JPH0617285A - Zinc alloy plated aluminum plate - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a surface-treated plate of aluminum or aluminum alloy having a plating film with good adhesion and excellent adhesive bondability. [Structure] A zinc-based alloy thin film layer formed on the surface of a base material by electroplating and a zinc-based alloy electroplated layer formed thereon, and the above-mentioned thin film layer has an average crack width.
An aluminum plate excellent in impact peeling resistance and adhesive bondability, characterized in that minute cracks of 0.001 to 5.0 μm are present at a density of 5 to 80% in terms of crack area fraction. [Effect] Excellent adhesion of the plating film and sufficient resistance to low-temperature impact load. Further, since it is also remarkably excellent in adhesive durability, it is also suitable for use in joining by an adhesive method instead of welding. This Al plate is highly practical especially for various members for automobiles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate of surface-treated aluminum or its alloy used for automobile bodies and the like, which has excellent press formability and coating adhesion and is used after being treated with zinc phosphate. The present invention relates to a plate of aluminum or aluminum alloy, which is suitable for use in the present invention, and which is remarkably excellent in the adhesiveness of the plating film against impact load and the adhesive bondability when bonded with an adhesive.

[0002]

2. Description of the Related Art In recent years, automotive materials have been increasingly required to have anti-corrosion measures by spraying anti-freezing agents in cold regions and weight-saving measures for improving fuel efficiency, such as zinc and zinc-based alloy plating. The use of surface-treated steel sheets and high-tensile steel sheets is being promoted. In automobile body manufacturing lines that use such steel sheets, it is common to press-mold into a predetermined shape, assemble each component, and then perform zinc phosphate treatment, electrodeposition coating, and spray coating. is there.

On the other hand, in recent years, aluminum or aluminum alloy plates (hereinafter,
These are collectively referred to as "Al plate") and are often used for vehicle bodies. Al plates are usually used together with steel materials. In this case, it is desirable to manufacture a part by also using a steel material processing line without newly establishing another manufacturing line for Al plate processing. This is because the cost of installing new equipment can be saved and the continuity of the process can be maintained.

However, for example, when the plated steel sheet and the Al sheet are treated on the same line, the following problems occur in the zinc phosphate treatment step. That is, when the zinc phosphate treatment is applied to the Al plate, not only a good zinc phosphate film is not formed on the Al plate surface, but also the Al plate surface is dissolved and Al ions are eluted in the zinc phosphate treatment bath. Will end up. As a result, the Al ion concentration in the zinc phosphate treatment bath was only a few ppm.
However, even if the above condition is satisfied, a good zinc phosphate treatment film is not formed on the steel plate surface.

As a method of solving the above problems, the present applicant previously developed an "Al plate having excellent zinc phosphate treatment property" and filed a patent application (Japanese Patent Laid-Open No. 61-157693). That is,
By forming a zinc plating layer, a zinc-based alloy plating layer, or an iron-based alloy plating layer on the surface of the Al plate with an adhesion amount of 1 g / m ² or more, the Al plate during the subsequent zinc phosphate treatment It is possible to prevent the elution of Al ions from the steel sheet and thereby to form a good zinc phosphate film on both the steel plate and the Al plate even if they are alternately processed in the same line.

By the way, in recent years, as a joining method of materials, attention has been paid to joining (adhesion method) using an adhesive instead of conventional welding. This is because according to the bonding method, it is possible to avoid poor corrosion resistance of the welded portion and poor appearance of the welded portion (existence of welding marks), and it is also possible to join materials or parts where welding is impossible or difficult. With the recent advances in adhesives and bonding techniques, the use of the bonding method in place of welding has been studied.

