JP2977651B2 - Surface treated aluminum and aluminum alloy plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Aluminum and aluminum alloy (hereinafter simply referred to as "aluminum") plates used for painting vehicles, buildings or home electric appliances, etc., which have been subjected to a surface treatment suitable for processing and painting. It relates to an aluminum plate.

[0002]

2. Description of the Related Art In recent years, an aluminum plate is often used as a structural material together with a steel plate. For example, an attempt has been made to use an aluminum plate for a part of an automobile body in order to reduce the weight. In such a case, the aluminum plate is often used in combination with the steel plate. These plates are joined by electric spot welding after molding, then subjected to a chemical conversion treatment as a pretreatment for painting, and finished by electrodeposition painting.

[0003] Therefore, the aluminum plate is required to have formability, weldability, chemical conversion treatment, electrodeposition coating property, corrosion resistance and the like.

[0004] Phosphate treatment is often recommended as a pre-coating treatment for steel plates from the beginning, and chromate treatment is recommended for aluminum plates. In the case of a combination of the two, a phosphate treatment is often performed by a steel plate process. In this case, it is natural that a problem is more likely to occur in the aluminum plate, and first, oxides and hydroxides generated on the surface of the aluminum plate, which are easily oxidized, hinder uniform formation of the phosphate treatment film. Next, there arises a problem that elution of aluminum into the processing solution hinders the formation of phosphate. If the chemical conversion property is poor, the adhesion of the coating film is poor, and the product may swell or peel off the coating film, or rust may be formed under the coating film.

Conventionally, in order to cope with such a problem, there has been proposed an aluminum plate plated with a metal capable of easily forming a phosphate film. For example, JP-A-63-166964
In the official gazette, there is an aluminum plate thinly plated with zinc,
Japanese Patent Application Laid-Open No. 61-157693 proposes an aluminum plate plated with zinc or iron.

[0006]

SUMMARY OF THE INVENTION With these proposals,
The chemical conversion property of aluminum sheets has been improved. However, no sufficient improvement has been seen in the difficulty in forming scratches and the moldability required in the process up to the phosphate treatment, the electrodeposition coating property required after the phosphate treatment, and the like.

To solve this problem, the present invention has been made. By forming a multi-layered plating layer on an aluminum plate, it is possible to improve the phosphatability as well as the weldability, moldability, electrodeposition coating property and the like. An object of the present invention is to provide an aluminum plate having excellent corrosion resistance after painting.

[0008]

Means for achieving the object is to provide a Zn plating layer having an adhesion amount of 0.1 g / m ² or more as a lowermost layer on the surface of an aluminum plate, and an intermediate layer on the Zn plating layer. A surface-treated aluminum plate having a Zn-Fe alloy plating layer having an Fe content of 30 wt% or less as a layer, and further having an Fe-Zn alloy plating layer having an Fe content of 50 wt% or more as an uppermost layer, It is practical and more appropriate that the adhesion amount of each plating layer is in the following range.

(1) The adhesion amount of the Zn—Fe alloy plating layer is 1 g / m ² or more and 50 g / m ² or less. (2) The adhesion amount of the Fe—Zn alloy plating layer is 0.5 g / m ² or more and 10 g / m ² or less.

It is preferable that the condition (1) or (2) is satisfied, and it is even more preferable that the conditions (1) and (2) are satisfied. In addition, Zn or F
e, a few other elements inevitably coexist, Pb,
Sn, Cd, Fe, Cu, Ni and the like are included.

[0011]

[Function] After long experience in painting and using steel plates, Z
Although plating and other pretreatments such as phosphate treatment have been developed and improved, the history of aluminum plates is still short.

[0012] Generally, aluminum has higher corrosion resistance than steel. This is because aluminum is a metal that is easily oxidized and forms a relatively stable oxide film on the surface in a normal use environment to protect the metal from corrosion. is there. Therefore,
In an environment where it is difficult to form a dense oxide film, aluminum having a low electrode potential is in an extremely unstable state. The instability varies depending on the type of alloy and the environment, but when used for painting such as automobiles, thread-like corrosion occurring under the coating film has been regarded as a problem. This thread-like corrosion occurs when an environment where local corrosion easily occurs appears. That is, the aluminum film is corroded in places where the adhesion of the coating film is insufficient or where there is a defect in the coating film, and the corrosion proceeds with a small width. Since the footprint of this corrosion looks like a thread, it is called thread-like corrosion.
This corrosion is unlikely to occur in a situation in which aluminum is protected by the action of the n-alloy.

The surface of the aluminum plate is made of Zn or Zn-F
Covering with the e-alloy plating layer can prevent the above-mentioned thread-like corrosion. That is, galvanizing according to JP-A-63-166964 and Z-plating according to JP-A-61-156793 are disclosed.
Plating mainly with n is effective in preventing thread-like corrosion.

[0014] However, these plating layers have a large friction with a press mold during molding, and may cause cracks in products, which is a major drawback.

