JPH0657393A - Flux treating method - Google Patents

Abstract

PURPOSE:To provide a flux treatment method for suppressing the generation of appearance defect such as pinhole and nonplating in a galvanized alloy plating. CONSTITUTION:(1) In the flux treatment process of the galvanized alloy plating, the flux treatment is executed by using the aqueous soln. of flux having 15wt.% or high concentration and then drying it at 150 to 300 deg.C. (2) In the flux treatment process of the galvanized alloy plating, the flux treatment is executed by using a aqueous soln. of flux having 1.0 to 5.5 hydrogen ion concentration and then drying it at a temp. between and 300 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux treatment method, and more specifically, in the flux treatment step of hot dip zinc alloy plating, by suppressing the formation of basic zinc chloride, zinc hydroxide, etc. , A flux treatment method for preventing plating defects such as non-plating.

[0002]

2. Description of the Related Art In recent years, various zinc alloy platings including zinc aluminum alloy plating have been developed and put into practical use in response to the demand for high corrosion resistance and maintenance-free.

Except for the case where continuous plating such as steel plate is performed, a method of immersing a steel material in a molten bath of molten zinc alloy in the atmosphere is generally used. In such hot-dip zinc alloy plating, usually, as a pretreatment step of steel material, degreasing for the purpose of removing oils and fats, pickling for the purpose of removing rust and oxides, and maintaining a clean surface of the steel material. The flux treatment is carried out for the purpose of causing wet adhesion when the plating layer is formed.

As the flux for hot-dip zinc alloy plating, ammonium chloride, zinc chloride, or a double salt of zinc chloride and ammonium chloride is used for zinc alloy plating containing no aluminum. For zinc alloy plating containing aluminum, the normal flux reaction is hindered by the selective oxidation of aluminum and the sublimation and dissipation of aluminum chloride. Therefore, it is necessary to use the flux described in JP-B-64-5110. There is.

These fluxes are usually made into an aqueous solution, and a steel material which has been subjected to pickling treatment and has a clean surface is immersed in this aqueous solution of the flux, and the flux is attached to the surface of the steel material. Be served.

Conventionally, zinc alloy plating baths have lower wettability to steel sheets than zinc plating baths. Therefore, the steel sheets are sufficiently cleaned during degreasing and pickling so that flux is evenly adhered. Consideration has been paid to ensure that the composition of the flux is properly maintained.

However, in the conventional flux treatment method, although the cleanliness of the surface of the steel sheet and the composition of the flux are appropriate, appearance defects, which are considered to be due to poor wettability such as pinholes, sometimes occur, so It was required to investigate the cause of the poor sex and take countermeasures.

On the other hand, the aqueous solution concentration of the flux or the hydrogen ion concentration of the aqueous flux solution has not been conventionally controlled, and it was thought that the flux should be physically attached. Also, regarding the drying after the flux treatment, the residual water content explodes due to contact with molten metal and causes the molten metal to fly off. Or, a drying method such as natural drying was used, and it was only considered that the flux was heated too much and was not decomposed or deteriorated.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a flux treatment method for suppressing the occurrence of appearance defects such as pinholes and non-plating in hot dip galvanizing.

[0010]

Means for Solving the Problems The inventors of the present invention have made diligent studies in accordance with the above objects, paying attention to the aqueous solution concentration and hydrogen ion concentration of the flux, and changing these values to change basic zinc chloride and hydroxide. When the conditions for producing zinc were examined, when the flux concentration decreased or the hydrogen ion concentration increased, basic zinc chloride and zinc hydroxide were produced in the flux aqueous solution or the flux adhering to the steel material, resulting in cloudiness. Was observed. FIG. 1 shows the X-ray diffraction peak of the flux cloudy matter in the case where the flux aqueous solution concentration is 5% by weight and the hydrogen ion concentration is 6.0. It has been found that the formation of basic zinc chloride and zinc hydroxide causes poor wettability, which results in poor appearance such as pinholes and non-plating.

Therefore, the above object can be achieved by controlling the concentration of the aqueous solution or the concentration of hydrogen ions so that the poor wetting does not occur and keeping the drying temperature within a certain range.

That is, according to the present invention, in the flux treatment step of hot dip galvanizing, the flux treatment is performed using a flux aqueous solution having a concentration of 15% by weight or more, or a flux aqueous solution having a hydrogen ion concentration of 1.0 to 5.5. And subsequently drying at 150 to 300 ° C.

In the present invention, in the flux treatment step of hot dip zinc alloy plating, a flux aqueous solution having a concentration of 15% by weight or more is used, or the hydrogen ion concentration is 1.0.
A flux aqueous solution of ~ 5.0 is used. If these conditions are not met, white turbidity due to the formation of basic zinc chloride or zinc hydroxide is observed, and when plating is performed using such an aqueous flux solution, poor appearance such as pinholes may result in poor plating surface. Recognized by.