In adopting the adhesion method, the adhesion strength at the interface of the adhesion part at the initial stage of adhesion (hereinafter referred to as initial adhesion)
High, and the decrease in adhesion strength at the interface of the adhesive part in a corrosive environment is small (hereinafter referred to as adhesive durability)
Is important, and there is a demand for a surface-treated material that is excellent in these properties even for Al plates. However, a surface treatment material having a sacrificial anticorrosive film, which is represented by zinc plating, generally has a
Since the initial adhesiveness is poor and the absolute value of the adhesive strength decreases with the progress of corrosion during use, it is hard to say that the adhesive durability in actual use is sufficient.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the surface-treated Al plate disclosed in Japanese Patent Publication No. 3, a good zinc phosphate film is formed, which does not adversely affect the zinc phosphate treatment of the steel sheet processed in the same line. However, the surface of the Al plate is usually covered with an oxide film, and when electroplating is only performed in a normal sulfuric acid acidic bath, only a film having poor adhesion is produced. Therefore, the film may be peeled off during press molding, and the intended effect may not be exhibited in the subsequent zinc phosphate treatment step. Furthermore, for example, 0 °
There is a problem in peeling resistance when a shocking load is applied at a low temperature of -50 ° C. Further, the adhesive bondability of the surface-treated Al plate plated with zinc is still insufficient in practical use.

The present invention provides a surface-treated Al plate having excellent corrosion resistance after coating and press formability, and excellent adhesion of a plated layer, on the premise that the zinc phosphate treatment property is excellent. The purpose is to provide.

Another object of the present invention is, when an adhesive joining method is adopted in place of the spot welding method, an adhesive durability that withstands initial adhesive strength and deterioration of adhesiveness over time (these are collectively referred to as “adhesive joining”). The property is referred to as “property”).

[0011]

Means for Solving the Problems In carrying out zinc-based alloy electroplating on an Al plate, the present inventor first forms a zinc-based alloy electroplating thin film layer having innumerable microcracks on the surface of a base material, and It has been found that the above two purposes can be achieved at the same time by applying zinc-based alloy electroplating on the treated layer. In particular, when the average width of the microcracks in the undercoating layer is 0.001 to 5.0 μm and the crack density is 5 to 80% in area fraction, the adhesion and adhesive bondability of the plating layer are significantly improved.

The present invention based on the above-mentioned findings is based on the following Al
Boards are the gist.

"A zinc-based alloy thin film layer formed on the surface of a base material by electroplating and a zinc-based alloy electroplated layer formed thereon, and the thin film layer has an average crack width of 0.001 Aluminum plate excellent in impact peeling resistance and adhesive bondability, characterized in that micro cracks of ~ 5.0 μm are present at a density of 5 to 80% in terms of crack area fraction "The Al plate of the present invention is 1000 Pure aluminum plate, M
It is a plate made of aluminum alloy such as 5000 series and 6000 series whose main alloy components are g, Cu and Mn.

It is essential that the Al plate of the present invention has a base thin film layer having the above-described minute cracks on the surface of the base material.

FIG. 1A is a sketch drawing of a micrograph of the surface of the underlying thin film layer, and FIG. 1B is a partially enlarged view thereof. (b) Distance between cracks shown in the figure
(For example, the distance between A and B) is called the crack width. As shown in the figure, innumerable minute cracks are formed in the electroplating base thin film layer on the surface of the base Al plate. The crack may or may not penetrate the underlying thin film layer to the surface of the base material. What is important is that the average width of cracks is
It is in the range of 0.001 to 5.0 μm, and its existing density is in the range of 5 to 80% in terms of area fraction.

The existence density of cracks is expressed by the area fraction,
This is done by observing the surface of the underlayer thin film with an electron microscope with a magnification of 5000 times, dividing the photographed picture into 100 equal parts 10 × 10 and checking for the presence of cracks in each square, Is calculated and expressed as a percentage.

The base thin film layer can be applied, for example, as follows. That is, first, an Al plate may be plated with a zinc alloy (Zn-Ni, Zn-Fe, Zn-Co, Zn-Cr, Zn-Mn, or other zinc alloy plating. In any case, the zinc content is 60 to 99. %
Which is desirable) is electroplated and then immersed in an acid solution such as the same electroplating bath without electric current, or subjected to anodic electrolysis in an electrolyte solution. Alternatively, it is possible to form a desired alloy electroplating thin film layer having fine cracks by pulse electrolysis such as DC pulse for interrupting energization for a certain period of time and AC pulse for reversing the polarity at every certain period of time.

What is plated on the underlying thin film layer is Zn--Ni, Zn--Fe, Zn--Co, Zn--C having a Zn content of about 60 to 99.5%.
Zinc alloy plating such as r and Zn-Mn, which is formed by electroplating. This plating layer guarantees basic properties such as corrosion resistance, phosphating property, powdering resistance, and paintability of the Al plate.

