JPS59205488A - Surface treatment of aluminum alloy material - Google Patents

Abstract

PURPOSE:To attain to enhance the close adhesiveness of a coating, by performing the surface treatment of a ground coat by removing an insoluble compound formed after an Al-alloy material is subjected to degreasing or etching treatment with a solution of a metal ion sequestrant. CONSTITUTION:A fragile insoluble compound such as Mg re-precipitated on the surface of an Al-alloy material containing Mg after the degreasing and/or etching treatment of said Al-alloy material is removed by a solution of a metal ion sequestrant such as polyphosphate to enable the formation of a coating having high close adhesiveness in the succeeding coating process.

Description

[Detailed description of the invention] The present invention relates to a method for surface treatment of aluminum alloy materials.

In particular, the present invention relates to a surface treatment method for an aluminum alloy material that can improve the adhesion of a coating film in the pre-painting treatment of an aluminum alloy material containing magnesium.

Examples are Al-Mg system, AI-Mn-IVIg
system, Al-Mg-8i system.

A I -Zn-Mg series If a product that requires painting is made of an aluminum alloy material containing other magnesium, the probability of poor adhesion of the paint film is higher than that of products made of other magnesium-containing aluminum alloy materials. known to be high.

That is, for example, in the case of a drinking water can, when pulling the pull ring on the can lid and cutting off the drinking spout, the paint film tends to peel off without being completely cut off along the cutting line. A coating film with high adhesion is desired.

Generally speaking, the coating process for aluminum alloy materials is slightly different for plates and shapes, but for plates, when the process is carried out continuously on a coil coating line, it involves degreasing, washing with water, etching, washing with water, and chemical conversion treatment. The process consists of washing, draining, drying, painting, and baking. That is, since a large amount of rolling oil is attached to the surface of the rolled plate material, it is first degreased with acid or alkali, and at the same time, the very thin natural oxide film is also removed. However, these removals are usually incomplete, so in order to remove these and ensure smooth reaction in the next chemical conversion treatment, etching treatment is further performed using an acid or alkali. Furthermore, in the case of shaped materials, there are cases in which the treatment is performed in the same process as for plate materials, and cases in which anodization treatment is performed instead of chemical conversion treatment. In these processes, degreasing and etching can be carried out using acids or alkalis, but strong acids cause equipment corrosion problems, while weak acids slow the etching process;
Since alkali has good etching properties and a large amount of etching, alkaline processing agents are generally used except in special cases. In this case, the amount is about 20 to 25 gr for purposes such as suppressing the luster of the metal and erasing die marks generated during extrusion. In this case, since a large amount of smut is generated by etching, it is essential to remove smut after etching.

When painting after such pretreatment, there are two general conditions for obtaining a coating film with strong adhesion.

In addition to selecting an appropriate paint, (1) the properties of the substrate surface (such as roughness, condition of surface treatment, presence of contamination, etc.);
2) Paint film composition and adhesion suitability, (cohesive force and internal stress of the current paint film, (4) difference in thermal expansion between the paint film and the substrate, and (5) environmental conditions. (Kozo Sato, Overview of Paint Physical Properties Engineering, Riko Publishing Co., Ltd.) In order to obtain a coating film with high adhesion, the present inventors have particularly investigated (1) the properties of the substrate surface among the above-mentioned factors. The results of examining the surface of a board obtained through each step of the current standard painting process using AA5052-0 material by Auger electron spectroscopy will be explained based on the attached drawings.

FIG. 1 shows the analysis results of the blank material before pretreatment, and the thickness of the oxide film is about 250X, and a concentrated layer of magnesium can be seen on the surface. Figure 2 is.

The results after alkaline degreasing treatment show that the oxide film has been uniformly dissolved, but has not yet been completely removed. FIG. 3 shows the analysis results after the alkaline etching treatment, and shows that there is a concentrated area of magnesium from the surface to a depth of approximately 100 to 600×, and that the relative concentration of the concentrated area is also within a range. The reason for this is that magnesium is an alloying element.

It is known that in areas with high alkalinity it becomes stable in the form of 2Mg (OH%), while the solubility of Mg (OH) decreases dramatically as the alkalinity increases; most of the magnesium is dissolved in aluminum as an insoluble residue. It is thought that it re-precipitates on the surface of the alloy plate.

Next, Figure 4 shows the analysis results after the chemical conversion treatment, which shows that the magnesium compound (Mg (OH)z, Mg0) layer produced by the alkali etching treatment has been dissolved. This is because the treatment liquid has a pH of 1.5 to 2 and contains phosphoric acid, chromic acid, and hydrofluoric acid as main components.
This is thought to be due to the fact that the liquid is acidic.

After the chemical conversion treatment, I painted it as usual.

Peeling of the paint film was observed.

Based on these facts, it is thought that magnesium compounds reduce the adhesion of paint films, as has been said in the past, and although the reason cannot be confirmed, phenomenologically, magnesium compounds It has been observed that the material is brittle and may not be able to follow plastic processing, or that the interface between the chemical conversion film and the magnesium compound may peel off when processing is applied.

As shown in Figure 4, after the chemical conversion treatment, the concentration of magnesium has decreased significantly, but there is still a considerable amount of magnesium compounds near the surface layer, which affects the adhesion of the paint film. It was recognized that it was interfering with the situation.

The present inventor has repeatedly conducted research on the removal of magnesium compounds, and by degreasing and/or etching and then treating with a sequestrant solution, magnesium compounds can be removed as shown in Figure 5, the analysis results after treatment. The present invention was created based on the recognition that the object can be achieved by efficiently removing . That is, the present invention is a surface treatment method for an aluminum alloy material, in which insoluble compounds generated after degreasing and/or etching the aluminum alloy material are removed using a sequestering agent solution.

