JP4583408B2 - Surface treatment method of aluminum material - Google Patents

Description

  The present invention relates to a surface treatment technique for an aluminum material obtained by aluminum die casting, casting or the like.

Aluminum is a lightweight metal with good workability, and the strength of the resulting product is relatively high. Therefore, various shapes of aluminum materials made of aluminum or its alloys are used in many fields.
By the way, corrosion resistance and alkali resistance are mentioned as the performance desired for the aluminum material used for various uses. Conventionally, chemical conversion treatment such as anodic oxidation treatment or chromate treatment is performed for the purpose of improving the corrosion resistance of the aluminum material surface. However, these conventional chemical conversion treatments require a complicated multi-stage treatment process (for example, a surface activation process including a degreasing process, a water washing process, removal of smut, and a water washing process) as a pretreatment stage. Furthermore, when a substance having an adverse effect on the environment such as chromium is used, a facility for the treatment is necessary, and an increase in cost required for the treatment cannot be avoided.
In addition, in the following patent documents listed as examples, a new chemical conversion treatment is performed for the purpose of simplifying the pretreatment process (Patent Document 1), eliminating substances that cause environmental problems (Patent Documents 2 and 3), and the like. Although several proposals have been made, the treatments described in these patent documents are not yet sufficient from the viewpoint of simply improving the alkali resistance of the aluminum material.

JP 2004-010998 A JP 2003-193253 A JP 2005008948 A

  Therefore, the present invention was created to solve the problems related to the conventional chemical conversion treatment of aluminum materials, and the surface of the aluminum material can be resisted by simple treatment without using heavy metals that cause environmental problems such as chromium. It aims at providing the surface treatment method which can provide alkalinity and corrosion resistance. Another object of the present invention is to provide an aluminum material with improved alkali resistance and the like treated by such a surface treatment method.

The method provided by the present invention is a method for treating the surface of an aluminum material made of aluminum or an aluminum alloy. The aluminum material surface treatment method of the present invention is characterized in that the surface of the aluminum material is brought into contact with an aqueous surface treatment liquid prepared by adding lithium fluoride and alkali metal silicate to water. Moreover, in the surface treatment method of this invention, before making it contact with the said aqueous | water-based surface treatment liquid, the said aluminum material surface is processed with the alkaline solution containing a chelating agent.
In the present specification, the “aluminum material” is a term indicating materials and members made of aluminum or an aluminum alloy, and is not limited by a specific form or manufacturing method unless otherwise specified. For example, what is called aluminum die casting (aluminum die casting) using various aluminum alloys as a raw material, or an aluminum cast product formed into a predetermined shape by casting or powdered or flaky aluminum material is referred to herein. This is a typical example included in an aluminum material.

In the surface treatment method of the said structure disclosed here, lithium fluoride and alkali metal silicate are used as a surface treating agent of an aluminum material. In this method, a chemical conversion film having excellent corrosion resistance and alkali resistance can be formed on the surface of the aluminum material by bringing the aluminum material into contact with the surface treatment agent.
Therefore, according to the present invention, it is possible to easily improve the alkali resistance of the surface of the aluminum material by a simple surface treatment without using a heavy metal component which is not preferable for the environment like the conventional chromate treatment.

Preferably, sodium metasilicate is used as the alkali metal silicate. By using sodium metasilicate, the alkali resistance of the aluminum material can be easily improved.
Preferably, the contact is performed using an aqueous surface treatment liquid heated to 90 ° C. or higher. By using such a high temperature aqueous surface treatment liquid, the efficiency of the surface treatment can be further increased. Therefore, the surface treatment of the aluminum material can be performed more rapidly.

The aqueous surface treatment liquid is particularly preferably prepared so that the content of alkali metal silicate (Si content) is 1 mol / L or more and a saturated solution of lithium fluoride.
By setting the content of these components as described above, a chemical conversion film having particularly excellent alkali resistance can be formed on the surface of the aluminum material by a simple treatment.

  Preferably, the aluminum material surface is washed after contacting with the aqueous surface treatment liquid. Although various types of cleaning methods can be employed for the cleaning step, ultrasonic cleaning is particularly preferable in such cleaning. By performing ultrasonic cleaning, it is possible to remove excess surface treatment agent components present on the surface of the aluminum material and in the vicinity thereof.

