JPH03146651A - Flux for hot dip zn-al alloy coating - Google Patents

Abstract

PURPOSE:To provide a flux reduced in corrosiveness and causing no uncoating by adding NH4Cl and specifying a composition in a flux containing SnCl2 and ZnCl2. CONSTITUTION:This flux has a composition consisting of, by weight, 5-50% SnCl2, 10-95% NH4Cl, and <=85% ZnCl2. Uncoating can be prevented by immersing iron and steel materials, etc., into the above aqueous solution to perform flux treatment. Since the above flux is free from fluorides, corrosiveness is reduced and the necessity of expensive flux-tank material is obviated, and further, the generation of noxious gas is prevented. As to the amount of SnCl2, surface activating action on a material to be treated becomes insufficient when it is <5%, and, when it exceeds 50%, the melting point of the flux-coated body formed by means of the flux treatment is elevated and complex salt with superior flowability is difficult to be formed at the time of plating. Further, the function of preventing the inhibition of the adhesion of plating layer due to Al2O3 as an oxidation product in a plating bath becomes insufficient when NH4Cl content is <10%, and, when it exceeds 95%, the amount of SnCl2 becomes insufficient. Moreover, when ZnCl2 content exceeds 85%, the amounts of other components become insufficient.

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, many new products with high added value have entered the market by using zinc plating as a base and adding surface treatments such as painting and finishing. Users' choices regarding products such as these 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, plating baths are known in which approximately 0.1 to 20% by weight of Al is added in order to ensure corrosion resistance of the plating layer. This plating bath usually applies ZnCj! to the workpiece such as steel parts. zIt is used after being subjected to flux treatment, such as by immersion in an aqueous solution.

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

In order to solve this problem of non-plating, SnCj! ! Various fluxes have been proposed whose main components are
125361, JP-A-60-141858, etc.).

[Problem to be solved by the invention]

However, these fluxes have fluoride added to suppress the hydrolysis of SnC1°.
The use of fluoride has the following drawbacks. In other words, due to its strong corrosivity, expensive materials are required for the flux tank, which not only increases the cost of equipment and maintenance, but also requires measures to protect the working environment as extremely harmful gases are generated. Become.

In view of the above conventional problems, an object of the present invention is to provide a flux for hot-dip Zn-A 1 alloy plating that contains 5nCj2° as a main component, does not contain fluoride, and does not cause non-plating.

[Means to solve the problem]

In order to achieve the above object, the present inventors have conducted various studies, and have found that conventionally it was thought that AI reacts with the plating bath and not only reduces the flux effect but also tends to cause non-plating. NHJCl removes Zn from processed materials such as steel parts.
-It is possible to improve the adhesion of Al alloy, and its NHJ
It has been found that the amount of Cl can be varied widely by adding ZnCl.

Uchi, the flux for hot-dip Zn-Al alloy plating of the present invention contains 5 to 50% by weight of 5nCj! , , 10-95% by weight of N)l#tJ and up to 85% by weight of ZnCj! 2
It consists of

Further, the present invention provides molten Zn-Aj! As a flux for alloy plating, the flux of the present invention may be dissolved in water to form an aqueous solution. The concentration of the flux of the present invention in this aqueous solution is preferably 150 to 1000 g/l.
It is. A small amount of acid such as hydrochloric acid or sulfuric acid may be appropriately added to this aqueous solution to make it easily soluble during preparation.

[Effect]

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

The amount of Al is preferably 0.1 to 20% by weight. If it is less than 0.1% by weight, the effect of maintaining the above-mentioned corrosion resistance is small, and even if the content of AI exceeds 20 heavy cylinders, it becomes difficult to obtain further improvement in corrosion resistance, and the melting point of the plating bath increases. This is because workability deteriorates.

The reason why 5nC1z is included in the flux of the present invention is to utilize the surface activating effect of the well-known SnCIt on the treated object, and if the content is less than 5% by weight, the above effect cannot be fully utilized. On the other hand, if it exceeds 50% by weight, the flux coating formed on the surface of the workpiece formed by flux treatment will have an increased melting point,
During hot-dip Zn-Al plating, complex salts with good fluidity are difficult to form.

