out the Invention

[0033] Hereinafter, embodiments of the present invention will be specifically described. In the examples, the method for measuring electrical resistance was performed using the direct current four-terminal method (voltage drop method), which is excellent for low-resistance measurement, between the film surface and the aluminum substrate as shown in Fig. 6. With a resistance meter RM3548 (manufactured by Hioki Electric Co., Ltd.) "8", electrodes "11" with gold plating on copper of 1 cm 2 were placed on the surface of the anodic oxide film "12" and the substrate "3". This electrode consists of four electrode terminals including current source terminals ▲a▼ and ▲d▼ that supply a constant current, and voltage detection terminals ▲b▼ and ▲c▼ that detect voltage drops. These were placed linearly with a distance of 1 cm between each electrode, with ▲a▼ and ▲b▼ on the substrate surface and ▲c▼ and ▲d▼ on the film surface. The outer electrode terminals ▲a▼ and ▲d▼ were held with alligator clips, and a load of 50 g / cm 2 was applied to the surface of the inner ▲b▼ and ▲c▼ electrodes to measure the electrical resistance. The electrical resistance was measured at least twice by changing the location of the terminals using the above method, and the average electrical resistance was used. The corrosion resistance test was carried out using a neutral salt spray tester of JIS-Z2371 (manufactured by Suga Test Instruments Co., Ltd.). After 336 hours of continuous spraying, the evaluation was performed according to JIS-H8679-1 (Evaluation method for pitting corrosion occurring in anodic oxide films of aluminum and aluminum alloys - Part 1: Rating number method (RN)). In practice, after removing the surface corrosion products physically and chemically after taking them out of the salt spray tester, and drying, they were evaluated by comparing with the rating number standard chart. The abrasion resistance is the measured value measured under the general film test conditions of a reciprocating plane abrasion tester manufactured by Suga Test Instruments Co., Ltd. with abrasive paper CP320, a pressing force of 3.9 ± 0.1 N, 40 ± 2 ds / min, a preliminary abrasion of 50 ds, and 300 ds of the number of times, according to JIS-H8682-1. The Vickers hardness test shows the average film hardness measured by using a microhardness tester (HMV-G-XY-D) manufactured by Shimadzu Corporation with a load of 10 gf for 15 seconds by the microscopic cross-section measurement method. However, when the film thickness is 20 μm or less, it is measured using a Knoop-type indenter with the same load and the same time. The film thickness shows the average thickness measured by an eddy current film thickness gauge (LH-373) manufactured by Kett Science Laboratory Co., Ltd. The measurement of the electromagnetic shielding effect represents the results of measuring the electric field and magnetic field up to 100 KHz - 1000 MHz (1 GHz) by the KEC method in the KEC Kansai Electronic Industry Promotion Center, Test Business Department of the General Incorporated Association KEC.

