JPH0539589A - Phosphated aluminum sheet excellent in corrosion resistance after coating - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an aluminum plate, which is subjected to a phosphate treatment with a zinc-based plating as a base and is used for automobile bodies and the like, which has excellent corrosion resistance after coating. [Constitution] The residual adhesion amount of the zinc-based plating after the phosphate treatment is restricted to less than 1.0 g / m ² . Further, the residual adhesion amount is preferably within the range of 0.1 to 0.5 g / m ² . Furthermore, as the zinc-based plating, it is preferable to use a plating bath to which a fluoride is added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphate-treated aluminum plate which is used as a car body or the like after being painted.

[0002]

2. Description of the Related Art Conventionally, steel sheets have been usually used for automobile bodies. As such steel plates for automobile bodies, in addition to ordinary steel plates and high-tensile steel plates, surface-treated steel plates such as galvanized steel plates and galvannealed steel plates are used. Of these, surface-treated steel sheets such as galvanized steel sheets and galvannealed steel sheets are excellent in corrosion resistance, and are therefore recommended especially for parts or vehicle models that require corrosion resistance.

In an automobile body assembly and production line using such steel plates, the body steel plate is formed into a predetermined shape by press working or the like to form each body part, and then each body part is assembled and spotted. After welding, and then degreasing the assembled body, a phosphate treatment, which is a kind of chemical conversion treatment, is performed to improve the adhesion between the steel plate and the coating and the corrosion resistance, and then the electrolytic treatment. It is common to carry out coating and ordinary spray painting.

On the other hand, recently, an aluminum plate is often used for the body of an automobile mainly for the purpose of reducing the weight of the vehicle body for improving the fuel consumption of the automobile. In this case, it is still rare to make the whole body of the automobile aluminized, and it is usual to use a steel plate and an aluminum plate together. In order to assemble and manufacture an automobile body by using such a steel plate and an aluminum plate together, it is required to use the same line as in the case of only the above-mentioned steel plate. That is, after assembling a body part made of a molded steel plate and a body part made of a molded aluminum plate to create a body, the whole body is degreased, then phosphated, and then electrodeposited. Painting and spray painting are performed. In this way, even if a steel plate and an aluminum plate are used together, it is not necessary to newly establish another assembly and production line, and the continuity of the steps can be maintained, which is advantageous in terms of manufacturing cost. However, in this case, since the aluminum plate is also subjected to the phosphate treatment at the same time as the steel plate, the following problems occur.

That is, when the aluminum plate is subjected to the phosphating treatment, the oxide film existing on the surface of the aluminum plate acts as a passive film, so that the phosphating film is uniformly and densely formed on the aluminum plate. As a result, there is a problem that the corrosion resistance after coating is poor. Further, the surface of the aluminum plate is dissolved during the phosphate treatment, and Al ions are eluted in the treatment bath. Therefore, as described above, the phosphate is simultaneously applied to the steel plate and the aluminum plate integrated as an automobile body. During the treatment, aluminum ions eluted from the aluminum plate form a passivation film of aluminum on the surface of the steel plate, which also inhibits the formation of a phosphate-treated film on the surface of the steel plate. There is a problem that sufficient corrosion resistance and sufficient adhesion of the coating film cannot be obtained.

As one measure against such a problem, there is a method of adding a fluorine compound to a phosphate treatment bath to remove the oxide film on the surface of the aluminum plate and form a phosphate treatment film uniformly. U.S. Pat. No. 3,619,300
Proposed in the issue. In this method, Al ions dissolved in the treatment bath are treated with elpasolite (K ₂ NaAlF).
₆ ) As the precipitate can be removed, the problems mentioned above can be solved. However, in the case of this proposed method, there are problems in the concentration control of the phosphating bath and the environment.

