JP2528698B2 - Method for producing oil-coated aluminum alloy sheet having excellent degreasing property - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an Mg-containing aluminum alloy sheet, and more specifically, it is used for automobile panel materials and the like, which are press-molded using a lubricating oil, and then painted. The present invention relates to a method for producing a Mg-containing oil-coated aluminum alloy plate having excellent degreasing properties, which is suitable for a surface-treated application.

(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 Mg 5 ×××
Al alloys such as a series, a 6xxx series, and a 7xxx series are used.

In the production of these Al alloy plates, first, press forming is usually performed, but in order to improve the formability, heat treatment such as softening treatment or liquefying treatment is performed during this process or in the final process. Next, it is generally suitable to degrease and to apply a surface treatment such as painting.

Of these, the degreasing treatment is carried out in order to remove the lubricating oil used during press molding and the rust preventive oil for the purpose of surface protection, and to effectively 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 intended to provide a Mg-containing oil-coated aluminum alloy sheet 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, in view of the fact that the oxide film produced by heat treatment contains a large amount of Mg, and that the affinity with lubricating oil and rust preventive oil is strengthened by the reaction with moisture in the atmosphere. The thickness of the oxide film and
By coating the Mg-containing aluminum alloy plate with controlled Mg / Al ratio with the method rust oil whose viscosity and oil film thickness are regulated, the degreasing property is excellent even if the press oil is re-coated after long-term storage. That is, the present invention has been made.

That is, the method for producing a Mg-containing oil-coated aluminum alloy sheet excellent in degreasing property according to the present invention is Mg: 0.5 wt% or more in an aluminum alloy sheet containing, by the chemical dissolution of the MgO-rich oxide film formed on the surface. , Oxide film thickness 45
Å or less, the Mg / Al ratio of the surface layer after dissolution is 0.5 or less, and the viscosity at the surface at a rapid temperature of 40 ° C. is 1.3 to 6.5 CS.
The rust preventive oil of T. is applied in an oil film thickness range of 0.05 to 5.0 μm.

 Hereinafter, the present invention will be described in more detail.

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 from 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 heat treatment is
Mg content in alloy, heat treatment conditions (temperature, time, atmosphere)
For example, in the case of an Al alloy containing 0.5 to 5 wt% of Mg, it 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.

Further, the Mg / Al ratio of the above oxide film analyzed by ESCA is about 1.0 to 3.5, and it 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.

Next, conditions for removing the oxide film in 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 cleaning agent, 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 thicker 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.

The composition of the Mg-containing aluminum alloy in the present invention is not limited as long as it is an Al alloy containing at least 0.5 wt% of Mg. In the case of Al alloy with Mg less than 0.5 wt%, the amount of MgO in the oxide film does not become so rich, and there is little problem of deterioration of degreasing property due to the MgO-rich oxide film.

Next, the conditions for oiling in the present invention will be described.

First, the inventors of the present invention conducted further research on the aluminum alloy sheet produced by the above method, and found that even if the oxide film was removed by washing with an acid or an alkali, the sheet was kept naked in the atmosphere. It was found that aluminum is an active metal and a dense natural oxide film is formed on the plate surface in a short time. The oxide film formed varies depending on atmospheric temperature, humidity, time, etc. during storage, but it will be about 50 to 60 Å when left for 2 to 3 months.

This oxide film thickness is heat treated (heated) in an oxidizing atmosphere
Although it is very thin as compared with the above-mentioned one, since it has been altered due to moisture in the atmosphere as described above, its affinity with oil increases and degreasing property remarkably decreases.

On the other hand, normally, when an aluminum alloy sheet is manufactured by a coil form in a factory, it is necessary to apply oil for the purpose of preventing scratches at the time of winding and preventing surface corrosion after washing with acid or alkali. Oil having a low viscosity is generally used because of the ease of applying oil during coil production. Although it depends on the composition of the oil, the oil having a low viscosity generally has a large amount of evaporation after being applied, and when stored for a long time, the oil content evaporates and the residual oil film thickness becomes very thin. Therefore, the rust preventive effect is reduced, an oxide film is likely to be formed on the surface of the aluminum plate, and when reapplying the press oil or the like, the degreasing property is lowered as a result.

In consideration of such circumstances, the inventors of the present invention have conducted earnest researches on measures against natural oxide film formation due to long-term storage after oxide film removal, and as a result, immediately after oxide film removal by the above-described method, It was found that by applying a rust preventive oil having a viscosity of 1.3 to 6.5 CST so that the oil film thickness is in the range of 0.05 to 5 μm, the storage period can be extended and the problem of lowering degreasing property can be eliminated.

That is, when the rust preventive oil having an oil viscosity of less than 1.3 CST is applied, the amount of residual oil on the plate surface becomes small after storage in the air, the effect of surface protection cannot be obtained, and an oxide film is formed. Degreasing property deteriorates. Conversely, when rust preventive oil with a viscosity exceeding 6.65 CST is applied, the surface protection effect is good and the formation of an oxide film is prevented, but the oil adsorption is large and the degreasing property deteriorates, leaving the oil residue. It is difficult to apply the oil during the coil production, and it is difficult to apply the oil uniformly. Therefore, the viscosity of the oil to be applied is 1.3-6.5C.
You need to use the ST one.

