JPH0432598A - Al or al alloy material having superior adhesion of coating film and corrosion resistance after coating - Google Patents

Abstract

PURPOSE:To produce an Al material having superior adhesion of a coating film and superior corrosion resistance after coating by forming a specified amt. or more of an islandlike Zn-based plating layer on the surface of an Al material at a specified rate of covering. CONSTITUTION:The surface of an Al or Al alloy material is cleaned and an islandlike Zn-based plating layer is formed on the cleaned surface by >=0.5g/m<2> so as to cover 60-95% of the apparent surface area. An Al or Al alloy material having superior adhesion of a coating film and superior corrosion resistance after coating is obtd. by succeeding chemical treatment.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to Al or Al alloy materials useful as exterior panel materials and building materials for automobiles, vehicles, household electrical appliances, etc., and particularly relates to the Al or Al alloy materials. The present invention relates to an Al or Al alloy material that exhibits excellent adhesion to a coating film when its surface is coated, and has excellent corrosion resistance after coating.

[Conventional technology] As outer panel materials for automobiles and various household electrical appliances, etc.
Conventionally, plated steel sheets coated with Zn plating or Zn alloy plating have been widely used as anti-corrosion measures. However, recently, especially in the automobile field, there has been an increasing demand for weight reduction from the viewpoint of improving fuel efficiency and reducing exhaust gas, and Al or Al alloys (hereinafter referred to as Al alloys) have attracted attention as materials that meet these demands, and their practical use is progressing. ing.

Al alloy materials are not only lightweight, but also have excellent corrosion resistance, and are highly anticipated. However, after being applied with electrodeposition coating as exterior panel materials, the corrosion resistance after painting is poor, and it is particularly difficult to use in corrosive environments. The downside is that thread rust occurs within a short period of time, so it cannot necessarily be said that it meets expectations.

Although the mechanism of occurrence and growth of thread rust has not yet been completely elucidated, one of the main causes of thread rust occurrence is thought to be poor adhesion of the coating film to the Al alloy material. In other words, the surface of the Al alloy material is covered with a dense passive film made of oxide, so even if paint is applied on top of this, a direct bond between the paint film and the Al alloy material base is formed. It is not. Furthermore, even if chemical conversion treatments such as phosphate treatment and chromate treatment, which are commonly used to improve the paintability of steel plates, are applied to Al alloy materials, the passivity film present on the surface of the Al alloy materials will hinder the chemical conversion treatment. , a satisfactory chemical conversion film is not formed.

In order to solve these problems, a method was proposed in which Zn-based plating was applied to the surface of an Al alloy material, and then chemical conversion treatment was applied to improve the adhesion of the coating (Japanese Unexamined Patent Application Publication No. 1983-1993).
No. 157693), and has achieved some results. However, although this method can delay the onset of thread rust, it was confirmed that paint film blisters occur relatively early in a corrosive environment, and corrosion rapidly progresses from this point. .

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to solve the problem of thread rust after painting, which is seen in conventional Al alloy materials, and to Al that can prevent the blistering phenomenon of the paint film and exhibit excellent corrosion resistance even after painting.
The aim is to provide alloy materials.

[Means for Solving the Problems] The structure of the Al or Al alloy material according to the present invention that can solve the above problems is based on the appearance of the surface of the Al or Al alloy material, which is assumed to be smooth. covers 60 to 95% of the surface area, and the amount of adhesion is 0.5 g/
The gist of this is that it is coated with island-shaped Zn-based plating having a thickness of la' or more.