Example 1

[0034] Using an aluminum A1050 material (Si 0.25%, Mn 0.05% or less) with a test piece of 70×150×t1.0 mm as pretreatment, emulsion degreasing at 45°C for 5 minutes ⇒ 5% nitric acid at room temperature for 3 minutes ⇒ etching with 20% sodium hydroxide at room temperature for 1 minute ⇒ desmearing with 10% sulfuric acid at room temperature for 3 minutes. The electrolyte for the first electrolysis is 2 mol / L sulfuric acid, 0.5 mol / L phosphoric acid, the bath temperature is 21±1°C, the power supply uses a DC waveform, and the current density is 1.2±0.1 A / dm 2 for 60 minutes. For the second electrolysis, without turning off the power supply, maintain the final voltage of the first electrolysis at 17V for 2 minutes, then lower it by 3V and hold at 14V for 60 seconds, further lower it by 3V and hold at 11V for 60 seconds, lower it by 3V and hold at 8V for 60 seconds, and then lower it by 2V each time while maintaining a 60-second hold at 6V, 4V, and 2V until reaching 0V with a hold time of 180 seconds. After the second electrolysis, thoroughly wash with water. For the third electrolysis, perform direct current electrolysis. The liquid composition is a solution of 300 g / L zinc sulfate, 28 g / L ammonium sulfate, and 25 g / L boric acid, with a pH of 2 - 3.5 and a bath temperature of 29±1°C. Immerse in the solution for 30 seconds, then raise the voltage to 15V in 2 seconds, hold for 20 seconds, and immediately lower it to 0V. For the fourth electrolysis, electrolyze in the solution of the third electrolysis at a bath temperature of 29±1°C, with a DC waveform and a voltage of 3V for 17 minutes to deposit metal in the pores. Furthermore, perform a sealing treatment by boiling water sealing at 95 - 98°C for 20 minutes. As a result, the average electrical resistance between the film surface and the aluminum substrate is 8.3×10 -3 Ω, the corrosion resistance is RN9.0 in a salt spray test for 336 hours, the hardness is an average film hardness of 263 HV measured by the microscopic cross-section measurement method, the wear resistance is 33 ds / μm under general film conditions, the average film thickness is 20.8 μm, the color tone is a dark brown system, and an electromagnetic wave shielding effect of a film with an electric field of 34 dB or more and a magnetic field of 30 dB or more was obtained. Comparative Example 1

[0035] The material, pretreatment, first, second, fourth, sealing treatment, and film measurement were carried out in the same manner as in Example 1, and the treatment was performed except for the third electrolysis. When measuring the average electrical resistance between the film surface and the aluminum substrate by the four-terminal method, it was 1.8×10 0Ω, corrosion resistance is RN7.0 in a salt spray test for 336 hours, hardness is an average film hardness of 283 HV by microscopic cross-section measurement method, wear resistance is 52 ds / μm under general film conditions, average film thickness is 20.6 μm, color tone is black-brown, and an electromagnetic wave shielding effect of a film with an electric field of 37 dB or more and a magnetic field of 33 dB or more was obtained. However, the material intended by the present invention cannot be obtained by this manufacturing method. Comparative Example 2

[0036] The material, pretreatment, sealing treatment, and film measurement were carried out in the same manner as in Example 1. The first step was 98 g / dm 3 sulfuric acid aqueous solution, 30 °C, voltage 20 V (about 3 A / dm 2 ), for 30 minutes, the counter electrode was carbon for electrolysis. For the barrier removal in the second step, the bath voltage was lowered to 0.08 V in 3 minutes before the end of electrolysis and the power supply was turned off, and further, while the test piece and the counter electrode (carbon) were connected with a conducting wire, galvanic dissolution was carried out in the solution for 15 minutes. The third step was electroplating of zinc. The solution composition was 350 g / L zinc sulfate - 30 g / L ammonium sulfate - 30 g / L boric acid - 15 g / L dextrin, the counter electrode was zinc, PH = 2 to 3.5, bath temperature 30 ± 1 °C, current density 1.0 A / dm 2 and electrolysis was carried out for 20 minutes. As a result, the average electrical resistance measured by the four-terminal method between the film surface and the aluminum substrate was 4 × 10 -1 Ω, cross-section film hardness was HV380, cross-section average film thickness was 26 μm, corrosion resistance was RN9.0 in a salt spray test for 336 hours, wear resistance was 110 ds / μm, color tone was black-brown, and an electromagnetic wave shielding effect of a film with an electric field of 35 dB or more and a magnetic field of 32 dB or more was obtained. However, the electrically conductive material intended by the present invention cannot be obtained by this manufacturing method.

