JP2537666B2 - Alloy bath and method for bright galvanizing - Google Patents

Description

TECHNICAL FIELD The present invention relates to a doppled hot dip galvanizing bath and a hot dip galvanizing method, and in particular, to a durable bright plated surface as it is without post-treatment. The present invention relates to the technique of galvanized hot dip galvanizing using a designated galvanizing alloy bath containing manganese and aluminium, which makes it possible to produce products having the same. INDUSTRIAL APPLICABILITY The present invention can be suitably applied to dobu-zuke hot-dip galvanized products which are required to have corrosion resistance and further decorative properties.

(Background of the Invention) Generally, hot dip galvanizing is known as a simple means for improving the corrosion resistance of steel materials. In recent years, the high anticorrosion ability of hot-dip galvanizing has been widely recognized, and not only general industrial steel parts but also hot-dip galvanized steel materials for outdoor structures have been widely used. In addition, taking advantage of the unique surface pattern and luster of hot-dip galvanized products, it is increasingly used for interior decoration applications.
It is a situation where its usefulness is once again attracting attention.

As the hot-dip galvanizing technology, there are a batch method in which a steel material is immersed in a plating bath in a batch method, and a continuous method in which a long steel material is continuously moved through the plating bath.
Since the two differ in pretreatment, plating adhesion mode, etc., they are different in operating conditions and cannot be discussed collectively. The present invention is exclusively related to the former hot dipped galvanizing technique of the two.

[Conventional technology]

In normal hot-dip galvanized products, especially those used outdoors, due to rainwater and condensation phenomena, even at its initial stage (several days to several months), on the plated surface,
Basic zinc carbonate (a complex compound of zinc oxide, zinc hydroxide, zinc carbonate, etc.), which is so-called white rust, is produced, and the appearance is significantly deteriorated. This white rust gradually disappears over time and changes to a gray corrosion product, but due to the uneven progress, the white color of the white rust and the gray color of the corrosion product are mottled. Is a fatal drawback. Even if it is installed indoors, the same discoloration problem as that of the outdoor installation occurs, although there are differences in time and degree depending on the atmosphere environment.

Chromate treatment is the most popular method for attempting to improve these white rust problems and discoloration problems due to aging. It has been said that the chromate film generated on the plating surface by this chromate treatment has excellent corrosion resistance and protects the galvanized surface, but it presents serious pollution problems, such as the treatment of waste liquid containing chromium, and measures to prevent it have been taken. However, if the concentration of the treatment liquid is too high, color unevenness will occur, reducing the commercial value, and if it is too thin, pinholes will occur and corrosion resistance will be deteriorated. There are many problems. In addition, the mechanical strength of the chromate film itself is poor, uneven discoloration is liable to occur at the exfoliated part of the chromate film, and the corrosion resistance of the chromate film itself is not yet sufficient. However, the reality is that even long ones are effective only for about two months.

To improve the luster of hot-dip galvanized products, use Al in the galvanizing bath.
It is known that the addition of a small amount of is effective. By adding a small amount of Al, it is possible to obtain a beautiful specular gloss immediately after plating, but discoloration appears early due to rainwater and dew condensation, and the effect of maintaining gloss for a long time is not recognized. Further, it has been proposed to increase the Al concentration to increase the corrosion resistance of the plating layer itself, but even in this case, it has a beautiful luster immediately after plating, but it is more likely to discolor more than before due to rainwater or condensation. Therefore, it cannot be a measure for maintaining gloss for a long time.

Under these circumstances, Japanese Examined Patent Publication No. 60-32700 has Al: 0.05-2%
And a zinc alloy for hot dip coating containing Mn: 0.01 to less than 0.1%. The purpose of this is to prevent the occurrence of intergranular corrosion of the plating film, which is the cause of this, as a countermeasure against the frequent occurrence of peeling phenomena in the plating film during bending. However, here, only the prevention of the occurrence of intergranular corrosion is concerned, and the problem of long-term gloss maintenance is not mentioned at all.

In this way, white rust and discoloration over time of hot dip galvanizing are inevitable, and they have been accepted as unavoidable in some cases by post-treatment such as chromate treatment at most.

(Problems to be Solved by the Invention) However, as a basic need, it is still required that white rust is unlikely to occur and that the gloss is maintained permanently for a long period of time. In addition, considering the enormous resource loss and facility investment loss due to iron rust that accompanies the further spread, the development of durable hot-dip galvanizing technology seems to be essential from now on. The post-treatment that has been conventionally performed has also been a factor that increases the price of hot-dip galvanized products, although it is not very effective. As mentioned at the outset, as the demand for hot-dip galvanized products for decorative applications grows, the problems of long-term gloss maintenance and tarnish prevention have to be solved. Conventionally, since there is little recognition of this problem, a practical solution has not been proposed yet.

Therefore, the problem of the present invention, in the dobbing hot-dip galvanizing, to the problem of the initial white rust generation and the discoloration due to aging, which is said to be the fate of hot-dip galvanizing, without resorting to post-treatment, practical The purpose is to develop a plating bath and a plating method for pickling dobu.

