KR101790975B1 - Surface treatment method of aluminium material - Google Patents

Abstract

The present invention relates to a method for producing an electrolytic solution, comprising: disposing an aluminum material as an anode in an electrolytic solution containing distilled water, citric acid, oxalic acid and boric acid; And an anodizing step of forming an oxide film by applying a constant voltage to the surface of the aluminum material. The method can remarkably increase the thickness of the oxide film compared to the conventional method of producing an aluminum film, and has excellent withstand voltage, corrosion resistance and thermal shock resistance , It does not require a post-treatment process such as a conventional sulfuric acid method or a chromic acid method, and thus it is excellent in economy and environment friendliness.

Description

TECHNICAL FIELD [0001] The present invention relates to a surface treatment method of an aluminum material,

The present invention relates to a surface treatment method of an aluminum material, and more particularly, to a surface treatment method of an aluminum material using anodizing.

Aluminum (Al) material is high in dimensional precision and can be mass-produced in a shorter time than iron in the production of lightweight castings. They are also widely used in a variety of industries due to their high castability, low density, high productivity, low shrinkage and relatively high strength.

Aluminum uses range from transportation equipment such as aircraft, railway and automobiles to electricity, electronics, and general machinery. Specifically, it is widely used in cases such as a transmission housing, an engine cylinder and a block, a fuel measuring device, and the like, and a component of a transportation device having a complicated shape. Along with the development of the IT industry, aluminum is also widely used in cases of portable electronic devices such as portable computers, tablet PCs and smart phones.

Despite these advantages and various applicability, aluminum needs to be improved in corrosion resistance and reliability, since corrosion may occur in less severe environments, resulting in deterioration of mechanical properties.

Methods for improving the disadvantages of aluminum include a method of using aluminum as an alloy by adding elements such as Mn, Mg, Si, and Cr, an anodizing method of producing an artificial anodic oxide coating on the surface of aluminum alloy, A chromate coating method and a phosphate coating treatment method which produce a chemical conversion coating capable of conducting electricity. Of these, the anodizing method can be considered as a method having a high functionality for forming a protective coating of an aluminum alloy material.

The anodizing method includes the acid method, the sulfuric acid method, and the chromic acid method depending on the type of electrolyte used in the electrolysis. Aluminum oxide (Al ₂ O ₃ ) coating is formed by oxidizing the surface of aluminum by the oxygen generated from the anode by applying a direct current power with an aluminum material to be surface treated as an anode, And is formed into a porous structure having a large corrosion resistance and a very small diameter. The higher the purity of aluminum, the more beautiful and glossy the coating can be obtained.

However, in the case of anodizing by the sulfuric acid method or the chromic acid method as described above, there is a phenomenon that a porous structure in which numerous fine pores are present in the oxide film layer formed on the aluminum surface is generated. Such a porous structure, Although it has advantages for coloring, it has a disadvantage in that it is not suitable for a product to be used for industrial use due to its poor mechanical, chemical and electrical characteristics. Therefore, a post-treatment process of a sealing process for filling micropores of the porous structure is indispensably required.

However, the sealing process has various problems such as difficulties in process control, whitening on the surface, and separation of the oxide layer easily.

On the other hand, when anodizing is carried out by the aquatic method, the thickness and the surface strength of the oxide film layer are difficult to reach a satisfactory level, resulting in a problem that the oxide film layer is easily corroded.

The present inventor has accomplished the present invention in order to sufficiently grow the thickness of the oxide film layer compared with the conventional sulfuric acid method or chromic acid method using the oxalic acid method and at the same time to improve the mechanical properties and chemical properties of the oxide film layer.

The object of the present invention is to provide a method for surface treatment of an aluminum material, which can significantly increase the thickness of an oxide film compared to an anodizing method using a conventional acid method.

Another object of the present invention is to provide a surface treatment method of an aluminum material capable of forming an oxide film having excellent resistance to voltage, corrosion resistance and thermal shock resistance.

Another object of the present invention is to provide a method for surface treatment of an aluminum material which is excellent in economy and is environmentally friendly because it does not require a post-treatment step such as a sealing process compared to the conventional anodizing method using a sulfuric acid method.

The above and other objects of the present invention can be achieved by the present invention described below.

One aspect of the present invention is a method for producing an electrolytic solution comprising: disposing an aluminum material as an anode in an electrolytic solution containing distilled water, citric acid, oxalic acid, and boric acid; And an anodizing step of forming an oxide film (Al ₂ O ₃ ) by applying a constant voltage to the surface of the aluminum material.

