KR101908321B1 - Method of surface treatment for roof rack - Google Patents

Abstract

The present invention relates to a surface treatment method for an aluminum material and, more specifically, relates to a surface treatment method for an aluminum roof rack for a vehicle, which can improve quality of appearance of a vehicle and increase durability of a roof rack by maintaining metal texture of aluminum through surface treatment with respect to the aluminum roof rack installed at the outside of the vehicle and increasing corrosion resistance.

Description

TECHNICAL FIELD [0001] The present invention relates to a surface treatment for roof rack for automobile,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for an aluminum material, and more particularly, to a surface treatment method for an aluminum material roof rack provided outside the vehicle, It is a surface treatment method of aluminum roof rack for automobile which improves the quality and raises the durability of the roof rack.

BACKGROUND ART [0002] In recent years, technologies for improving fuel efficiency by reducing the weight of a vehicle have been steadily developed. In order to lighten the weight of such vehicles, materials made of aluminum, magnesium and titanium as main materials or auxiliary materials are used for the weight reduction of the material itself, that is, steel plates using the existing iron as the main material, and automobile parts using aluminum as a main material are typical. There is a roof rack installed in the vehicle.

The roof rack is widely used in vehicles, particularly sports utility vehicles (SUVs), and is used to fix various leisure products such as camping goods and water sports goods to the outside of the vehicle.

In the case of such aluminum materials, surface treatment technology is indispensable as it is a light metal because its corrosion resistance is insufficient. Surface treatment technology required for improving the mechanical properties of the material itself requires additional technology for surface enhancement as an exterior material.

As a conventional technique related to the surface treatment of an aluminum material, a pretreatment step of removing foreign matter and an oxide layer on the surface of an aluminum alloy using a strong acid aqueous solution as disclosed in Patent No. 10-1224537; The aluminum alloy having been subjected to the pretreatment step is immersed in an aqueous electrolyte solution having a concentration of 50 g / L to 70 g / L and a current density of 1.0 A / dm 2 to 2.0 A / dm 2 at a temperature of 20 ° C. to 40 ° C. for 30 minutes to 90 minutes An anodic oxidation step of forming a film of aluminum oxide by applying a direct current having And a sealing step of sealing the coated aluminum alloy, wherein the strong acid aqueous solution comprises an aqueous solution comprising 150 g / L to 200 g / L of H2SO4, 5 g / L to 10 g / L of an alpha-alcoholhexobutyric acid alkyl ester, A surface treatment method of an aluminum alloy for a plastic injection mold, which is a technique for surface treatment of an aluminum alloy, has limitations in its use for surface treatment for maintaining the exterior material of a vehicle, i.e., a metal texture.

Another conventional technique is an alkaline surface treatment method for a vehicle exterior material proposed in Japanese Patent Application Laid-Open No. 10-1291062.

The patent discloses a method for surface treatment of a vehicle exterior member, which comprises a pretreatment step (S 10) of pretreating a surface unevenness or foreign matter of an aluminum alloy material part, and an oxide film forming a dense pore layer excellent in alkali resistance (S30) for forming an alkali-resistant layer for preventing surface discoloration against strong alkali, a step (S30) for forming an alkali- (S 20) is a step of forming an alkali-resistant oxide film having a dense pore layer, wherein the electrolytic solution is sulfuric acid (specific gravity 1.8) An alkali-resistant surface of a car exterior material characterized by comprising 150 to 180 g / L of citric acid, 10 to 20 g / L of citric acid, 10 to 15 g / L of hexafluorosilicic acid, 1 to 2.5 g / L of glycerin and 1.5 to 2.75 g / A treatment method is proposed However, in the case of the alkaline oxidation film, the durability due to the oxidation film is improved to some extent. However, in the case of the exterior material installed outside the vehicle, it is important to improve the surface for maintaining the metal texture.

Korean Registered Patent No. 10-1224537 Korean Registered Patent No. 10-1291062

Accordingly, it is an object of the present invention to provide a surface treatment method of an aluminum roof rack for automobiles in which the surface of a roof rack made of an aluminum material is treated to increase the durability while keeping the metal texture intact, thereby preventing rust from occurring even for a long period of time.

Further, the sealing step is performed using the silicate-containing aqueous solution for filling the pore layer formed through the anodic oxidation, and the alkali layer coating film is thickly formed on the surface of the roof rack through the long life processing step after the sealing step Another object of the present invention is to provide a surface treatment method of an aluminum roof rack for automobiles having an original surface texture even when used for a long period of time by further improving durability by blocking surface corrosion of roof racks.

