JPH04157147A - Flux for hot-dip zn-al alloy coating - Google Patents

Abstract

PURPOSE:To prevent the occurrence of uncoated state at the time of hot-dip Zn-l alloy coating and to improve corrosion resistance by incorporating specific amounts of SnCl2, ZnCl2, and the chlorides of alkali metal elements and/or alkaline earth metals. CONSTITUTION:This flux for hot-dip Zn-Al alloy coating has a composition consisting of, by weight, 5-50% SnCl2, 50-94.5% ZnCl2, and 0.5-32% of chlorides of alkali metal elements and/or alkaline earth metals. A material to be treated, such as iron and steel material, is immersed in an aqueous solution prepared by dissolving the above flux for alloy plating in water, by which the surface of the material to be treated is coated with Sn. By this method, a plated film free from the occurrence of uncoated state and having high corrosion resistance can be formed.

Description

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

[Conventional technology]

BACKGROUND ART Conventionally, in order to prevent corrosion of steel materials, etc., hot-dip galvanizing is sometimes applied to the surfaces thereof.

Recently, additional value has been increased by using galvanizing as a base and then performing surface treatments such as painting and processing. Various plating bath compositions have been proposed to perform hot-dip galvanizing treatments suitable for these treatments.

In particular, in order to improve the corrosion resistance of the plating film, Af
A molten Zn-Af gold alloy plating bath containing 0.1 to 20% by weight of Zn-Af is used. Usually, the workpiece is ZnC1
Hot-dip galvanizing is performed after so-called flux treatment, in which the workpiece is immersed in an aqueous solution containing T, NH4Cf, or a mixture thereof to form a flux film on the surface of the workpiece. Even when flux treatment is applied, a so-called non-plating state is likely to occur, in which no plating film is formed.This is due to aluminum chloride produced by the reaction of Af in the plating bath with chloride in the flux, or aluminum chloride formed on the surface of the plating bath. It is said that the aluminum oxide produced causes non-plating.

In order to prevent this unplated state from occurring, a flux coating consisting of potassium fluoride or sodium fluoride and zinc chloride is formed (for example,
3071), fluxes consisting of acidic fluorides, alkali chlorides, tin chloride, and zinc chloride (for example, JP-A-60
-125361), one or more chlorides, fluorides, or silicofluorides of alkali metal elements or alkaline earth metal elements, ammonium chloride, tin, lead, indium, thallium, antimony, bismuth, cadmium chlorides A flux consisting of one or more of these and zinc chloride (for example, Japanese Patent Publication No. 64-5110), a flux consisting of an ammonium salt of an organic acid and zinc chloride (for example, Japanese Patent Application Laid-Open No. 1-283353), etc. have been proposed.

However, since flux containing fluoride is highly corrosive, it requires expensive materials for the flux tank, which not only increases the cost of equipment and maintenance, but also creates extremely harmful gases that can be used in a working environment. There was a problem that required measures to improve the situation.

Also, regarding fluxes containing ammonium salts,
There was a problem in that the working environment deteriorated due to the generation of a large amount of white smoke due to the generation of ammonia gas during the hot-dip galvanizing process.

[Problems to be Solved by the Invention] The present invention is capable of forming a highly corrosion-resistant plating film without any unplated state when hot-dip Zn-Af gold alloy plating is applied to steel mesh materials, etc. Molten Zn does not require expensive equipment as it is not highly resistant, and does not degrade the working environment as it does not generate a large amount of white smoke due to the generation of ammonia gas.
-A 1 provides a flux for alloy plating.

[Means for Solving the Problem] In order to achieve the above object, the molten Zn~Af of the present invention
The flux for alloy plating is 5-50% by weight of 5nCf.
t, 50-94.5% by weight of ZnCj2z and 0.
It is characterized by containing 5 to 32% by weight of at least one chloride selected from alkali metal elements and alkaline earth metal elements. Further, the present invention is characterized in that the above-described flux of the present invention is dissolved in water to form an aqueous solution as a flux for hot-dip Zn-/I1 alloy plating.

[For production]

When the 5nCfz in the flux is immersed in an aqueous solution containing the flux, the 5nCfz causes a reaction with the surface of the workpiece as shown in equation (1) below, and the The surface is covered with tin.