As another measure, Japanese Patent Laid-Open No. 61-
No. 157693 proposes a method in which zinc-based plating is performed in advance before the phosphate treatment. This proposed method is based on the fact that a Zn plating layer or Z
The n-alloy plating layer is formed with a deposition amount of 1 g / m ² or more. By forming the zinc-based plating film in advance in this way, it is possible to remove Al from the aluminum plate during the subsequent phosphate treatment. Ions do not elute into the bath, and therefore, even when the body is a combination of an aluminum plate and a steel plate and the body is subjected to phosphating treatment, a sufficient phosphating film can be formed on the steel plate, and the aluminum plate itself It is said that a phosphating film can be formed on the surface of the.

[0008]

Generally, a coated aluminum sheet has remarkably excellent corrosion resistance unless the coating film has defects such as scratches and pinholes, but the coating film is damaged by flying stones while the vehicle is running. If this occurs, corrosion of the aluminum of the base proceeds from the scratched portion and the coating film swells, resulting in poor appearance. The appearance defect due to the blister of the coating film is affected not only by the corrosion resistance of the base aluminum material itself, but also by the uniformity and denseness of the phosphate-treated coating as the coating base. In particular, when a phosphate film is formed by using a zinc-based plating layer as a medium as proposed in JP-A-61-157693, it is necessary to form a uniform and dense zinc-based plating layer without pinholes. However, in the case of the above proposal, the adhesion of the zinc-based plating layer to the aluminum substrate is low,
It was difficult to reliably form a uniform and precise zinc-based plating layer without pinholes.

On the other hand, the present inventors have already filed Japanese Patent Application No. 2-1914.
In No. 44, as a method capable of forming a uniform and dense zinc-based plating film without pinholes, which has a high adhesion of the zinc-based plating film to the aluminum substrate, a plating bath containing a fluoride during the zinc-based plating treatment is used. Proposes a method to use. Specifically, after degreasing the aluminum plate surface, a fluoride and a zinc salt are added to the bath so that the F ⁻ ion concentration is 0.4 to 80 g / l and the Zn ²⁺ ion is 0.1 to 0.1 g. It is characterized in that electrogalvanic plating is performed in a plating bath containing it so as to be in the range of 75 g / l.

According to the method using the fluoride addition bath as described above, it is possible to form a uniform and dense zinc-based plating film having good adhesion to an aluminum substrate and no pinholes. However, when the present inventors further researched, the corrosion resistance after coating when a zinc-based plating film was formed on an aluminum plate and then subjected to phosphate treatment showed that the zinc-based plating film was uniform and dense. In addition, it was newly found that the amount of residual zinc after phosphating has a great influence. That is, even if the zinc-based plating film on the surface of the aluminum plate is formed uniformly and densely, the corrosion resistance after coating may not be good unless the amount of residual zinc after phosphate treatment is appropriate. There was found.

The present invention has been made in view of the above circumstances. As an aluminum plate for coating, the surface of which is subjected to a phosphate treatment through a zinc-based plating film, the corrosion resistance after coating is sure and stable. The purpose is to provide an excellent aluminum plate.

[0012]

[Means for Solving the Problems] As a result of various experiments and investigations by the present inventors, in order to improve the corrosion resistance after coating of an aluminum plate that has been subjected to a phosphate treatment through a zinc-based plating film, , The residual amount of zinc-based plating after phosphating has a great influence on the corrosion resistance after coating, and controlling the residual amount to be less than 1.0 g / m ² improves the corrosion resistance after coating. The present invention has been completed and the present invention has been completed.

Specifically, in the invention according to claim 1, in an aluminum plate having a zinc-based plating on its surface and a phosphate treatment applied on the zinc-based plating, the zinc-based plating remains It is characterized in that the adhered amount is less than 1.0 g / m ² .

Here, it is desirable to use a fluoride bath containing a fluoride and a zinc salt as the plating bath in the zinc plating, and the residual adhesion amount of the zinc plating after the phosphate treatment is among the above-mentioned 1.0 g / m ² less than the range is also optimal particularly from 0.1 to 0.5 g / m ^2.