A surface treatment method of an aluminum roof rack for a vehicle according to the present invention is a surface treatment method of an aluminum roof rack provided on the outside of a vehicle, comprising: a material polishing step (S 10) for realizing metal luster through polishing of the material surface; An organic cleaning step (S 20) for removing organic substances remaining on the surface of the polished workpiece; a racking step (S 30) for fixing the organically cleaned workpiece using a jig to fix the organically cleaned workpiece in the treatment tank; (S 40) for removing organic substances, a pickling step (S 50) for washing with acid to form a film having a uniform thickness through activation of a material surface, an electrolytic treatment through transparent anodic oxidation on the surface of the pickled material A sealing step (S70) for filling the pore layer formed through the anodic oxidation; a bale pressing step (S80) for washing the functional coating remaining on the surface of the sealed material with hot water; And a drying step (S 90) of drying the molten material.

The surface treatment method of the aluminum roof rack for automobiles according to the present invention has a remarkable effect of preventing the generation of rust even when used for a long period of time by increasing the durability while maintaining the metal texture as it is by surface treatment of the roof rack of aluminum material, A sealing step is performed using a silicate-containing aqueous solution to fill the pore layer formed through the long lifetime treatment step, and after forming the sealing step, the alkali layer coating film is thickly formed on the surface of the roof rack through the long- And the durability is further improved, so that there is a remarkable effect of having the original surface texture even after long-term use.

BRIEF DESCRIPTION OF THE DRAWINGS Fig.
Figs. 2 to 8 are photographs showing test pictures of the materials treated by the present invention
9 is a graph showing an experimental result table of the anodizing step according to the present invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for an aluminum material, and more particularly, to a surface treatment method for an aluminum material roof rack provided outside the vehicle, It is a surface treatment method of aluminum roof rack for automobile which improves the quality and raises the durability of the roof rack.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is an overall block diagram of the present invention. The method for surface treatment of aluminum roof rack for vehicle according to the present invention is a method for surface treatment of aluminum roof rack provided outside the vehicle, A material polishing step (S 10); An organic cleaning step (S 20) for removing organic substances remaining on the surface of the polished workpiece; a racking step (S 30) for fixing the organically cleaned workpiece using a jig to fix the organically cleaned workpiece in the treatment tank; (S 40) for removing organic substances, a pickling step (S 50) for washing with acid to form a film having a uniform thickness through activation of a material surface, an electrolytic treatment through transparent anodic oxidation on the surface of the pickled material A sealing step (S70) for filling the pore layer formed through the anodic oxidation; a bale pressing step (S80) for washing the functional coating remaining on the surface of the sealed material with hot water; And a drying step (S 90) of drying the molten material.

Further, a long life processing step (S75) for generating a functional inorganic composite layer of an oxide film is added between the sealing step (S70) and the bending step (S80).

First, the material polishing step (S 10) is an etching step for realizing metal luster through polishing on the surface of the workpiece. In order to make the luster of the workpiece surface matte, it may be omitted in some cases. Or a mechanical polishing method using a buff polishing machine or a barrel polishing machine.

The material polishing step (S 10) may be performed by a mechanical polishing method in order to lower the surface gloss of the workpiece if it is excessively high, and this kind of processing may be carried out using an acidic ammonium fluoroborate and a nitrate- It is a process of killing gloss by adhering an oxide to a part of the surface of a material using a treatment liquid.

A chemical polishing method may be used as a chemical polishing method. In the chemical polishing method, a solution prepared by mixing 100 parts by weight of an undiluted solution consisting of 80% by weight of phosphoric acid, 15% by weight of sulfuric acid and 5% by weight of nitric acid and 400 to 800 parts by weight of water, The material can be immersed in the temperature range of 95 ~ 105 ℃ for 30 ~ 60 seconds.

Next, the organic cleaning step (S 20) is a step of immersing 100 g / L of sodium tripolyphosphate (Na 5 P 3 O 10) and 1 to 4 g / L of sodium carbonate (Na 2 CO 3) In an alkali degreasing solution at a temperature of 50 to 70 ° C for 5 minutes.

The next step of sacking (S30) is a step of fixing the material through the organic cleaning step (S20) by using a jig in order to place the material in the treatment tank, and a titanium jig made of titanium can be used.