On the other hand, although the oil film thickness after oiling is less than 0.05 μm, since the oil film thickness is thin, the surface protective action is small, an oxide film is easily formed, and scratches are easily caused. On the contrary, 5μ
If it exceeds m, the surface protecting effect is good, but degreasing property such as oil residue is deteriorated. Therefore, the oil film thickness needs to be in the range of 0.05 to 5 μm.

In addition, it is necessary to apply the above-mentioned oil immediately after removing the oxide film by the above-mentioned method, and preferably within about 10 days. If the period until oiling is too long, a natural oxide film will be formed and the oil removal property will be deteriorated, which is not preferable.

(Example) Next, the Example of this invention is shown.

Example 1 A cold-rolled sheet made of 6061 alloy (Mg content 1.0 wt%) and 5182 alloy (Mg content 4.5 wt%), which are widely used for press forming, was used, and heat treatment conditions as shown in Table 1 were used. The cleaning conditions were changed and the test materials were prepared.

The thickness and Mg / A of the surface oxide film of the obtained test material
The l ratio was investigated. The results are also shown in Table 1.

Next, for this test material, immediately after washing, JIS K 224
NP-3 type rust preventive oil (viscosity 4.7 CST) specified in 6 was applied (oil film thickness 0.2 μm) 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 evaluation of degreasing was performed by water leakage after immersion degreasing. In this case, those with complete water leakage were evaluated with ◯, those with partial water cissing were marked with Δ, and those with full water cissing were marked with X. 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 inferior. 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 Representative No. 5 and No. 8 materials were selected from the test materials excellent in degreasing property in Example 1, and the viscosity of oil and the amount of oil coating were variously changed, and after cleaning, oil coating was performed. Oil was applied for different periods and left indoors for 3 to 6 months.

Then, using 2% bath of the test material commercially available alkaline degreasing agent "Ridorin # 322N _4" (manufactured by Nippon Paint), temperature 60
Immersion degreasing was performed under the conditions of ° C and time of 30 seconds. The results of evaluation of degreasing properties are shown in Table 2.

The degreasing property was evaluated by the water leakage property after the immersion degreasing treatment. In this case, the one that leaked completely was marked with a circle,
Evaluations were made by marking a part of water cissing with Δ and a mark of all water cissing with x.

From Table 2, it can be seen that Examples 1 to 12 of the present invention have excellent degreasing properties even after long-term storage for 6 months after plate production.

On the other hand, in Comparative Examples No. 14 to No. 18 in which either the viscosity of the coating oil or the oil film thickness is out of the range of the present invention, the degreasing property is lowered or significantly deteriorated after 3 to 6 months. In Comparative Example No. 18, which was not immediately applied with oil after washing, the degreasing property was reduced after 3 months. Of course, Comparative Example No. 13 which is not oiled is inferior in degreasing property.

Example 3 The test materials evaluated for water leakage in Examples 1 and 2 were 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 and Example 2, the chromate film was normally formed in the water leak portion, and excellent base treatability was recognized, but in the case of Comparative Example and Conventional Example,
No chromate film was formed or non-uniform in the water cissing part.

Example 4 With respect to the test material subjected to the chromate treatment in Example 3, an epoxy 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 cellophane peeling test to evaluate the coating adhesion.

As a result, as in the case of the present invention, the adhesion of the coating film on the part where the chromate film was uniformly formed was good, but in the comparative example and the conventional example, the part where the chromate film 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 and Mg / Al ratio of the oxide film, and further remove the oxide film. Promptly,
Since a rust preventive oil having a controlled viscosity and oil film thickness is applied, the degreasing property is excellent even after long-term storage, and therefore, a significant improvement effect can be obtained in the adhesion of the undercoating coating film.

In particular, in the field of demand such as automobile panel materials and home appliance panel materials where degreasing and surface treatment after molding are important, providing an aluminum material having excellent degreasing property is extremely advantageous.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Yoshiki Nakamura 2-159 Takase-cho, Moka-shi, Tochigi Prefecture (72) Inventor Yoichi Ozawa 51-2 Otanidai-cho, Moka-shi, Tochigi Prefecture (56) Reference JP-A-57 -78493 (JP, A) JP 61-291982 (JP, A) JP 1-319692 (JP, A)

Claims (1)

(57) [Claims] 1. An aluminum alloy sheet containing Mg in an amount of 0.5 wt% or more, the thickness of the oxide film is 45Å or less due to the chemical dissolution of the MgO-rich oxide film formed on the surface, and the Mg / Al of the surface layer after dissolution is Mg / Al. The ratio is 0.5 or less, and
A method for producing an oil-coated aluminum alloy sheet having excellent degreasing properties, which comprises applying a rust-preventive oil having a viscosity of 1.3 to 6.5 CST at 40 ° C in an oil film thickness range of 0.05 to 5.0 µm.