JP2767065B2 - Manufacturing method of galvanized aluminum plate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a surface-treated aluminum plate used for a body of an automobile or the like, and more particularly to a method for producing a zinc-plated aluminum plate used for a zinc phosphate treatment. It relates to a manufacturing method.

2. Description of the Related Art Conventionally, a steel plate is usually used for a body of an automobile. As this type of steel sheets for automobile bodies, surface-treated steel sheets such as galvanized steel sheets and alloyed galvanized steel sheets are used in addition to ordinary steel sheets and high-tensile steel sheets. Among these, surface-treated steel sheets such as galvanized steel sheets and alloyed galvanized steel sheets have excellent corrosion resistance, and are therefore recommended especially for parts or vehicles that require corrosion resistance.

By the way, in an automobile body assembly manufacturing line using such a steel sheet, after forming the body steel sheet into a predetermined shape by pressing or the like to form each body part, assembling and spot welding each body part, Thereafter, the assembled body is subjected to a degreasing treatment, and then, for the purpose of improving the adhesion between the steel sheet and the coating film and improving the corrosion resistance, is subjected to a zinc phosphate treatment, which is a kind of chemical conversion treatment, and then is subjected to electrodeposition coating and Generally, normal spray coating is performed.

On the other hand, recently, an aluminum plate is often used for a body of a vehicle mainly for the purpose of weight reduction of a vehicle body for improving fuel efficiency of the vehicle. In this case, the entire body of the automobile is rarely aluminized, and generally, a steel plate and an aluminum plate are used in combination. 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 the above-described steel plate alone.
That is, after assembling and welding a body part made of a formed steel plate and a body part made of a formed aluminum plate, and then creating a body, the entire body is degreased and then subjected to a zinc phosphate treatment. It is desired to perform electrodeposition coating or spray coating. In this case, even when a steel plate and an aluminum plate are used in combination, it is not necessary to newly establish another assembly production line, and the continuity of the process is maintained, which is advantageous in terms of production cost. However, in this case, the aluminum plate is subjected to the zinc phosphate treatment simultaneously with the steel plate, so that the following problem occurs.

That is, when zinc phosphate treatment is applied to an aluminum plate, not only is the zinc phosphate film not sufficiently formed on the surface of the aluminum plate, but also the surface of the Al plate is dissolved, and Al ions are eluted into the zinc phosphate treatment bath. Resulting in. for that reason,
As described above, when zinc phosphate treatment is applied simultaneously to a steel plate and an aluminum plate integrated as an automotive body, the formation of a zinc phosphate film on the surface of the steel plate is also inhibited by Al ions eluted from the aluminum plate, As a result, there arises a problem that sufficient corrosion resistance and sufficient adhesion of the coating film cannot be obtained.

As a method for solving such a problem, Japanese Patent Application Laid-Open
No. 61-155763 proposes a method for producing an aluminum plate having excellent zinc phosphate treatment properties. The proposed method is to apply a Zn plating layer, a Zn alloy plating layer or an Fe alloy plating layer on the aluminum surface in advance at 1 g / m ^2.
It is formed with the above adhesion amount.
By forming a plating layer and the like, Al ions do not elute from the aluminum plate into the bath during the subsequent zinc phosphate treatment, so that the body using both the aluminum plate and the steel plate is subjected to the zinc phosphate treatment. It is said that even in this case, a zinc phosphate film can be sufficiently formed on a steel sheet, and a zinc phosphate film can be formed on the surface of the aluminum plate itself.

Problems to be Solved by the Invention However, when the method proposed in JP-A-61-157693 is actually applied, there are the following problems. That is, electroplating the surface of aluminum or an aluminum alloy is much more difficult than electroplating other metals. If only an aluminum plate is electroplated in zinc, only a plating film with extremely poor adhesion is generated. The degree of adhesion is so low that the film easily peels off even with a cellophane tape. Therefore, especially in the case of a pre-coated plate that has been plated before forming, the plating film is broken at the time of forming processing and the like, and the plating film is broken at the time of zinc phosphate treatment in the automobile body assembly manufacturing line as described above. Al ions are eluted from the bent portion. In other words, even if a plating layer such as a Zn plating layer is formed for improving the zinc phosphate treatment property, the zinc phosphate treatment property is actually improved due to the low adhesion of the plating layer. Was difficult.

