JPH07116629B2 - Method for producing Mg-containing aluminum alloy sheet excellent in degreasing property - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to the production of Mg-containing aluminum alloy sheets, and more specifically, to the surface of automobile panel materials, etc., which are press-molded using lubricating oil and then painted. The present invention relates to a method for producing a Mg-containing Al alloy plate having excellent degreasing properties, which is suitable for the purpose of treatment.

(Prior art and problems to be solved) Al alloy plates for various forming processes, such as automobile panel materials and home electric appliance panel materials, usually contain 5 ××× system containing Mg,
Al alloys such as 6xxx series and 7xxx series are used.

These Al alloy plates are subjected to heat treatment such as softening treatment or solution treatment during the manufacturing process or in the final process in order to improve the formability.

And this Al alloy plate is usually first press-molded,
Then, it is generally degreased and subjected to a surface treatment such as painting.

Of these, the degreasing treatment is performed to remove the lubricating oil used during press molding and the rust preventive oil for the purpose of surface protection, and to efficiently obtain the effect of surface treatment such as painting in the subsequent steps. It is a thing.

However, conventionally, even this degreasing treatment could not effectively remove the surface lubricating oil, rust preventive oil, etc., so that there were many problems such as uneven surface treatment and poor adhesion of the coating film. .

The present invention has been made in order to solve the problems of the above-mentioned prior art, and can easily remove oil components such as lubricating oil used at the time of press molding in a degreasing process, and has excellent degreasing properties. It is an object of the present invention to provide a method for producing a Mg-containing aluminum alloy plate having the above.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the inventors of the present invention have sought to find out the cause of the poor degreasing property and have conducted earnest research to find a countermeasure therefor. As a result, the oxide film produced by the heat treatment in the manufacturing process of the aluminum alloy plate has Mg
In view of the fact that it is contained in a large amount and further strengthens the affinity with lubricating oil and rust preventive oil by the reaction with moisture in the atmosphere, the thickness of the oxide film and the Mg / Al ratio are It was found that the degreasing property can be remarkably improved by controlling, and the present invention has been made here.

That is, the method for producing an Mg-containing aluminum alloy excellent in degreasing property according to the present invention is, in producing an aluminum alloy plate containing 0.5 wt% or more of Mg, after heat treatment, chemically forming an MgO-rich oxide film formed on the surface. The thickness of the oxide layer is 45Å or less, and the surface layer after dissolution has a Mg / Al ratio of 0.5
It is characterized by the following.

The present invention will be described in more detail below.

First, the result of the present inventors' investigation of the cause of poor degreasing property in the past will be described.

When a Mg-containing Al alloy is heat-treated (heated) in an oxidizing atmosphere such as in the air, Mg contained in the Al alloy is preferentially oxidized, and as a result, the Mg concentration in the Al alloy near the surface layer decreases. When the Mg concentration decreases in this way, Mg diffuses in the Al alloy toward the surface, and acts to reduce the concentration difference. Due to these actions, the heat treatment of the Mg-containing Al alloy forms an oxide film containing a large amount of Mg on the surface.

The thickness of the oxide film formed by the heat treatment varies depending on the Mg content in the Al alloy, the heat treatment conditions (temperature, time, atmosphere), etc., but in the case of an Al alloy containing 0.5 to 5 wt% Mg, for example, Is usually about 50 to 100Å. Note that the film thickness of the oxide film here is a value obtained from the capacitance when an alternating current of 50 mV and 1 KHz is used and the dielectric constant of the oxide film is 7.

The Mg / Al ratio of the above oxide film analyzed by ESCA is
It is about 1.0 to 3.5 and contains a remarkably large amount of Mg with respect to the Mg concentration contained in the Al alloy.

As a result of various studies, it has been found that such an oxide film has a strong affinity with a lubricating oil used in press molding and is difficult to be removed by degreasing in the next step. In addition, it was also clarified that the affinity of the oil component such as the lubricating oil of the oxide film is further increased when the quality is changed by the moisture in the atmosphere than immediately after it is generated by the heat treatment, and the degreasing property is inhibited.

Therefore, in order to find a means for solving the problem of insufficient degreasing property of the lubricating oil used during press forming, various investigations were conducted on the lubricating oil, degreasing conditions, etc. It was found that the removal of the oxide film containing a large amount was the most effective. It should be noted that such an oxide film is liable to be deteriorated by moisture in the air and impairs corrosion resistance, but removal of the oxide film alleviates such a problem.

Next, the conditions of the present invention will be described.