Next, the degreasing step (S 40) is a step of removing foreign matter or organic matter from the surface of the workpiece placed in the treatment tank, and is performed at a temperature of 40 to 60 ° C for 10 to 300 seconds in an alkali solution containing 100 g / L of sodium hydroxide Etching is performed.

The next pickling step (S50) is a step of washing with acid to form a uniform thickness film through activation of the material surface. A raw material having a nitric acid (HNO3) concentration of 68% is mixed with water in a ratio of 1: Is a de-smut process for removing smut generated at room temperature for 1 to 5 minutes.

After the next pickling step (S50), the material is subjected to an anodizing step (S60). The anodizing step (S60) is a step in which the passivation film of aluminum oxide and the pores of several 탆 in size The electrolyte used is an electrolyte solution containing 10 to 20 wt% of sulfuric acid and 1 to 5 wt% of aluminum sulfate. The temperature is maintained at 10 to 25 ° C. and the applied current density is 2 to 5 A / dm ² The anodic oxidation step (S 60) is performed at a concentration of sulfuric acid (H ₂ SO ₄ ) of 150 to 250 g / L, and an oxalic acid, a tartaric acid and an organic acid A step of forming a layer of aluminum oxide (Al ₂ O ₃ ) on the surface of the workpiece by applying a current into the electrolyte containing the organic additive.

The sealing step S 70 is a step for filling the pore layer formed through the anodizing step S 60, filling the pores of the aluminum oxide (Al ₂ O ₃ ) layer formed on the material surface through a sealing process, SS2 treatment (Long Life Treatment, S75) is carried out to make the roof rack to have appropriate luster and corrosion resistance, especially alkali resistance.

≪ Example 1 >

For the test for establishing the pretreatment condition, a plurality of samples of the roof rack are prepared and subjected to a polishing treatment so as to have an appropriate gloss through a material polishing step (S 10) (A / D) was performed and the appearance was observed.

division
No
Etching condition
Anodizing
(165 g / L, 25 < 0 > C)
result density
(g / L) Temperature
(° C) time
(min) time
(min) Film thickness
(탆)
1. Darker as the film becomes thicker (No 1, 2, 3)
2. The higher the concentration of the etching solution, the darker the color (No 4 and 6)



Etching condition
change

One
50


50


One

25 9.1 2 20 7.3 3 23 8.2 4 × 5 80
50
One
23 8.1 6 × Kinds
change
(AE-1)
7
45

25
5 × 1. The longer the etching time, the darker the surface.
2. Set general purpose etching agent (AE-1) 1.5min to optimum condition considering the change of appearance depending on temperature and time. 8 3 × 9 1.5 × 10 3 23 8.2

The results of Table 1 are shown in FIG. 2, and the colors of the materials 1, 2 and 3 are darker than the thickness of the film formed through etching by 7.3 μm or more. In the case of the material 4, And the products that did not perform anodizing appeared bright. As a result of using the general-purpose AE-1 by changing the kind of the etching solution, it is confirmed that the longer the etching time, the darker the surface, and it is difficult to produce a bright-colored product requiring the roof rack even though the anodizing is not performed.

In the case of the 7th to 10th materials tested by changing the kind of the etchant, the etching time was 1.5 to 3 minutes is most preferable because the colors of the materials 7 and 10 are too dark to be quality.

Therefore, in the pretreatment conditions of the aluminum roof rack for vehicle to be developed in the present invention through Example 1, the etching time is preferably 1.5 to 3 minutes, and the anodizing time is preferably 23 minutes or less for the anodizing treatment.

≪ Example 2 >

In order to test for establishing the pretreatment condition, several samples of the roof rack are prepared and subjected to an abrasive treatment through a material polishing step (S 10) so as to have appropriate gloss, Anodizing (A / D) was carried out through S 60 and sealing treatment and long life treatment were performed.

division
Easy condition
A / D
Film thickness
(탆)
Alkali resistance
result
density
(g / L) Temperature (℃) time
(min) density
(g / l) Voltage
(V) electric current
(A)
One
Not processed

165

13.3 4.2 7.8 NG -SS2 alkali resistance due to untreated
- Appearance is transparent 2 200
(city) 30 1.5 1.8 8 OK - Alkaline OK with SS2 treatment
-When the ABF treatment time is longer, 3 200
(city) 30 3 2.0 8.5 OK One 114
(ball) 30 3 165


13.4


2.4 8.2 OK -ABF (vac) decreases etch response over time
-ABF (City) Continuous Etching
Appearance gloss changes according to the etching degree of ABF 2 114
(ball) 30 0.5 2.4 7.9 OK 3 114
(ball) 30 5 2.2 7.9 OK 4 114
(city) 30 6 1.4 OK

Here, the 200 (hours) used in the Easy treatment (etching treatment) was an acid / alkali chemical abrasive with an ammonium acid concentration of 200 g / L and an acid / alkali chemical abrasive, Acid ammonium fluoride industry was used.

