JP2609345B2 - Flux for hot-dip zinc alloy plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a flux for hot-dip zinc alloy plating of a steel material or the like, and more particularly to a flux for plating used when applying a Zn—Al alloy plating process to a steel material or the like.

[Prior art]

BACKGROUND ART Conventionally, to prevent corrosion of steel materials and the like, it has been known to apply hot-dip galvanizing and electrogalvanizing to the surface thereof. In recent years, a number of new products with high added value have begun to enter the market by adding a zinc plating treatment as a base material and further adding a surface treatment such as painting and processing to the base material. User choices for products are also becoming increasingly diversified. In order to satisfy these requirements for diversification of the galvanizing process, it has been considerably attempted to improve the properties of the galvanized layer of the hot-dip galvanized product by selecting the additive elements and the amounts of the components that constitute the plating bath composition. . In particular, to ensure the corrosion resistance of the plating layer, Al
A plating bath to which about 0% by weight is added is known. When using this plating bath for workpieces such as steel parts,
Usually, before that, flux treatment is performed by immersing the object in an aqueous solution of ZnCl ₂ . However, in the plated product manufactured in this manner, a portion where the plating layer does not adhere, that is, an unplated portion is easily generated. That is, because Al is an extremely active element for oxygen, selective oxidation occurs, and further, when ammonium salts are contained in the flux,
It is said that the reaction represented by the formula (1) results in the generation of aluminum chloride which causes the formation of an unplated portion. 3NH ₄ Cl + Al → AlCl ₃ + 3NH ₃ + 2 / 3H ₂ (1) In order to solve the problem of generation of the non-plated portion, an ammonium salt containing fluoride as a main component is used for the purpose of not causing the reaction of the formula (1). Flux not included (Japanese
No. 60-125361, Japanese Patent Publication No. 61-33071) or Al
Flux mainly composed of more active alkali metal chlorides (JP-B-64-5110) and flux mainly composed of ammonium salts of organic acids (JP-A-1-283353)
And so on.

[Problems to be solved by the invention]

However, the flux to which fluoride is added has the following disadvantages. That is, due to its strong corrosiveness, the material of the flux treatment tank is required to be expensive to withstand the strong corrosiveness, and not only costs for equipment and its maintenance are high, but also extremely harmful gas is generated. Measures are needed. In addition, any flux that does not use fluoride,
Since the chloride and the ammonium salt coexist in the flux, there is a drawback that the reaction of the formula (1) cannot be prevented at all. The present invention has been made in view of the above problems, and contains InCl ₃ as a main component,
An object of the present invention is to provide a flux for hot-dip zinc alloy plating that does not cause non-plating even when aluminum chloride is generated, and as a result, forms an alloy film having high corrosion resistance.

[Means for Solving the Problems]

The present inventors have conducted various studies to achieve the above object, and as a result, have found the following. a) By using InCl ₃ as a main component of flux, cementation occurs on the surface of the steel component as the workpiece, and the indium deposited on the surface of the steel component during plating is melted, so that the zinc alloy can be processed on the workpiece. That can improve the adhesion. b) NH ₄ Cl, which has been considered not only to reduce the flux action but also to easily generate a non-plated portion by reacting with Al in the zinc alloy plating bath, has been used for zinc alloy to be processed on steel parts and the like. That can improve the adhesion. Therefore, the flux for hot-dip zinc alloy plating of the present invention is composed of 15 to 60% by weight of InCl ₃ and the balance of NH ₄ Cl. Further, the flux for hot-dip zinc alloy plating of the present invention,
A flux composed of 15 to 60% by weight of InCl ₃ and the balance of NH ₄ Cl was dissolved in water to form an aqueous solution. The concentration of the flux in this aqueous solution is preferably 250-1200 g /
It is. Incidentally, hydrochloric acid may be appropriately added to this aqueous solution in order to make the aqueous solution easily soluble.