The surface treatment layer consisting of the base thin film layer and the zinc-based alloy plating layer thereon may be present on only one side of the Al plate.

[0020]

As described above, the Al plate of the present invention is characterized by having a thin film layer having a large number of microcracks as an underlayer of the plating layer. The minute cracks in the underlying thin film layer have a great effect on improving the adhesion of plating. In particular, the impact delamination resistance when a shocking load is applied, such as when a vehicle hits a pebbles, is significantly improved by the presence of the above-mentioned base thin film layer.

Although the mechanism by which such an effect appears is still unclear, since the underlying thin film layer having fine cracks serves as an absorbing layer for impact force against external impacts, impact peeling resistance especially at low temperature is obtained. It is estimated to improve. In addition, since the base material is an Al plate, during the process of generating minute cracks in the base plating layer, part of the cracks penetrates into the base material and is plated on the base plating layer. It is considered that the anchor effect of the layer occurs and the adhesion is improved.

The average width of the above microcracks is 0.01 μm
When it is less than 5.0 μm or when it is more than 5.0 μm, the above-mentioned effect is not significant. In addition, the existence density of microcracks in the underlying thin film layer also has a great influence on the improvement of low temperature impact resistance and adhesive bondability, particularly the improvement of adhesive durability. That is, if the microcrack density is less than 5%, an effective impact force absorption effect cannot be exhibited, so that low temperature impact resistance cannot be secured, and conversely, if it exceeds 80%, adhesive durability cannot be secured.

The amount of the underlying thin film layer deposited is preferably in the range of 0.1 to 10 g / m ² . If it is less than 0.1 g / m ^2, the density of the generated microcracks and the thickness of the underlayer are too small to obtain sufficient effects of improving low temperature impact peel resistance and adhesion durability. On the other hand, when the adhesion amount exceeds 10 g / m ² , the electroplating film becomes dense and it may not be possible to generate microcracks having a desired density.

[0024]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples.

The base material used was a Mg-added Al alloy (JIS 5000
It is a plate with a thickness of 1 mm. The treatment was applied to both sides.

A base thin film layer was electroplated on the above base material under the following conditions 1), and microcracks were formed after the base plating or during the base plating by any one of the methods 2) to 2) below.

1) Undercoating conditions Plating bath: Sulfuric acid acidic bath (pH 1 to 3) The bath composition was adjusted so as to have the alloy content shown in Table 1. Temperature: 40-60 ° C Current density: 10-100 A / dm ² Adhesion amount: Adjusted as shown in Table 1 by controlling the energization time.

2) Conditions for forming microcracks Non-energized immersion: After applying a predetermined amount of base plating,
Immersion in the same plating bath without electricity.

Anodic dissolution: After applying a predetermined amount of base plating, 5 A / d using the test piece as an anode in the same plating bath
Electrolysis with current density of m ² .

AC pulse melting: A crack is formed at the same time as plating by superposing an alternating current (60 Hz) of ± 10% on a predetermined current density.

DC pulse melting: Crack formation at the same time as plating with a direct current pulse current of 0.5 seconds of energization time and 0.5 seconds of non-energization time.

On the underlying plating thin film layer formed as described above, various upper layer zinc-based alloy platings shown in Table 1 were applied under the same conditions as the underlying plating conditions of 1) above. Using the surface-treated plate thus obtained, the following tests were conducted.

(A) Low Temperature Impact Peeling Resistance Test The test method and evaluation method are as follows. That is, zinc phosphate treatment (using Chemfil's CF168 treatment liquid) cationic electrodeposition coating (using PPG's Uniprime paint.
30 μm) Intermediate coating (using the company's epoxy ester-based paint. Film thickness 15 μm) Top coating (using the company's acrylic / enamel-based paint.
A film thickness of 45 μm) was subjected to the chemical conversion treatment and coating by the above procedure. Diamond particles (about 3 mm in diameter) were made to collide with this at 10 locations at 170 km / h, and then the following corrosion resistance exposure test was performed. That is, the test was conducted once every month for 30 minutes by immersing it in a 3% NaCl aqueous solution, and then exposing it to an industrial zone environment (Amagasaki City, Hyogo Prefecture) for 5 years.