Therefore, the invention of claim 2 is the phosphate-treated aluminum plate of the invention of claim 1, wherein the zinc-based plating is carried out in a fluoride bath containing a fluoride and a zinc salt. Is characterized in that According to a third aspect of the present invention, in the phosphate-treated aluminum sheet according to the first aspect of the present invention, the residual adhesion amount of the zinc-based plating is within the range of 0.1 to 0.5 g / m ^2. It is a feature.

In this specification, zinc-based plating includes not only pure zinc plating but also zinc alloy plating (eg, zinc-nickel alloy plating, zinc-iron alloy plating), and a combination thereof (multilayer). It is used to include the case of.

[0017]

[Function] When a zinc-based plating is applied to the surface of an aluminum plate and then a phosphate treatment is applied, in order to form a dense and uniform phosphate film, the underlying zinc-based plating film must have no pinholes. However, according to the experiments conducted by the present inventors, it has been found that the remaining amount of the zinc-based plating remaining after the phosphate treatment has a great influence on the corrosion resistance after coating. That is, although the underlying zinc-based plating film is etched during the phosphate treatment, it remains to some extent. The residual amount of the zinc-based plating after the phosphoric acid treatment has a great influence on the corrosion resistance after coating, for example, the blister width of the coating film after coating is used as an index. The experimental results are shown in FIG. ..

The solid line in FIG. 1 is zinc after the phosphate treatment when electrogalvanizing is applied as the zinc-based plating and a fluoride bath is used as the plating bath, as will be described later as Example 1 again. The relationship between the residual amount of plating and the blister width of the coating film after the corrosion test is shown. In addition, the broken line in FIG. 1 shows the result after the phosphate treatment in the case where electrogalvanizing is performed as a zinc-based plating using a normal zinc plating bath containing no fluoride, as will be described later as Example 2 again. The relation between the amount of residual zinc plating adhered and the blister width of the coating film after the corrosion test is shown. In both the solid line and the broken line in FIG. 1, it is clear that there is a clear correlation between the residual adhesion amount of zinc plating and the bulging width of the coating film. It can be seen that when the amount is 0 g / m ² or more, the blister width of the coating film becomes large and the corrosion resistance after coating deteriorates.

The reason why the corrosion resistance after coating deteriorates when the amount of residual zinc-based plating after the phosphate treatment increases is not yet completely clarified. It is considered that if the plating is exposed, the exposed zinc-based plating dissolves quickly, which promotes blistering of the coating film in the vicinity of the exposed portion. Of course, if the thickness of the zinc-based plating film becomes thicker, the number of pinholes in the plating film will decrease, resulting in fewer pinholes in the phosphate treatment film. It is presumed that the corrosion resistance will decrease. In addition to pure zinc plating, zinc alloy plating such as Zn-Fe alloy plating and Zn-Ni alloy plating can be applied as the zinc-based plating. In addition to such influence of zinc, Fe and Ni remaining after the phosphate treatment have a higher noble potential than the aluminum of the base material, which promotes corrosion of the aluminum base material of the scratched portion and causes defects such as perforation. Therefore, even when these zinc alloy platings are applied, it is preferable that the residual adhesion amount of the plating is small. Further, from the viewpoints of not only the corrosion resistance after coating as described above but also the weldability and the prevention of powdering during press molding, it is preferable that the residual adhesion amount of the zinc-based plating is small.

Here, as the corrosion resistance after coating, it is generally said that the coating film bulge width is preferably 1 mm or less, but as shown by the solid line in FIG. When used, if the residual amount of zinc plating is less than 1.0 g / m ² , the blister width of the coating is 1 mm.
It can be: Also, the blister width of the coating film is 0.5 mm.
The following is more preferable, but in the case of electrogalvanizing using a fluoride addition bath, the residual adhesion amount of plating is 0.1 to 0.
Within the range of 5 g / m ² , the coating film bulge width can be suppressed to 0.5 mm or less.