[Action]

By incorporating InCl ₃ and NH ₄ Cl into the flux of the present invention, these effects are combined to improve the adhesion between the Zn—Al alloy plating layer and the workpiece such as a steel part. The behavior of InCl ₃ and NH ₄ Cl will be described below. InCl ₃ causes the reaction of the formula (2) on the surface of the non-processed material, and precipitates on the surface of the non-processed material to form an indium layer covering the surface.
It is considered that the wettability of the Zn-Al plating bath to an untreated material is improved. ^{2In 3+ + 3Fe → 2In + 3Fe} 2+ (2) Thus, in less than 15% by weight content of InCl _3, the effect can not be sufficiently utilized, whereas, the content of InCl ₃ 6
If it exceeds 0% by weight, the amount of coexisting H ₄ Cl becomes too small, and the effect of improving the wettability of the plating on the surface of the workpiece by the addition of NH ₄ Cl cannot be sufficiently utilized. NH ₄ Cl is decomposed on the surface of the object by the reaction of the formula (3),
In the reaction according to (5), the boiling and foaming caused by the formation of a complex salt having a low boiling point, and the decomposition of the generated oxide that has caused the non-plated portion, cause the Zn-Al alloy plating bath to be untreated. It is believed that the contact is better. NH ₄ Cl → NH ₃ + HCl (3) Fe ₃ O ₄ + 8NH ₄ Cl + Fe → 4FeNH ₃ Cl ₂ + 4NH ₃ + H ₂ O (4) FeCl ₂ .FeO + 2NH ₄ Cl → 2FeNH ₃ Cl ₂ + H ₂ O (5) Therefore, NH _If the content of ₄ Cl is less than 40% by weight, the above effect cannot be sufficiently utilized, while if it exceeds 85% by weight,
Since the amount of coexisting InCl ₃ is too small, the effect of improving the wettability of plating by InCl ₃ cannot be sufficiently utilized. As described above, the flux composed of InCl ₃ and NH ₄ Cl is used to improve the adhesion between the zinc alloy plating layer and the object to be processed without adding a fluoride so as not to generate a non-plated portion. Can be.

【Example】

Using distilled zinc ingot (one kind) according to JIS H2107 and aluminum ingot with a purity of 99.9% by weight or more,
A hot dip galvanizing bath containing Al in the amount shown in the table and having a balance of Zn and unavoidable impurities was melted in a No. 20 graphite crucible at 520 ° C. using an electric furnace. On the other hand, a width of 75m from a rolled steel sheet for general structure with a thickness of 3.2mm
m, a test piece with a plate length of 150 mm was cut out, the surface of the test piece was degreased with a heated 10% by weight aqueous solution of sodium hydroxide, and then immersed in a 12% by weight hydrochloric acid solution for 30 minutes. Was subjected to a flux treatment by dipping in an aqueous flux solution having the composition and concentration shown in Table 1 heated to 70 ° C. for the time shown in Table 1 and pulling it up, and finally kept at 150 ° C. By drying in a constant temperature bath for 5 minutes, a test piece for evaluating the degree of generation of a non-plated portion with respect to the hot-dip galvanized product was prepared. Next, the temperature of the hot-dip galvanizing bath previously melted as described above was adjusted to the bath temperature shown in Table 1, dross on the surface of the plating bath was removed, and the test piece adjusted as above was placed in the plating bath. Then, the dross on the surface of the plating bath was removed again, and the test piece was pulled up from the plating bath and then air-cooled to collect a plated test piece. The degree of formation of the non-plated portions of these test pieces was visually observed. As a result, the test pieces of this example (test Nos. 1 to
In 8), no unplated portions were observed, whereas in the test specimens of the comparative examples (Test Nos. 9 to 12), all unplated portions were observed. In addition, the corrosion resistance of the test pieces of the examples (test Nos. 1 to 8) was measured by JI.
It was confirmed by a salt spray test according to SZ2371. The results are shown in Table 1. In all of these test pieces, generation of red rust was not observed even after 1000 hours, and it was confirmed that very high corrosion resistance was exhibited.

【The invention's effect】

As is clear from the above, when the flux for hot-dip zinc alloy plating of the present invention is used, no unplated portion is produced even when an ammonium salt is present. As a result, it is possible to provide a flux suitable for use in hot-dip zinc alloy plating having an action of forming an alloy film having high corrosion resistance.

Claims (2)

(57) [Claims] 1. A flux for hot-dip zinc alloy plating comprising 15 to 60% by weight of InCl ₃ and the balance of NH ₄ Cl. 2. A flux for hot-dip zinc alloy plating, which is an aqueous solution in which the flux according to claim 1 is dissolved.