In addition, as described above, in the surface treatment method of the present invention, an alkaline solution (typically an alkali metal compound such as sodium hydroxide is added to the surface of the aluminum material containing a chelating agent before contacting with the aqueous surface treatment liquid. (Preferably, the surface of the aluminum material is washed after the alkaline solution treatment ). By performing such alkali treatment (hereinafter also referred to as “pre-alkali treatment”), smut (black soot-like impurities), sebum, and the like can be easily removed from the surface of the aluminum material. For this reason, the chemical conversion film which is excellent in alkali resistance etc. can be more reliably formed in the surface of an aluminum material by performing this pre-alkali treatment.

As another aspect, the present invention provides an aluminum material surface-treated by any of the surface treatment methods disclosed herein and a method for producing the same. The aluminum material (for example, aluminum die-cast product) produced by surface treatment by the surface treatment method of the present invention is particularly excellent in corrosion resistance and alkali resistance.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The surface treatment method disclosed herein can treat an aluminum material without using a heavy metal such as chromium or an organic solvent, which is troublesome to perform post-treatment. For this reason, the aluminum material of various uses and forms can be processed simply, without requiring a special post-processing facility.
The aluminum material to be applied is aluminum or an aluminum alloy, typically an alloy containing aluminum as a main component and containing manganese, copper, magnesium, silicon, nickel, zinc or the like, for example, A1000 series (pure aluminum), A2000 in JIS designation Bands (Al-Cu alloys), A3000s (Al-Mn alloys), A4000s (Al-Si alloys), A5000s (Al-Mg alloys), A6000s (Al-Mg-Si alloys) A7000 series (Al—Zn—Mg alloy) pure aluminum or aluminum alloy, or AC1A and AC1B (Al—Cu alloy), AC2A and AC2B (Al—Cu—Si alloy), AC3A (Al -Si alloy), AC4A and AC4C (Al-Si-Mg alloy), AC B (Al—Si—Cu alloy), AC4D (Al—Si—Cu—Mg alloy), AC5A (Al—Cu—Ni—Mg alloy), AC7A (Al—Mg alloy), AC8A and AC8B ( Al-Si-Cu-Ni-Mg alloy), AC9A and AC9B (Al-Si-Cu-Ni-Mg alloy), ADC1 (Al-Si alloy), ADC3 (Al-Si-Mg alloy), Casting alloys such as ADC5 (Al-Mg-based alloy), ADC6 (Al-Mg-Mn-based alloy), ADC10 and ADC12 (Al-Si-Cu-based alloy), ADC14 (Al-Si-Cu-Mg-based alloy) Aluminum materials of various uses and shapes composed of It is particularly effective for the surface treatment of aluminum die cast products obtained by aluminum die casting.

The aqueous surface treatment liquid (surface treatment agent according to the present invention) disclosed herein is an aqueous solution and does not contain an organic solvent, and therefore, preparation and post-treatment (including disposal) are easy. Typically, the surface treating agent according to the present invention can be easily prepared by adding lithium fluoride and alkali metal silicate to water as a solvent.
As the alkali metal silicate to be used, sodium silicate, potassium silicate, commercially available water glass or the like can be used. In particular, sodium silicate (sodium metasilicate Na ₂ SiO ₃ , sodium orthosilicate Na ₄ SiO ₄ , Na ₂ Si ₂ O ₅ , Na ₂ Si ₄ O _9, etc.), particularly sodium metasilicate and sodium orthosilicate are preferred. Sodium metasilicate is preferred. By using alkali metal silicate, excessive elution of the aluminum component can be prevented.
Preferably, the amount of sodium silicate content is 1 mol / L or more in terms of Si, and about 1 to 3 mol / L is appropriate. About 1-2 mol / L is preferable.