As can be seen from FIG. 1, when the residual adhesion amount of the zinc-based plating after the phosphate treatment is extremely small (0.
The coating film blister width is slightly increased even in the case of less than about 1 g / m ² ), and the cause is considered as follows. That is, as the residual adhesion amount of the zinc-based plating decreases, the number of pinholes in the plating film increases and the phosphate treatment film also increases in number of pinholes, as described above. It appears that the effect of suppressing the corrosion due to the reduction of the residual adhesion amount of the zinc-based plating is greater, and the corrosion resistance after coating is slightly deteriorated.

[0022] As described above, the zinc-based residual adhesion amount less than 1.0 g / m ² after phosphating plating can be applied, preferably by regulating the 0.1 to 0.5 g / m ^2, after coating Excellent corrosion resistance can be obtained, and the occurrence of blistering of the coating film can be reduced.

The component composition of the aluminum material which is the base material of the phosphate-treated aluminum plate of the present invention is not particularly limited as long as it is subjected to the phosphate treatment and used for the purpose of coating. Besides, various aluminum alloys can be used. In particular, in the case of automobile body applications, which are the main targets of the present invention, Al-Mg
Series alloy (JIS 5000 series alloy), Al-Mg-S
The i-based alloy (JIS 6000 series alloy) is most suitable.
The manufacturing method of the base aluminum plate itself is not particularly limited, and may be a plate thickness of about 1 to 2 mm through usual manufacturing processes such as casting, heating, hot rolling, cold rolling, and annealing.

A method for producing the phosphate-treated aluminum plate of the present invention using the above-mentioned blank aluminum plate will be described below.

Usually, first, the surface of the aluminum plate is cleaned according to a conventional method. Specifically, for example, after removing the surface oil with an alkaline degreasing agent, the surface oxide film is removed by pickling. After that, electrozinc plating is applied to the surface. Here, in electrogalvanic plating, it is desirable to use a bath containing a fluoride as a plating bath, as proposed by the present inventors in Japanese Patent Application No. 2-291444. That is, as can be seen by comparison with the solid line in FIG. 1 (when using a fluoride-added zinc plating bath) and the broken line (when using a normal zinc-plating bath in which fluoride is not added), plating with fluoride added When using a bath,
Corrosion resistance after coating is much better than when it is not added. The reason is that the zinc-based plating film itself has many pinholes when a fluoride-free plating bath is used, whereas the zinc-based plating film itself has many pinholes when a fluoride-added plating bath is used. This is because the number of holes can be significantly reduced.

Desirable conditions for using the above-mentioned fluoride-added plating bath are Japanese Patent Application No. 2-29144.
This is as disclosed in No. 4, but specifically as follows. That is, when plating pure zinc, a plating bath containing a fluoride and a zinc salt is used, and when plating zinc alloy, in addition to the fluoride and zinc salt, an alloy element such as nickel or iron is used. Electroplating is performed in a plating bath containing the salt of. At this time, the plating bath had an F ⁻ ion concentration of 0.4 to 80 g / l and a Zn ²⁺ ion concentration of 0.1 to
It is desirable to adjust it to be 75 g / l. When the nickel salt is contained, the Ni ²⁺ ion concentration is 0.
It is suitable to adjust the concentration to 1 to 70 g / l, and the Fe ²⁺ ion concentration to 0.1 to 70 g / l when an iron salt is contained.

By immersing an aluminum plate in such a plating bath and energizing the aluminum plate as a cathode,
While the surface layer of the aluminum plate is dissolved by F ⁻ ions in the plating bath, Zn ²⁺ ions or Zn ²⁺ ions and N 2
The i ²⁺ ions or Fe ²⁺ ions are electrolytically deposited as a metal on the surface of the aluminum plate which is the cathode to form a zinc plating film or a zinc alloy plating film (these are collectively referred to as a zinc-based plating film). At this time, as described above, the surface layer of the aluminum plate is dissolved by the F ⁻ ions to expose the active surface, so that electrolytic deposition of zinc or zinc and nickel or iron is performed on the active surface, so that zinc-based plating is performed. The film is formed with high adhesion to the aluminum plate. That is, even if an intermediate layer is not formed in advance by a zincate treatment or the like, a zinc-based plating film having good adhesion and few pinholes is formed only by electroplating.

