JP3009269B2 - Hot-dip zinc alloy plating coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized alloy coating of a steel material, and more particularly to a hot-dip zinc alloy-plated coating having a good appearance and obtaining a thick coating having good corrosion resistance.

[0002]

2. Description of the Related Art In recent years, zinc-aluminum alloy plating has attracted attention because of its higher corrosion resistance than zinc plating, and has been widely used in outdoor applications such as building materials, suspension wires, and overhead wire hardware. It is positioned as a rust prevention method for steel materials in severe corrosive environments such as oceans, coastal areas and hot spring areas, and when maintenance-free is required.

[0003] As a method of zinc-aluminum alloy plating, a steel material is degreased or annealed, pickled or reduced to clean the surface, and then subjected to a flux treatment or to a reduction atmosphere. Generally, a method of immersing or passing through a hot-dip plating bath is used. The immersion method in the hot-dip plating bath can be roughly classified into the following two methods.
(1) Direct immersion method: Direct immersion in a hot-dip zinc aluminum alloy bath, (2) Indirect immersion method: Once zinc plating (both hot-dip plating and electroplating are possible) or metal plating, and then Immersion in a molten zinc aluminum alloy bath.

Generally, the relationship between the plating thickness of zinc plating or zinc aluminum alloy plating and the corrosion resistance is proportional, and the thicker the plating thickness, the longer the time until the appearance of rust on the base steel material becomes, and the higher the corrosion resistance. For this reason, zinc aluminum alloy plating is the same plating thickness and zinc plating 3
Even if the corrosion resistance is doubled, the corrosion resistance is the same if the plating thickness is only 1/3 of the zinc plating. Therefore, to exhibit high corrosion resistance, a thickness similar to that of zinc plating is required. In hot-dip galvanizing or zinc-aluminum alloy plating, the factors that determine the plating thickness are the wet adhesion and viscosity of the plating bath, and Fe-Zn, Fe-Al or Fe-Al-Zn generated at the interface between the steel and the plating layer.
The thickness of the intermetallic compound layer (alloy layer), the pulling speed from the plating bath, the wiping conditions of the plating layer until the molten coating layer cools and solidifies, and the cooling conditions.

In general, in the case of zinc plating or zinc aluminum alloy plating, the wet adhesion and viscosity of the plating bath are almost uniquely determined by the composition and temperature of the plating bath, and therefore are difficult to change. Although it is possible to increase the plating thickness to some extent by increasing the pulling speed from the plating bath (for example, increasing the line speed),
Due to vibration or the like, it is difficult to obtain a uniform thickness. Further, the pulling speed can be easily changed in continuous plating of a long material such as a steel plate or a steel wire, but the pulling speed cannot be easily changed in batch immersion plating. The wiping and cooling conditions after pulling up the plating bath are incidental, and the plating thickness is determined at the time of pulling up. It is a way to be. For this reason, the overall plating thickness is generally controlled by controlling the thickness of the alloy layer generated at the interface between the steel and the plating layer.

For example, in zinc plating, Fe-Z
An n-alloy layer is formed at the interface. The alloy layer thickness is substantially determined by the type of steel, the plating bath temperature, and the immersion time of the steel material in the plating bath. The alloy layer thickness can be increased by increasing the plating bath temperature or increasing the immersion time.
Therefore, a thick plating of 30 μm or more is easily possible by zinc plating. Further, when used in applications requiring workability such as galvanized steel sheets, it is necessary to suppress the development of the Fe-Zn alloy layer, and therefore, aluminum is contained in the plating bath by 0.1 to 0.5. The plating thickness is suppressed to 10 to 30 μm by using the effect of suppressing the Fe—Zn alloying reaction of aluminum by containing about% by weight.

On the other hand, the behavior of zinc aluminum alloy plating changes greatly depending on the Al concentration in the bath. In the case of an aluminum concentration of about 3 to 7% by weight, which is commonly used, the most common plating bath temperature is relatively low.
In a relatively short immersion time of 30 to 460 ° C. and the immersion time is also within 3 minutes, the above-mentioned aluminum Fe-Z
The development of the Fe—Zn alloy layer is suppressed by the n-alloying reaction suppressing action, resulting in thin plating of less than 30 μm.
At this time, if the plating bath temperature is set to 460 ° C. or higher, or the immersion time is extended, the Fe—Al alloy layer rapidly develops, and thick plating involves appearance defects such as burns, surface roughness, and peeling. The plating will have no commercial value.