In addition, NH, CI are hot-dip Zn-A It plating rvr
a. Zn-Al! due to A It zOi generated by oxidation of the plating bath. It has the effect of preventing the alloy plating layer from coming into close contact with the surface of the workpiece. This is presumed to be due to the following mechanism. In other words, scale smuft (Fe304°F
eCj! A complex salt with a low melting point is produced by the reaction shown in the following formula with Alc, etc. produced by the reaction between the flux and the plating bath, and it boils.

Fe5Oa+8NH<Cj? +Fe -4FeNHz
C12z+4NHs+4HzOFeCj! z・F
eO+2NH#CIt →2FeNH3Cj! ,+)
12゜AjICj23+ NHaCI! -AICIs・
NHaC1 Furthermore, foaming occurs on the surface of the object to be treated due to the decomposition of NHJCfi as shown in the following equation.

NH4Cj! →N11s+HCp It is thought that such boiling and foaming can prevent the above-mentioned disturbing effects of A # and 03.

If the content of NHac i is less than 10% by weight, the above effect cannot be fully utilized, while if it exceeds 95% by weight, the content of 5nCj! Since the amount of 5nC1 is too small, the effect of 5nC1 cannot be fully utilized.

And ZnCj! , allows the above-mentioned NH and CA' contents to be widely adopted, and also allows Zn-A I! Improves the gloss and smoothness of alloy plating surfaces. The amount of SnC1 contained exceeds 85% by weight.

and NH4Cl are too small to take full advantage of their effects.

As mentioned above, 5nC1! z, NH4cI! Oyohi Zn
Cl! By using the flux consisting of Z, it is possible to improve the adhesion between the Zn-A 1 alloy plating layer and the workpiece without adding fluoride, and to prevent unplating from occurring.

〔Example〕

Examples and Comparative Examples Distilled zinc ingot (one type) according to JIS H2107
Using an aluminum ingot with a purity of 99.9% by weight or more, a hot-dip galvanizing bath containing the amount of AI shown in Table 1, with the balance consisting of Zn and unavoidable impurities was electrolyzed in a No. 30 graphite crucible. It was melted at 520°C using a furnace.

On the other hand, the plate width is 75 m from a general structural rolled steel plate with a plate thickness of 3.
A test piece with a plate length of 150 mm was cut out, and the surface of the test piece was degreased with a heated 10-layer aqueous solution of sodium hydroxide, and then immersed in a 12% by weight sulfuric acid solution for 30 minutes to clean the surface of the test piece. After pickling, it was further heated to 70°C and subjected to flux treatment by immersing it in a flux aqueous solution having the composition and concentration shown in Table 1 for 1 minute and pulling it out, and finally placed in a constant temperature bath kept at 200°C. A test piece was prepared for evaluating the degree of non-plating of the hot-dip galvanized product by drying it for 5 minutes.

Next, the temperature of the hot-dip galvanizing bath prepared in advance as described above was adjusted to the bath temperature shown in Table 1, the plating bath was thoroughly stirred, the dross on the surface of the plating bath was removed, and the galvanizing bath was prepared as described above. The prepared test piece was immersed in the plating bath, the dross on the surface of the plating bath was removed again, the test piece was pulled out of the plating bath, and the test piece was left to cool, thereby obtaining a plated test piece. .

(Table 2) The degree of non-plating of these test pieces was visually observed. As a result, the test pieces of the example (tests 11hl to 28)
No plating was observed in any of the test specimens of Comparative Examples (Tests N129 to 33), whereas non-plating was observed in all of the test pieces of comparative examples (tests N129 to 33).

A hammer test according to the provisions of JIS H0401 was conducted on the test pieces of the above examples (Test!lhl~28). As a result, it was confirmed that all the test pieces had good adhesion.

〔Effect of the invention〕

As is clear from the above, the present invention can provide a flux suitable for use in hot-dip Zn-Al alloy plating, which does not contain fluorides and does not cause unplated surfaces.

Claims (2)

[Claims] 1.5-50% by weight SnCl_2, 10-95% by weight
A flux for hot-dip Zn-Al alloy plating consisting of NH_4Cl and 85% by weight or less of ZnCl_2. 2. A flux for hot-dip Zn-Al alloy plating, which is an aqueous solution in which the flux according to claim 1 is dissolved.