(Means for Solving the Problem) The inventors of the present invention, as a result of repeated studies aimed at the above-mentioned object, focused on the potential usefulness of the alloy bath containing Al and Mn described above, and confirmed that the initial white rust Research was repeated to convert and optimize discoloration due to generation and aging. As a result, it has been found that a combination of a trace amount of Al and a relatively large amount of Mn is effective for the purpose of the present invention. The optimum range was found to be Mn: 0.2-0.8% by weight and Al: 0.01-0.04% by weight.

Based on the above findings, the present invention is characterized in that 1) manganese and aluminum are added to a hot dip galvanizing bath so that the concentration range of manganese: 0.2 to 0.8% by weight aluminum: 0.01 to 0.04% by weight. , An alloy bath for hot-dip galvanizing hot-dip galvanizing that produces a long-lasting bright plating surface, and 2) after degreasing, pickling, and fluxing an iron and steel material in a hot dip galvanizing bath, manganese: 0.2- 0.8% by weight aluminum; Manganese and aluminum are added so that the concentration range is 0.01 to 0.04% by weight. Provided is a method of hot dip galvanizing which is characterized in that it produces a glittering plated surface having properties.

In the present invention, the “hot dip galvanizing bath” means a general hot dip galvanizing bath commonly used in the art, and the bath composition of the general hot dip galvanizing bath is one of the following and.

When using distilled zinc (zinc grade> 98.5%) as a raw material Zinc grade about 98.3% Lead grade about 1.2% Iron grade about 0.045% Aluminum grade 0 to 0.005% Others (total of components inevitable from distilled zinc etc. of raw materials) ) About 0.4% When using pure zinc (zinc grade> 99.99%) as the raw material Zinc grade about 99.95% Lead grade <0.003% Iron grade about 0.045% Aluminum grade 0-0.005% Others (from the pure zinc etc. of raw material) Inevitable total of about 0.01%) That is, in the present invention, manganese and aluminum are added to the hot-dip galvanizing bath of or, and the manganese grade is 0.2 to 0.8.
The present invention provides a new alloy bath for hot dip galvanizing which exhibits glitter by forming a composition having a weight percentage of aluminum and an aluminum grade of 0.01 to 0.04 wt%, and a plating method using the alloy bath.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to steel materials and parts in general that require a dullable and durable bright plated surface.

The pretreatment before hot dip galvanizing may be performed according to the conventional embodiment. For example, 10-15% NaOH or several% sodium silicate (Na ₂ O · nSiO ₂ ) solution is used to carry out alkaline degreasing at 60-80 ° C, followed by washing with water and 10-15% at room temperature. The fluxing treatment is carried out after pickling with HCl or a H ₂ SO ₄ solution at a temperature of 40 to 60 ° C. and washing with water. For the fluxing treatment, a special flux is not necessary and a general flux such as a halide can be used. For example, ZnCl ₂ : NH ₄ Cl = 1: 3 to 3:
A 30-40% solution of 1 (molar ratio) is used at a temperature of 70-80 ° C.

Incidentally, the hot dipped galvanized galvanizing is very different from the continuous hot dip galvanized in which the heating degreasing and the gas reduction steps are carried out only from the point of pretreatment.

After that, dope pickling is performed in the hot dip galvanizing bath using a hot dip galvanizing alloy bath in which manganese and aluminum are added so that the concentration range of manganese: 0.2 to 0.8 wt% aluminum: 0.01 to 0.04 wt%, Only by cooling with hot water or by allowing to cool, a permanent bright plated surface is generated without any post-treatment.

The raw material zinc for the hot dip galvanizing bath is distilled zinc (purity 9
8.5% level, including Pb, Fe, Cd) or pure zinc (purity 9
9.99% level) is applicable, but using pure zinc is more advantageous for maintaining gloss. Therefore, the bath composition of the hot dip galvanizing bath is either of the following and.

When using distilled zinc (zinc grade> 98.5%) as a raw material Zinc grade about 98.3% Lead grade about 1.2% Iron grade about 0.045% Aluminum grade 0 to 0.005% Others (total of components inevitable from distilled zinc etc. of raw materials) ) About 0.4% When using pure zinc (zinc grade> 99.99%) as the raw material Zinc grade about 99.95% Lead grade <0.003% Iron grade about 0.045% Aluminum grade 0-0.005% Others (from the pure zinc etc. of raw material) The total amount of inevitable ingredients is about 0.01%. The feature of the present invention is that the relatively large amount of Mn of 0.2 to 0.8% by weight and 0.01 to 0.04% by weight for the purpose of preventing discoloration due to initial white rust generation and aging. % Al in the range of
This is because the combination of the above was used as an additive. The suppression of white rust and the maintenance of high gloss have not been completely clarified because both Mn and Al added to the plating bath are metals that are more easily oxidized than zinc, but the light transmissivity on the plating surface It is considered that a certain complex oxide film is formed, and the gloss of the lower layer metal is maintained by this oxide film. In addition, manganese oxide is unlikely to be transformed by contact with moisture or carbon dioxide present in the atmosphere, and therefore it is considered that the presence of manganese oxide or a compound based on it causes the gloss to be maintained for a long time. The above range is optimum for forming the film for the purpose of the present invention. Addition
There is a close relationship between the amount of Mn and the amount of Al, and addition of Mn alone does not give high gloss, and the plated surface is colored variously, so Al is indispensable to prevent this coloring and add high gloss. It is an ingredient. The ratio of Mn content to Al content is 10: 1.
~ 30: 1, optimally 20: 1.