[0008] When the aluminum concentration is 7 to 60% by weight, the plating becomes of no commercial value due to the abnormal development of the Fe-Al alloy layer. Therefore, silicon corresponding to 3 to 5% by weight of the aluminum content is used. Can be contained in the plating bath to suppress the development of the Fe-Al alloy layer. The effect of suppressing silicon is exerted even at 3 to 7% by weight of aluminum. However, due to this suppression effect, the Fe—Al alloy layer hardly grows, resulting in a thin plating of less than 30 μm.

Hitherto, in zinc plating, Fe-Z
Attempts have been made to add a small amount of nickel of 1% by weight or less to a zinc plating bath for the purpose of controlling the n-alloy layer. However, at present, there is almost no study for controlling the Fe-Al alloy layer in zinc aluminum alloy plating except for silicon. In addition, there is an example of adding a trace amount of copper of 1% by weight or less for the purpose of improving corrosion resistance in zinc aluminum alloy plating, but it is not possible to control the Fe-Al alloy layer with such an added amount.

As described above, in zinc aluminum alloy plating, it was difficult to obtain a good-appearance thick plating of 30 μm or more by the direct immersion method. Therefore, conventionally, 30 μm
When obtaining a zinc-aluminum alloy plating having a thickness of at least m, zinc plating is performed once, a Fe-Zn alloy layer is developed, and a required plating thickness is secured. Therefore, the indirect immersion method of forming a plating layer composed of a Zn—Fe—Al ternary alloy layer and a zinc aluminum alloy layer by replacing zinc and a zinc aluminum alloy in a plating layer or by diffusing aluminum must be used. Was. However, the indirect immersion method requires a plurality of plating baths, which complicates the process. For example, it is necessary to take measures against changes in the aluminum concentration of the zinc aluminum alloy bath and fluctuations in the level of the molten metal. In addition, a measure for avoiding mixing of aluminum into the zinc bath is required. Therefore, there is a strong demand for a method of obtaining a zinc-aluminum alloy plating having a thickness of 30 μm or more and a good appearance and high commercial value by a simple and inexpensive direct dipping method.

According to the present invention, it is possible to obtain a hot-dip zinc alloy alloy having a thickness of 30 μm or more, a good appearance and a high commercial value by a direct immersion method which has been impossible in the past. It is an object of the present invention to provide a simple and inexpensive high corrosion-resistant hot-dip galvanized aluminum alloy plating coating which overcomes the disadvantages of the method.

[0012]

Means for Solving the Problems The hot-dip zinc alloy plating coating of the present invention contains 0.10 aluminum in a plating bath.
In a zinc-aluminum alloy plating consisting of zinc except for unavoidable impurities, the plating bath contains 1.5 to 10% by weight of copper so that the thickness is 30 μm or more, and This problem has been solved by forming thick plating with good appearance.

According to the present invention, in a zinc-aluminum alloy plating containing 0.10 to 10% by weight of aluminum in a plating bath and the remainder excluding unavoidable impurities, plating of 30 μm or more by direct immersion method In order to obtain a thick zinc-aluminum alloy plating, various additives were added to the plating bath, and the effects of the addition on the plating thickness and the alloying reaction at the interface of the steel substrate were obtained as a result of earnest examination. According to the study, it is very effective to contain 1.5 to 10% by weight of copper in the plating bath in order to obtain a plating having a good appearance and a uniform thickness of 30 μm or more. understood.

That is, if copper is less than 1.5% by weight, Fe
When the control of the Al alloy layer cannot be performed and the thin plating of less than 30 μm or the poor thickness plating in which the Fe-Al alloy layer has abnormally developed occurs, the effect of the addition of copper does not appear. The melting point becomes high, the bath must be kept at a high temperature, and the cost increases and waste occurs.

In the present invention, the object to be plated is not particularly limited as long as it is a steel material to be subjected to zinc-aluminum alloy plating. However, since the plating thickness varies depending on the steel type, it is necessary to determine plating conditions in advance according to the steel type. Pretreatment of the steel material is performed by a known method. When plating in air, flux treatment is required,
In this case, it is necessary to use a flux for zinc aluminum alloy plating as disclosed in JP-B-64-5110. With a normal zinc plating flux, there is no wettability at the time of plating, resulting in non-plating.

The plating bath has only to have the composition of the present invention, and the mixing method may be any method. For example, zinc,
Aluminum or copper may be mixed alone, or a zinc aluminum alloy and copper, or a zinc-copper alloy may be used. In addition, magnesium, sodium, misch metal, generally added in zinc aluminum alloy plating,
Lanthanum or cerium may be further added. Since the melting point of the plating bath composition changes, the temperature of the plating bath cannot be unambiguously determined, but is desirably in the range of the melting point +20 to 50 ° C. The immersion time may be the same as that of general hot-dip plating. Since the plating thickness is determined by a combination of the plating bath temperature and the immersion time, it is necessary to determine the plating bath temperature and the immersion time in advance according to the target plating thickness. Known methods can be applied for pulling and cooling after plating.

