JPH11158654A - Production of duplex-coated steel product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the adhesion of an Al-Mn alloy plating film by treating the surface of a galvanizing film with an alkali solution, successively treating the surface with an acid solution to remove a specific amount of plating film by dissolution, and then applying Al-Mn alloy plating. SOLUTION: The surface of a galvanizing film is first treated with an alkali solution, by which an oxide film on the surface is dissolved. As the alkali solution, an aqueous solution of sodium hydroxide, etc., is preferred. Successively, the surface is treated with an acid solution. The purpose of this treatment is to auxiliary dissolve the plating film and also to neutralize the alkali solution remaining on the surface. As the acid solution, hydrochloric acid, sulfuric acid, etc., are preferred. The amount of dissolution of the galvanizing film is regulated to (0.05 to 5) g/m<2> . When the amount of dissolution is below the lower limit, the oxide film on the surface of the plating film cannot be removed sufficiently. When it exceeds the upper limit, ruggedness at the plating surface after dissolution is increased and alkali or acid remain in the recessed part and, as a result, desired adhesion cannot be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a two-layer plated steel material comprising Al-Mn and Zn-based materials having excellent corrosion resistance after forming.

[0002]

2. Description of the Related Art As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 61-261496, a two-layer plated steel sheet in which a Zn-based plating film is plated with an Al-Mn alloy by a molten salt electrolysis method has extremely high corrosion resistance. It is excellent and is expected to be applied in various fields such as automobiles, home appliances, and building materials.

[0003] Usually, when producing a plated steel sheet, a pretreatment for activating the surface of the base material is performed before plating in order to improve the adhesion of the plating film. When an Al-Mn alloy plating is performed on a steel material by a molten salt electrolysis method, as disclosed in Japanese Patent Application Laid-Open No. 63-143280, the base material surface is coated with a degreasing agent such as sodium orthosilicate. After degreasing, a pretreatment for pickling is performed. Conventionally,
Al-Mn on the Zn-based plating film by molten salt electrolysis
When manufacturing double-layer plated steel products to be alloy plated,
The same degreasing and pickling treatment was performed.

[0004] However, even if the surface of the Zn-based plating film is degreased and pickled, and then subjected to Al-Mn alloy plating,
The adhesion of the Al-Mn alloy plating film may be insufficient. In particular, when the Zn-based plating film surface is highly contaminated or oxidized, the adhesion of the Al-Mn alloy plating film is not ensured, and the peeling resistance of the plating film during processing and the corrosion resistance after processing may be unfavorable. There is a need for improvement.

Japanese Patent Application Laid-Open No. 3-173796 discloses a method of improving the electrodeposition property of flash plating in a method of manufacturing a two-layer plated steel sheet in which an Fe-based flash plating is performed on an alloyed hot-dip Zn-plated steel sheet. ing. This is because the Al / Zn atomic ratio of the surface of the lower plating film is 0.1%.
A of the alloyed hot-dip Zn plating film surface
(1) Pretreatment for dissolving the oxide film is performed. However, on the Zn-based plating film, A
When l-Mn alloy plating is performed, the adhesion of the upper plating film is not sufficiently improved even if the pretreatment as disclosed herein is performed.

[0006]

The problem to be solved by the present invention is to provide a method for producing a two-layer plated steel material in which an Al-Mn alloy plating is performed on a Zn-based plating film by a molten salt electrolysis method. An object of the present invention is to provide a method for improving the adhesion of an alloy plating film.

[0007]

The gist of the present invention is as follows.
The present invention relates to a method for producing a two-layer plated steel material comprising l-Mn and Zn.

[0008] In a method for producing a two-layer plated steel material in which an Al-Mn alloy is plated on a Zn-based plating film by a molten salt electrolysis method, the surface of the Zn-based plating film is treated with an alkali solution and then treated with an acid solution. , 0.05-5 g / m
After dissolving and removing the plating film of No. ² , Al-Mn plating and Zn plating are performed.
A method for producing a two-layer plated steel material comprising a system plating.