Table 2 shows the appearance and chemical corrosion resistance of the roof rack after performing the Easy treatment on the prepared roof rack sample and then performing the A / D (anodizing) treatment and the primary sealing and the secondary sealing (long life treatment) And the results are shown in Figs. 3 to 5. Fig.

In the case of FIG. 3, the acid treatment was carried out using an acidic ammonium fluoride reagent grade having a concentration of 200 g / L and anodizing was carried out. After that, 2 ~ 3 drops of GMW 14665-0.1N NaOH solution was dropped on the surface of the material and allowed to stand at room temperature for 10 minutes. After washing the surface, the surface was discolored or not.) As a result, And it can be seen that the existing roof rack product also shows some degree of corrosion, and it can be confirmed that the sealing treatment and the long life treatment are required to have alkali resistance.

In the case of FIG. 4, an easy treatment is performed using an acidic ammonium fluoride reagent grade having a concentration of 200 g / L, anodizing is carried out, a primary sealing and a secondary sealing (long life treatment) are performed through a post- As a result of the test, it is confirmed that the test of the No. 1 material shows a part which is eroded off against the alkali resistance, and the case of the No. 2 or No. 3 material has a higher alkali resistance.

In the case of FIG. 5, an easy processing was carried out using an acidic ammonium fluoride industrial chemical abrasive having a concentration of 114 g / L and an acidic ammonium fluoride industrial chemical abrasive of 114 g / L, followed by anodizing, As a result of performing a car-sealing (long-life treatment) and testing for alkali resistance, it is confirmed that all of them are highly alkaline.

Therefore, the sealing step (S 70) and the long life processing step (S 75) suitable for the present invention are carried out by mechanical polishing or chemical polishing, and the metal texture having excellent glossiness is maintained (A / D) treatment by using acidic ammonium fluoride and acid / alkali chemical abrasive at 30 ℃ for 0.5 ~ 3min. That is, a step of flowing an electric current of 1.4 to 2.4 A / dm ² at a voltage of 13.3 to 13.4 V at a concentration of 165 g / L for an anodic oxidation treatment for 10 to 30 minutes, and the post-treatment (sealing step and long- And filling the pore layer formed in the coating film generated in the step (a) with alkali.

≪ Example 3 >

A plurality of roof rack samples are prepared, polished so as to have appropriate gloss through the material polishing step (S 10), anodizing (A / D) is performed through an anodizing step (S 60) And then subjected to a secondary sealing process, that is, a long life process, through a long life process step (S75), and then tested for appearance and corrosion resistance. 3 is a result table according to changes in conditions, including the electrolytic solution performed in the anodic oxidation step (S60).

division
Electrolyte condition

Film thickness
(탆)

Alkali resistance
result
density
(g / L) Temperature
(° C) electric current
(A) Current density
(A / dm ² ) 10 Untreated NG 11
130
15 0.6 0.4 0.5 OK 1. The film thickness increases in proportion to the concentration and temperature (however, the increase is not large at 165 g / L and 200 g / L).
2. The thicker the film, the darker the appearance.
3. Alkalinity is satisfactory under all conditions in SS2 treatment. 12 20 0.9 0.6 2.2 OK 13 25 1.5 One 5.6 OK 14
165
15 0.9 0.6 4.4 OK 15 20 1.5 One 6.1 OK 16 25 2.2 1.47 8.5 OK 17
200
15 1.3 0.87 4.7 OK 18 20 2.2 1.47 6.8 OK 19 25 2.8 1.87 9.6 OK

In the example according to Table 3, the material No. 10 is the result of testing the alkali resistance of the product subjected to the primary sealing treatment in the sealing step (S 70), the sealing step (S 70) and the long life treatment step (S 75) and tested for the alkali resistance of the products subjected to the first and second sealing.

As can be seen in FIG. 6, it can be seen that the material subjected to the primary sealing treatment is corroded after the completion of the test, and that the materials 11 to 13 have passed the alkali resistance test.

As can be seen in FIG. 7, all of the materials 14 to 16 passed the alkali resistance test, and it was confirmed that the materials 17 to 19 passed the alkali resistance test as shown in FIG.