After the flux treatment, it is dried quickly. In the present invention, the drying temperature is 150 to 3
It must be 00 ° C. If the drying temperature is lower than 150 ° C., basic zinc chloride or zinc hydroxide is produced as in the above case, and poor appearance such as pinholes is recognized on the plating surface. The cause of this is H based on the deliquescent property of zinc chloride.
It is considered that this is due to an increase in ₂ O and OH ⁻ ions. Further, if the drying temperature exceeds 300 ° C., the flux is decomposed and the appearance becomes poor. For this drying, hot air drying, oven drying or the like is adopted, and is not particularly limited.

The present invention is not limited to Zn-Al plating, but can be applied to Z
It is applicable to all zinc alloy plating such as n-Ni plating and Zn-Al plating. For example, Japanese Patent Application No. 3-267006
It is also applicable to the zinc alloy plating of No.

Further, the flux composition can be widely applied to fluxes containing zinc salts and chlorine compounds and is not particularly limited, and an example thereof is the flux described in Japanese Patent Publication No. 64-5110.

[0017]

The flux treatment liquid when the wettability is good or bad and the steel material adhered flux are investigated by using an analysis means such as X-ray diffraction method. Zn ₅ (OH) ₈ Cl _{2
· XH 2 O, ZnCl 2 ·} 4Zn (OH) 2, ZnCl 2 ·
Basic zinc chloride and zinc hydroxide such as 4Zn (OH) ₂ were confirmed (Fig. 1).

That is, even if the flux composition is proper, the concentration of the flux aqueous solution becomes dilute, the OH increases, and the one left at room temperature during drying is, for example, 5Zn ₂ + 8OH ⁻ + 2Cl ⁻ + xH ₂ O. → Zn
₅ (OH) ₈ Cl ₂ · xH ₂ O and Zn ²⁺ + 2OH ⁻ → Zn
The reaction of (OH) ₂ causes the formation of basic zinc chloride and zinc hydroxide, and the concentration of Zn ²⁺ ion and Cl ⁻ ion (which should be Zn ²⁺ ion after drying) should be the proper concentration as a flux.
(Cl ₂ concentration) deviates from the proper range, and the composition balance of the flux is lost.

As described above, it has been found that a flux treatment method for suppressing the formation of basic zinc chloride or zinc hydroxide is necessary. Next, the concentration of the flux aqueous solution, the hydrogen ion concentration,
The drying method and temperature were changed, and the presence or absence of basic zinc chloride and zinc hydroxide was examined at this time, and the relationship with the pinhole defect rate on the plated surface was examined.

As a result, the flux concentration of the steel material is increased by increasing the flux concentration or by using the flux aqueous solution kept on the acidic side by the addition of hydrochloric acid, and then the moisture in the flux adhered to the steel material is promptly removed. By drying at a temperature at which it can be sufficiently vaporized, a zinc alloy plating that did not cause poor wettability and did not cause appearance defects such as pinholes was stably obtained.

[0021]

EXAMPLES The present invention will be specifically described below based on Examples and the like.

Examples 1 to 14 and Comparative Examples 1 to 4 SS 400 Rolled steel for general structure 50 mmW × 100 m
After cleaning the surface by subjecting mL × 3.2 mmT to ordinary alkaline degreasing and pickling, the surface is cleaned, and then 60 mol% zinc chloride, 10 mol% sodium chloride, 5 mol% potassium chloride, 24 mol% ammonium chloride, 1 mol tin chloride. Special public account 6 consisting of%
Using the flux of the composition described in 4-5110,
As shown in Table 1, immersion treatment was carried out at 90 ° C. for 5 minutes in a flux aqueous solution in which various aqueous solution concentrations and hydrogen ion concentrations were adjusted. The hydrogen ion concentration was adjusted with hydrochloric acid.

Subsequently, drying was performed under the drying conditions (temperature, method) as shown in Table 1, and hot dip zinc alloy plating was performed at 460 ° C. for 1 minute using various zinc alloy plating baths. The time from the flux treatment to the drying and the time from the drying to the plating were each within 1 to 2 minutes.

Thus, the presence or absence of pinholes on the surface of the hot-dip galvanized layer was examined with a magnifying glass and a microscope, and the results are shown in Table 1.
It was shown to.

[0025]

[Table 1]

As a result, no pinholes were observed in Examples 1 to 14, but pinholes were generated in Comparative Examples 1 to 4.

[0027]

As described above, in the flux treatment step, good wettability is exhibited by drying the flux aqueous solution concentration or hydrogen ion concentration within a certain range and at a certain temperature, and pinholes, etc. are exhibited. It is possible to stably obtain the zinc alloy plating without the appearance defect.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction peak of a flux cloudy substance on the surface of a steel material when a flux aqueous solution having a concentration of 5% by weight and a hydrogen ion concentration of 6.0 was used.

Claims (2)

[Claims] 1. In the flux treatment step of hot dip zinc alloy plating, flux treatment is performed using a flux aqueous solution having a concentration of 15% by weight or more, and subsequently 150 to 3
A flux treatment method characterized by drying at 00 ° C. 2. The flux treatment step of hot dip zinc alloy plating is performed by using an aqueous flux solution having a hydrogen ion concentration of 1.0 to 5.5 and subsequently drying at 150 to 300 ° C. Flux treatment method.