JP3211413B2 - Surface treatment method for Al or Al alloy material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for exhibiting excellent post-painting corrosion resistance of Al or Al alloy material (hereinafter referred to as Al alloy material) even under severe corrosive environment. The alloy material is useful as a panel material for vehicles such as automobiles, an outer plate material of home electric appliances, a building material, and the like.

[0002]

2. Description of the Related Art Since Al alloy sheets have excellent corrosion resistance and design properties, they have been conventionally used in a wide range of fields, such as outer panels of home electric appliances and building materials. In recent years, also in the field of automobiles, weight reduction of a vehicle body has been called out from the viewpoint of improving fuel efficiency, and Al alloy sheets, which are lighter than conventional steel sheets, have begun to attract attention.

[0003] In the panel material of automobiles and household appliances,
Usually, it is used after being subjected to processing such as press molding and then applied. In particular, a cationic electrodeposition coating method is widely used for automobile panel materials from the viewpoint of corrosion resistance and the like.

[0004] However, since the surface of the Al alloy material is covered with a dense and strong oxide film, not only is the phosphate treatment property performed as a pretreatment for coating insufficient, but also the elution of Al ions is prevented. Deteriorates phosphatability. As a result, the adhesion of the coating film and the corrosion resistance after painting (for example, thread-like corrosion) become serious problems. Therefore, as a means for solving such a problem, for example, Japanese Patent Application Laid-Open No. S61-157693 discloses a method in which the surface of an Al alloy plate is coated with Zn, Zn-based alloy or Fe-based alloy to prevent elution of Al. Is disclosed.

[0005]

According to the above method,
Although the dissolution of Al is prevented, the deterioration of the processability of the phosphating solution is prevented. Problems such as peeling of the coating film occur.

The present invention pays attention to such a situation, and has studied to provide a surface treatment method capable of exhibiting excellent post-painting corrosion resistance even in a severe corrosive environment. As a result, on the surface of the Al alloy material, Z satisfying the requirements of the following formula [I] is satisfied.
n based or Fe-based plated layer _{0 ≦ (E Al -E m)} ≦ 0.5 (V) ... [I] where E _Al: Al or Al 5% corrosion potential in saline alloy (V) E _m: Plating The layer whose corrosion potential (V) was formed in 5% saline solution had excellent performance in terms of coating blistering resistance, thread rust resistance, and perforated corrosion resistance after cationic electrodeposition coating, etc. And applied for a patent based on such knowledge (Japanese Patent Application No. 4-158721).
issue).

[0007] However, even with such a surface-treated Al alloy material, depending on the type of plating material, coating film swelling and thread rust may occur in a severe corrosive environment. In view of the above, an object of the present invention is to establish a surface treatment method capable of reliably exhibiting even more excellent post-painting corrosion resistance even in a severe corrosive environment.

[0008]

The surface treatment method according to the present invention, which can achieve the above object, comprises a surface treatment method for forming a surface film having excellent corrosion resistance after painting on the surface of Al or Al alloy material. Wherein the dissolution rate at the time of spraying a 5% saline solution onto the surface of the Al or Al alloy material is less than 0.5 g / m ² / h, and the corrosion potential when immersed in a 5% saline solution for 5 hours is as follows: I] has a gist in that it is covered with a Zn-based or Fe-based plating layer that satisfies the requirements of the formula [I]. 0 ≦ (E _Al −E _m ) ≦ 0.5 (V)... [I] where E _Al : Corrosion potential (V) of Al or Al alloy material in 5% saline solution Em: 5% of plating layer Corrosion potential in saline solution (V)

[0009]

The present inventors have been studying the suitable types of plating and the amount of plating applied in terms of corrosion resistance after painting, that is, coating adhesion, coating swelling resistance, yarn rust resistance, and perforation resistance. As a result, it is effective to apply Zn-based or Fe-based plating, which is excellent in phosphate treatment, to improve coating film adhesion. It has been confirmed that it is effective to minimize the amount of adhesion of the plating to improve the property.

[0010] Furthermore, as a result of a similar study on the perforation resistance, it was found that more strict control of the plating structure was necessary to improve the perforation resistance. In other words, although the Al alloy material itself has extremely excellent puncture resistance compared to steel plates and the like, when plating is performed thereon, the pitting corrosion of the Al alloy material is accelerated depending on the type of plating. This phenomenon also appears remarkably in the case where the phosphate treatment is performed.

Therefore, as a result of further detailed studies on the perforation resistance of the coating material, the Zn-based or Fe-based plating types in which the potential difference of the Al alloy material as the base material satisfies the relationship of the above formula [I] are as follows. It was also found that the Al alloy material does not deteriorate the excellent perforation resistance inherently provided therein, and exhibits excellent performance in coating film adhesion, coating blister resistance, and yarn rust resistance.

Here, when the potential of the plating layer is more noble than the potential of the Al alloy material [that is, (E _Al -E _m ) <0]
(V)] indicates that the plating layer is a cathode in a corrosive environment,
A local battery in which the Al alloy material serves as an anode is formed,
Perforated corrosion of the alloy material is accelerated. Conversely, when the potential of the plating layer becomes lower than the potential of the Al alloy material by 0.5 (V) or more [that is, (E _Al −E _m )> 0.5 (V)], a local battery opposite to the above is formed. Corrosion of the plating layer becomes severe, and coating film blisters easily occur.

However, as described above, even if a plating layer that satisfies the relationship of the above formula [I] is formed, depending on the type of plating material, it may be necessary to form a coating layer after chemical conversion treatment or cationic electrodeposition coating. The coating film may blister or rust in a relatively short period of time.

