JPS59179797A - Surface treatment of aluminum and alloy thereof - Google Patents

Abstract

PURPOSE:To improve considerably corrosion resistance by subjecting Al or the alloy thereof to a Zn diffusion-cementation treatment then anodizing the surface thereof. CONSTITUTION:Al or an Al alloy is subjected to a Zn diffusion-cementation treatment. The surface thereof is anodized to elute a part of Zn and to form an oxide film consisting essentially of Al, thereby controlling the concn. of the diffused Zn and improving considerably the corrosion resistance. After an oxide film consisting essentially of Al is formed, the alloy is dipped in boiling water or exposed in steam to form the hydrate of Zn and Al or the alloy is dipped thereafter in a chemical conversion liquid contg. dichromate or chromate to change the Zn in the oxide film to insoluble zinc chromate, by which more preferable result is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for processing aluminum oxide L and its alloy in a thickness of 1 m in order to obtain aluminum products with excellent corrosion resistance.

Aluminum and its alloys (hereinafter referred to as "aluminum") are light, and with appropriate surface treatment, corrosion resistance is improved, and their electrical and heat transfer performance is also excellent.As a result, they are used not only as construction materials and aircraft materials, but also as heavy industrial products and for general household use. As is well known, it is widely used in supplies and other products.In particular, its excellent heat transfer and light weight properties lead to reduced product weight and energy savings, so its applications will continue to expand in the future. I'm in a good mood.

Currently, there are a large number of types of surface treatments for the purpose of corrosion prevention of this type of aluminum products, and these are being put to practical use in each field. Specific examples include the following.

(1) Chemical conversion treatment using dichromate or a chemical treatment solution containing chromate; (2) Anodization treatment in sulfuric acid, oxalic acid, or chromic acid water bath solution, and an external Q-type oxide film is completely formed on the surface. let

(3) (After the treatment in 11 and (2), apply an appropriate coating. (4) After the treatment in +2), immerse it in boiling water or expose it to steam to hydrate the aluminum inside the porous oxide film. The corrosion resistance is improved by forming a substance and filling all the pores (referred to as sealing treatment). This action completely protects aluminum from corrosion.

The present invention belongs to the technical field of processing (5), and is intended to improve all the drawbacks of processing (5) as shown below.

That is, since the method (5) relies on the sacrificial anode action of zinc, it inevitably corrodes faster than the aluminum base material. For this reason, the surface of aluminum treated with this treatment develops white rust and corrodes more quickly than that of untreated aluminum, which has the disadvantage of severely deteriorating its appearance. However, while zinc is present, this corrosion is limited to its surface layer and does not penetrate deeply into the interior. However, once the bent lead is worn out, corrosion will eventually invade the interior and cause large scratches. A corrosion phenomenon peculiar to aluminum occurs. Therefore, it is important to use K to maintain the effect of zinc over a long period of time while minimizing the consumption of zinc as much as possible, but this method has not yet been developed.

The purpose of the present invention is to develop a method that can overcome all the drawbacks of the above-mentioned aluminum corrosion prevention method that utilizes the sacrificial anode action of zinc. After zinc has diffused into the entire aluminum surface, the surface is anodized. Therefore, the above objective has been achieved.

In the present invention, zinc is diffused into the surface of an aluminum base material, and the surface is anodized to form an aluminum oxide film containing zinc on the zinc diffusion layer. That is, in the present invention, aluminum and its alloys are subjected to a zinc diffusion and penetration treatment, and then the surface is subjected to an anodizing treatment to elute some zinc and form an entire oxide film containing aluminum as the main component. By this,
The present invention relates to a method for surface treatment of aluminum and its alloys, which is characterized by controlling the concentration of diffused zinc. This method has the following characteristics.