If the amounts of Mn and Al are less than the respective lower limits, the effect of maintaining glossiness is weak.

On the other hand, the upper limit of the amount of Mn and Al may be more useful for other purposes as shown in the section of the prior art, but when Mn exceeds 0.8% by weight, the bending of plated products For the purpose of preventing white discoloration and discoloration due to aging, since there is a risk that non-plating may occur because Al, which is necessary for preventing coloring, exceeds 0.04% by weight, etc. Was determined as the effective limit.

The synthesis bath of the above composition range, Mn and Al may be added individually to the molten zinc bath, separately prepared bath composition Mn-Al master alloy, Zn-Al master alloy, or Zn-Mn- Al
A mother alloy may be used.

The temperature of the plating bath is the same as the conventional temperature
0-460 ℃), Medium temperature (460-480 ℃), High temperature (480-520 ℃)
Can be used at a temperature suitable for isoplated materials. Bath temperature is 520 ℃
Although the plating is possible even if it exceeds the above, the necessity is not particularly recognized.

(Example) Hereinafter, an example and a comparative example are shown.

 The following various hot-dip galvanized products were prepared.

The most common plated product in the distilled zinc alone bath, the plated product in a bath in which 50 ppm of Al for improving gloss which has been conventionally generally performed in the distilled zinc bath is added, the distilled zinc bath according to the present invention Mn = 0.3% by weight and A
l = 0.015 wt% added alloy bath plated product, said pure zinc alone bath plated product, according to the present invention said pure zinc bath Mn = 0.25 wt% and
Plating products in alloy bath with Al = 0.012% by weight and importance of Mn amount
Plating products in an alloy bath containing 0.1% by weight and Al = 0.005% by weight, looking at the weight of Mn amount.
Brightness immediately after plating and outdoor test 1 for each plated product in alloy bath with 1 wt% and Al = 0.01 wt% addition
The glossiness was measured at the months and 3 months. The results are shown in the table below. For reference purposes, the table also shows an example of measuring the glossiness of a stainless plate.

In addition, the glossiness measurement is based on the reflectance, GS (20 °)
And the unit is% (standard piece glossiness 82%). The measuring instrument was manufactured by Nippon Denshoku Industries Co., Ltd., and the measuring method was in conformity with JIS Z-8741.

From these results, in general hot dip galvanizing using distilled zinc in the plating bath, the addition of aluminum sufficiently improves the gloss immediately after plating, but has no effect on maintaining the gloss in outdoor use. It can be seen that there is no white rust control effect at all.

On the other hand, as can be seen from the distilled zinc base alloy bath sample and the purest zinc base alloy bath sample of the present invention, when the alloy bath for hot dip galvanizing of the present invention is used, the finish immediately after plating is extremely high gloss, In addition, even in the outdoor exposure test, the same luster as that of stainless steel was maintained, and white rust and discoloration to gray did not occur, effectively achieving the initial purpose.

From the sample, it is also confirmed that the effect is not sufficient when the amount of Mn is insufficient.

The one using pure zinc as the raw material zinc is superior to the one based on distilled zinc in maintaining gloss.

(Effect of the invention) The hot-dip galvanized product according to the present invention does not require the chromate treatment that has been conventionally adopted as a white rust inhibiting method, and has a higher white rust inhibiting effect than before without such post-treatment. Although the glossiness will gradually decrease over time, it can be expected that stainless-like luster can be maintained for several years to several decades depending on the environment.

In this way, the economic burden is not increased and the ripple effect is large due to the fact that hot-dip galvanized products with excellent appearance can be supplied with the advantage of not requiring post-treatment, and indoor Contributing to the spread of hot-dip galvanized products in decorative applications such as. There is no need to change the conventional galvanized galvanizing process line.

Claims (2)

(57) [Claims] 1. Permanent bright plating, characterized in that manganese and aluminum are added to a hot-dip galvanizing bath in a concentration range of manganese: 0.2 to 0.8% by weight, aluminum: 0.01 to 0.04% by weight. An alloy bath for hot dip galvanizing that produces a surface. 2. Iron and steel materials are degreased with an alkaline solution, pickled and fluxed, and then, in a hot dip galvanizing bath, manganese: 0.2 to 0.8% by weight aluminum; manganese and aluminum to a concentration range of 0.01 to 0.04% by weight. The hot-dip galvanized galvanizing is characterized by producing a durable bright plated surface without post-treatment by immersing it in an alloy bath for hot-dip galvanizing in the temperature range of 440 to 520 ℃. Method.