On the surface of the Zn-based plating film, there is an oxide film composed of other elements such as Zn and Mg together with the Al oxide film. Since these oxide films have poor electric conductivity, even if an Al-Mn alloy plating is applied thereon, the adhesion at the interface between the oxide film and the plating film is poor, and the upper plating film is formed from the interface with the lower layer. Peel off. Therefore, it is necessary to remove all of these oxide films before plating the upper layer. The present inventors have conducted various studies on a method of removing an oxide film from the surface of a Zn plating film. As a result, in order to remove the oxide film, a conventional method of degreasing using a degreasing agent such as sodium orthosilicate and then pickling is used. Instead, it was found that treatment with an alkali solution having excellent oxide film solubility followed by treatment with an acid solution was effective.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The surface of a Zn-based plating film is first treated with an alkaline solution to dissolve an oxide film on the surface.
The alkaline solution is not particularly limited as long as it has a property of dissolving an oxide film such as ZnO, Al ₂ O ₃ , and MgO, and the type thereof is not particularly limited. It is suitable. An aqueous solution of sodium hydroxide, potassium hydroxide, or the like has an excellent ability to dissolve an oxide film formed on a Zn-based plating film, and has an advantage that it can be treated in a shorter time than a method in which the surface is dissolved only with an acid. Dissolution with acid alone takes a long time to dissolve,
A smut or the like is formed on the surface to impair the adhesion of the upper plating. However, such a problem does not occur if an alkaline solution is used.

Although the concentration of the alkaline solution is arbitrary, it is desirable to use a solution having a somewhat high pH in order to rapidly dissolve the alkaline solution. For example, in the case of an aqueous solution of sodium hydroxide or potassium hydroxide, the concentration is 0.5% by weight.
As described above, the pH is preferably set to 11 or more.

Subsequent to treatment with an alkali solution, treatment with an acid solution is performed. The purpose of the treatment with the acid solution is to supplementarily dissolve the plating film and neutralize the alkali solution remaining on the surface. The type of the acid solution is not particularly limited as long as it does not generate a hardly soluble salt by reacting with the above-described alkali solution, and hydrochloric acid and sulfuric acid are suitable. If smut occurs during pickling, the adhesion is impaired. Therefore, the acid concentration is preferably 1% by weight or less and the pH is preferably 0.1 or more.

Known methods can be applied to the treatment with an alkali solution and an acid solution, but a method of immersing the Zn-based plating film in these solutions or spraying the solution is preferred. The temperature of the alkali solution and the acid solution is arbitrary, but in order to make the reaction rate and workability suitable, it is preferable that the temperature of each solution is in the range of 40 to 60 ° C.

The dissolution amount of the Zn-based plating film is 0.05 to
The range is 5 g / m ² . If the dissolution amount is less than 0.05 g / m ² , the oxide film on the surface of the plating film cannot be sufficiently removed. When the dissolution amount of the plating film exceeds 5 g / m ² , unevenness of the plating surface after dissolution becomes severe, and an alkali or an acid may remain in the concave portion and a desired adhesiveness may not be obtained. Preferably, the amount of dissolution is in the range of 0.05 to 1 g / m ² .

In order to improve the adhesion, it is preferable to wash the surface of the plating film each time the treatment with each of the solutions is performed, and it is preferable that the plating surface is dried after all the treatments are completed. If a mechanical treatment such as brushing of the plating surface is used in combination during the treatment with the above solution, the surface is further activated, so that the adhesion is improved.

The lower Zn-based plating film to be subjected to the method of the present invention may be one containing at least 30% by weight of Zn, and may include pure Zn, Zn and other metals such as Fe, A and the like.
Alloys with 1, Ni, Co, Cr and the like can be applied. The adhesion amount of the plating film is not particularly limited, but when importance is attached to corrosion resistance, 20 to 150 g / m2 per side.
^It is preferred to be in the range of ² . The plating method need not be limited, and may be a plating method known in the art, such as hot-dip plating, electroplating, or vacuum deposition plating. For example, hot-dip Zn plating, alloyed hot-dip Zn plating, hot-dip Zn
-Applicable to Al alloy plating, electric Zn plating, electric Zn-Ni alloy plating and the like.