By the way, generally, in the electroplating of aluminum, as a method of increasing the adhesion of a plating layer, an intermediate layer is formed as a pretreatment. For example, a zincate treatment is typical as a pretreatment for forming an intermediate layer when a zinc plating layer is formed. However, performing electrogalvanization again after forming the intermediate layer by such a zincate treatment or the like has a problem that productivity is remarkably lowered. In particular, it is industrially inappropriate to apply the present invention to a case where a coiled aluminum plate is processed as a precoated plate. Therefore, it is difficult to apply the method of forming an intermediate layer by zincate treatment or the like and then performing electrogalvanizing in the case of mass processing such as an aluminum plate for an automobile body.

The present invention has been made in view of the above circumstances,
When forming a galvanized layer on an aluminum plate to improve zinc phosphate treatment properties, a zinc plated layer with good adhesion and uniformity of the film can be obtained without the need for the formation of an intermediate layer by zincate treatment, etc. It is an object of the present invention to provide a method that can be generated at low cost.

Means for Solving the Problems The present inventors have conducted intensive experiments and studies, and as a result, a chlorine compound such as hydrochloric acid and an inorganic acid salt of zinc such that Zn ²⁺ ion concentration and pH are within a predetermined range. By electrogalvanizing an aluminum plate in a bath containing
The inventors have found that the above-mentioned object can be achieved, and have accomplished the present invention.

Specifically, the present invention relates to a method for producing a galvanized aluminum plate for use in which the surface is subjected to a zinc phosphate treatment. A plating bath containing a salt so that the concentration of Zn ²⁺ ions in the bath is in the range of 0.1 to 75 g / and the pH is 3.5 or less is subjected to electrogalvanizing.

In the method of the present invention, after the aluminum plate is subjected to a degreasing treatment, electroplating is performed in a plating bath containing a chlorine compound and an inorganic acid salt of zinc. At this time, the plating bath is Zn
Adjust so that the ²⁺ ion concentration is 0.1 to 75 g / and the pH is 3.5 or less.

Such an aluminum plate is immersed in a plating bath, if energized the aluminum plate as a cathode, Cl in the plating bath from the chlorine compounds ^- by the H ⁺ ions present by this adjusted into ions and the pH While the surface layer of the aluminum plate is dissolved, Zn ²⁺ ions are electrolytically deposited as zinc metal on the surface of the aluminum plate serving as a cathode, and a zinc plating film is generated. At this time, Cl ^- ions and H ⁺
Since the surface layer of the aluminum plate is dissolved by the ions and the active surface is exposed, the electrolytic deposition of zinc is performed on the active surface, so that the galvanized film is formed with high adhesion to the aluminum plate. That is, a galvanized film having good adhesion and good film uniformity can be formed only by electroplating, even if an intermediate layer is not formed in advance by a zincate treatment or the like.

The aluminum plate on which the galvanized layer is formed in this manner is subjected to zinc phosphate treatment as a pre-coating treatment.Although the aluminum plate has a zinc layer on the surface, aluminum can be dissolved in the zinc phosphate treatment bath. Therefore, for example, when zinc phosphate treatment is applied to an automobile body assembled using steel sheets, the formation of a zinc phosphate treatment film on the steel sheet surface is not hindered by Al ions. The zinc phosphate treated film is also sufficiently formed on the plating layer surface).

Here, the pH of the plating bath in the method of the present invention is 3.5
If it exceeds, a sufficient dissolving effect on the aluminum plate cannot be obtained. In addition, the Zn ²⁺ ion concentration in the plating bath was 0.1 g /
If it is less than 1, the generation rate of the galvanized layer becomes slow and the treatment takes a long time, while the Zn ²⁺ ion concentration is 75 g /
If the concentration exceeds the limit, the salt becomes higher than the saturation solubility, and the salt is not dissolved and accumulates on the bottom, which has an adverse effect. Therefore, the Zn ²⁺ ion concentration of the plating bath is set in the range of 0.1 to 75 g /
3.5 or less.