[Function] Zn-based plating was originally developed as a means to improve the corrosion resistance of steel materials, but on the other hand, in the invention disclosed in the above-mentioned publication (Japanese Patent Application Laid-open No. 157693/1983), Zn-based plating was It is used as a means to increase the phosphate treatment properties of materials and improve paint film adhesion. That is, the expected effects of the Zn-based plating layer are quite different in the latter case. According to research conducted by the present inventors, in the case of steel materials, even after phosphate treatment is performed after Zn-based plating, Zn-based plating on the entire surface is necessary to ensure the perforability of the steel material. It is necessary for the layer to remain, but since Al alloy material itself has excellent perforation properties, it is treated with phosphate to improve the adhesion of the paint film. After improvements have been made, there is almost no necessity for the Zn-based plating layer to remain; rather, if the Zn-based plating layer remains on the entire surface, a corrosion reaction of the Zn-based plating layer itself will occur in a corrosive environment. It has become clear that this can cause paint film blistering.

Based on this knowledge, we conducted further research and found that
When Zn-based plating is formed on the surface of an Al alloy material in the form of islands, the adhesion of the paint film is improved by subsequent chemical conversion treatment, and even when the coated Al alloy material is exposed to a corrosive environment, the paint film does not swell. It was confirmed that no corrosion occurred and that excellent corrosion resistance could be maintained for a long period of time.

The reason why the swelling of the coating after painting is prevented by forming the Zn-based plating in an island shape in this way can be considered as follows.

In other words, when a Zn-based plating layer is formed on the entire surface as in the past, when exposed to a corrosive environment, the corrosion reaction progresses widely over the entire surface of the Zn-based plating layer, reducing the adhesion between the base and the coating film. However, if the Zn-based plating layer is formed into islands, the corrosion reaction stops within the islands, and further progress of the corrosion reaction is inhibited.

The effect of preventing blistering of the coating film is such that the surface of the Al alloy material, which is considered smooth, covers 60 to 95% of the surface area, and the amount of coating is 0.5 g/m2 or more. It has become clear that this can be achieved by applying Zn-based plating. However, if the total area covered by Zn-based plating exceeds 95% of the apparent surface area, the plating layer becomes continuous, making it impossible to separate the corrosion reaction, which is expected in the present invention. The corrosion resistance improvement effect cannot be effectively exhibited. On the other hand, if it is less than 60%, the effect of improving coating S adhesion by chemical conversion treatment will not be effectively exhibited, and it will not be possible to obtain a sufficient effect of improving corrosion resistance. In addition, the amount of Zn-based tsugi attached is 0.5 g7
If it is less than m2, the effect of improving coating film adhesion by subsequent chemical conversion treatment will not be effectively exhibited, and a satisfactory effect of improving corrosion resistance will not be obtained. The preferred area ratio of island plating is 6.
The range of 0 to 95%, more preferably 70 to 95%, and the more preferable coating amount of rice grains is 0.8 to 10.0 g/m2, and the occupied area ratio of Zn-based plating and the coating amount should be within this range. Once set, the subsequent chemical conversion treatment will provide excellent paint film adhesion, and the effect of isolating the corrosion reaction of the Zn-based plating layer in a corrosive environment will also be effectively exhibited, preventing paint blistering and providing excellent post-painting results. Corrosion resistance can be obtained.

Methods for forming islands of Zn-based plating on the surface of the Al alloy material include, for example, methods of directly coating or thermal spraying Zn-based plating material on the surface of the cleaned Al alloy material in the form of islands; A method is adopted in which a porous or uneven base layer such as an alumite film is formed and a Zn-based pottery is applied near the top of the base layer, but the present invention is of course not limited to these methods. Any method may be used as long as the plating layer can be formed into an island shape. In addition, the shape of the islands may be dotted, streaked, band-like, lattice-like, etc., and the type of Zn-based plating may be any type as long as it can exhibit the effect of improving paint film adhesion through chemical conversion treatment. The most common material is pure Zn or a Zn-based alloy of Zn and Fe, Ni, Mn, Cr, etc.

Next, the configuration and effects of the present invention will be specifically explained with reference to examples, but the present invention is not limited by the following examples.

[Example] After cleaning the Al plate, 1 mou/j! A porous alumite film was formed by anodizing in a phosphoric acid solution, and then a plated layer made of Zn or Zn-Ni was formed in the form of islands on the alumite film by electroplating.