(1) The concentration of zinc in a cross section of an aluminum base material subjected to zinc diffusion differs depending on the diffusion conditions (temperature for 1 hour), but the concentration of zinc in a cross section of an aluminum base material that has been subjected to zinc diffusion differs depending on the diffusion conditions (temperature for 1 hour). A method in which zinc is deposited on the surface, washed with water, and thoroughly heated to diffuse into the interior has the disadvantage that the amount of zinc deposited on the surface is not necessarily constant. Therefore, if diffusion treatment is performed at a constant temperature and time, the depth of zinc diffusion into the aluminum base material can be controlled, but the concentration of zinc in the outermost layer will be high when the amount of adhesion is large, and the amount of adhesion will be small. In this case, it will be lower. This phenomenon greatly affects the anticorrosion effect of zinc.

In the present invention, even in the above state, for example, when anodized in oxalic acid, high-concentration zinc is dissolved into the solution even during the oxidation treatment, and the zinc concentration decreases until it reaches a certain concentration. For the first time, an oxide film on aluminum begins to form, and along with this, the elution of zinc is stopped, resulting in the following effects.

(a) The zinc concentration of the aluminum base material can be kept almost constant.

(Ron) Since zinc is contained in the aluminum oxide film formed on the surface, this has a sound effect in improving the corrosion resistance of the oxide film.

(c) Even if the oxide film is corroded during use as an aluminum product, the zinc that has diffused and penetrated into the aluminum base material directly below it will not penetrate deeply into the interior, and the sacrificial anode effect of zinc will continue. can be used effectively.

Since the tetraoxide film can be sealed by conventional methods, the invention can utilize the effects of both the anodic oxide film, which has excellent corrosion resistance, and the zinc diffusion treatment.

(e) Since the zinc concentration on the surface can be kept constant,
The quality of the anodic oxide film containing zinc can also be kept constant, making quality control easy and always possible to obtain a good film.

(2) Even if a member in which the present invention is fully implemented is subjected to processing such as heating in a vacuum container, zinc does not evaporate or transpire, so the effect is that there is no fft [I approximately (zinc diffusion) When the material to be treated is heated in a fully vacuum container, zinc with a high vapor pressure evaporates, making this type of processing impossible in the past.

As described above, the present invention (1) performs zinc diffusion and penetration treatment on aluminum and its alloys, and then performs anodization treatment on the surface to completely elute some of the zinc, and at the same time The present invention relates to a surface treatment method for aluminum and its alloys, which is characterized by controlling the concentration of diffused zinc by forming a film on the entire surface. After the dipping treatment, hydrates of lead and aluminum can be generated in the oxide film by immersing it in boiling water and exposing it to steam, thereby improving its corrosion resistance.

Furthermore, in non-invention (3) +11 processing? After implementing
By immersing the zinc in dichromic acid or a chemical solution containing chromic acid, the zinc in the oxide film is completely transformed into insoluble zinc chromate, and the oxide film itself is completely passivated, thereby improving its corrosion resistance. (41 (After performing the treatment in 21, dichromic acid or chromic acid solution treatment in (3) is performed to improve its corrosion resistance, and (5) After performing the treatment in (1), silicon compound The oxide film is completely filled with zinc (part of the diffused zinc), aluminum (the oxide film and part of the base material), and the silicon compound (silicon permeated). The corrosion resistance can also be improved by boiling water sealing treatment, steam sealing treatment, or immersion in a chemical conversion treatment solution containing dichromate or the like.

Various treatment methods such as zinc diffusion treatment and anodic oxidation treatment in the present invention are known, and commonly used conditions can be employed, but generally speaking, they are as follows.

(1) Zinc substitution method After washing the surface of aluminum and its alloy with water, immerse it in alkali (caustic soda 10%) for 30 seconds (7 CJ) or in concentrated nitric acid (60 wt%) for about 2 to 5 seconds, and then wash it with water. Then, immerse it in the following alkaline solution for about 50 seconds to 2 minutes.

Through this operation, part of the aluminum and its alloy is dissolved in the alkali, but instead, zinc in the liquid is deposited on the surface of the aluminum and its alloy.