As a method for removing the oxide film, either a mechanical method or a chemical method may be used, but in consideration of the processability with the coil foam in the factory, for example, 10% nitric acid, a commercially available alkaline cleaner, etc. It is convenient to carry out chemical acid and alkali bath cleaning using.

In the case of cleaning by a chemical method, the degree of removal of the oxide film changes depending on the conditions such as bath concentration, temperature and time. The present inventors have found that the oxide film thickness and the surface layer after cleaning are
As a result of testing various combinations of the relationship between the Mg / Al ratio and the degreasing property after applying the lubricating oil, the oxide film thickness measured by the capacitance method described above was 45 Å or less, and the surface layer analyzed by ESCA It was found that when the Mg / Al ratio is 0.5 or less, good degreasing property can be obtained.

If the oxide film thickness is greater than 45Å, or even if the oxide film thickness is 45Å or less, if the Mg / Al ratio exceeds 0.5, the degreasing effect will be insufficient and the degreasing property will decrease. Becomes noticeable.

Further, the Mg-containing aluminum alloy in the present invention, if at least Mg is an Al alloy containing 0.5 wt% or more,
Its composition is not limited. In the case of Al alloy with less than 0.5 wt% Mg, the amount of MgO in the oxide film does not become so rich that M
There is little problem of deterioration of degreasing property due to gO-rich oxide film.

(Examples) Examples of the present invention will be shown below.

Example 1 6061 alloy (Mg content, which is widely used for press forming
1.0 wt%), 5182 alloy (Mg content 4.5 wt%) was used, and the heat treatment conditions and surface cleaning conditions were changed as shown in Table 1 to obtain test materials.

The thickness of the surface oxide film and Mg / Al
Checked the ratio. The results are also shown in Table 1.

Then, the NP- specified in JIS K 2246
Type 3 rust preventive oil was applied and left indoors for 20 days. Then, using 2% bath of a commercially available alkali degreasing agent "Ridorin # 322N _4" (manufactured by Nippon Paint), temperature 60 ° C., was immersed degreased at the conditions of time of 30 seconds.

The degreasing property was evaluated by the water wettability after the immersion degreasing treatment. In this case, evaluations were made by giving a mark of ○ completely wetted with water, a mark of partially repelled water and a mark of completely repelled water. The results are also shown in Table 1.

From Table 1, it can be seen that the invention examples No. 1 to No. 13 all have excellent degreasing properties. On the other hand, in Comparative Examples and Conventional Examples in which either the thickness of the surface oxide film or the Mg / Al ratio is out of the range of the present invention, the degreasing property is lowered or remarkably deteriorated.
Although Comparative Example No. 20 has good degreasing property, it is an example of surface cleaning by a mechanical method and cannot be said to be practical.

Example 2 The test material evaluated for water wettability in Example 1 was subjected to chromate treatment using a commercially available chromate treatment bath. The uniformity of the chromate film was the same as the degreasing evaluation standard.

As a result, in each of the examples of the present invention in Example 1, a chromate film was normally formed in the water-wetted portion and excellent base treatment property was recognized, but in the comparative example and the conventional example, the chromate film was not formed in the water cissing portion. It did not form or was non-uniform.

Example 3 With respect to the test material subjected to the chromate treatment in Example 2, an epoxy-based baking type coating material was applied to a film thickness of 20 μm. The coating adhesion was evaluated by immersing it in boiling pure water for 30 minutes, taking it out, and immediately after that, performing a cellotape peeling test to evaluate the coating adhesion.

As a result, as in the case of the present invention, the coating adhesion of the portion where the chromate coating was uniformly formed was good, but in the comparative example and the conventional example, the portion where the chromate coating was not formed and the formation was uneven. Peeling of the coating film was observed at various locations.

(Effects of the Invention) As described in detail above, according to the present invention, the oxide film formed during heat treatment is removed by a chemical method to regulate the thickness of the oxide film and the Mg / Al ratio. Is excellent in degreasing property, and therefore, a significant improvement effect can be obtained in the base treatment and coating film adhesion.

In particular, in the field of demand for automobile panel materials, home appliance panel materials, etc., where degreasing and surface treatment after molding are important, provision of an aluminum material having excellent degreasing properties is extremely advantageous.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-205488 (JP, A) JP-B-62-10304 (JP, B2)

Claims (1)

[Claims] 1. An aluminum alloy plate containing 0.5 wt% or more of Mg is heat treated, and then the MgO-rich oxide film formed on the surface of the aluminum alloy plate is chemically dissolved to give an oxide film thickness of 45 A or less, A method for producing an Mg-containing aluminum alloy plate having excellent degreasing properties, characterized in that the surface layer after melting has a Mg / Al ratio of 0.5 or less.