Example 2

[0037] The material, pretreatment, sealing treatment, and film measurement were carried out in the same manner as in Example 1. The first electrolysis was carried out with sulfuric acid 1.2 mol / L, oxalic acid 0.02 mol / L, solution temperature 20 ± 1 °C, using a DC waveform, voltage 14 to 30 V, current density 0.8 to 1.2 A / dm 2, perform a 70-minute treatment. As the second electrolysis, after maintaining at 30V for 2 minutes at the liquid and liquid temperature of the first electrolysis, lower the voltage by 5V, hold for 120 seconds, further lower the voltage by 5V, repeat the 120-second hold, and continue until 10V. After holding at 10V for 120 seconds, sequentially lower the voltage to 8V, 6V, 4V, 2V with a holding time of 120 seconds each, perform until 0V for 18 minutes, hold at 0V for 3 minutes, then take out and wash thoroughly with water. As the third electrolysis, use direct current electrolysis. The liquid composition is a solution of 300g / L zinc sulfate, 28g / L ammonium sulfate, and 25g / L boric acid, with a pH of 2 - 3.5, a bath temperature of 29 ± 1°C. After immersion in the liquid, leave it for 30 seconds, then raise the voltage to 30V in 3 seconds, hold for 15 seconds, and immediately lower it to 0V. The fourth electrolysis is carried out in the liquid of the third electrolysis at a bath temperature of 29 ± 1°C, with a direct current waveform, a voltage of 3V, and electrolysis for 7 minutes to deposit metal at the bottom of the pores, then wash thoroughly with water. The fifth electrolysis is for two-stage metal deposition, with 280g / L nickel sulfate, 45g / L nickel chloride, 30g / L boric acid, 15g / L cobalt sulfate, 1g / L saccharin, a pH of 4.0, a liquid temperature of 47 ± 1°C, and a current density of 0.15A / dm 2 , perform the treatment for 20 minutes with a counter electrode of Ni. After thoroughly washing with water, perform a sealing treatment by boiling water sealing at 95 - 98°C for 20 minutes. As a result, the average electrical resistance measured by the four-terminal method between the film surface and the aluminum substrate is 7.9×10 -3 Ω, the corrosion resistance is RN8.0 in a salt spray test for 336 hours, the hardness is an average film hardness of 293HV by the microscopic cross-section measurement method, the wear resistance is 46ds / μm under general film conditions, the average film thickness is 22.7μm, the color tone is a dark brown system, and an electromagnetic shielding effect of a film with an electric field of 38dB or more and a magnetic field of 34dB or more is obtained. Comparative Example 3

[0038] For the materials, pretreatment, first, second, sealing treatment, and film measurement, perform them in the same manner as in Example 1. For the third electrolysis solution, use 250g / L nickel sulfate, 40g / L nickel chloride, 25g / L boric acid, 15g / L cobalt sulfate, 1g / L saccharin, a pH of 4.0, a liquid temperature of 47 ± 1°C, with a counter electrode of Ni. After immersion in the liquid, leave it for 30 seconds, then raise the voltage to 10V in 2 seconds, hold for 15 seconds, and immediately lower it to 0V. The fourth electrolysis is carried out in the same liquid at a current density of 0.15A / dm 2 , perform the treatment for 20 minutes. After thoroughly washing with water, perform a boiling water sealing treatment at 95 - 98°C for 20 minutes. As a result, the average electrical resistance measured by the four-terminal method between the film surface and the aluminum substrate is 4×10 -3Ω, the average cross-sectional film hardness is HV326, the average cross-sectional film thickness is 21.8 μm, the corrosion resistance is RN7.0 in a salt spray test for 336 hours, the abrasion resistance is 127 ds / μm, the color tone is a dark brown system, and an electromagnetic wave shielding effect of a film with an electric field of 37 dB or more and a magnetic field of 33 dB or more was obtained. However, with this manufacturing method, a material excellent in corrosion resistance aimed at by the present invention cannot be obtained. Comparative Example 4