Zinc oxide 70-100 t/l Liquid temperature 25℃
Caustic soda 400-500 t/1 (2) Zinc diffusion treatment (after performing the treatment in step 11, wash with water and soak in excess alkaline solution. In this case, the deposited zinc remains on the aluminum, so it is heated with electricity. When placed in a furnace and heated, zinc diffuses into the aluminum base material.The temperature conditions vary depending on the purpose, but in general, the melting point of zinc (approximately 420°C)
This will be done in F.

(3) Positive 4'f1. Oxidized aluminum and its alloys are used as anodes and electricity is applied in the following electrolyte.

Oxalic acid method Sulfuric acid method Chromic acid method (4) Boiling water, steam-treated boiling water: Deionized water is heated to 80-100℃, and 1
0-60 minutes immersion steam treatment: 20-60 minutes in steam at 120-150℃
(5) Dichromate, Chromate Potassium dichromate or sodium dichromate is usually used, but potassium chromate and sodium chromate are also effective.

Immersion at 80-100℃ for 5-20 minutes in a solution dissolved at 2-4% (6) The silicon treatment compound is mainly sodium sulfate, but methyl silicate kumquat can also be used. Zinc diffusion treatment temperature and inside of aluminum substrate in the invention An example of the distribution of zinc concentration is shown in Figure 1.

In the figure, A, B, and C are 300°C, 40(]°C, and 500°C, respectively.
Zinc concentration on the surface after zinc diffusion treatment at ℃,
It varies considerably depending on the temperature. D is a zinc diffusion layer that dissolves during anodizing treatment, and E is an anodic oxide film layer, and this oxide film contains a zinc compound. A', B', G'
is the zinc concentration when subjected to anodic fermentation treatment after zinc diffusion at each of the above temperatures, and the differences due to temperature are small. Although the zinc concentration on the surface of this oxide film has decreased, it remains at a sufficient concentration to prevent corrosion of the aluminum base material.

As can be seen from the figure, the zinc concentration on the aluminum surface increases at the diffusion temperature (
To be precise, it changes depending on the time (also influenced by time). Therefore, there is a difference in corrosion resistance in this state (high zinc concentration causes zinc to corrode quickly and cause white rust. However,
This highly concentrated zinc layer is then dissolved when anodized.
An aluminum oxide film forms when the zinc concentration drops to a certain level and prevents subsequent elution of zinc. Therefore, a treated layer consisting of an inventive anodic oxide film and a zinc diffusion layer is formed. Moreover, since this anodic oxide film contains zinc, its corrosion resistance is further improved.

Example 1 The aluminum material used is JIS H4000 (1982)
Two types of standard I [151) and 3003 were finished in p5 dimensions of width 50 x length 100 x thickness 1 m.

The aluminum material was sequentially subjected to the following treatments.

(1) Pretreatment: +04 caustic soda, immersion at 50°C for 30 seconds → washing with water, (2) Zinc replacement treatment: Caustic soda 4509/l.

Aqueous solution containing 60 l/l of zinc oxide, immersed in 40°C for 3 minutes → washed with water → dried (3) Zinc diffusion treatment = 350°C x 5h5 (4) Anodizing treatment = 4% oxalic acid, 25°C as an anode Electrolysis 0.5
Time, (5) Sealing treatment: ■ 60 minute immersion in boiling water or 50 minute treatment in steam at 0120°C. The above treatment was applied to the items after the treatment in (4) and the items after the treatment in (5). All aluminum materials were tested for corrosion resistance. Corrosion resistance was evaluated by conducting a continuous +oooh test according to the method specified in Salt Spray Test J Engineering 5Z257+, and investigating the occurrence of white rust. In this test, for comparison, we used a known method of sealing the pores by anodic oxidation without any treatment, immersion in boiling water or exposure to steam, and a method of zinc diffusion infiltration treatment. Table 1 shows the results of these salt spray tests.

