JPH03100152A - Flux for hot dip zn-al alloy plating - Google Patents

Abstract

PURPOSE:To enable complete plating by a single plating operation by incorporating specified amts. of ZnCl2, NaCl and CH2CHCOOH into an aq. soln. as a flux. CONSTITUTION:A flux for hot dip Zn-Al alloy plating is formed with an aq. soln. contg. 150-300g/l ZnCl2, 20-40g/l NaCl and 10-120g/l CH2CHCOOH (acrylic acid). The third compd. ensures complete plating and acts to form a smooth plated surface. When the flux is used, a hot dip Zn-Al alloy plated product having corrosion resistance and improved adhesion of the plating layer to the base can be obtd. by a single plating operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plating flux used when hot-dip Zn-Al alloy plating is applied to steel materials and the like.

[Conventional technology]

Traditionally, for the purpose of preventing corrosion of steel materials,
It is known to apply hot-dip galvanizing and electrogalvanizing to the surface.

Recently, a large number of new, high value-added products have entered the market by using zinc plating as a base and adding surface treatments such as painting and finishing. , and the choices of users regarding these products are becoming increasingly diverse.

In order to satisfy these demands, considerable efforts have been made to improve the properties of the galvanized layer by selecting the additive elements and amounts added in the plating bath composition for hot-dip galvanized products.

In particular, a plating bath containing about 3 to 10% by weight of ^i is known in order to ensure the corrosion resistance of the plating layer.

This plating bath is usually used after subjecting an object to be treated, such as a steel part, to a flux treatment by immersing it in an aqueous ZnCl2 solution.

However, the plated product manufactured in this way does not have a plating layer and is likely to be unplated.

Therefore, primary plating is performed in a Zn plating bath that does not contain Al, and after the above-described flux treatment, secondary plating is performed in the Zn-A 1 alloy plating bath.

[Problem to be solved by the invention]

However, the above method has the disadvantage that it is complicated because it requires two plating steps, and the manufacturing cost is also high.

The present invention has been made in view of the above-mentioned conventional problems.
The purpose of the present invention is to provide a flux for hot-dip Zn-A1 alloy plating that does not cause unplated surfaces on objects to be treated such as steel parts even in a single plating operation.

[Means to solve the problem]

In order to achieve the above object, the present inventors have conducted various studies and found that ZnCl t+NaCl t+NaCl as a flux.
The workpiece is subjected to flux treatment using an aqueous solution containing CH2CHCOOH (acrylic acid) and ZnCl g, NaCl and CI (zcHcOO
It has been discovered that the adhesion of Zn-A1 alloy to the workpiece can be improved by attaching H, and the details thereof will be described below.

That is, the present invention uses 150 to 300 g/l of ZnC1 as a flux for hot-dip Zn-A1 alloy plating.

20-40 g/l of NaCl and CH2CHCOOH
The above problem was solved by using an aqueous solution containing 10 to 120 g/l of.

A small amount of acid such as hydrochloric acid or sulfuric acid may be added to this aqueous solution.

[For production]

The reason why the flux of the present invention is used for hot-dip Zn-Al alloy plating and A1 is contained in the galvanizing bath is to maintain the corrosion resistance of the plating layer.

The amount of Al is preferably 3 to 10% by weight. If the Al content is less than 3% by weight, the effect of maintaining the above-mentioned corrosion resistance is small (Also, if the Al content exceeds 10% by weight, it becomes difficult to obtain further improvement in corrosion resistance, and the melting point of the plating bath increases. This is because workability deteriorates.

In addition, ZnCI Z+N is added to the aqueous flux of the present invention.
The reason for containing aCl and CH2CHCOOH is
This is to improve the adhesion between the ZnA1 alloy plating layer and the object to be treated, thereby preventing unplatedness and forming a smooth plating surface.

ZnCf, content, NaCIl content and C)lzc
If at least one of the HcOOR contents is below the respective lower limits, the above effects will not be sufficient, and if the ZnC1 content exceeds 300 g/l, not only will the above effects not necessarily be increased, but the entire amount will dissolve. It becomes difficult to do. Also, NaCl acts to prevent unplating, but
When the content exceeds 40 g/l, the melting point of the mixed salt of ZnC1, NaC1 and CHICHCOOH that adheres to the object to be treated increases, and the flux property decreases.

Furthermore, CH2CHCOOH not only does not cause unplatedness but also acts to form a smooth plated surface, but this effect does not necessarily increase even if its content exceeds 120 g/l.

The flux of the present invention may be used by dipping the object to be treated therein or by applying it to the surface of the object.

〔Example〕

Examples, Comparative Examples, Conventional Examples Distilled zinc ingot (class 1) according to JIS 82107
Using an aluminum ingot with a purity of 99.9% by weight or more, a hot-dip galvanizing bath with a composition of 15% by weight of A, the balance being Zn and unavoidable impurities was heated at 520°C in a No. 30 graphite crucible using an electric furnace. Melted.

On the other hand, a test piece with a width of 75 mm and a length of 150 mm was cut from a general structural rolled steel plate with a thickness of 3 mm, and the surface of the test piece was degreased with a heated 10% by weight aqueous solution of sodium orthosilicate. The surface of the test piece was pickled by immersing it in a sulfuric acid solution of 10% by weight for 10 minutes, and then it was immersed in an aqueous solution heated to 70°C with the composition shown in Table 1 for 3 minutes and pulled up to obtain a flux. Processed and finally 80
A test piece was prepared for evaluating the degree of non-plating on a hot-dip galvanized product by drying it in a constant temperature bath maintained at ℃.

Next, the temperature of the hot-dip galvanizing bath prepared in advance as described above was adjusted to 440°C, the plating bath was sufficiently stirred, and the dross on the surface of the plating bath was removed. By immersing the piece in the plating bath for 60 seconds, removing the dross on the surface of the plating bath again, lifting the test piece from the plating bath, holding it in the air for 60 seconds, putting it into water, and pulling it up, A test piece that had been subjected to plating treatment was taken.

The degree of non-plating of these test pieces was visually observed. The results are shown in Table 1.

〔Effect of the invention〕

As is clear from the above, according to the flux for hot-dip Zn-A R alloy plating of the present invention, a hot-dip Zn-A 1 alloy plated product with ensured corrosion resistance can be obtained in a single plating operation.

Claims (1)

[Claims] 1. ZnCl_2 150-300g/l, NaCl
20-40 g/l and CH_2CHCOOH 10
A flux for hot-dip Zn-Al alloy plating consisting of an aqueous solution containing ~120 g/l.