[0039] The material, pretreatment, sealing treatment, and measurement of the film were carried out in the same manner as in Example 1. For the first electrolysis, 95 g / L of sulfuric acid, a liquid temperature of 20 - 21°C, a DC waveform was used, the voltage was 14 - 16 V, and the current density was 1.0 - 1.1 A / dm 2 and treatment was carried out for 30 minutes. After sufficiently washing with pure water, for the electrolytic coloring of tin, with a liquid composition of 12.5 g / L of stannous sulfate, 10 g / L of tartaric acid, 10 g / L of boric acid, and a pH of 0.7 - 1.2, after immersing the workpiece in the liquid at a liquid temperature of 20 - 21°C for 2 minutes, an AC waveform was used, electrolysis treatment was carried out at a voltage of 12.5 V for 10 minutes, and then a sealing treatment was carried out. As a result, the average electrical resistance measured by the four-terminal method between the film surface and the aluminum substrate was 2.5 - 7.5×10 4 Ω, the corrosion resistance was RN9.8 or more, the average film thickness was 9.3 μm, the Vickers cross-sectional average hardness HV284, and a black film was obtained. With this manufacturing method, the material aimed at by the present invention cannot be obtained.

Industrial Applicability

[0040] The material of the present invention is an anodic oxidation film of aluminum, having a low-resistance film of 1×10 -2 Ω or less and a corrosion resistance of RN8 or more for 336 hours. By having both, it has conductivity, is corrosion-resistant, is lightweight and difficult to be damaged, prevents damage due to electrostatic sparks in a housing and electronic devices, has a remarkable magnetic field shielding effect from 500 KHz to 1000 MHz, and is expected to be used as a conductive material having corrosion resistance.

Brief Description of the Drawings

[0041]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Explanation of symbols

[0042] 1. Micropore 2. Wall 3. Material (aluminum) 4. Porous layer 5. Barrier layer 6. Metal precipitation serving as nuclei at the bottom in the micropores 7. Metal precipitation into the micropores 8. Resistance meter: RM3548 9. DC constant voltage power supply 10. Voltmeter 11. Gold plating electrode 12. Anodic oxide film

Claims

1. When anodizing aluminum or its alloy, as the liquid composition, for the first electrolyte, an inorganic acid-based sulfuric acid-based or sulfamic acid-based electrolyte is used, and / or one or more of an organic acid-based aliphatic or aromatic sulfonic acid, carboxylic acid, or its anhydride or their salts are used to perform the first electrolysis. As the second electrolysis, the voltage is gradually decreased in the same or a different electrolyte as the first electrolyte until it is substantially decreased to 0 V. After the second electrolysis is completed, the anodized product is taken out and thoroughly washed with water. As the third electrolysis, the voltage is rapidly increased in an acidic solution containing a metal at a liquid temperature of 10 to 40°C, and then rapidly decreased to 0 V after 1 to 30 seconds. The fourth electrolysis is performed in the same solution as the third electrolysis. The average electrical resistance measured by the four-terminal method between the film surface and the substrate is 1×10 －２ Ω or less, the corrosion resistance is tested by a salt spray test for 336 hours, RN8 or more, and the film cross-sectional hardness has a performance of 200 HV or more and less than 300 HV in a Vickers hardness test. A manufacturing method of a material made of aluminum or its alloy having an anodized film with such properties.