However, the materials of 15, 16, 18, and 19 were found to be less suitable for roof racing of automobiles due to the lack of surface gloss of the material due to the formation of the film thickness of 6.1 탆 or more formed on the material.

Therefore, since the color of the roof rack appears bright when the surface thickness of the material subjected to the anodizing step S 60 is 0.5 to 5.6 μm, the concentration of the electrolyte used in the anodizing step S 60 is 130-200 g / L , A current density of 0.4 to 1.87 A / dm ^{2 at} a current of 0.6 to 2.8 A at a temperature of 15 to 25 캜, and a film thickness of 0.5 to 5.6 탆.

Of course, when the concentration of the electrolyte is 200 g / L under the above conditions, the temperature of the electrolyte should be kept below 15 ° C or the current and the current density should be lowered so that the thickness of the coating is not too thick.

FIG. 9 is a graph showing an experimental result of the anodizing step according to the present invention. As shown in FIG. 9, the thickness of the coating formed on the surface of the material becomes thicker as the concentration of the electrolytic solution is increased, L and the result of using an electrolyte having a concentration of 200 g / L were similar. Therefore, it can be confirmed that the thickness of the coating gradually changes according to the condition in the anodic oxidation step when the electrolyte has a certain concentration or more.

division
Primary sealing
(Sealing step) Secondary sealing
(Long Life Processing Step)
Checklist
density
(g / L) Temperature
(° C) time
(min) density
(g / L) Temperature
(° C) time
(min)
Surface treatment solution
density


5


25


10 40 75 10

Alkali resistance test
60 75 10 90 75 10 120 75 10 150 75 10 Surface treatment solution
Temperature
5
25
10 At the lowest concentration
fixing 50 10 75 10

Table 4 is a table according to the concentration, temperature, and time of the surface treatment solution that can be used in the sealing step (S 70) and the long life treatment step (S 75) of the present invention, wherein the surface treatment solution concentration used for the primary sealing 5 g / L, and the temperature is 25 DEG C for 10 minutes. In the second seal-in long life treatment step (S75), the concentration of the surface treatment solution is changed from 40 g / L to 150 g / The concentration of the solution was fixed at the lowest concentration, the temperature of the surface treatment solution was treated at 50 캜, then raised to 75 캜, and secondary sealing was performed again.

As the surface treatment solution that can be used at this time, an aqueous solution of silicate containing an alkali metal based silicate is used. As the silicate that can be used at this time, potassium silicate (K ₂ SiO ₃ ), lithium silicate (Li ₄ SiO ₄ ) ₂ SiO ₃ ). The most suitable is an aqueous sodium silicate solution having a sodium silicate content of 2.0 to 3.5 wt%, based on the total weight of the aqueous solution.

If the content of the sodium silicate is less than 2.0 wt% with respect to the weight of the aqueous solution of the silicate, the silicate content is low and the time required for the sealing step (S 70) and the long life processing step (S 75) It is difficult to obtain a seal layer having a desired thickness at the same time as the cost is increased. On the contrary, when the amount exceeds 3.5 wt%, the silicate is unevenly distributed on one side in a state of being aggregated in the aqueous solution and the thickness of the coating layer formed on the material may not be uniform Such a non-uniform thickness of the coating layer may cause deterioration of the quality of the aluminum roof rack.

To the silicate aqueous solution, 2.0 to 5.0 wt% of sodium polyacrylate and 1.0 to 2.0 wt% of polystyrene acrylate were mixed and stirred. Then, 1.5 to 2 mol of water was mixed with 1 mol of the silicate compound, 0.03 g / L may be added.

The polystyrene acrylate refers to a polymer compound obtained by mixing polystyrene with polymethyl methacrylate, and is usually a PS-PMMA block copolymer solution.

The material filling the pore layer in the aluminum oxide layer by the sealing step (S 70) and the long life processing step (S 75) includes a bale enrichment step (S 80) of washing the functional film remaining on the surface of the hot water furnace, A drying step (S 90) for drying the material proceeds.

As described above, the present invention is a surface treatment solution for surface treatment of an aluminum roof rack for a vehicle, wherein the surface treatment solution is an aqueous solution of silicate containing an alkali metal-based silicate, wherein the silicate used is potassium silicate K ₂ SiO ₃ ), lithium silicate (Li ₄ SiO ₄ ), and sodium silicate (Na ₂ SiO ₃ ).

The silicate aqueous solution has a sodium silicate content of 2.0 to 3.5% by weight based on the total weight of the aqueous solution.

