JPH03153882A - Surface-treated al or al alloy material having superior filiform corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain a surface-treated Al or Al alloy material having superior filiform corrosion resistance, improved adhesion of a coating film and improved corrosion resistance by forming a Zn-based plating layer contg. a hydrophilic polymer on the surface of an Al or Al alloy base material and a chromate film contg. a specified amt. or more of Cr<6+> on the surface of the plating layer. CONSTITUTION:A Zn-based plating layer contg. a hydrophilic polymer such as polyacrylamide by 0.1-5wt.% (expressed in terms of C) is formed on the surface of an Al or Al alloy base material preferably in >=0.1mum thickness. A chromate film is then formed on the surface of the plating layer by coating, reaction, electrolysis or other treatment. It is necessary that the amt. of hexavalent Cr in the chromate film is regulated to iota10 atomic%, preferably >=30 atomic% of the amt. of total Cr in the film from the viewpoint of corrosion resistance. By this method, a surface-treated Al or Al alloy material having superior filiform corrosion resistance is obtd.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to aluminum or aluminum alloys (hereinafter also referred to as Al) that have excellent thread rust resistance and are used in vehicles, building materials, household appliances, etc. (a) related to materials. Although the shape of the surface-treated material according to the present invention may be a plate material, a corrugated sheet material, a pipe material, or a bar material, the following description will mainly be made using a plate material.

[Prior art] Cold-rolled steel sheets have been widely used for the above-mentioned purposes, but
In response to the demand for lighter products, the use of Al plates and the like is increasing.

Al plates, etc. undergo natural oxidation and their surfaces are covered with a passive oxide film, making them relatively rust-resistant materials, but the oxide film is thin and uneven, so it does not have sufficient corrosion resistance or protection. Rust resistance cannot be obtained.

Therefore, it is desired to paint Al plates etc. to improve corrosion resistance, rust prevention, and decorative properties, but if painting is done without pretreatment, the paint will deteriorate due to the oxide film. It is difficult to adhere to, and is generally subjected to chemical conversion treatments such as chromate treatment and phosphate treatment.

[Problems to be solved by the invention] Even if chemical conversion treatment is performed, the oxide film itself is difficult to undergo chemical conversion treatment, so the commonly performed chromate treatment cannot improve paint film adhesion or corrosion resistance. The secondary adhesion and thread rust resistance after painting are inferior to those of general plated steel sheets. When pre-assemble occurs, there is a problem that not only does the appearance deteriorate, but also that the pre-assemble becomes a starting point and develops into crevice corrosion and pitting corrosion. Furthermore, there is also the problem that Al and the like dissolve into the chemical conversion treatment solution, causing the chemical conversion treatment solution to deteriorate.

The present invention was made in view of these circumstances, and
The present invention aims to provide a surface-treated Al or Al alloy material with excellent thread rust resistance by improving coating film adhesion and corrosion resistance.

[Means for Solving the Problems] The surface-treated Al or Al alloy material according to the present invention has a Zn-based plating layer containing 0.1 to 5% by weight of a hydrophilic polymer in terms of C, and has a surface-treated surface of the plating layer. The key point is to have a chromate film in which the ratio of hexavalent chromium to the total chromium amount is 10 at % or more.

[Function] The present inventors conducted various studies on the causes of poor thread rust resistance of Al plates, etc., and found that: (1) insufficient paint film adhesion between the material surface and the paint; (2) poor corrosion resistance in a corrosive environment. It was found that this was insufficient.

The present inventors previously discovered that a Zn-based plating layer containing a hydrophilic polymer, particularly an acrylamide-based polymer, exhibits good film adhesion due to hydrogen bonding between the polar groups of the organic polymer present on the plating surface and the coating film. We also discovered that excellent workability could be obtained due to the internal lubrication effect of the polymer in the plating layer, and filed a patent application (Japanese Patent Application No. 63-25811).
5) It was found that hydrophilic polymers tend to absorb moisture in corrosive environments where moisture and oxygen are present, resulting in a decrease in corrosion resistance. Therefore, we investigated applying a chemical conversion treatment on the polymer-containing Zn-based plating layer to improve its corrosion resistance.We found that when a chromate film mainly composed of hexavalent ROM was formed, it was possible to improve corrosion resistance while maintaining good film adhesion. It was found that excellent yarn rust resistance was obtained. Moreover, excellent workability was maintained.

