JP3811109B2 - Hot-dip zinc-aluminum alloy plating method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot dip zinc-aluminum alloy plating method for performing zinc-aluminum alloy plating on the surface of a steel material.
[0002]
[Prior art]
Conventionally, in order to prevent corrosion of steel materials used for building materials, automobile parts, general structural members, etc., hot dip galvanization and hot dip zinc-aluminum alloy plating have been applied to steel materials. In particular, in recent years, in order to prevent the effects of environmental degradation, the demand for hot-dip zinc-aluminum alloy plating with higher corrosion resistance has increased, and there are a wide variety of products that require hot-dip zinc-aluminum alloy plating. ing.
[0003]
As a general method of such hot dip zinc-aluminum alloy plating, there is a method called a two-bath method disclosed in Japanese Patent No. 2924894. This two-bath method is a method in which a steel material is immersed in a zinc bath and galvanized, and then the galvanized steel material is immersed again in a zinc-aluminum alloy bath for plating. As another method, a method of performing molten zinc-aluminum alloy plating of a steel material by a single dipping using a molten salt as a flux in a pretreatment stage of a steel material plating step has been put into practical use.
[0004]
[Problems to be solved by the invention]
However, the two-solution method of hot dip zinc-aluminum alloy plating requires two plating tanks, and there is a problem that the facility is large. Further, it is very difficult to perform zinc-aluminum alloy plating on a 10 m class large structure, and it is almost impossible to perform such plating in view of the finished quality. There is no plating tank that can handle 10m class large structures, and it is difficult to set plating conditions (plating temperature, immersion time) for large structures, and it can handle non-plating (no plating). (In the case of zinc plating, re-dipping is applied when non-plating occurs, but in the case of zinc-aluminum alloy, re-dipping does not result in plating, and the surface condition deteriorates.) .
[0005]
On the other hand, the method using the molten salt flux requires a step of pickling and removing the molten salt flux adhering to the plating surface, and requires a washing tank for that purpose. Therefore, it is necessary to make a corresponding capital investment, and there is a problem that efficiency decreases and costs increase due to an increase in the number of processes.
[0006]
Further, the hot dip galvanized layer applied to the steel material is strengthened by forming a zinc-iron alloy layer between the plated layer and the iron base by an alloying reaction of zinc and iron, and further, a zinc-aluminum alloy. By reacting with the molten metal, an aluminum-iron alloy layer and a zinc-aluminum-iron alloy layer are formed. Therefore, it is a problem how to react the hot dip galvanized layer and the molten zinc-aluminum alloy, but it is difficult to immerse the steel in the molten zinc-aluminum alloy as described above. Other methods are required.
[0007]
Therefore, in view of such a conventional problem, the present invention can prevent a decrease in efficiency and an increase in cost due to an increase in the number of processes, and can easily and reliably apply zinc-aluminum alloy plating to a large steel material. An object is to provide a zinc-aluminum alloy plating method.
[0008]
[Means for Solving the Problems]
As a result of diligent research to solve the above problems, the present inventors performed galvanization on the surface of the steel material in advance, heated the plated surface to a temperature at which the plated surface can react, By pouring the molten aluminum alloy, it was found that a highly corrosion-resistant aluminum-iron alloy layer and zinc-aluminum-iron alloy layer free from surface irregularities and burns were formed, and the present invention was completed.
[0009]
That is, in the hot dip zinc-aluminum alloy plating method according to the present invention, the surface of a steel material is galvanized and solidified, and then heated to a temperature (420 ° C.) or higher at which the plated layer can be in a molten state. holding, zinc on the surface of the steel zinc plated - characterized by sprinkle the molten aluminum alloy.
[0010]
In this molten zinc-aluminum alloy plating method, it is preferable that the molten zinc-aluminum molten metal contains 1 to 60 wt% of aluminum, and the balance contains zinc. Furthermore, it is preferable that the molten zinc-aluminum melt contains 0.1 to 3 wt% of at least one selected from Mg, Si, Ni and Bi. Moreover, it is preferable that the temperature of molten zinc-aluminum molten metal is 420-650 degreeC.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the embodiment of the hot dip zinc-aluminum alloy plating method according to the present invention, after the galvanization is performed on the surface of the steel material and the plating is solidified, the temperature at which the zinc layer on the plating surface can be in a molten state (420 ° C. ) or higher. heated to and held in, zinc four hundred twenty to six hundred and fifty ° C. on the surface of the steel zinc plated - by subjecting pouring molten aluminum alloy, the molten zinc steel - subjecting an aluminum alloy plating.
[0012]
As a method of performing hot dip galvanizing on the outer surface of a steel pipe, a method of pouring molten zinc on the steel surface has already been proposed, but in the embodiment of the hot dip zinc-aluminum alloy plating method according to the present invention, it has been conventionally considered difficult. It is possible to continuously perform hot dip zinc-aluminum alloy plating of large structures and large steel pipes.
[0013]
In addition, in the conventional method of immersing the object to be plated in the molten zinc-aluminum alloy, the size of the object to be plated is limited by the size of the plating tank, but the hot dip zinc-aluminum alloy plating method according to the present invention is implemented. If it is the method of pouring a zinc-aluminum alloy molten metal like a form, it will become possible to apply | coat continuously, without being influenced by the magnitude | size of a plating tank.
[0014]
In the embodiment of the hot dip zinc-aluminum alloy plating method according to the present invention, after a normal hot dip galvanizing step such as degreasing, pickling, flux treatment, galvanizing, etc., a step of preheating and pouring molten zinc-aluminum alloy is performed. After that, wiping and cooling are performed to obtain a final product.