The evaluation of the low temperature impact peeling resistance was carried out when the maximum diameter of the coating film blister (blister) at the collision point of the diamond grains was 5 mm.
Table 1 shows the above items as ×, 3 mm or more and less than 5 mm as △, 1 mm or more and less than 3 mm as ○, and 1 mm or less as ◎.
Described in.

(B) Adhesive bondability Samples having a width of 25 mm and a length of 100 mm were taken from the Al plates plated under the above-mentioned conditions, and two plates were set as a set and the plated surfaces were superposed with the adhesive 3 interposed therebetween as shown in FIG. , 175 ℃ × 30min heating
Bonding was performed by drying to produce a simple lap joint (according to JIS-K6850). Further, the phosphate chemical conversion treatment and the cation electrodeposition coating were applied under the above conditions. This sample was subjected to a complex corrosion test under the conditions shown in FIG. 3, the sample was taken out every 10 cycles, and the adhesion durability was evaluated by a shear tensile test.

As the adhesive, a one-pack type epoxy Araldite XB 3062 (manufactured by Japan Ciba-Gaiki) was used.
Bonding was performed so that the thickness of the adhesive layer was 100 μm. The bonded portion had a width of 25 mm.

The types and conditions of the phosphate treatment and the cationic electrodeposition coating used here are the same as those described above except that the thickness of the cationic electrodeposition coating was 10 μm.
The tensile test was conducted at a temperature of 25 ° C. and a tensile speed of 50 m / min. The evaluation of the adhesiveness was performed by the area percentage of the part of the peeled surface where the adhesive cohesively failed. The larger this value, the better the adhesion. The evaluation criteria shown in Table 1 are as follows.

◎: Area of cohesive failure portion 100% ○: Less than 100, up to 90% △: Less than 90%, up to 70% ×: Less than 70%, up to 50% ×: Less than 50%

[0039]

[Table 1]

In Comparative Examples 1 to 4 in Table 1, the values marked with * do not satisfy the conditions defined in the present invention. That is, in Comparative Example 1, the average crack width of the underlayer is too small, and in Comparative Example 2, it is too large. Comparative Example 3 is an example in which the density of cracks is too small, and Comparative Example 4 is an example in which it is too large. All of them are inferior in low temperature impact peeling resistance and adhesion durability. In particular, in Comparative Example 2 in which the average crack width of the underlayer is too large and Comparative Example 3 in which the crack density is small, the adhesion durability is extremely poor. On the other hand, the present invention example in which the crack average width and the crack density of the underlayer are appropriate does not depend on the alloy composition of the underlayer plating layer, and is not affected by the composition of the overlayer plating layer, and is resistant to low temperatures. It has excellent properties in both impact peelability and adhesion durability.

[0041]

EFFECTS OF THE INVENTION The surface-treated Al plate of the present invention is excellent in the adhesion of the plating film and has the property of sufficiently withstanding the load of low temperature impact. Further, it is also excellent in adhesive durability, and therefore, it is suitable for use in joining by an adhesive method instead of welding. This Al plate is highly practical especially for various members for automobiles.

[Brief description of drawings]

FIG. 1 (a) is a sketch drawing of a micrograph of a base thin film layer of a surface-treated Al plate of the present invention, and FIG. 1 (b) is a partially enlarged view thereof.

FIG. 2 is a perspective view showing the shape of a simple lap joint used in an adhesion durability evaluation test.

FIG. 3 is an explanatory diagram showing steps and conditions of a complex corrosion test adopted in an adhesion durability evaluation test.

[Explanation of symbols]

 1: microcrack, 2: test material, 3: adhesive layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Ikeda 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industries, Ltd. (72) Inventor Takao Aibu 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industry Co., Ltd.

Claims (1)

[Claims] 1. A zinc-based alloy thin film layer formed on the surface of a base material by electroplating, and a zinc-based alloy electroplated layer formed thereon, wherein the thin film layer has an average crack width. An aluminum plate excellent in impact peeling resistance and adhesive bondability, characterized in that minute cracks of 0.001 to 5.0 μm are present at a density of 5 to 80% in terms of crack area fraction.