Specific description for carrying out the invention The component composition of the aluminum plate targeted in the present invention is
There is no particular limitation as long as the use is subject to zinc phosphate treatment, and various types of aluminum alloy plates other than pure aluminum plates are applicable. Particularly, in the present invention, Al-Mg-based alloys (JIS 5000-series alloys) and Al-Mg-Si
It can be suitably applied to a series alloy (JIS No. 6000 series alloy).

The step of applying electrogalvanizing to the aluminum plate according to the method of the present invention may be after forming into a required shape by press working or the like, but the step before forming as a precoated plate,
In particular, a great effect can be obtained when applied in a coiled stage. That is, according to the method of the present invention, a galvanized layer having extremely excellent adhesion can be obtained, so that the galvanized layer does not peel off even if a molding process is performed after the plating, and therefore, the zinc phosphate treatment after that is performed. However, it is because Al ions are reliably prevented from being eluted into the zinc phosphate treatment bath, and the treatment can be performed with high efficiency, so that continuous treatment can be performed on the coiled aluminum plate.

In the first degreasing treatment performed on the aluminum plate, it is desirable to use a degreasing agent that not only removes oils and fats on the surface of the aluminum plate but also removes oxides by etching the surface. A soda-based degreasing agent or caustic soda can be used.

After degreasing, it is preferable to perform a desmutting treatment for removing surface smut after performing a rinsing once with water, and then perform a rinsing again with water and then electrogalvanizing.

Zinc chloride (ZnCl ₂ ) is preferable as the inorganic acid salt of zinc used in the plating bath in the electrogalvanizing, but ZnSO ₄ , (NH ₄ ) ₂ ZnCl _{4 and the} like can also be used. Of course, two or more inorganic salts of zinc may be mixed. As a chlorine compound used in the plating bath, hydrochloric acid (HCl) is preferable, but in addition, AlCl ₂ , HClO,
HClO ₂ , HClO _{3 and the} like can also be used. In addition, the plating bath contains additives that are added to the normal electrogalvanizing bath,
For example, aluminum chloride (NH ₄ Cl), H ₃ BO ₃ , Na ₂ SO ₄ , and other various brighteners may be contained. When using HCl as the chlorine compound here, the HCl concentration in the plating bath is 0.
It is desirable to be about 01 to 1N.

The current density at the time of electroplating is not particularly limited as long as it is about the same as that of general electrogalvanizing,
Usually, it may be about 5 to 50 A / dm ² . The thickness of the galvanized film to be formed is optional, but is usually 0.1 to 10
It may be about μm.

After the electrogalvanizing is performed in this manner, it is usually washed and dried according to a conventional method to obtain a galvanized aluminum plate product.

Example The composition of the component is 0.85 wt% of Mg, 0.98% of Si, 0.27 wt% of Cu,
An aluminum alloy (AA6010-equivalent alloy) plate of 38 wt%, the balance of which is substantially Al, is degreased with a sodium phosphate-based degreaser, washed with water, desmutted, and then re-coated. Washed with water. Then a mixed aqueous solution of zinc chloride and hydrochloric acid, or as an additive to it
Electrogalvanizing was performed using an aqueous solution to which NH ₄ Cl was added as a plating bath. Here, the composition of each plating bath is shown in Examples 1 to 6 of the present invention in Table 1 in terms of Zn ²⁻ ion concentration, Cl ⁻ ion concentration, HCl concentration and pH. In addition, the current density, time, and thickness of plating film formation in electrogalvanizing are the first.
Also shown in the table. After electrogalvanizing, washing and drying were performed.

On the other hand, by the method shown in the following Comparative Examples 1 to 3 as a comparative example,
An aluminum plate having the same composition as described above was treated.

Comparative Example 1: An aluminum plate was subjected to a degreasing treatment in the same manner as described above, washed with water, and an electrogalvanizing bath was prepared by adding NH ₄ Cl to an aqueous solution of zinc chloride to which no hydrochloric acid was added as shown in Table 1. The resultant was subjected to electrogalvanizing, followed by washing with water and drying.