In the present invention, the reason for setting the range of aluminum in the plating bath to 0.10 to 10% by weight is as follows. That is, usually, aluminum 0.10
When the content is less than 0.1% by weight, the alloy layer formed at the interface between the plating layer and the steel material is made of an Fe-Zn intermetallic compound (typically, ζ, δ ₁ phase). An alloy layer forms. From this, in the present invention, the lower limit of aluminum is set to 0.1% by weight in order to control the Fe-Al alloy layer. Further, when the content of aluminum exceeds 10% by weight, copper Fe-A
Although the effect of controlling the alloy layer is recognized, the melting point is increased and high-temperature plating is performed, so that the practical use value is reduced. Therefore, the upper limit of aluminum is set to 10% by weight, but the present invention can be applied to Al of 10% by weight or more.

The plating bath temperature and immersion time used in the embodiments of the present invention are selected from the type, shape, quantity and industrial value of the plating material, and the higher temperature or the immersion time is shortened or extended. Is the type, shape,
It is a factor that changes as appropriate according to the change in the quantity, and the plating bath temperature and the immersion time are not constraints of the present invention.

Not only in plating but also in various processes such as smelting, melting, blending, alloy production, casting such as die casting using a zinc aluminum alloy, and use in a mold, iron, stainless steel are used as pots, jigs and stirrer materials. There are many opportunities to use products made from these products. In this case, since copper is added in the present invention,
This copper has an ancillary effect of suppressing the elution of iron and steel into the molten zinc aluminum alloy and the corrosion reaction.

[0020]

According to the present invention as described above, if the components of the plating bath are controlled, the plating bath temperature and the immersion time can be kept constant in one plating bath (direct immersion method) as in the case of zinc plating. By doing so, a zinc-aluminum alloy plating can be obtained without requiring advanced operations and special operations, without unevenness or poor appearance, and without impairing plating quality such as corrosion resistance. In addition, as a result of obtaining a uniform thick zinc aluminum plating, in addition to the effect of aluminum,
High corrosion resistance can be stably obtained by the effect of the increase in plating thickness.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Rolled steel for general structure (SS 41) of 50 W × 100 L × 3.2 Tmm and low carbon S of 0.3 mm thickness
PCC cold-rolled steel sheet was used as a raw material, and pre-treatment was performed using alkali degreasing (sodium orthosilicate 20 wt% aqueous solution, 80 wt.
10 ° C.)-Washing-Pickling (10 wt% aqueous hydrochloric acid, room temperature, 20 minutes) -Washing-Flux treatment (Japanese Patent Publication No. 64-5)
Each step of 110-30 wt% flux aqueous solution for Zn-Al plating, 90 ° C., 1 minute) -drying was sequentially performed.

Next, plating was carried out in the air under the following conditions using baths having the compositions shown in the following table. Plating bath temperature 430-500 ° C Immersion time 0.5-5 minutes Pulling speed 5-10m / min Cooling speed 10-20 ° C / sec

After plating, the thickness of the plating layer was measured by a magnetic force type thickness gauge and observation of the plating layer cross section with a microscope. The plating appearance was visually evaluated by the following three-step evaluation. ：: good (no burns and roughness) △: some burns and roughness ×: burnt and bad

Further, a salt spray test was conducted in accordance with JISZ2371 to examine the time until red rust appeared on the steel base, and to examine the corrosion resistance of the plating layer. These results are also shown in Table 1.

[0025]

[Table 1]

From the results shown in the above table, it can be seen that a stable thick plating is obtained in the zinc aluminum alloy plating, and at the same time, high corrosion resistance is exhibited.

[Brief description of the drawings]

FIG. 1 is a photomicrograph showing thin normal plating containing no copper at 400 × magnification.

FIG. 2 is a photomicrograph showing thick abnormal plating containing no copper at 400 × magnification.

FIG. 3 is a photomicrograph showing thick normal plating containing copper according to the present invention at 400 × magnification.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-110658 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein the plating bath contains aluminum of 0.10 to 0.10.
In a zinc-aluminum alloy plating containing 10% by weight and the balance being zinc except for unavoidable impurities, a plating bath contains 1.5 to 10% by weight of copper, a thickness of 30 μm or more, and a good appearance. A hot-dip galvanized alloy coating comprising a thick plating.