[0014] Therefore, further research was carried out to solve these problems and to more reliably exert excellent post-painting corrosion resistance. As a result, the quality of the corrosion resistance after painting has a high correlation with the bare corrosion resistance of the plated Al alloy material. Corrosion resistance after painting is also insufficient, and film swelling and yarn rust occur in a relatively short period of use, while those with excellent bare corrosion resistance surely demonstrate excellent performance in corrosion resistance after painting. I found out.

[0015] As the evaluation standard of the bare corrosion resistance, "5
% Salt solution spray rate (that is, corrosion loss of plating layer: g
/ m ² / h) ", the value of which is less than 0.5 g / m ² / h and at the same time satisfying the relation of the above formula [I], ensures a high level of post-paint corrosion resistance. It was confirmed. By the way, when the dissolution rate exceeds 0.5 g / m ² / h, the sacrificial corrosion prevention action of the plating layer defined by the above formula [I] is lost early after the chemical conversion treatment and the electrodeposition coating, etc. The material may cause perforated corrosion in a short time or
Rust is generated between the alloy base material and the coating, causing the coating to bulge.

As described above, according to the present invention, an appropriate sacrificial anticorrosive action is imparted to the plating layer by the above formula [I], and the dissolution rate is suppressed to enhance the durability of the sacrificial anticorrosion. A preferred plating material that reliably develops post-corrosion resistance and satisfies such requirements is Zn with an appropriate amount of Fe, Ni, Cr, Mg.
And the like are exemplified.

The amount of plating is not particularly limited.
In order to more effectively achieve the object of the present invention of improving the durability of corrosion resistance after painting, 0.5 g / m ² or more, more preferably 1.
It is good to be 0 g / m ² or more. There is no particular limitation on the plating method, and any method such as normal electroplating, wet plating such as chemical plating, or vapor phase plating such as vapor deposition plating can be adopted. Of course, it is also effective to perform displacement plating, anodic oxidation, or the like as plating pretreatment.

There is no particular limitation on the type of Al alloy material to which the present invention is applied, and Mg, Cu, Mn, S
Various Al alloys containing one or more of i, Zn, Cr, Ni and the like as alloy components are included, and the most common of these are Al-Mg based alloys and Al-Mg-Si.
It is a system alloy. It is of course possible to use pure Al as the base material. In addition to the most versatile plate-like materials (thin plates and thick plates), tubular shapes, rod-like objects, linear objects, and the like can be selected and used according to the application and purpose.

[0019]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples.

[0020] Example surface cleaning treatment of Al or Al alloy plate was subjected, plated with various compositions and coating weight by electroplating, for each plating material obtained, dissolved at 5% brine spraying Measure the speed (at 25 ° C) and 25% in 5% saline
The potential of the plating layer was measured at ℃ and compared with the potential of each Al material under the same conditions.

After immersion-type phosphate treatment was applied to each of the obtained plating materials, cationic electrodeposition coating (epoxy-based electrodeposition coating, coating thickness: about 20 μm) was performed, and the corrosion resistance after coating was evaluated. The result shown in FIG. The evaluation method is as follows.

After the cross-cut, a salt spray test is performed for 1000 hours, and the coating blister width from the cut portion is evaluated. ；: Blister width 2 mm or less △; 〃 2 to 5 mm ×; ５ 5 mm or more

[0023] Yarn rust resistance: After cross-cutting, the following corrosion test was performed for 8 cycles, and evaluation was made based on the blister width of the coating film from the cut portion. ；: Blister width 2 mm or less △; 〃 2 to 5 mm ×; ５ 5 mm or more

Perforation resistance: After cross-cutting, the following corrosion test was performed for 100 cycles, and evaluated by the perforation depth of the cut portion. ；: Perforated depth 0.1 mm or less △; 〃 0.1 to 0.3 mm ×; 〃 0.3 mm or more

[0025]

[Table 1]

As is evident from Table 1, the surface-treated Al alloys of Nos. 1 to 8 satisfying the requirements of the present invention after coating, such as coating blistering resistance, thread rust resistance, and perforation resistance. While all of the corrosion resistances are very good, the corrosion loss (dissolution rate) of the plating layer and the potentials of the Al material and the plating layer, which are lacking the requirements of the present invention, are No. 9 to 13. Either the coating blistering property, the thread rust resistance, or the perforation resistance is poor.
Insufficient corrosion resistance after painting. In this example, an example in which an Al-Mg-based alloy was used as a plating substrate was shown, but substantially the same results as described above were obtained when a pure Al plate or an Al-Mg-Si-based alloy was used.

[0027]

According to the present invention, the potential difference between the metal plating layer formed on the surface of the Al or Al alloy substrate and the substrate is specified, and the dissolution rate of the plating layer is determined. By specifying the above, it has become possible to provide a surface-treated Al or Al alloy material that reliably exhibits more excellent corrosion resistance after painting.

Continuation of the front page (72) Inventor Toshiki Ueda 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Kobe Steel, Ltd. Kobe Research Institute (58) Field surveyed (Int.Cl. ⁷ , DB name) ) C23C 30/00

Claims (1)

(57) [Claims] 1. A surface treatment method for forming a surface film having excellent corrosion resistance after coating on the surface of an Al or Al alloy material,
The dissolution rate at the time of spraying 5% saline solution on the surface of Al or Al alloy material is less than 0.5 g / m ² / h, and the corrosion potential when immersed in 5% saline solution for 5 hours is represented by the following formula [I]. A surface treatment method for Al or an Al alloy material, characterized by coating with a Zn-based or Fe-based plating layer satisfying requirements. 0 ≦ (E _Al −E _m ) ≦ 0.5 (V)... [I] where E _Al : Corrosion potential (V) of Al or Al alloy material in 5% saline solution Em: 5% of plating layer Corrosion potential in saline solution (V)