[0015]
In the embodiment of the hot dip zinc-aluminum alloy plating method according to the present invention, it is preferable that the hot dip zinc-aluminum molten metal contains 1 to 60 wt% of aluminum, and the balance contains zinc. The reason why the aluminum concentration is 1 to 60 wt% is that the corrosion resistance obtained is not changed when it exceeds 60 wt%, but the melting point of the alloy is increased due to the increase in concentration, while the workability is deteriorated. This is because the effect of maintaining the corrosion resistance is diminished.
[0016]
Furthermore, it is preferable that the molten zinc-aluminum melt contains 0.1 to 3 wt% of at least one selected from Mg, Si, Ni and Bi. The reason for adding Mg, Si, Ni, Bi is that workability, adhesion, hot water flowability, etc. are improved, and the reason for setting these concentrations to 0.1-3 wt% is 0.1 wt%. On the other hand, if the ratio is less than 3 wt%, the effect is reduced. On the other hand, if it exceeds 3 wt%, the workability is deteriorated and the quality is adversely affected (there may be cracking during bending, and the occurrence of sagging is also considered. )
[0017]
【Example】
Hereinafter, examples of the hot dip zinc-aluminum alloy plating method according to the present invention will be described in detail.
[0018]
[Example 1]
As a test piece, an SS material plate (100 × 70 × 3.2 mm) of a general structural material was prepared. This test piece is immersed in an aqueous NaOH solution at 70 ° C. for 10 minutes for degreasing, washed with water, immersed in an HC1 solution for 60 minutes, pickled, rinsed with water, immersed in a flux solution at 70 ° C. for 1 minute, and dried. And galvanizing was performed by immersing in a zinc bath at 440 to 470 ° C. for 5 to 10 minutes. In addition, the bath which melt | dissolved the electrolytic zinc ingot was used as a zinc bath.
[0019]
The galvanized plate was suspended in an electric heater and heated until the surface temperature reached 430 ° C. (a temperature at which the zinc layer on the plating surface could be in a molten state (420 ° C.) or higher).
[0020]
Next, a 420-450 ° C. molten zinc-aluminum alloy consisting of 5 wt% Al and the balance zinc was poured onto the plate taken out from the electric heater (contact time was about 10 seconds). In addition, the electrozinc ingot was used as zinc used for a zinc-aluminum alloy molten metal.
[0021]
Observation of the plating state of the plate plated with zinc-aluminum alloy in this way revealed that the surface was uneven, burned (due to the influence of impurities in the steel to be plated, the plating temperature being too high, etc. -The Fe alloy layer grew abnormally and the plated surface turned gray), and there was no unplating or sagging, and the plating state was good.
[0022]
[Example 2]
Except for pouring a 530-570 ° C molten zinc-aluminum alloy consisting of 30 wt% Al and the balance zinc, zinc-aluminum alloy plating was carried out in the same manner as in Example 1; No plating, no sagging, and no plating were observed.
[0023]
[Example 3]
Zinc-aluminum alloy plating was performed in the same manner as in Example 1 except that a molten zinc-aluminum alloy at 610 to 650 ° C. consisting of 55 wt% Al, 1.6 wt% Si, and the balance consisting of zinc was poured. However, there were no surface irregularities, burns, non-plating, or sagging, and the plating state was good.
[0024]
[Example 4]
Zinc-aluminum alloy plating was performed in the same manner as in Example 1 except that 5 wt% Al, 1 wt% Mg, and the balance zinc-aluminum molten metal were poured. No plating, no sagging, and no plating were observed.
[0025]
[Example 5]
Zinc-aluminum alloy plating was performed in the same manner as in Example 1 except that 5 wt% Al, 1 wt% Ni, and the balance zinc-aluminum molten metal was poured. No plating, no sagging, and no plating were observed.
[0026]
[Example 6]
Zinc-aluminum alloy plating was performed in the same manner as in Example 1 except that 5 wt% Al, 1 wt% Bi, and the balance zinc-aluminum molten metal was poured. No plating, no sagging, and no plating were observed.
[0027]
【The invention's effect】
As described above, according to the hot dip zinc-aluminum alloy plating method of the present invention, it is possible to prevent a decrease in efficiency and an increase in cost due to an increase in the number of steps, and to easily and reliably apply zinc-aluminum alloy plating to large steel materials. Can do.

Claims (5)

After galvanizing the surface of the steel material and solidifying the plating, the galvanized layer is heated to a temperature higher than the temperature at which it can be melted and held, and the zinc-aluminum alloy molten metal is applied to the surface of the galvanized steel material. A hot dip zinc-aluminum alloy plating method, wherein: 2. The hot dip zinc-aluminum alloy plating method according to claim 1, wherein the molten zinc-aluminum molten metal contains 1 to 60 wt% of aluminum, and the remainder contains zinc. The molten zinc-aluminum alloy plating method according to claim 2, wherein the molten zinc-aluminum molten metal contains 0.1 to 3 wt% of at least one selected from Mg, Si, Ni and Bi. . The hot dip zinc-aluminum alloy plating method according to any one of claims 1 to 3 , wherein a temperature at which the zinc layer on the plating surface can be in a molten state is 420 ° C. The hot-dip zinc-aluminum alloy plating method according to any one of claims 1 to 4, wherein the molten zinc-aluminum molten metal has a temperature of 420 to 650 ° C.