As the Al-Mn alloy plating of the upper layer, a known plating film can be applied. 50 to 99.9% by weight of Al;
Mn is preferably contained in an amount of 0.1 to 50% by weight, and one of Zn, Pb, In, Sn, and Cu may be contained as a third alloy element in an amount of 5% by weight or less. When these third alloying elements are contained, the corrosion potential of the Al-Mn plating film becomes low, the sacrificial corrosion resistance is improved, and the corrosion resistance in the damaged portion or the processed portion can be improved. Although the amount of the upper plating film is not particularly limited,
It is preferable that the content be in the range of 1 to 30 g / m ² per one side. The plating method of the Al—Mn alloy plating is performed by a known molten salt electrolysis method. The plating conditions are described in, for example,
A known method as disclosed in the embodiment of JP-A-213393 can be applied.

The form of the steel is arbitrary, and is not limited to a steel plate.
Bars, wires, steel pipes, sections, etc. may be used.

[0019]

(Example 1) A 0.8 mm thick Zn-based plated steel sheet having a plating film having a chemical composition shown in Table 1 was immersed in an alkali solution, washed with water, immersed in an acid solution, and washed with water. → drying] under various conditions.

[0020]

[Table 1]

The following alkaline and acidic solutions were used, and their concentrations and pH were changed in the following ranges in order to confirm the effect on adhesion.

[0022]

The immersion time in the alkali solution and the acid solution was set to 20 seconds. In addition, as comparative examples, the case where degreased and pickled with sodium orthosilicate (Test No. 6) and the case where the pickling was omitted (Test Nos. 3, 8, and 12) were also evaluated. Before and after the pre-treatment, test samples were cut out and the amount of the plating film was measured, and the amount of the film dissolved by the pre-treatment was determined from the difference.

The steel sheet after the pretreatment was plated with an Al—Mn alloy by a molten salt electrolysis method under the following conditions to obtain a two-layer plated steel sheet.

[0025]

The performance of the obtained two-layer plated steel sheet was evaluated by the following method.

Adhesion of Al-Mn alloy plating film: After tightly bending the obtained two-layer plated steel sheet, attaching an adhesive tape to the outside of the bent portion, peeling off the tape, and peeling off the zinc-based plating film surface. The state of peeling of the Al—Mn alloy plating film was visually observed.

Corrosion resistance: Lubricating oil is applied to the obtained two-layer plated steel sheet, subjected to cylindrical drawing under the following conditions, the obtained cup is degreased, its end face and inner face are sealed, and A salt spray test in accordance with JIS-Z-2371 was carried out, and a test time until red rust was generated was measured to evaluate corrosion resistance.

[0029]

Table 2 also shows details of the pretreatment conditions, the dissolution amount of the Zn-based plating film, and the performance evaluation results of the obtained two-layer plated steel sheet.

[0031]

[Table 2]

The symbols in the performance evaluation result column in Table 2 have the following meanings.

[0033]

As can be seen from Table 2, test numbers 3, 4, 9 to 11, 13 to 18 pretreated within the range specified by the present invention.
And 20 all showed good adhesion and corrosion resistance. As shown in Test No. 6, when the degreasing and pickling treatments were performed in the same manner as before as the pretreatment, the Zn plating surface was hardly dissolved, and the adhesion during processing and the corrosion resistance after processing were reduced. It was not good. When the treatment with the acid solution was omitted as shown in Test Nos. 8 and 12, the alkali was not sufficiently neutralized, and poor electrodeposition occurred during the upper plating, and the adhesion of the Al-Mn plating film was not preferable. , Corrosion resistance was not good. Even when the alkali solution treatment and the acid solution treatment are performed as shown in Test Nos. Corrosion resistance was impaired.

[0035]

According to the production method of the present invention, a plated steel material having excellent corrosion resistance after processing without peeling of the plating film even during processing can be stably manufactured.

Claims (1)

[Claims] In a method for producing a two-layer plated steel material in which an Al-Mn alloy is plated on a Zn-based plating film by a molten salt electrolysis method, the surface of the Zn-based plating film is treated with an alkali solution and then treated with an acid solution. And 0.05 to 5 g / m
After dissolving and removing the plating film of No. ² , Al-Mn plating and Zn plating are performed.
A method for producing a two-layer plated steel material comprising a system plating.