In one embodiment, the concentration of citric acid in the electrolytic solution is 8 to 11 M, the concentration of oxalic acid is 0.8 to 8 M, and the concentration of boric acid may be 0.5 to 1 M.

In one embodiment, the application of the constant voltage may be a constant voltage of 25 V to 35 V, a constant voltage of 3 V to 30 V, a constant voltage of 5 V, and a constant voltage of 180 to 380.

In one embodiment, the constant voltage application includes a first step of applying a constant voltage from 25V to 35V; A second step of increasing the voltage by 5 V every 3 minutes for 12 minutes and applying a constant voltage; A third step of increasing the voltage by 5 V every 10 minutes for 60 minutes and applying a constant voltage; A fourth step of increasing the voltage by 5 V every 30 minutes for 120 minutes and applying a constant voltage; And a fifth step of applying a constant voltage from 95V to 105V for 120 minutes to 150 minutes.

In one embodiment, the temperature of the electrolytic solution may be 10 to 25 캜.

Another aspect of the present invention relates to an aluminum material comprising an oxide film formed by the above-mentioned method of surface treatment of an aluminum material.

In one embodiment, the thickness of the oxide film may be 40 占 퐉 to 100 占 퐉.

The surface treatment method of the aluminum material of the present invention can remarkably increase the thickness of the oxide film compared to the conventional anodizing method according to the method of the present invention, and provides an oxide film excellent in withstand voltage, corrosion resistance and thermal shock resistance.

The surface treatment method of the aluminum material of the present invention does not require a post-treatment step such as a sealing process or the like compared to the conventional anodizing method according to the sulfuric acid method or chromic acid method, and thus is excellent in economy and environment friendliness.

Fig. 1 schematically shows an anodizing apparatus used in Example 1. Fig.
Fig. 2 (a) is a photograph of the surface of the oxide film formed in Example 1, and Fig. 2 (b) is a photograph of the surface of the oxide film formed in Comparative Example 1, respectively, taken by an electron microscope (X500).
Fig. 3 (a) is a cross section of the oxide film formed in Example 1, and Fig. 3 (b) is a photograph of the cross section of the oxide film formed in Comparative Example 1, respectively, by an electron microscope (X500).

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

In the present invention, the aluminum material is defined to include both an aluminum alloy for commercial processing or high-purity aluminum having a purity of 99% or more.

The present invention relates to a method for surface treatment of an aluminum material using aluminum anodizing.

Hereinafter, the surface treatment method of the aluminum material of the present invention will be described in more detail.

First, various foreign substances formed on the surface of the aluminum material are removed. Specifically, the foreign matter removal includes a degreasing step, an etching step, and a desmut step.

The degreasing step is a step of removing various kinds of oil adhering to the aluminum surface by flowing into the mold in an aluminum die casting molding step, for example, by a method in which aluminum is precipitated in washing water at 25 to 35 ° C for 10 to 30 minutes . At this time, surfactants such as nonionic, anionic, and cationic surfactants may be further added to the washing water. In particular, TX-100, which is a nonionic surfactant, is preferably used.

Next, the etching step is a step for removing surface impurities such as foreign substances and scratches present on the aluminum surface. The aluminum is wiped with an alkaline component such as sodium hydroxide for 15 to 30 seconds at 30 to 45 ° C to remove the component .

The desmutting step is a step for removing impurities generated on the aluminum surface after the etching, and may be performed by a method of cleaning an aluminum surface using a nitric acid or a hydrogen peroxide mixture. At this time, the desmutting step may be performed at room temperature.

During the degreasing, etching, and desmutting steps, the flushing process may be performed, and the flushing process may be performed after the flushing process is performed using the spraying or bathing process.

The foreign matter removing process including the degreasing, etching, and dismounting steps may not necessarily be performed all at once, but may be carried out selectively as needed. In addition, it is needless to say that the cleaning agent and the chemical concentration, the temperature, and the treatment time may be variously changed according to the size and shape of the aluminum during the foreign substance removing process.

After removing the foreign substances on the aluminum material surface as described above, a surface treatment method using anodizing is performed.

According to an embodiment of the present invention, there is provided a method for surface treatment of an aluminum material, comprising: disposing an aluminum material as an anode in an electrolytic solution containing distilled water, citric acid, oxalic acid, and boric acid; And an anodizing step of forming an oxide film by applying a constant voltage.

The electrolytic solution uses distilled water (DI water) as a solvent and includes citric acid, oxalic acid, and boric acid as solutes.

