JPH05287483A - Production of galvanized alloy coating object - Google Patents

Abstract

PURPOSE:To obtain the plated coating object having a smooth plating surface by maintaining the temp. of a plating bath in a specific range. CONSTITUTION:Iron and steel products are immersed into the bath contg. 0.10 to 10wt.% aluminum and 1.5 to 10wt.% copper and the balance consisting of zinc aside from inevitable impurities, by which the zinc aluminum alloy plating is applied on the surfaces thereof. The temp. of the plating bath is maintained in the range exceeding the solidification initiation temp. of the bath by 65 to 140 deg.C. As a result, the easy plating is executed without limitation even in such a case handling time is required and long-term immersion is involved as in large-sized steel products. The plated coating object having high practicability is thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-dip zinc alloy coating having a good appearance and a uniform plating thickness when forming a hot-dip zinc alloy coating on the surface of a steel material.

[0002]

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

The zinc aluminum alloy plating method includes degreasing or annealing a steel material, pickling or reducing the surface to clean the surface, and then performing a flux treatment or in a reducing atmosphere. Generally, a method of immersing in or passing through a hot dip bath is generally used. The dipping method in the hot dip plating bath can be roughly classified into the following two.
That is, (1) direct dipping method: a method of directly dipping in a molten zinc aluminum alloy bath, (2) indirect dipping method: zinc plating (both hot dipping method and electroplating method are possible) or metal plating, and then Is a method of dipping in a molten zinc aluminum alloy bath.

Good appearance and uniform plating thickness of these zinc aluminum alloy plated coatings are extremely important for practical use. Usually, in zinc plating, in order to obtain a good appearance and a uniform plating thickness, Fe-Z
It is necessary to suppress abnormal development of the n-alloy layer, and if the Fe-Al alloy layer develops rapidly, thick plating causes poor appearance such as burns, surface roughness, and peeling, and uniform plating cannot be obtained. The plating is worthless. Therefore, 0.1 to 0.1% aluminum is added to the plating bath.
Fe-Zn of aluminum containing about 0.5% by weight
Utilizing the alloying reaction suppression effect.

Up to now, in zinc plating, Fe-Z
Attempts have been made to add a trace amount of nickel of 1% by weight or less to a galvanizing bath for the purpose of controlling the n alloy layer. However, in the current situation, there is almost no study example for controlling the Fe-Al alloy layer in zinc aluminum alloy plating except silicon. Further, there is an example of adding a trace amount of copper in an amount 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 this amount of addition.

Further, when the aluminum concentration is 7 to 60% by weight, since the plating is of no commercial value due to the abnormal development of the Fe-Al alloy layer, silicon corresponding to 3 to 5% by weight of the aluminum content is obtained. Can be contained in the plating bath to suppress the development of the Fe-Al alloy layer. The suppression effect of silicon is also exhibited in aluminum of 3 to 7% by weight. However, due to this suppressing effect, the Fe-Al alloy layer hardly grew, and the corrosion resistance, which is an advantage of zinc aluminum plating, could not be obtained.

Conventionally, it has been considered desirable that the bath temperature be 20 to 50 ° C. higher than the melting point of the bath in the case of direct plating in zinc plating and zinc aluminum plating. However, under such conventional conditions, when the immersion time of the steel material becomes long, nonuniform plating thickness or poor appearance often occurs. For this reason, the immersion time must be suppressed within 5 minutes, which is difficult to apply to large steel materials and the like.

An object of the present invention is to provide a method capable of producing a zinc aluminum alloy plated coating which has a uniform plating thickness and does not cause a poor appearance even after a long immersion time such as 10 minutes.

[0009]

[Means for Solving the Problems] As a result of intensive studies made by the present inventors in order to solve the above problems, as a result, a zinc-aluminum alloy plating coating that has a uniform plating thickness and does not cause a poor appearance even during a long immersion time. In order to obtain a product, it has been found that the bath temperature is an extremely large factor, and the present invention has been completed. A characteristic of the present invention is that the steel material is made of aluminum in an amount of 0.10 to 10% by weight and Copper 1.5
10 to 10% by weight, the remainder being immersed in a bath consisting of zinc except for inevitable impurities, and when the surface is plated with a zinc aluminum alloy, the temperature of the plating bath is 65 to 140 ° C. higher than the solidification start temperature of the bath. To keep it in range.

That is, according to the present invention, when a steel material is immersed for a long time of more than 5 minutes, the development of the Fe-Zn-Al-Cu alloy layer is in the range of 50 to 60 ° C from the solidification temperature of the bath, and from the solidification temperature. Based on the finding that the temperature is very high in the range over 140 ° C, the bath temperature should be 65 to 140
℃ higher, for stability of plating, preferably 70-130 ℃ higher than the solidification temperature of the bath, the growth of the Fe-Zn-Al-Cu quaternary alloy layer is suppressed, A plated coating having a uniform plating thickness and a good appearance can be obtained. This is because the steel base of the steel material reacts with Zn-Al-Cu, which is the object to be plated, to form a quaternary alloy layer of Fe-Zn-Al-Cu, resulting in a uniform plating thickness. This is because it becomes possible to keep it.

[0011]

According to the present invention as described above, it is possible to maintain a uniform plating thickness and to obtain a plated coating having a smooth plating surface without causing a defective appearance called burn. Further, it has the same effect in long time immersion such as more than 10 minutes. Therefore, even if it takes a long handling time like a large steel material and long immersion time, plating can be easily performed without limitation. A highly practical plated coating can be obtained.

[0012]

Example 1 Rolled steel for general structure (SS 41) of 50 W × 100 L × 3.2 Tmm and low carbon SPCC cold rolled steel plate of 0.3 mm thickness were used as materials, and alkali degreasing (sodium orthosilicate was used as a pretreatment. 20 wt% aqueous solution, 80
C., 10 minutes) -Washing-Pickling (hydrochloric acid 10 wt% aqueous solution, room temperature, 20 minutes) -Water washing-Flux treatment (JP-B-64-5)
110 steps of a 30 wt% flux aqueous solution for Zn-Al plating, 90 ° C., 1 minute) -drying were sequentially performed.

Next, using the baths and bath temperatures having the compositions shown in Table 1, immersion was performed in the atmosphere for 8 minutes for plating.

[0014]

[Table 1]

[0015]

Example 2 Al 4.0%, Cu 5.1% as a bath, a composition consisting of Zn except for the remaining impurities (solidification temperature 430
(° C), the bath temperature and the immersion time were changed to perform plating. The results are shown in FIG. 1 and Table 2.

[0016]

[Table 2]

From the above table and the results shown in FIG. 1, in producing the zinc aluminum alloy plated coating, the bath temperature was maintained at a range of 65 to 140 ° C. higher than the solidification temperature of the bath, so that the plating thickness was uniform and the appearance was improved. It is understood that a good plated coating can be obtained.

[Brief description of drawings]

FIG. 1 is a relationship diagram of a plating bath temperature of 4% Al-5% Cu-Zn, a plating thickness, and a plating appearance defect.

Claims (1)

[Claims] 1. A steel material comprising aluminum 0.10 to 1
0% by weight and 1.5 to 10% by weight of copper, the balance being immersed in a bath consisting of zinc except for unavoidable impurities to apply zinc aluminum alloy plating on the surface thereof, the temperature of the plating bath is set to the solidification of the bath. A method for producing a hot dip galvanized alloy coating, which is maintained in a range of 65 to 140 ° C. higher than the starting temperature.