2. The first electrolysis of the electrolysis method is carried out using an inorganic and / or organic electrolyte solution at a liquid temperature of 10 to 40 °C, an electrolysis time of 20 to 90 minutes, and a current density of 0.6 to 3.0 A / dm ２ , by an electrolysis method with a voltage of 10 to 100 V or an average current density of the positive current in one cycle of 0.1 to 3 A / dm ２ , and an average current density of the negative current of 0.0 to 3 A / dm ２ . The second electrolysis is carried out in the same solution by gradually decreasing the voltage from the final voltage to 0 V in steps of 1 to 10 V and holding for 5 to 120 seconds in that state, then further decreasing by 1 to 10 V and repeating the holding for 5 to 120 seconds. After decreasing to around 10 V and holding for 5 to 120 seconds, it is sequentially decreased to 8 V, 6 V, 4 V, 2 V, 1 V, and then to 0 V. The holding time at this time is 5 to 120 seconds. After a total of 5 to 40 minutes, thorough water washing is carried out. Then, as the third electrolysis, in an acidic solution containing metal, at a liquid temperature of 10 to 40 °C, the electrolysis uses a DC, pulse, or PR pulse waveform to raise the voltage from 10 to 30 V in 1 to 10 seconds and then immediately return to 0 V after 1 to 30 seconds. Furthermore, the fourth electrolysis is carried out in the same solution as the third electrolysis using a DC, AC, pulse, or PR pulse waveform with an electrolysis current density of 0.1 to 5.0 A / dm ２ , and an electrolysis time of 2 to 30 minutes. A manufacturing method of a material made of aluminum or an alloy thereof having an anodic oxide film excellent in conductivity and corrosion resistance according to claim 1, characterized in that the above is carried out.

3. When anodizing aluminum or its alloy, the first electrolysis is carried out using an organic and / or inorganic electrolyte solution at a liquid temperature of 10 to 40 °C, a current density of 0.6 to 3.0 A / dm ２ , a voltage of 10 to 100 V, an electrolysis method for 20 to 90 minutes, or an electrolysis method with an average current density of positive current of 0.0 to 3 A / dm ２ , and an average current density of negative current of 0.1 to 3 A / dm2. The second electrolysis is carried out in the same solution by gradually lowering the voltage from the final voltage of the first electrolysis to 0 V. From the final voltage to around 10 V, it is lowered by 1 to 15 V, held for 5 to 120 seconds, lowered by 1 to 15 V, held for 5 to 120 seconds, and repeated until around 10 V. After holding for 5 to 120 seconds, it is sequentially lowered to 8 V, 6 V, 4 V, 2 V, 1 V, and then to 0 V. The holding time at this time is 5 to 120 seconds. After a total of 3 to 40 minutes, thorough water washing is carried out. Further, as the third electrolysis, in an acidic solution containing a metal, at a liquid temperature of 10 to 40 °C, the electrolysis uses a DC, pulse, or PR pulse waveform to raise the voltage from 10 to 30 V in 1 to 10 seconds, and after 1 to 60 seconds, it returns to 0 V at once. Further, as the fourth electrolysis, at the same liquid and liquid temperature as the third electrolysis, the current density is 0.1 to 3.0 A / dm ２ , or a voltage of 3 to 8 V, and an electrolysis time of 2 to 30 minutes. Then, as a further electrolysis, in an acidic solution containing a metal salt different from the third and fourth electrolyses, at a liquid temperature of 10 to 40 °C, the electrolysis uses a DC, pulse, or PR pulse waveform, and the current density is 0.1 to 3.0 A / dm ２ , or a voltage of 3 to 8 V, and an additional electrolysis with an electrolysis time of 2 to 30 minutes is carried out at least once. A method for manufacturing a material made of aluminum or its alloy having an anodic oxidation film excellent in conductivity and corrosion resistance, characterized in that the average electrical resistance measured by the four-terminal method between the film surface and the substrate is 1×10 －２ Ω or less, the corrosion resistance is tested by a salt spray test for 336 hours, RN8 or more, and the hardness is 200 HV or more and less than 300 HV.

4. A method for manufacturing an aluminum or its alloy material having an anodic oxidation film excellent in conductivity and corrosion resistance according to any one of Claims 1 to 3, characterized in that a current or voltage waveform of the first electrolysis and / or the second electrolysis of anodic oxidation treatment of aluminum or its alloy is a direct current waveform, an alternating current waveform, an alternating current / direct current superimposed waveform, a pulse waveform, a PR pulse waveform, alone or in combination of two or more of these waveforms.

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