Examination of the coefficient of friction of the surface of a Mg-containing aluminum plate, which is expected to be frequently used for automobiles, shows that the aluminum plate is larger than a cold-rolled steel plate. When a Zn-based plating layer is provided on the surface of the aluminum plate, the coefficient of friction is further increased. However, when the upper layer is thinly coated with Fe-based plating having a high Fe content, the friction coefficient becomes smaller than that of the original aluminum plate, and the problem of friction during molding is solved.

Another disadvantage of the Zn alloy plating layer is that a small depression called cratering occurs in the coating film when the electrodeposition coating is applied. Cratering is difficult to cover even with additional paint, leading to appearance defects. This defect is likely to occur in a plating layer containing a small amount of Fe in Zn, and the occurrence can be prevented by increasing the content of Fe.

These two drawbacks are described in JP-A-61-157.
No. 693 discloses an improved plating layer mainly composed of Fe, while an Fe-based plating layer alone has a poor anticorrosion effect and tends to cause powdering during molding. In powdering, when the plating layer is brittle, cracks occur where stress is concentrated, and the plating layer becomes powdery and peels off.
If this occurs, the press die and the product may be damaged.

A surface treatment which can simultaneously solve such disadvantages is a Zn-based and Fe-based multilayer plating layer. The idea of this multilayer plating layer is that the lowermost Zn plating layer having high ductility makes it difficult to cause powdering at the time of molding, and a Zn—Fe alloy having a small Fe content (hereinafter referred to as Z
The corrosion resistance is ensured by using a plating layer as an intermediate layer, which is referred to as an n-alloy), and the Fe—Zn alloy or the Fe (hereinafter, referred to as Fe-based) plating layer having a high Fe content is provided as a thin layer on the upper layer, whereby the friction coefficient is increased. The main objective is to reduce electrodeposition and enhance electrodeposition coating properties. Then, the synergistic action of these plating layers is intended to further enhance the effect and to cope with other remaining problems. Other problems include flaws caused by stacking and rubbing of plates during handling, and a problem of the life of an electric spot welding electrode in a welding process.

The function and effect of each plating layer will be described below. When the Zn plating layer is provided as the lowermost layer, it acts as a strong bonding layer with good adhesion to the aluminum plate and the Zn alloy plating layer, and works together with the Zn alloy plating layer to prevent corrosion of the aluminum plate. Furthermore, it is rich in ductility and relaxes the stress concentration of the relatively brittle Fe-based plating layer during molding,
Suppress the occurrence of powdering. The amount of this layer does not need to be so large, but the amount of 0.1 g / m ² is necessary in order to expect the effect of relaxing the stress concentration. 5 g / m ² is sufficient.

The Zn alloy plating layer as the intermediate layer mainly has an anticorrosion action such as prevention of thread-like corrosion. For this reason, an adhesion amount of 1 g / m ² or more is desirable, and the Fe content is limited to 30 wt% or less. This layer has excellent phosphatability together with the Fe-based plating layer, and is involved in the treatment when the uppermost Fe-based plating layer is thin. Further, with respect to the flaw resistance, a synergistic effect with the Fe-based plating layer produces a surface property that is not easily flawed.
That is, although the Fe-based plating layer is originally hard to be scratched, its performance is not sufficiently exhibited if the underlayer is as soft as the Zn plating layer because it is thin. The hardness of the Zn alloy plating layer is higher than that of the Zn plating layer, and by providing the Zn alloy plating layer as a base, sufficient scratch resistance is imparted to an upper layer having a high hardness but a thin plating layer.

The greater the amount of the Zn alloy plating layer adhered, the better the anticorrosion performance. However, if the amount of adhesion is 50 g / m ² , the corrosion resistance is more than sufficient.
Coating amounts exceeding g / m ² are not advisable.

The uppermost Fe-based plating layer has an Fe content of 5%.
The hardness is increased due to the high Fe content of 0 wt% or more,
Synergy with the middle layer prevents surface flaws during handling,
Also, the friction between the metal mold and the mold during molding is reduced. The effect of lowering the coefficient of friction is greater as the amount of Fe contained is larger, but in particular, Fe
This effect is remarkable when the content is 50 wt% or more. Furthermore,
Since the Zn concentration is low, the degree of electrode wear is reduced during electric spot welding, and craters are prevented during electrodeposition coating.

However, if the upper Fe-based plating layer is too thick, powdering may occur during molding. In order to avoid this problem, it is desirable that the adhesion amount be 10 g / m ² or less.

[0024]

EXAMPLE A surface-treated aluminum plate having a thickness of 1.0 mm, in which Zn plating was applied to a lower layer, Zn alloy plating was applied to an intermediate layer, and Fe-based plating was applied to an uppermost layer, and the scratch resistance was examined.
This was molded and examined for moldability, painted, and examined for electrodeposition paintability and corrosion resistance after painting. JIS- for aluminum plate
H-A5182P, A1050P and A6009P were used.

Regarding the scratch resistance, the tip is 50 μmR
A 5g load is applied to the sapphire needle to scratch the surface,
The results were observed. The evaluation was made based on the degree to which the flaw was conspicuous, and was evaluated as Δ when the flaw was not recognized, as Δ when the flaw was inconspicuous but discriminated, and × when the flaw was conspicuous.