The concentration of citric acid may be 8M to 11M, preferably 8.5M to 10.5M. The corrosion resistance and the withstand voltage of the oxide film formed in the above range can be improved.

The concentration of oxalic acid may be from 0.8M to 8M, preferably from 2M to 5.5M. If the concentration of oxalic acid is less than 0.8M, the formation rate of the oxide film may be lowered, and if it is more than 8M, the quality of the oxide film may be deteriorated.

The concentration of the boric acid may be 0.5M to 1M. When the concentration of the boric acid is less than 0.5 M or exceeds 1 M, it is difficult to sufficiently increase the thickness of the oxide film.

The temperature of the electrolytic solution may be 10 to 25 ° C, and may be 12 to 18 ° C. When the temperature is less than 10 ° C, the rate of formation of the oxide film can be remarkably slowed. When the temperature exceeds 25 ° C, the oxide film is formed unevenly and a product of good quality can not be obtained

The application of the constant voltage in the anodizing step may be performed by applying a constant voltage from 25 V to 35 V for the first time, then increasing the voltage by 5 V at intervals of 3 minutes to 30 minutes, and applying a constant voltage. At this time, the constant voltage application time may be 180 minutes to 380 minutes.

Specifically, the constant voltage application may include a first step of applying a constant voltage from 25V to 35V; A second step of increasing the voltage by 5 V every 3 minutes for 12 minutes and applying a constant voltage; A third step of increasing the voltage by 5 V every 10 minutes for 60 minutes and applying a constant voltage; A fourth step of increasing the voltage by 5 V every 30 minutes for 120 minutes and applying a constant voltage; And a fifth step of applying a constant voltage from 95V to 105V for 150 to 210 minutes.

The present invention also provides an aluminum material surface-treated in the same manner as described above. The thickness of the oxide film (Al ₂ O ₃ ) formed by the surface of the aluminum material may be 40 μm to 100 μm. The oxide film is transparent or semitransparent and has a significantly thicker film thickness than that of the oxide film formed by the conventional acid method, and has excellent characteristics of withstand voltage, corrosion resistance and thermal shock resistance.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

Example  One

Pretreatment of specimen

Aluminum material (A6061) having a purity of 99.0% or more was degreased and etched to remove impurities and oils and oxides on the surface of the specimen. The etching was dipped in a 10 wt% aqueous solution of NaOH at 45 ° C for 40 seconds.

Alkali degreasing of the specimen leaves a black metal alloy component on the surface of the specimen, which is called a smut. Generally, when the content of the alloy component in the aluminum alloy material is large, many smut is formed and the color becomes black. The desmut exposes the pure aluminum substrate to the surface. The desmut process was immersed in a 50 vol.% Nitric acid (HNO ₃ ) solution at room temperature for 60 seconds. After each process, rinsing was performed with secondary distilled water to remove the pretreatment solution and impurities remaining on the surface of the sample, and residual H ₂ O was removed using an air gun.

Anodizing  step

Fig. 1 schematically shows an anodizing apparatus used in Example 1. Fig. The anodizing step performed in Example 1 will be described with reference to FIG.

The anodizing step was carried out by a constant voltage method. The temperature of the electrolytic solution 110 was 15 占 폚.

In order to keep the temperature of the electrolytic solution constant during the anodizing process, the cooling water was forcibly circulated by using a circulating water bath (100) having a circulator (120), and the temperature of the electrolytic solution Agitating was performed using an air pump 120 for the purpose of uniformizing the distribution and thickness of the oxide film, preventing burning due to high-speed electrolysis, supplying oxygen, and increasing the cleaning effect.

The pretreated aluminum specimen A6061 was disposed as an anode 130 and the aluminum specimen A6061 was disposed as a counter electrode 140. The electrode distance was fixed to 5 cm Anodizing was performed.

The electrolytic solution 100 contained citric acid, oxalic acid, and boric acid as distilled water (DI water) and an electrolyte, and the concentrations of electrolytes were citric acid 9M, oxalic acid 5M, and boric acid 0.8M.

With constant voltage

The constant voltage applied in the anodizing step and the application time are shown in Table 1 below. The total time required to apply the constant voltage was 333 minutes.