As the zinc salt used in the plating bath in the electrogalvanic plating, zinc sulfate is preferable, but zinc chloride, zinc borofluoride and the like can also be used. Of course, two or more zinc salts may be mixed.
Nickel sulfate is preferable as the salt of nickel used in the case of zinc-nickel alloy plating, and nickel chloride can be used in addition to this. Of course, two or more kinds of salts may be mixed and used. Further, iron sulfate or the like can be used as the iron salt used in the zinc-iron alloy plating, and of course, two or more kinds of salts may be mixed and used.
On the other hand, the fluorides used in the plating bath include hydrogen fluoride (HF) and ammonium hydrogen fluoride (NH ₄ F · H).
F) is preferable, but not limited to this. Furthermore, the plating bath contains additives such as boric acid, sodium sulfate, aluminum sulfate, ammonium sulfate, magnesium sulfate, ammonium chloride, sodium acetate, glucose, and various brighteners that are added to ordinary electrogalvanic plating baths. It may be.

The electric current density in the electroplating using the fluoride-added plating bath as described above is not particularly limited as long as it is approximately the same as in the case of general electrogalvanizing, but is usually 5 to 5. It may be about 30 A / dm ² .

As described above, it is desirable to use a fluoride-added bath as the zinc-based plating bath, but in some cases a normal fluoride-free plating bath may be used. However, in this case, in order to obtain almost the same level of corrosion resistance as in the case where a plating bath containing a fluoride is used, it is desirable to perform a zincate treatment as a pretreatment.

The plating amount in the electrogalvanizing plating is determined in consideration of the etching amount in the subsequent phosphate treatment.
The amount of residual adhesion after phosphating is 1 g /
It may be determined to be less than m ² , preferably 0.1 to 0.5 g / m ² . Since the etching amount in the usual phosphate treatment is about 0.5 g / m ² , the plating amount may be less than about 1.5 g / m ² . In this case, the plating amount may be about 0.6 to 1.0 g / m ^{2 in} order to obtain the most suitable residual deposit amount.

After the electrogalvanizing plating is performed as described above, a phosphate treatment such as a zinc phosphate treatment may be performed according to a conventional method. The amount of the phosphate coating deposited is preferably 0.5 to 7 g / m ² .

Thus, the phosphate-treated aluminum plate of the present invention having excellent corrosion resistance after painting is obtained.

[0034]

【Example】

Example 1 The surface of an aluminum plate having a plate thickness of 1.0 mm, which was composed of Mg 4.5 wt%, Mn 0.2 wt% and the balance substantially Al, was degreased with a sodium phosphate solution and then pickled with a sulfuric acid solution. Then, as fluoridated galvanizing bath, ZnSO ₄ · 7
H ₂ O 250 g / l, HF 10 g / l, Na ₂ SO
Electrogalvanizing was carried out using a solution containing 500 g / l of ₄ each. At this time, the current density and the plating time were adjusted so that the plating film had various thicknesses. Then, the phosphate treatment was performed using a commercially available phosphate treatment liquid.

Each of the obtained phosphate-treated aluminum plates was subjected to cationic electrodeposition coating with a thickness of 25 μm, and further subjected to finish coating. The coating film surface of the coated plate was cut with a cutter in the L direction and the C direction, and the coating film corrosion resistance was evaluated by the coating film bulge width in accordance with ASTM D2083 method. Further, with respect to each plate after the phosphate treatment, the phosphate film was dissolved and removed with a 5% chromic acid solution, and the residual adhesion amount of zinc plating was examined. The relationship between the coating film blistering width and the residual amount of zinc plating is shown by the black circles and solid line in FIG.