Table 1 shows the amount of plating and coverage on the obtained Zn-based plated Al plate.

After this Zn-based plated Al plate was treated with a phosphate, a paint made of an alkyd melamine resin or an epoxy resin was applied to the plate to a dry film thickness of about 20 μm to obtain a coated Al plate. The following paint film adhesion test and paint film adhesion test were conducted using each of the obtained coated At plates as test materials.
The results shown in Table 1 were obtained.

(Coating film adhesion) After each test material was immersed in deionized water at 50° C. for 240 hours, the amount of coating film peeled off was measured by a base tape peeling test, and the coating film adhesion was evaluated according to the following criteria.

○: Amount of paint film peeled off less than 5% △: Amount of paint film peeled off more than 5% but less than 10% ,
It was subjected to a salt spray test for 840 hours, and evaluated based on the width of the coating film blistering from the cross-cut portion (maximum width on both sides divided by 2) according to the following criteria.

○: Paint film blistering width less than 0.5 mm △: Paint film blistering width more than 0.5 olG1 and less than 3 may ×:
Coating film blistering width exceeding 3 nm Table 1 From Table 1, the following can be considered.

Nos. 1 to 5 are examples that meet the specified requirements of the present invention, and the coating film adhesion and post-painting corrosion resistance are both good, and almost no coating blistering is observed even after the corrosion test.

On the other hand, Nos. 016 to 10 are comparative examples that lack any of the requirements stipulated in the present invention, and are insufficient in one or both of coating film adhesion and post-painting corrosion resistance.

No, 6.7 Coverage rate of zZn plating is insufficient Sufficient paint film adhesion even after chemical conversion treatment The corrosion resistance after painting is also poor. Always bad.

No, 8. 9: Because the coverage of Zn-based plating is too high, a corrosion reaction occurs on the entire surface of the plating layer in a corrosion test, causing swelling of the coating film, resulting in poor corrosion resistance after coating.

: The coverage rate of ZN-based wipes is appropriate. However, because the amount of plating is insufficient, No, 10 , paint film adhesion and corrosion resistance after painting. Neither gender is sufficient.

Figure 1 shows the surface coverage and coating peeling rate obtained in the same manner as above except that the amount of Zn-based plating was set at 1.0 g/m' and the surface coverage by the plating was varied. This shows the results of investigating the relationship. As is clear from this figure, it can be seen that a high level of coating film adhesion can be ensured by increasing the surface coverage by the plating material to 60% or more. However, if the surface coverage exceeds 95%, as mentioned above, the coating film will swell significantly and the corrosion resistance after painting will deteriorate, so the upper limit of the coverage should be 95%.

Figure 2 shows the same method as above except that the surface coverage by Zn plating was set to 70% and the amount of plating was changed.
This figure shows the results of investigating the relationship between the amount of plating deposited and the maximum width of coating blistering in a cross-cut salt water spray test. As is clear from this figure, in order to prevent blistering of the coating film, the amount of Zn-based plating applied should be 0.5 g/a2 or more.

[Effects of the Invention] The present invention is configured as described above, and an island-shaped Zn-based plating layer is formed on Al or an Al alloy material so that the coating amount is more than a specific amount and the surface coverage is within a specific range. By forming this, it is possible to provide an Al or Al alloy material that exhibits excellent paint film adhesion and post-painting corrosion resistance through subsequent chemical conversion treatment.

[Brief explanation of drawings]

Figure 1 shows the surface coverage and coating peeling rate (
Figure 2 is a graph showing the relationship between plating adhesion and maximum coating blistering width (post-painting corrosion resistance).

Claims (1)

[Claims] Covering 60 to 95% of the apparent surface area of the surface of Al or Al alloy material when considered smooth,
An island-shaped Z whose adhesion amount is 0.5 g/m^2 or more
An Al or Al alloy material with excellent paint film adhesion and post-painting corrosion resistance, characterized by being subjected to n-based plating.