The sequestering agent used in the present invention is a chelating agent that binds with metal ions in an aqueous solution to form a soluble chelate complex and prevents the metal ions from being precipitated by other reagents. There are dipolymer phosphates (Physical and Chemical Dictionary: Iwanami Shoten), such as dipolymer phosphates, ethylenediaminetetraacetic acid (EDTA), dihydrox7ethylglycine nitrilotriacetate, gluconates, citrates, and tartrates. In general.

It has two or more phosphorus atoms in its molecule, and has an alkali metal,
It is a general term for compounds bonded to an alkaline earth metal atom and an oxygen atom, and an example of an alkali metal salt of heptapolymerized phosphoric acid is t Na<, RC) + I Na.

RuP, α, NaIROwn, NaaPaO+s
, Na0p7 o22, Na12R.

OsH, (Nai'Os)ny NaaPa o+l
+ LP207, K5Pl 010 + (KP
Os)n, Na, KtPsO,o, Na,
There are KR01+1, etc. These sequestering agents include Ca, Sr, Ba, Mg.

Zn, Nj, Pb, AI, Be,
La, Th, Zr, Ce.

It forms complex salts with many metal ions such as Fe, and the insoluble compound components generated by pretreatment vary depending on the alloy system, but are generally included in the above element group and are insoluble compounds immediately after generation. Since it is in a chemically unstable state, it easily reacts to form a soluble complex salt, which can be removed from the surface.

Therefore, as aluminum alloy materials to which the present invention can be applied, 3000 series containing magnesium, 5
Of course, the 000 series can be applied to aluminum alloy materials containing elements included in the above-mentioned element groups, and can be used as plate materials (either coils or cut plates) or shapes.

The treatment conditions for metal ion sequestering agent treatment include degreasing and/or
or a layer of insoluble compounds produced by etching,
For example, t Mg (oH) * > Mgo The concentration that can dissolve a layer containing a magnesium compound.

Any temperature and time may be used, and there is no problem even if the base material is slightly melted.

Therefore, the method of the present invention is usually carried out as a pretreatment when painting aluminum alloy materials, and is preferably carried out after deoxidizing and etching the aluminum alloy materials and before chemical conversion treatment. It may be performed either after only degreasing treatment or after only etching treatment.

9. After turning the method of the present invention, follow the conventional method.

Chemical conversion treatment, painting, etc. can be carried out, and the chemical conversion treatment agent may be of the chromate type, non-chromate type, or coating type, and can be carried out without any problems regardless of the type of paint.

In the present invention, since the treatment with a sequestering agent solution is performed after the degreasing and/or etching treatment, the insoluble compounds generated by the pretreatment can be removed, and the degree of armor of the insoluble compounds is the same as that of the base material. It has a low value and is distributed evenly, which can strengthen the adhesion of the paint film.
In addition, excellent effects are recognized, such as the deterioration of the chemical conversion treatment solution can be minimized and the equipment used does not require special corrosion-resistant materials.

Next, an example will be described.

Example 1 Extruded aluminum alloy material (AA5056-0 material.

Spray at 10g at 7465℃ using a non-etching alkaline cleaner (product name: FC-359, manufactured by Nippon Parriki Rising Co., Ltd.). (Discharge pressure 1 and sound 2)
After degreasing by spraying for 5 seconds at 35'//L at 65℃ for 5 seconds at 65℃ and washing with water, use an etching agent based on Kasonda to make the surface uniform. etching process (etching t7
fir/m'') and washing with water to remove alkali components, a trichloride solution of sodium hexametaphosphate was sprayed at 50° C. for 1 minute to remove insoluble compounds generated by etching. Then, washing with water was performed.

After drying, apply a non-chromate agent (Bonderite 3757
After washing with water, a thermosetting acrylic paint (trade name: Magikron K 2, manufactured by Kansai Paint Co., Ltd.) was applied using an electrostatic coating device, and then heated at 170°C for 30 minutes. A minute baking process was performed to obtain a coating film with a thickness of 15 μm. The resulting coating film was measured for impact adhesion and cast corrosion resistance (24 hours) using a DuPont impact tester under a load of 1 kg and a fall distance of 5 Qcm according to a conventional method. The results obtained are shown in the table below.

Example 2 A sample was treated under the same conditions as in Example 1, except that 1% ethylenediaminetetraacetic acid was used instead of sodium thihexamethanoate, and tested in the same manner. The results are shown in the table below.

Comparative Example 1 A sample was treated under the same conditions as in Example 1, except that no insoluble compound removal treatment was performed, and the results of the same tests are shown in the following table.

Comparative Example 2 The same conditions as in Example 2 were used except that the insoluble compound removal treatment was not performed, and the results of the same tests are shown in the following table.

[Brief explanation of the drawing]

Figure 1 shows an example of the relationship between the relative concentrations of Auger electrons in +AA50560 material, Figure 2 shows the results after degreasing, and Figure 3 shows the results after etching. Figure 4 is a diagram showing the results up to further chemical conversion treatment, and Figure 5 is a similar diagram showing an example of the results after treatment with a sequestering agent solution according to the method of the present invention. be. Patent applicant: Nippon Light Metal Co., Ltd. (Figure 1, Figure 2) 3 sides 4 sides

Claims (1)

[Claims] 1) A method for surface treatment of an aluminum alloy material, which comprises removing insoluble compounds generated after degreasing and/or etching the aluminum alloy material using a sequestering agent solution.