Example 2 The same aluminum plate as in Example 1 was degreased and pickled in the same manner as in Example 1. Then as an electric galvanizing bath without the addition of fluoride, a ZnSO ₄ · 7H ₂ O 250g
/ L and Na ₂ SO ₄ at 50 g / l, respectively, were used for electrogalvanizing. At this time, the plating film was adjusted to have various thicknesses. For each of the obtained phosphate-treated aluminum plates, the corrosion resistance of the coating film after coating was evaluated in the same manner as in Example 1, and the residual amount of zinc plating was examined. The results are shown by the X mark and the broken line in FIG.

Comparative Example Using the same aluminum plate as in Example 1, direct phosphate treatment was performed without electrogalvanizing. With respect to the plate after the phosphate treatment, the corrosion resistance of the coating film after coating was examined in the same manner as in Example 1. The result is shown by a circle in FIG.

As is apparent from FIG. 1, Example 1 in which electrogalvanization was performed and then phosphate treatment was performed, as compared with the case of Comparative Example in which phosphate treatment was performed without electrogalvanization. In all of the cases of Example 2, the corrosion resistance after coating is improved, but particularly when the amount of residual deposit of zinc plating is less than 1.0 g / mm ^2, good corrosion resistance after coating is exhibited. And especially the zinc plating deposit residue is 0.1
Excellent corrosion resistance after coating is exhibited in the case of up to 0.5 g / mm ² . In the case of Example 1 using the plating bath containing fluoride, the corrosion resistance after coating is excellent as compared with the case of Example 2 using the plating bath containing no fluoride.
Therefore, it is clear that the best effect can be obtained by combining the regulation of the residual adhesion amount after the phosphate treatment and the use of the fluoride addition bath.

[0039]

In the phosphate-treated aluminum plate of the present invention, the residual adhesion amount after the phosphate treatment of the zinc-based plating formed as the base of the phosphate-treated film is 1.
By controlling the amount to be less than 0 g / m ² , excellent corrosion resistance after coating can be reliably and stably obtained. And especially the residual adhesion amount of zinc-based plating is 0.1-0.5 g / m
It became possible to obtain more excellent corrosion resistance after painting by regulating within the range of ² . Furthermore, by using a fluoride salt-added bath as a plating bath in electrogalvanizing plating and controlling the residual adhesion of zinc-based plating as described above, it is possible to obtain even better corrosion resistance after painting. Became.

Therefore, the phosphate-treated aluminum plate of the present invention is most suitable for applications such as automobile bodies to which coating is applied.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of residual zinc plating adhered after a phosphate treatment and the coating film bulge width after coating in each of Examples and Comparative Examples.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Saito 4-3-18 Nihombashi Muromachi, Chuo-ku, Tokyo Sky Aluminum Co., Ltd. (72) Toshiaki Kobayashi 4-3-18 Nihombashi Muromachi, Chuo-ku, Tokyo No. Sky Aluminum Co., Ltd. (72) Inventor Hiromasa Nomura 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Co., Ltd.Technology Development Division (72) Inventor Kimitaka Hayashi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Stock Company Technology Development Division

Claims (3)

[Claims] 1. An aluminum plate having a zinc-based plating on its surface and a phosphate treatment on the zinc-based plating, the residual adhesion of the zinc-based plating is 1.0 g /
A phosphate-treated aluminum plate having excellent corrosion resistance after painting, which is characterized by being less than m ² . 2. The phosphate-treated aluminum plate having excellent corrosion resistance after coating according to claim 1, wherein the zinc-based plating is performed in an electroplating bath containing a fluoride and a zinc salt. .. 3. The residual adhesion amount of the zinc-based plating is 0.1.
The phosphate-treated aluminum plate having excellent corrosion resistance after coating according to claim 1, which is in the range of 0.5 g / m ² .