As is clear from this result, all comparative products had white rust mainly composed of aluminum hydrate or white rust (zinc diffused) caused by zinc and aluminum irrigators. On the other hand, pitting corrosion was observed in the non-passivated specimens. When zinc diffusion permeation materials were not passivated, pitting corrosion was noticeable in areas where zinc had completely disappeared.

On the other hand, when the product of the present invention is not subjected to chemical conversion treatment, it changes to a grayish white color but no white rust occurs, and when the product is passivated, almost no abnormalities are observed and it shows good corrosion resistance. . Regarding the material of the present invention, the zinc concentration in the cross section is
As a result of investigation using a wire microanalyzer, it was found that zinc was present in the pores of the anodic oxide film, and 0.5 to 0.5% zinc remained in the aluminum base material directly under the oxide film. . Therefore, even if the oxide film is consumed by conducting a corrosion test for a longer period of time, the corrosion resistance can be maintained as long as residual zinc exists.

Example 2 Using aluminum + D5D material, anodic oxidation treatment was performed on aluminum with different zinc substitution conditions and diffusion treatment conditions, and the relationship between zinc concentration and diffusion depth was investigated.

(1) Zinc replacement treatment: Caustic soda 450? /l
.

Zinc oxide 60'j/l, immersion temperature 25℃, 50℃ (2) Zinc diffusion treatment 500℃X5h, 24h4
00°C x 5h 500°C x 5h (3) Anodic oxidation treatment Zinc concentration on the surface and diffusion depth after 05 hours of zinc diffusion treatment using 4% oxalic acid as anode at 25°C and with a thin anodic oxide film. Checked with analyzer and fc. As a result, in the zinc substitution treatment, the longer the immersion time at the same temperature, the higher the zinc concentration on the surface of the aluminum substrate, and in the diffusion treatment, the higher the temperature, the lower the concentration.

However, the diffusion depth becomes longer. Therefore, in order to obtain a deep zinc diffusion layer, a long time is required at low temperatures, and 1-1 working efficiency becomes extremely poor. A deep diffusion layer can be obtained by heating at a high temperature, but in this case, the diffusion of zinc mainly passes through the grain boundaries of the aluminum base material, so there is a risk that the base material will become brittle.

On the other hand, when anodic oxidation is performed, some of the zinc on the surface of the aluminum base material is eluted into the oxalic acid solution and an oxide film on aluminum is formed at the same time, so the difference in zinc concentration under the above treatment conditions is not large. There is a tendency towards uniformity. In particular, when diffused at high temperatures for a short period of time, even if the grain boundaries of the aluminum base material are weakened, an oxide film is formed on the surface, which can compensate for the weak points, reducing the time required for diffusion work. It is highly effective.

In the present invention, the anodizing treatment was carried out in an oxalic acid solution, but as is clear from its nature, it is also possible in solutions of chromic acid, sulfuric acid, etc., and in particular, in chromic acid, the passivation treatment may be omitted. (See Table 3).

Table 6 Effects of the present invention due to differences in anodizing treatment [Notes]
Sealing treatment conditions The passivation treatment conditions and the salt spray corrosion test conditions are the same as in Table 1.

In the case of sulfuric acid, the zinc concentration on the surface decreases due to the intense elution of zinc, but the treatment itself is possible.

JIS H4000 (19827) as an aluminum alloy material
It is clear from the results of Example 1.2 that materials containing 5 to 6% zinc oxide, such as standard 7075, can be treated; however, this type of material has mechanical properties of 105%.
0.5005, etc., so it is important to select materials from this point of view.

Furthermore, as a matter of course, it is also possible to apply appropriate coating after carrying out the present invention.

Example 3 Using 1050.6005 and 5005 materials, Example 1
After the treatments (1) to (4) were performed, the following treatments were performed, and the anticorrosion effect was investigated by a salt spray test of '1+oooh.

(5) Immersed in an aqueous solution containing 3% sodium silicate, then pulled up and dried. (6) Dipped in an ethyl silicate solution, pulled up and dried. (7) Examples of products treated in (5) or (6>) 1. (6) Passive treatment was carried out.