Step Progress Time (min) Application time (min) The applied voltage (Volt) One t = 0 3 30 2 3 3 35 3 6 3 40 4 9 3 45 5 12 10 50 6 22 10 55 7 32 10 60 8 42 10 65 9 52 10 70 10 62 10 75 11 72 30 80 12 102 30 85 13 132 30 90 14 162 30 95 15 192 141 100

The properties of the oxide film formed on the aluminum sample after completion of the anodizing step were measured according to the following evaluation methods, and the results are shown in Table 2 below.

Comparative Example  One

Anodizing was carried out by the sulfuric acid method using the anodizing apparatus of Example 1, and anodizing was carried out by a constant current method using a direct current.

The composition of the electrolytic solution was only 1M of sulfuric acid (H ₂ SO ₄ ) as the electrolyte, and the temperature of the electrolytic solution was 0 ° C. The current density of the applied constant current was 2 A / dm ² , and the applied time was 120 minutes.

The properties of the oxide film formed on the aluminum sample after completion of the anodizing step were measured according to the following evaluation methods, and the results are shown in Table 2 below.

Comparative Example  2

Anodizing was carried out in the same manner as in Example 1, except that only the citric acid 9M and oxalic acid 5M were used as the electrolyte in the composition of the electrolytic solution.

Comparative Example  3

Anodizing was carried out in the same manner as in Example 1, except that anodizing was conducted in a constant current manner using a direct current. The current density of the applied constant current was 1 A / dm ² and the applied time was 120 minutes.

Property evaluation

Dielectric strength: Measured using a Hi-pot Tester 7600 according to KS D 8541. After grounding the oxide film formed on the test piece, the voltage at which the oxide film starts to be destroyed by the applied voltage was measured.

Corrosion resistance: Measured using KD-1M according to KS D 8316. Using a 10M aqueous solution of NaOH, the time required for dissipation and removal of the oxide film formed on the specimen was measured.

Heat shock resistance: The specimens were heated to 400 over 1 hour, then heat treated at 400 for 2 hours, and allowed to cool. The surface of the oxide film of the heat-treated specimen was observed for cracking using an electron microscope (magnification: X500). (O: crack occurrence, X: crack occurrence)

Oxide film
Thickness (㎛) Withstand voltage (V) Corrosion resistance (sec) Thermal shock resistance AVG V / m AVG sec / 탆 Example 1 44.5 탆 2.37 kV 53.26V 299s 6.7s O Comparative Example 1 50.2 탆 1.22 kV 24.30V 167s 3.3s X Comparative Example 2 28.7 탆 0.84 kV 17.25V 97s 1.2s X Comparative Example 3 35.4 탆 1.13 kV 21.15V 120s 1.8s X

As can be seen from the results shown in Table 2, the oxide film of Example 1 containing the citric acid, oxalic acid, and boric acid in the composition of the electrolytic solution and anodizing by the constant voltage method was superior to the oxide film of Comparative Example 1 formed by the conventional sulfuric acid method Has an equivalent level of thickness, and is excellent in withstand voltage, corrosion resistance and thermal shock resistance.

2 (a) and 2 (b) are photographs respectively showing the surface of the oxide film formed in Example 1 and Comparative Example 1, and Figs. 3 (a) and 3 (b) 1 is a photograph of a cross section of an oxide film formed in each case. 2 and 3, it can be seen that the oxide film formed by the sulfuric acid method of Comparative Example 1 cracked, while the oxide film of Example 1 did not crack.

The oxide film of Example 1 is significantly thicker than the oxide film of Comparative Example 2 in which boric acid is excluded in the composition of the electrolytic solution and Comparative Example 3 in which the anodization is carried out by the constant current method, Corrosion resistance and thermal shock resistance.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

Disposing an aluminum material as an anode in an electrolytic solution containing distilled water, citric acid, oxalic acid, and boric acid; And
And an anodizing step of applying an electrostatic voltage to form an oxide film,
Wherein the concentration of citric acid in the electrolytic solution is 8 to 11 M, the concentration of oxalic acid is 0.8 to 8 M, the concentration of boric acid is 0.5 to 1 M,
The constant voltage is applied by applying a constant voltage between 25V and 35V; A second step of increasing the voltage by 5 V every 3 minutes for 12 minutes and applying a constant voltage; A third step of increasing the voltage by 5 V every 10 minutes for 60 minutes and applying a constant voltage; A fourth step of increasing the voltage by 5 V every 30 minutes for 120 minutes and applying a constant voltage; And a fifth step of applying a constant voltage from 95V to 105V for 120 minutes to 150 minutes.
delete delete delete The method according to claim 1,
Wherein the temperature of the electrolytic solution is 10 to 25 占 폚.
delete delete

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