JPH02298243A - Hot dip galvanizing bath - Google Patents

Abstract

PURPOSE:To stick a proper amt. of zinc to a body to be treated such as steel parts and to improve the corrosion resistance by specifying the compsn. of a hot dip galvanizing bath. CONSTITUTION:The compsn. of a hot dip galvanizing bath is composed of, by weight, 0.001-0.1% Al, 0.01-0.2% Ni, 0.01-0.5% Mg and the balance Zn with a small amt. of inevitable impurities. Al is contained in the bath so as to maintain the surface luster of a product hot dip galvanized in the Mg-contg. bath. Ni is contained in the bath because Ni is effective in reducing the amt. of zinc sticking to the surface of a product to be hot dip galvanized. Mg is contained in the bath because Mg improves the corrosion resistance of the hot dip galvanized product. The amt. of zinc stuck can be controlled and the corrosion loss of the hot dip galvanized product can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a plating bath used when hot-dip galvanizing a steel material or 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, hot-dip galvanizing of steel materials that form pipes, general structures, and small parts is often performed using a punch method, and the plating bath uses Al to ensure the gloss of the plated surface. Plating baths containing about a few tenths of a percent by weight have been used.

[The problem that the invention aims to solve! ! However, when zinc plating is applied to killed steel and cast metals, the demand for which has been increasing in recent years, Zn-Aj with AN added!
When hot-dip galvanizing is performed using an alloy plating bath,
Zinc, which exceeds twice the standard value, adheres to the objects to be treated such as steel materials, which increases product costs and causes a large amount of white talk when the plated products are exposed to a corrosive atmosphere. .

The present invention has been made in view of the above-mentioned conventional problems.
The purpose of the present invention is to provide a plating bath for hot-dip galvanizing that can deposit an appropriate amount of zinc on objects to be treated, such as steel parts, and can perform galvanizing with excellent corrosion resistance.

[Means to solve the problem]

In order to achieve the above object, the present inventors have conducted various studies and found that the workpiece can be coated by hot-dip galvanizing using an alloy plating bath in which appropriate amounts of AI, Ni, and Mg are added to Zn. It has been discovered that it is possible to reduce the amount of Zn adhering to a suitable amount and improve corrosion resistance, and the details thereof will be described below.

That is, in the present invention, Al is contained in an amount of 0.001 to 0. 111%, N
i is 0. O1-0.2 overlay%, Mg 0゜01-0.5
The above problem has been solved by using a plating bath for hot-dip galvanizing that has a bath composition of Zn and a small amount of unavoidable impurities.

[Function] The function of each component constituting the plating bath for hot-dip galvanizing according to the present invention and the reason for setting the content as described above will be described below.

The reason for containing An in the above galvanizing bath is Mg
This is to maintain the gloss of the surface of the treated plated product in the galvanizing bath where The Al content was set to 0.001 to 0.1% by weight because o, oo
If it is less than i% by weight, the effect of maintaining the above gloss is small;
Furthermore, if the AN content exceeds 0.1% by weight, plating adhesion tends to occur on the surface of the plated product.

Further, the reason why Ni is contained in the above plating bath is to utilize the effect of reducing the amount of zinc plating that adheres to the surface of the galvanized product. The Ni content is 0.
The reason why the Ni content is set at 0.01 to 0.2% by weight is because if it is less than 0.01% by weight, it lacks the ability to reduce the amount of zinc plating that adheres to the plated product during galvanizing treatment. Even if the double plating percentage is increased, there is a limit to the ability to reduce the amount of zinc plating that adheres to the plated product during galvanizing, and not only will the above effects not necessarily be increased, but the raw material price during galvanizing will be reduced. This is because it will only increase the value unnecessarily.

Furthermore, Mg was included in the above plating bath.
This is because g improves the corrosion resistance of galvanized products, and is especially effective in suppressing the amount of white rust. The content of M is 0.01 to 0.5% by weight
If it is set at less than 0.01% by weight, the corrosion resistance effect will be small, and if it exceeds 0.5% by weight, the surface gloss of the galvanized product will decrease and the commercial value will decrease significantly, and the plating bath This is because the amount of top dross formed on the surface layer of the zinc plating bath increases, reducing the effective utilization of the galvanizing bath.

Incidentally, the zinc ingot used as a plating bath for hot-dip galvanizing treatment contains l as an unavoidable impurity.

Some products contain less than 5% lead by weight, less than 0.1% iron, less than 0.3% by weight cadmium, less than 0.1% by weight tin, etc. The object of the present invention can be fully achieved even by using a plating bath for molten galvanizing treatment prepared using a zinc base metal containing zinc.