The aqueous surface treatment liquid (surface treatment agent) according to the present invention is preferably prepared so as to be a saturated solution with respect to lithium fluoride (LiF) which is another main component. However, since the solubility of lithium fluoride is low, lithium fluoride is preferably added while the solvent is heated. Moreover, you may use the thing of the state disperse | distributed in the process liquid, without being able to melt | dissolve a part of lithium fluoride. Lithium fluoride may be added excessively so that a saturated solution is obtained so that the concentration is 0.01 mol / L or more in terms of Li. In particular, a treatment liquid in which excess lithium fluoride is present exceeding the solubility (typically dispersed) is preferable. In this state, a part of the excessively existing (non-dissolved) portion is dissolved so as to supplement the component consumed by the surface treatment (for example, Li component), and a saturated solution can always be maintained with respect to lithium fluoride. For this reason, many surface treatments can be performed continuously without exchanging the treatment liquid.
Preferably, the lithium fluoride dissolution amount (concentration) can be increased by adding lithium fluoride in a state of being heated to room temperature or higher, for example, 40 ° C. or higher (for example, about 40 to 90 ° C.). It is particularly preferable that the aqueous surface treatment liquid prepared in such a high temperature range is subjected to a dipping treatment described later in the high temperature range while continuing heating.
The pH of the aqueous surface treatment solution disclosed herein is preferably a value indicating alkalinity, but is not particularly limited. A pH of about 9 to 13 is preferred.

At least the surface to be treated of the aluminum material to be treated is brought into contact with the aqueous surface treatment liquid obtained as described above. Such a contact step is typically performed by immersing an aluminum material in the aqueous surface treatment liquid for an appropriate time. The contact time (for example, immersion time) is not particularly limited as long as the desired purpose is achieved, but the treatment is performed at room temperature (for example, 10 to 35 ° C.) for 2 hours or longer (for example, 2 to 12 hours), and at a higher temperature than that. Time can be shortened. For example, it is preferably 70 ° C. to 90 ° C. for 1 hour or longer (for example, 1 to 2 hours), 90 ° C. or higher (for example, 90 to 100 ° C.) for about 5 minutes to 1 hour (for example, 10 to 30 minutes).
In place of the immersion treatment, a highly viscous treatment liquid (that is, a high sodium silicate concentration) may be applied or sprayed.

Preferably, after the contact step (typically, a dipping step or a coating or spraying step), the surface of the aluminum material is washed in order to remove excess treatment agent components. As the cleaning means, there are methods such as cleaning the surface of the aluminum material using running water or putting the aluminum material into a water tank containing cleaning water, but ultrasonic cleaning is particularly preferable. The temperature condition of ultrasonic cleaning is typically from room temperature (for example, 10 ° C. to 35 ° C.) to about 70 ° C., but is not particularly limited.
Thereby, the chemical | medical component (excess lithium fluoride component and silicic acid component) adhering to the aluminum material surface can be removed rapidly and efficiently. Although it depends on the shape of the aluminum material, a commercially available ultrasonic cleaner (for example, an ultrasonic cleaner having a frequency of about 28 to 45 KHz) can be suitably used.

Preferably, the above-mentioned pre-alkali treatment is performed as a pre-treatment for performing the surface treatment (chemical conversion film forming treatment excellent in alkali resistance) disclosed herein.
The alkaline aqueous solution (hereinafter referred to as “pretreatment alkaline solution”) used in this treatment is typically an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, phosphoric acid or other substances in water as a solvent. It is prepared to show alkalinity by adding an alkali metal compound such as alkali metal salts of various organic acids. The use of sodium hydroxide is preferred because an alkaline solution can be easily prepared at low cost.
Moreover, as a suitable example of the chelating agent used for the alkali liquid for pre-treatment, gluconic acid, oxalic acid, citric acid, malonic acid, maleic acid, malic acid, tartaric acid and salts thereof (for example, alkali metals such as sodium salt) Salt). Gluconic acid or a salt thereof (for example, sodium gluconate) is particularly preferable because of its high chelating effect.

  The alkali solution for pretreatment used in the practice of the present invention is not particularly limited as long as the pH is 11 or more (for example, 11 to 13) and the alkali concentration is suitable for etching the aluminum material surface. It is an alkaline solution having a sodium content (concentration) of about 0.5 to 1 mol / L and a chelating agent of about 0.1 to 1 mol / L (for example, sodium gluconate has a mass percentage of about 2 to 2). It is preferably contained in a relatively large amount so that it is about 20% by mass). By including a chelating agent (particularly preferably gluconic acid or a salt thereof) at such a high concentration, it is possible to suitably remove smut and oily dirt (press oil, machine oil, hand dust, etc.) present on the aluminum material surface. it can. Therefore, subsequent surface treatment can be more effectively performed by performing such pre-alkali treatment. In particular, for the surface treatment of aluminum die-cast products, it is preferable to perform such pre-alkali treatment.