Sn”10Fe’ −−→Sn’+ Fe” (1
) Since the tin precipitated on this surface is eluted into the plating bath during the hot-dip Zn-Af gold alloy plating process, even if aluminum chloride or aluminum oxide is present in the flux or the plating bath, it will not be coated. Processed object surface and Zn-Aj!
Direct contact with the alloy ensures wettability and prevents unplated state.

If the content of 5nCfz is less than 5% by weight, the reaction of formula (1) will not proceed sufficiently, and if the content exceeds 50% by weight, the reaction of formula (1) will proceed too much, causing tin on the surface of the object to be treated. SnC precipitates excessively and cannot form a good plating film.
It is necessary that the content of 42g be 5-50% by weight.

ZnCl in flux! , z is the molten Zn
-Scale and smut, whose main components are FeC1z #eO, Fe5e4, are generated on the surface of the workpiece during the hydrochloric acid cleaning, water cleaning, and drying treatments before the Af gold alloy plating treatment. The reaction of formulas (2) and (3) below may be caused to produce a complex salt with a low boiling point, or Fe3
0a + nZnCl1z + Fe 4 (nZncf,
4eO) (2) FeCfz FeO+nZn
C1z nZnclz 4eO (3) A reaction is caused between the zinc oxide generated on the surface of the plating bath and the following formula (4) formula (4) to prevent an unplated state from occurring. ZnCf! If the content of z is less than 50% by weight, (2)
, (3), (4) reactions do not occur sufficiently and the scale/smut cannot be sufficiently decomposed, and if it exceeds 94.5% by weight, the contained 5nCf, or alkali metal elements and alkaline earth metal elements. The amount of at least one chloride selected from ZnCj! is too small to fully utilize the action it contains. The content of z is 50 to 94.5% by weight
It is necessary to do so.

Chlorides of alkali metal elements or chlorides of alkaline earth metal elements are oxidized more preferentially than Zn, and depending on the element, more preferentially than Al. This improves the gloss and smoothness of the surface of the Zn-Al alloy plating film by suppressing the formation of Zn or AA oxides and lowering the melting point of the flux to make it easier for the flux to separate from the workpiece. .

If the content of at least one chloride selected from alkali metal elements and alkaline earth metal elements is less than 0.5% by weight, the above effects cannot be fully utilized;
If the melting point of the flux is exceeded, the melting point of the flux increases, making it difficult for the flux to separate from the workpiece, and the surface deteriorates. It is necessary that the content be 0.5 to 32% by weight.

Usually, the flux according to the present invention is used in an aqueous solution, and in this case, the concentration of the flux according to the present invention in the aqueous solution is 100 to
1500g/I! is preferred.

When hydrochloric acid is added to flux dissolved in water, SnCl□
The solubility of will increase and the reaction of equation (1) will proceed more easily, so
When it is desired to shorten the flux treatment time or when the surface of the object to be treated is complex, it is preferable to add hydrochloric acid.

In the present invention, the concentration of ZnCfz is increased and 5nC4
Chloride, which has been conventionally used to decompose scale smut and lower the melting point of flux, by coexisting with at least one chloride selected from 2z, alkali metal elements and alkaline earth metal elements. Without using ammonium, we were able to form a highly corrosion-resistant plating film that does not leave an unplated state. Therefore, since it does not contain ammonium salt, molten Zn-A
A large amount of white smoke was not generated due to the generation of ammonia gas during the 1-alloy plating process, and a great effect was obtained in that the environment during the plating work was not deteriorated.

〔Example〕

Distilled zinc ingot (JIS H2107, type 1) and purity 9
Using 9.9% by weight or more of aluminum ingot, A7 in the amount shown in Table 1! A molten Zn-A 1 alloy plating bath having a composition of Zn and unavoidable impurities was
It was melted in a black graphite crucible at 520°C using an electric furnace.