The surface treatment solution is prepared by mixing 2.0 to 5.0 wt% of sodium polyacrylate and 1.0 to 2.0 wt% of polystyrene acrylate in an aqueous solution of silicate, stirring the mixture, mixing 1.5 to 2 moles of water per mole of the silicate compound And 0.01 to 0.03 g / L of a surfactant is further added.

As a result, the surface treatment method of the aluminum roof rack for automobiles according to the present invention has a remarkable effect of preventing the generation of rust even when used for a long period of time by increasing the durability while maintaining the metal texture, A sealing step is performed using a silicate-containing aqueous solution for filling the pore layer formed through the anodic oxidation, and after the sealing step is performed, the alkali layer coating film is thickly formed on the surface of the roof rack through the long- Surface corrosion is basically blocked and durability is further improved, and there is a remarkable effect that the original surface texture is used even in long-term use.

S 10; Material polishing step S 20; Organic cleaning step
S 30; Racking step S 40; Degreasing step
S 50; Pickling step S 60; Anodization step
S 70; Sealing step S 75; Long life processing stage
S 80; A boiling step S 90; Drying step

Claims (7)

A surface treatment method of an aluminum roof rack provided outside of a vehicle,
A material polishing step (S 10) for realizing metal luster through polishing of the material surface; An organic cleaning step (S 20) for removing organic substances remaining on the surface of the polished workpiece; a racking step (S 30) for fixing the organically cleaned workpiece using a jig to fix the organically cleaned workpiece in the treatment tank; (S 40) for removing organic substances, a pickling step (S 50) for washing with acid to form a film having a uniform thickness through activation of a material surface, an electrolytic treatment through transparent anodic oxidation on the surface of the pickled material A sealing step (S70) for filling the pore layer formed through the anodic oxidation; a bale pressing step (S80) for washing the functional coating remaining on the surface of the sealed material with hot water; And a drying step (S 90) of drying the molten material,
The organic cleaning step (S 20) may be carried out by using 100 g / L of sodium tripolyphosphate (Na 5 P 3 O 10) and 1 to 4 g / L of sodium carbonate (Na 2 CO 3) as a fixing for removal of organic substances remaining on the surface of the ground material Treating the constituted alkali degreasing solution at a temperature of 50 to 70 DEG C for 5 minutes,
Between the sealing step (S 70) and the boiling step (S 80), a long life processing step (S 75) for generating a functional inorganic composite layer of an oxide film is added,
The sealing step S 70 is a step of filling the pore layer formed on the surface of the material through the anodic oxidation step S 60. The pore of the aluminum oxide (Al ₂ O ₃ ) layer formed on the material surface through the sealing process The pore layer on the surface of the material produced in the anodic oxidation step (S 60) is treated with a silicate (SiO ₄ ) by using an aqueous solution of silicate containing citrate as a surface treatment solution,
The long life treatment step S 75 may be performed by sealing the pore layer of the material surface subjected to the sealing step S 70 by using the silicate aqueous solution containing silicate on the surface of the material having undergone the sealing step S 70,
The long-life treatment step surface treatment that is used for (S 75), and a solution is used the silicate solution containing the silicate of the alkali metal series, as the silicate that can be used, but this time the sodium silicate (Na ₂ SiO _3),
The silicate aqueous solution has a silicate concentration of 2.0 to 3.5 wt% based on the total weight of the aqueous solution and a silicate concentration of 40 to 150 g / L of the surface treatment solution at a temperature of 50 to 75 DEG C for 10 minutes Processing,
The surface treatment solution is prepared by mixing 2.0 to 5.0 wt% of sodium polyacrylate and 1.0 to 2.0 wt% of polystyrene acrylate in an aqueous solution of silicate, stirring the mixture, mixing 1.5 to 2 moles of water per mole of the silicate compound, 0.01 to 0.03 g / L is further added to the surface of the aluminum roof rack.
delete The method according to claim 1,
The anodizing step (S 60) is a step of forming a passive film of aluminum oxide and a pore of several 탆 to several 탆 in size on the surface of the material. The electrolytic solution contains 10 to 20 wt% of sulfuric acid aqueous solution and 1 to 5 wt% Wherein the anodic oxidation treatment is performed for 10 to 30 minutes at an applied current density of 2 to 5 A / dm ² and an applied voltage of 10 to 25 V while maintaining the temperature at 10 to 25 ° C. / RTI >
delete delete delete delete

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