Typically, at least the surface of the aluminum material to be treated is brought into contact with the pretreatment alkaline solution prepared as described above. Preferably, the aluminum material is immersed in an alkali solution for pretreatment for an appropriate time. The contact time (for example, immersion time) is not particularly limited as long as the desired purpose is achieved, but immersion for about 5 to 30 minutes in the normal temperature range (for example, 10 to 35 ° C.) is preferable. Too long contact (immersion) is not preferable because the surface of the aluminum material may be excessively etched.
Preferably, after the pre-alkali treatment step, the surface of the aluminum material is washed in order to remove excessive alkali components. As the cleaning means, there are methods such as cleaning the surface of the aluminum material using running water or putting the aluminum material into a cleaning tank containing cleaning water, and the like is not particularly limited.

As is clear from the above description, in the aluminum material surface treatment method of the present invention, a chemical conversion film having excellent corrosion resistance and alkali resistance is easily and quickly formed on the surface of an aluminum material by an aqueous surface treatment agent that does not contain heavy metals or organic solvents. Can be formed. In addition, since post-processing for environmental conservation is also prepared, energy saving can be realized as compared with the conventional surface treatment method. Therefore, this invention provides the manufacturing method of the aluminum material in which the chemical conversion film excellent in alkali resistance is formed characterized by performing the surface treatment disclosed here.
For example, the following is mentioned as a process flow of the aluminum die-cast product to which the present invention is applied. That is, the first step: pre-alkali treatment, the second step: water washing treatment, the third step: surface treatment (chemical conversion film forming treatment) with the aqueous surface treatment liquid, the fourth step: water washing treatment (preferably ultrasonic treatment). And the fifth step: a drying step (natural drying in the air or forced drying by ventilation or heating). The conversion coating on the aluminum material surface obtained in each of these simplified steps is excellent in corrosion resistance and alkali resistance, and also in coating film adhesion, so that it is easy to paint the surface of the aluminum material after the surface treatment. It is possible to form a coating film that can be performed and has excellent texture.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the specific examples.

<Example 1>
At room temperature, 3 g of sodium hydroxide was dissolved in 100 mL of water (distilled water), and 10 g of sodium gluconate was further added and stirred well. As a result, a pretreatment alkali solution according to this example was obtained.
Further, 60 g of sodium silicate (here, sodium metasilicate Na 2 SiO 3) was dissolved in 300 mL of water (distilled water) heated to 40 ° C., and 10 g of lithium fluoride was further added and stirred well. As a result, an aqueous surface treatment liquid according to this example, which was a saturated solution of lithium fluoride (in a state where excessive lithium fluoride was dispersed), was obtained.

An aluminum die cast product (made of pure aluminum) having a size of 22 mm × 18 mm × 1.5 mm was used as a test aluminum material, and the following surface treatment was performed.
First, at room temperature (here, 20 to 25 ° C.), the test aluminum material was immersed in the prepared pretreatment alkali solution prepared in a water tank. After the immersion treatment for 7 minutes, the aluminum material was taken out from the pretreatment alkaline solution. Immediately after the surface of the aluminum material was washed with running water (tap water), the test aluminum material was immersed in distilled water in a water tank for 3 minutes.

The aluminum material after the pre-alkali treatment was then treated with an aqueous surface treatment solution.
The aluminum material after the pre-alkaline treatment was immersed in the aqueous surface treatment liquid heated to 95 ° C. in a water bath. After the immersion treatment at 95 ° C. for 10 minutes, the aluminum material was taken out from the aqueous surface treatment liquid.
Next, the test aluminum material was placed in a cleaning tank (distilled water) of a commercially available ultrasonic cleaner, and ultrasonic cleaning (frequency: 28 to 40 KHz) was performed at room temperature for 4 minutes.