The moldability was evaluated by friction coefficient measurement and cup drawing test, the degree of cratering was observed for the electrodeposition coating property, and the occurrence of thread-like corrosion was examined for the corrosion resistance.

The friction coefficient was determined by applying a lubricating oil, applying a surface pressure of 4 kg / mm ² using a tool steel indenter, and testing at a test speed of 1000 mm / m 2.
Measured in. The measurement results show that the coefficient of friction was less than 0.13,
0.13 or more and less than 0.16 were evaluated as Δ, and 0.16 or more as X.

In the cup drawing test, a test piece was cut into 60 mmφ, drawn into a cup having a punch diameter of 30 mm-5R, a die diameter of 33 mm-5R and a height of 25 mm, and the number of broken cups was checked.
Further, a scotch tape was stuck to the processed portion, the plating layer was forcibly peeled off, and the degree of powdering was examined. The test results were as follows: cracks were not generated in all of the 30 test pieces; cracks were generated in 1 to 4 pieces;
The case where five or more cracks occurred was evaluated as x. Regarding the powdering, the degree of contamination of the tape was observed, and the evaluation was made as 〇 when hardly any blackening was observed, △ when slight blackening was observed, and x when blackening was obvious.

As for the electrodeposition coating property, after the phosphate treatment, a cationic electrodeposition coating was applied at 20 μm by instantaneous application of 240 V, and after baking and curing, the occurrence of lettering was observed. A sample in which no defect was observed was evaluated as “〇”, a sample in which 1 to 9 / dm ^{2 was} observed, and a sample in which 10 or more / dm ² or more were evaluated.

The corrosion resistance was determined by subjecting to a phosphate treatment and cationic electrodeposition coating, then coating the melamine alkyd-based paint with a middle coat and a top coat to form a test piece having a thickness of 100 μm. Cycling was performed and thread corrosion was observed. The cycle test is JIS-Z-2
One cycle consists of conducting a wet test (humidity 90%, temperature 50 ° C.) for 240 hours after 24 hours of the salt spray test by 371. After the cycle test, observe the thread rust condition under the coating film,
良好 for good, △ for slightly bad, × for bad
Was evaluated.

These investigations were carried out for a comparative example which does not fall within the scope of the invention and a conventional example according to the prior art, as well as the embodiment of the present invention, and compared these. Table 1 shows the results of the survey.

[0032]

[Table 1]

In the examples, satisfactory results were obtained in all of moldability, electrodeposition coating property, and corrosion resistance. On the other hand, in the comparative example and the conventional example, any of the characteristics remains unsatisfactory. That is, when the lower plating layer is not provided, powdering is likely to occur when the Fe content of the other plating layers is high and the amount of adhesion is large.
If there is no intermediate plating layer, the corrosion resistance and the scratch resistance are insufficient. If the content of Fe in the intermediate plating layer is too large, powdering is likely to occur and corrosion resistance becomes insufficient. When there is no upper plating layer, the coefficient of friction is large, cup cracking cannot be prevented, and cratering occurs. A similar tendency occurs when the Fe content of the uppermost layer is insufficient.

In the conventional example having a single plating layer, in the case of Zn-based plating, the coefficient of friction is large, it is not possible to prevent the occurrence of cracks in cup drawing, and the scratch resistance is insufficient. Absent. In addition, in the case of Fe-based plating, powdering occurs due to the absence of a stress dispersion layer, and the formation of thread rust cannot be prevented since the Zn-based anticorrosive action cannot be obtained.

[0035]

As described above, according to the present invention, a Zn plating layer is formed on the surface of an aluminum plate, a relatively thick Zn alloy plating layer is formed thereon as an intermediate layer, and a thin Fe layer is formed on the uppermost layer. It has a system plating layer. The uppermost layer reduces friction during molding, improves electrodeposition coatability, and prevents surface flaws by interaction with the intermediate layer. The intermediate layer protects the aluminum plate from corrosion under the coating, and the lowermost layer reduces localized stress concentration in the upper layer during molding and prevents powdering, so plating aluminum plate with excellent moldability and corrosion resistance etc. Is obtained. As described above, the effect of the present invention in which the painting use value of the aluminum plate is enhanced is great.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuhiro Koike 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Ida Iwao 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (72) Inventor Kiyoshi Kurima 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Masakazu Nikura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C 28/00

Claims (3)

(57) [Claims] Claims: 1. An aluminum or aluminum alloy plate has a Zn plating layer having an adhesion amount of 0.1 g / m ² or more on the surface thereof.
A Zn-Fe alloy plating layer having an Fe content of 30 wt% or less is further provided thereon, and a F-content having an Fe content of 50 wt% or more is further provided thereon.
A surface-treated aluminum and aluminum alloy plate having an e-Zn alloy plating layer or an Fe plating layer. 2. The coating amount of a Zn—Fe alloy plating layer is 1 g /
m ² or more 50 g / m ² or less surface treated aluminum and aluminum alloy plate according to claim 1. 3. The coating amount of the Fe—Zn alloy plating layer is 0.
3. The surface-treated aluminum alloy sheet according to claim 1, which has a content of 5 g / m ^{2 to} 10 g / m ² .