Hydrophilic polymers to be contained in the Zn-based plating layer according to the present invention include, in addition to acrylamide-based polymers, polymers having amide groups, sulfonic acid groups, hydroxyl groups, carboxyl groups, etc. as functional groups. Further, the polymer content in the plating layer needs to be 0.1 to 5% by weight, including carbon. As shown in FIG. 1, if it is less than 0.1% by weight, sufficient coating film adhesion cannot be obtained, and if it exceeds 5% by weight, hydrophilicity becomes too strong and sufficient corrosion resistance cannot be obtained. In addition, in order to obtain such coating film adhesion, the plating layer thickness should be 0.
It is desirable that it be 1 am or more. In addition, Ni is added for the purpose of improving the corrosion resistance of the plating layer itself.

It is also possible to contain 1 to 30% by weight of one or more of Fe, Co, Cr, Mn, etc.

The method of forming the chromate film according to the present invention is not particularly limited, and can be formed by coating, reaction, electrolytic, or other treatments. In this case, as shown in FIG. 2, the amount of hexavalent chromium relative to the total amount of chromium in the chromate film must be at least 10 at.%, preferably at least 30 at.%, from the viewpoint of corrosion resistance. If the value is less than this value, the corrosion inhibiting effect of the chromate film will not be sufficiently exhibited; however, even in the case of a reactive type, etc., since Zn plating is applied, the treatment solution will not deteriorate much.

[Example] After cleaning the surface of an Al plate, Zn-based plating containing 0.1 to 5% by weight of acrylamide-based polymer in terms of C was applied to the surface, and the ratio of hexavalent chromium to the total chromium amount was 10 atoms. % or more, and furthermore
A coating of 0 μm was applied. Corrosion resistance, paint film adhesion, and thread rust resistance were evaluated in the following manner.

Corrosion resistance: Salt water spray using samples after chromate treatment
The white rust generation time was measured by the test.

Paint film adhesion: After painting, the sample was immersed in ion-exchanged water at 50° C. for 240 hours, and then a cross-cut tape peeling test was conducted.

Thread rust resistance: Using a sample after painting, make a cross cut that reaches the substrate, perform salt water spray for 1 day, and then perform a 40°C, 85% RH humidity test for 4 days, repeating the cycle test 5 times. After that, the length of the rust from the cross cut was measured.

The evaluation criteria were as shown in Table 1.

Table 2 The results obtained are shown in Table 2. Table 2 also shows the results of comparative examples prepared under various conditions and evaluated in the same manner.

As is clear from Table 2, the Examples showed good results in all of the corrosion resistance, coating adhesion, and string rust resistance. On the other hand, comparative example 1
Comparative Example 2 has a high polymer content and has a slightly inferior corrosion resistance.
Comparative Examples 3 and 4 have poor corrosion resistance because the proportion of hexavalent chromium in the chromate film is low, and Comparative Example 5 has poor corrosion resistance and coating adhesion because there is no Zn-based plating layer. Each of the comparative examples described above is inferior in one or more of the corrosion resistance and coating adhesion, and therefore, sufficient thread rust resistance is not obtained.

[Effects of the Invention] Since the present invention is configured as described above, surface treatment A that improves corrosion resistance and coating adhesion and has good string rust resistance
It has become possible to provide Al or Al alloy materials.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between polymer content in Zn-plated materials containing polymers and coating peeling rate during paint film tightness tests, and Figure 2 is a graph showing the total amount of chromium in the chromate-treated film of chromate-treated materials. It is a graph showing the relationship between the ratio of the amount of hexavalent chromium to the amount of hexavalent chromium and the white rust generation time during the salt water spray n test.

Claims (1)

[Claims] The base material is Al or Al alloy, and has a Zn-based plating layer containing 0.1 to 5% by weight of a hydrophilic polymer in terms of C on the surface layer, and the amount of hexavalent chromium relative to the total amount of chromium is on the surface of the plating layer. A surface-treated Al or Al alloy material having excellent thread rust resistance, characterized by having a chromate film having a chromate coating of 10 atomic % or more.