When the surface of the aluminum material subjected to the surface treatment as described above was comparatively observed with that before the treatment, the aluminum material before the treatment (after aluminum die casting) as shown in FIG. On the surface of the aluminum plate, dark coloring, which was considered to be a stain due to smut, was recognized, but as shown in FIG. 1B, the surface of the aluminum material after the above treatment had a whitish metallic color.
Further, when the surface was observed with an electron microscope, the surface after the treatment (FIG. 2B) was appropriately etched as compared with the surface before the treatment (FIG. 2A), and dirt such as smut was found. Was not recognized.
Further, although detailed data is not shown, according to Auger electron spectroscopy analysis, it was recognized that the amount of carbon contained in the aluminum material was decreased after the treatment as compared with that before the treatment. Also from this analysis, it was confirmed that dirt such as smut adhering to the surface of the test aluminum material was removed by the above treatment.

<Example 2>
The improvement in alkali resistance by the surface treatment was evaluated. That is, an aluminum die cast product (made of pure aluminum) having a size of 44 mm × 18 mm × 1.5 mm and an aluminum cast product (made of pure aluminum) having a size of 53 mm × 36 mm × 8 mm were prepared. These test aluminum materials were subjected to a series of surface treatments with a pre-alkali treatment and an aqueous surface treatment solution in the same manner as in Example 1 above.
Thus, the ultrasonically cleaned aluminum material (the aluminum die cast product and the aluminum cast product) is immersed in a room temperature 3% sodium hydroxide solution (hereinafter referred to as “alkaline water”), and the surface change is observed. did. The results are shown in FIGS. 3A and 3B for the aluminum die cast product and in FIGS. 4A and 4B for the aluminum cast product.
The aluminum die-cast product not subjected to the above surface treatment had turned black as shown in the photograph of FIG. 3 (A) at 49 seconds after immersion in alkaline water. On the other hand, the aluminum die-cast product after the above surface treatment maintained a white metal color as shown in the photograph of FIG. 3B at 55 seconds after being immersed in alkaline water.
Similarly, aluminum castings that were not subjected to the above surface treatment had already turned black as shown in the photograph of FIG. 4A at 12 seconds after immersion in alkaline water. On the other hand, the aluminum casting after the above surface treatment maintained a white metallic color as shown in the photograph of FIG. 4B at 99 seconds after being immersed in alkaline water.

  As is clear from the results of Example 2 above, according to the surface treatment method of the present invention, an aqueous surface treatment liquid having a composition that can be easily prepared and treated is used to form a conversion coating having high alkali resistance. Can do. Further, by performing the pre-alkali treatment as a pre-treatment before the treatment with the aqueous surface treatment liquid, it is possible to remove stains such as smut and form a strong chemical conversion film.

It is a photograph which shows the effect by the surface treatment method of the present invention concerning one example, (A) shows the surface of the sample aluminum material before processing, and (B) shows the surface of the sample aluminum material after processing. . It is in the electron micrograph (The scale in a photograph is 1 micrometer) which shows the effect by the surface treatment method of this invention which concerns on one Example, (A) shows the surface of the test aluminum material before a process, (B) is The surface of the test aluminum material after a process is shown. It is a photograph which shows the effect by the surface treatment method of this invention which concerns on one Example, (A) shows the surface of the test aluminum material (aluminum die-cast product) before a process, (B) is the test after a process The surface of an aluminum material is shown. It is a photograph which shows the effect by the surface treatment method of this invention which concerns on one Example, (A) shows the surface of the test aluminum material (aluminum casting product) before a process, (B) is the test aluminum after a process. The surface of the material is shown.

Claims (6)

A method of treating a surface of an aluminum material made of aluminum or an aluminum alloy,
Treating the aluminum material surface with an alkaline solution containing a chelating agent;
A surface treatment method comprising bringing an aluminum surface treated with the alkaline solution into contact with an aqueous surface treatment solution prepared by adding lithium fluoride and an alkali metal silicate to water.   The surface treatment method according to claim 1, wherein sodium metasilicate is used as the alkali metal silicate.   The surface treatment method according to claim 1, wherein the contact is performed using an aqueous surface treatment liquid heated to 90 ° C. or more.   The aqueous surface treatment liquid is prepared such that the content of alkali metal silicate (Si content) is 1 mol / L or more and is a saturated solution with respect to lithium fluoride. The surface treatment method in any one of 1-3.   The surface treatment method according to claim 1, wherein the surface of the aluminum material brought into contact with the aqueous surface treatment liquid is subjected to ultrasonic cleaning. A method for producing an aluminum material made of aluminum or an aluminum alloy,
A method for producing an aluminum material, wherein the surface treatment method according to claim 1 is performed on the aluminum material.