The test results are as shown in Table 4, which shows that it exhibits much better corrosion resistance than the comparative example shown in Table 1, which was tested under the same conditions.

/ Aluminum materials 1050 and 5005' (z samples were subjected to zinc substitution treatment and then anodization in oxalic acid according to the procedure of Example 10, and then subjected to the passivation treatment of Example 1 without sealing treatment.

On the other hand, a ligature without passivation treatment was prepared, and a salt water spray test was conducted continuously for +000 hours to evaluate its corrosion resistance. The results are shown in Table 5, and the results were good, with no white rust occurring at all in those subjected to passivation treatment.

In addition, those that were not subjected to passivation treatment were discolored to gray, but no white rust occurred.

As shown in Table 1 above, if zinc diffusion treatment is not performed, white rust is observed even after anodization and passivation treatment. Therefore, in this example, the effects of zinc diffusion treatment and Subsequent passivity Table 5 Effect of passivation treatment (Note J ◎ No abnormality, ○ Discoloration but no white rust Example 5 Treatments 1 to 4 of Example 1 were applied as aluminum material + 050.5003i test material. After that, the treatments 5 and 6 of Example 5 were carried out, and then the passivation treatment of Example 1 was carried out again,
Corrosion resistance was evaluated by a continuous salt spray test. The results are as shown in Table 6. If the uninvented method is applied, there will be no abnormality after the i o o oh test, and the product will be healthy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the distribution of zinc diffusion treatment temperature and zinc concentration inside an aluminum base material in the present invention. Within the sub-agent 1) Distance from the sub-agent Ryo Hagiwara - Figure 1 surface force)

Claims (6)

[Claims] (1) After zinc diffusion and penetration treatment is applied to aluminum and its alloys, the surface is anodized to elute some zinc and form an oxide film containing aluminum as the main component. A method for surface treatment of aluminum and its alloys, which is characterized by controlling the zinc concentration. (2) After zinc diffusion and penetration treatment is applied to aluminum and its alloys, the surface is anodized to elute some zinc and form an oxide film mainly composed of aluminum. After π, boiling is performed. 1. A method for surface treatment of aluminum and aluminum alloys, the method comprising forming a hydrate of zinc and aluminum in an oxide film by immersing it in water or exposing it to steam. (3) After zinc diffusion and penetration treatment is applied to aluminum and its alloys, the surface is anodized to elute some zinc and form an oxide film mainly composed of aluminum, and then A surface of aluminum and its alloy, characterized in that zinc in the oxide film is changed to insoluble zinc chromate and the oxide film is completely passivated by immersion in a chromate or a chemical solution containing the chromate. Processing method. (4) After zinc diffusion and penetration treatment is applied to aluminum and its alloys, the surface is anodized to elute some of the zinc and form an oxide film containing aluminum as the main component. All characteristics are that hydrates of zinc and aluminum are generated in the oxide film by immersion in boiling water or exposure to steam, and then immersion in dichromate or a chemical solution containing chromate. Surface treatment method for aluminum and its alloys. (5) After zinc diffusion and penetration treatment is applied to aluminum and its alloys, the surface is subjected to anodic oxidation treatment to elute some zinc and form an oxide film mainly composed of aluminum, and then, A method for surface treatment of aluminum and alloys thereof, which comprises immersing the aluminum in a solution containing a silicon compound to fill the oxide film with zinc, aluminum and a silicon compound, and then subjecting the aluminum to a boiling water sealing treatment and a steam treatment. (6) After zinc diffusion and penetration treatment is applied to aluminum and its alloys, the surface is subjected to anodization treatment to elute some zinc and form an oxide film that is the entire aluminum component, and then silicon Zinc, aluminum and silicon compounds are filled into the oxide film by immersion in a solution containing the compound, and then dichromic acid or chromium i
A method for surface treatment of aluminum and its alloys, characterized by immersion in a chemical conversion solution containing k.