〔Example〕

Example 1 Distilled zinc class 1 ingot according to JIS regulations and each purity 9
Using aluminum ingots, electrolytic nickel ingots, and magnesium ingots that are guaranteed to have an Al content of 9.9% or more, the Al content is 0.
003% by weight, Ni 0°07% by weight, Mg 0.03% by weight
A plating bath for hot-dip galvanizing with a composition in which the balance was Zn and a small amount of unavoidable impurities was melted in a No. 30 graphite crucible at 520'C using an electric furnace.

On the other hand, from a general structural rolled killed steel plate with a thickness of 3 m containing 0.07% by weight of Si, the plate width is 75cm and the plate length is 150+w+.
After degreasing the surface of the test piece with a 10% aqueous solution of sodium orthosilicate, the surface of the test piece was pickled by immersing it in a 10% dilute sulfuric acid solution for 10 minutes. Flux treatment is applied by immersing in a 20% aqueous solution of n Cl x 3NH4 (l) and then pulling it straight up. Test pieces were prepared to evaluate the amount of plating deposited and the corrosion resistance of the plated product.

Next, the temperature of the hot-dip galvanizing bath prepared in advance as described above was adjusted to 460°C, the plating bath was sufficiently stirred, and the dross on the surface of the plating bath was removed. Immerse the test piece in the plating bath for 90 seconds,
Dross on the surface of the plating bath was removed again, the test piece was lifted from the plating bath, held in the air for 60 seconds, placed in water, and pulled up to collect the test piece that had been subjected to plating treatment. .

As a result, the amount of plating determined from the weight change of the test piece before and after being immersed in the plating bath was 510 gems.
Based on the salt spray test method specified in S Z 2371, a corrosion test was conducted in which a solution of sodium chloride with a pH of 7.0 was dissolved in deionized water and a salt concentration of 5% was sprayed at a temperature of 35°C. When applied for one day, the required corrosion weight loss was 170g/11! Met.

Example 2 The bath composition of the molten galvanizing bath is A within the scope of the claims.
Calculation of the plating adhesion amount in the same manner as in Example I except that the sample contained 0.005% by weight of L, 0.11% by weight of Ni, and 0.05% by weight of Mg, with the remainder being zinc and a small amount of unavoidable impurities. and corrosion tests were conducted.

As a result, the amount of plating deposited on the test piece was 470 g/i, and the corrosion loss of the test piece was 130 g/w''.

Comparative Example 1 Plating was deposited in the same manner as in Example 1, except that the bath composition of the hot-dip galvanizing bath was conventionally used, containing 0.004% by weight of Al, with the balance being Zn and a small amount of unavoidable impurities. When the amount was calculated and a corrosion test was performed, the amount of plating deposited on the test piece was 790 g7m'', and the corrosion weight loss of the test piece was 230 gem''.

In addition to the above Examples and Comparative Examples, test pieces were plated in the same manner as above with different plating bath compositions for hot-dip galvanizing, and the coating weight was calculated and corrosion tests were conducted. The results are summarized in the table below.

As is clear from the test results in the table above, by using the plating bath of the present invention, it is possible to suppress an excessive increase in the amount of plating deposited on the plated product, and also improve the corrosivity of the plated product. I understand.

In addition, Comparative Examples 1, 3, and 6 have a particularly large amount of plating deposited compared to Examples 1 to 6 of the present invention, and Comparative Example 2 is inferior in terms of corrosion resistance.

Furthermore, Comparative Examples 4 and 5 all showed low values for coating weight and corrosion loss, but in Comparative Example 4, several areas where no plating was adhered were observed on the surface of the test piece, and in Comparative Example 5,
When a large amount of dross is generated on the surface of the plating bath,
It was found that both were not suitable as plating baths for hot-dip galvanizing.

〔Effect of the invention〕

As explained above, by using the plating bath of the present invention, it is possible to sufficiently suppress the amount of plating deposited on hot-dip galvanized products, which has been a concern in the past, and to reduce the corrosion loss of galvanized products. This has the effect of not only improving the quality of hot-dip galvanized products whose application fields are increasingly expanding, but also reducing production costs.

Claims (1)

[Claims] (1) 0.001 to 0.1% by weight of Al, 0.0% of Ni
1 to 0.2% by weight, 0.01 to 0.5% by weight of Mg, and the remainder consists of zinc and a small amount of unavoidable impurities.