On the other hand, the plate width is 7
A test piece of 5 mm in length and 150 m in length was cut out, and the surface of the test piece was degreased with a 10% by weight aqueous solution of sodium hydroxide heated to 70°C, followed by a 12% by weight aqueous hydrochloric acid solution heated to 70°C. The surface of the test piece was pickled by immersing it in water for 30 minutes, and then it was immersed in an aqueous solution heated to 70° with the composition and concentration shown in Table 1 for 1 minute and then pulled up to undergo flux treatment. Finally, the molten Zn-Al
A test piece was prepared for alloy plating treatment.

Next, to the molten Zn- previously melted as described above! After adjusting the temperature of the alloy plating bath to the temperature shown in Table 1, molten Zn-Al. After removing the dross on the surface of the alloy plating bath, the test piece prepared as above was coated with molten Zn-A.
j! Immersed in an alloy plating bath. After being immersed for the time shown in Table 1, the dross on the surface of the hot-dip Zn-A 1 alloy plating bath was removed again, and the above specimen was pulled out of the hot-dip Zn-A 1 alloy plating bath, and then left in the air naturally. Cooled.

The state of the plating film on these test pieces was visually observed and the degree of non-plating was evaluated on a four-level scale, and the results are shown in Table 1. Also, molten Zn-Al! The amount of white smoke generated during the alloy plating process was also observed, and the results are shown in Table 1.

Furthermore, molten Zn-Ap! The corrosion resistance of the alloy-plated test piece was determined by a salt spray test (JIS
z2371), and the results are shown in Table 1.

In Table 1, in test numbers 1 to 6, a flux containing NaCl as at least one chloride selected from alkali metal elements and alkaline earth metal elements was used, and the flux composition, flux concentration, etc. These tests varied the treatment conditions, and in each test, molten Zn-Al! There was no unplated condition in the alloy-plated test piece, and the plating evaluation was good. In addition, the salt spray test results showed that red rust occurred over 1000 hours, indicating high corrosion resistance, and no white smoke was generated during the molten Zn-Al alloy plating process, giving good results.

In test numbers 7 to 10, a flux having a composition containing NaCl as at least one chloride selected from alkali metal elements and alkaline earth metal elements was used.・A in the plating bath! This is a test in which the hot-dip Zn-Al alloy plating conditions such as concentration were changed, and no unplated state appeared in any of the tests, so the corrosion resistance was high.
No white smoke was generated during the n-Affi alloy plating process, and good results were obtained.

Test numbers II to 17 were tests in which a substance other than NaCl was used as at least one chloride selected from alkali metal elements and alkaline earth metal elements, and in this case as well, no unplated state appeared; Therefore, the corrosion resistance was good, and no white smoke was generated during the hot-dip Zn-A2 alloy plating process, giving good results.

In test numbers 18 to 22 and 28.29, the 5nCfz content in the flux is less than 5% by weight or more than 50% by weight, and in test number 24.25, the NaCj2 content in the flux is 0. In test numbers 23 and 26.27, ZnCfz in the flux was less than 50% by weight or more than 94.5% by weight, and in either case Even in this case, visual inspection showed that no plating was present, and therefore the condition of the plating film was poor.

In test number 30, 5nCffiz in flux.

ZnCj! 2. NaC1 is within the composition range of the claims of the present application, and is a case where a flux containing NH and Cf is used, and no unplated state appears, so the state of the plated film is good. However, white smoke was generated during the hot-dip Zn-A 1 alloy plating process, indicating a poor working environment.

In the plating evaluation (visual inspection) in Table 1, ◎ indicates that there is no unplated state, ○ indicates that there is an unplated area of 1 ead or less, and △ indicates that several to tens of percent of the area ratio is unplated. The symbol "x" indicates that there is a plating film, and the mark "x" indicates that there is almost no plating film.

[Effects of the Invention] As described above, the flux for hot-dip Zn-A 1 alloy plating of the present invention has no unplated state, and therefore,
A highly corrosion-resistant plating film can be formed, and good effects such as preventing the production of white smoke from worsening the working environment can be obtained.

Patent applicant: Sumitomo Metal Mining Co., Ltd.

Claims (2)

[Claims] (1) 5-50% by weight of SnCl_2,50-94.5
A flux for molten Zn-Al alloy plating containing % by weight of ZnCl_2 and 0.5 to 32% by weight of at least one chloride selected from alkali metal elements and alkaline earth metal elements. (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.