Comparative Example 2: An aluminum plate was subjected to a degreasing treatment in the same manner as described above, washed with water, further subjected to a desmut treatment, and then washed with water and subjected to a zincate treatment. As the zincate treatment, after the Zn substitution treatment, acid pickling with nitric acid is performed, and then Zn
A double zincate treatment method with substitution was applied. Then, after washing with water, electrogalvanizing was performed using an electrogalvanizing bath to which no hydrochloric acid was added in the same manner as in Comparative Example 1, and further washed with water and dried.

Comparative Example 3: In Comparative Example 3, an aluminum plate was not subjected to any surface treatment such as plating.

With respect to the plates according to Examples 1 to 6 of the present invention and Comparative Examples 1 to 3, various coating properties (however, the surface properties of the aluminum plate in Comparative Example 3) were examined. The results are shown in Table 2.

In each of the film performances shown in Table 2, "adhesion" was evaluated by performing a test in which the film was cut in a grid pattern and peeled off with a cellophane tape, and the ratio at which no peeling occurred was evaluated. In addition, the `` adhesion after molding '' is observed by observing the appearance after press processing, and when there is no peeling of the film at all, ○ mark, when slight peeling occurs, △ mark, When remarkable peeling occurred, the cross mark was given. Further, "weldability" evaluated the weldability in resistance spot welding. The "chemical conversion property" was evaluated by evaluating the state of formation of a zinc phosphate treatment film on the surface of the steel sheet and the deterioration state of the zinc phosphate treatment bath by subjecting the steel sheet to zinc phosphate treatment. "Thread rust resistance" was evaluated based on the thread rust length in accordance with the method of ASTM D2083. "Efficiency" was evaluated by the time required for the treatment. Further, the “coating uniformity” was evaluated for the uniformity of the coating thickness by observing the appearance.

As is clear from Table 2, in the case of Examples 1 to 6 of the present invention, the adhesion of the coating is excellent, and therefore, the chemical conversion treatment (zinc phosphate treatment) is also excellent, and the other coating properties are also low. It is good and has a high processing efficiency. On the other hand, in the case of Comparative Example 1 in which electrogalvanizing was performed using an electrogalvanizing bath to which hydrochloric acid was not added, the adhesion of the film was poor, and thus the zinc phosphate treatment property was also poor. In the case of Comparative Example 2 in which an intermediate layer was formed by performing a double zincate treatment and then electrogalvanized in the same manner as in Comparative Example 1, the adhesion of the film was good, but there was a problem in terms of processing efficiency. is there.

As is clear from the above embodiments, according to the method of the present invention, it is not necessary to form an intermediate layer by zincate treatment, etc. It is possible to form a galvanized film having excellent properties. Therefore, the aluminum plate on which the galvanized film is formed by the method of the present invention does not peel or break the plated film even if it is subjected to a forming process or the like, and therefore, the aluminum plate is not subjected to zinc phosphate treatment during the subsequent zinc phosphate treatment. Dissolves Al and reliably prevents Al ions from being eluted into the treatment bath, so it has excellent zinc phosphate treatment properties.Especially, even when aluminum plate and steel plate are simultaneously treated with zinc phosphate, A zinc phosphate treated film can be reliably formed. In addition, the method of the present invention does not require the formation of an intermediate layer by a zincate treatment or the like as described above, so that the productivity is high and the equipment cost is low, and thus the method is suitable for continuous processing on a mass-production scale. It is suitable for continuously processing an aluminum plate.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshitaka Hiroma 4-3-1-18 Nihonbashi Muromachi, Chuo-ku, Tokyo Inside Sky Aluminum Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) C25D 3 / 00-3/64 C25D 5/00-5/56

Claims (1)

(57) [Claims] 1. A method for producing a galvanized aluminum plate for use in which the surface is subjected to a zinc phosphate treatment, wherein the surface of the aluminum plate is degreased, and then a chlorine compound and an inorganic acid salt of zinc are mixed. , The Zn ²⁺ ion concentration in the bath is 0.1-7
A method for producing a galvanized aluminum plate, wherein electrogalvanizing is performed in a plating bath containing a pH of 3.5 or less within a range of 5 g /.