JPS61288039A - Zinc alloy for zinc hot dipping having crystal - Google Patents

Abstract

PURPOSE:To obtain a Zn alloy suitable for use as plating bath in manufacture of a zinc hot-dipped steel sheet presenting a spangle-accentuated clear and attractive appearance by providing an alloy made by incorporating specific amounts of Al and Bi to Zn. CONSTITUTION:The zinc alloy has a composition consisting of 0.1-0.5wt% Al, 0.01-0.1wt% Bi and the balance Zn with inevitable impurities, in which the total content of the inevitable impurities is regulated to <0.01wt%. Zinc hot dipping is applied to the steel sheet surface by the use of a plating bath of the above zinc alloy.

Description

[Detailed Description of the Invention] The present invention relates to a crystalline hot-dip galvanized steel sheet, particularly a crystal pattern (
This invention relates to a zinc alloy used as a plating bath to produce hot-dip galvanized steel sheets exhibiting spangles and a clear appearance.

Bloody blood! Traditionally, hot-dip galvanized steel sheets have been used in a wide range of fields such as automobiles and home appliances, but in recent years, with the diversification of their uses, emphasis has been placed on the so-called spangles on the galvanized layer. There is an increasing demand for hot-dip galvanized steel sheets that exhibit a clear and beautiful appearance. Therefore, if such hot-dip galvanized steel sheets can be provided, wide demand can be expected.

Conventionally, crystalline hot-dip galvanized steel sheets have been produced in which crystals are formed in the plating layer of hot-dip galvanized steel sheets, but the plating bath used for this production is usually made of a zinc alloy containing AI and PB. In this case, AI is added to improve the adhesion of the plating layer to the steel substrate, and PB is added to increase the appearance of spangles.

Therefore, the content (quality) of AI in the plating bath is 0.
Approximately 2 to 0.5% by weight, PB content (grade) is 0.1
~0.2% by weight is generally used,
If the content is increased to around the upper limit of 0.5% by weight for the purpose of improving the adhesion, the appearance and expansion of spangles caused by PB will be suppressed or prevented, and the appearance of spangles on galvanized iron sheets may become unclear. Therefore, there are drawbacks that reduce the product value. Furthermore, in this case, if the content is increased to more than 0.2% by weight in order to promote the effect of spangles caused by PB, the adhesion of the plating layer will be reduced and intergranular corrosion will be promoted.

Therefore, using a plating bath consisting of molten zinc containing AI and PB, which is conventionally used in the production of crystalline hot-dip galvanized steel sheets, it is difficult to emphasize the spangles described above and achieve a clear and beautiful appearance. It is actually difficult to obtain a hot-dip galvanized steel sheet that exhibits the following properties.

is trying to do so. In view of the above-mentioned situation, the inventors of the present invention investigated plating baths that can produce the above-mentioned spangles in the galvanized layer in hot-dip galvanized steel sheets. By using a zinc base metal from which impurities such as PB and Cds Fes Sn, which have a negative effect on the adhesion of the plating layer, are removed as much as possible from the plating bath composition, the adhesion of the plating layer is good.
Moreover, the present inventors have discovered that it is possible to produce an accentuated spangle, and have completed the present invention.

Therefore, an object of the present invention is to provide a zinc alloy that can be used as a plating bath in the production of hot-dip galvanized steel sheets that exhibit a clear and beautiful appearance with accentuated spangles.

The present invention will be explained in detail below.

The present invention is characterized by a zinc alloy for crystalline hot-dip galvanizing, which contains 1 to 0.5% by weight of AtO, and 0.01 to 0.1% by weight of Bi, and further contains PB,
The total content of impurities such as Cd, Fe, and Sn that are unavoidably mixed in zinc is less than 0.01% by weight.

The total content of such unavoidable impurities is 0.01% by weight
Zinc with a purity of less than 0.0% is defined as a zinc ingot specified by JIS H2107 with a zinc purity higher than special zinc, and the impurity contained in the zinc ingot is, for example, Pb 0.0.
0.07 wt% or less, and CdO, 0.04 wt% or less.

In the present invention for fortune-telling, the above-mentioned high-purity zinc metal is used,
Add aluminum (AI) 0.1 to 0.5% by weight
and bismuth (Bi) at a bath temperature of 4.
After the steel plate is immersed for a short time at about 50 to 470°C, it is taken out of the double bath, left to cool in the atmosphere for a short time, and then cooled with hot water. Next, the obtained hot-dip galvanized steel sheet is immersed in an aqueous solution of hydrochloric acid or the like to etch the plating film, thereby obtaining a crystalline hot-dip galvanized steel sheet with clear and beautiful spangles.

Next, the effects of AI and aluminum and their contents in the zinc alloy according to the present invention will be explained.

1) Function and content of A1: As mentioned above, AI has the function of ensuring the adhesion of the hot-dip galvanized layer to the steel substrate, but the A1 content in the plating bath consisting of the hot-dip zinc alloy is If it is less than 0.1% by weight, it inhibits the uniform formation of the Fe-Al-Zn alloy layer necessary to ensure the above-mentioned adhesion of the plating layer, and also inhibits the growth of the Fe-Zn alloy layer, which is brittle against workability. This is not desirable because it encourages On the other hand, if the content exceeds 0.5% by weight, the amount of AI liberated within the plating layer increases, which in turn promotes embrittlement of the plating layer over time.

For these reasons, in the present invention, the AI content in the zinc alloy is specified to be 0.1 to 0.5% by weight.

2) Effect and content of Bi: Bi has a strong spangle expression effect, but
If the Bi content in the plating bath is less than 0.01 ffi amount%, the spangle expression effect is insufficient;
．． If it exceeds 1% by weight, the spangles will become coarse and the plating film will have an uneven surface.As a result, the plating film will be prone to scratches (and cracks will easily form from the spangle grain boundaries, resulting in poor plating). This will encourage corrosion of the layer.

Therefore, in the present invention, the Bi content in the zinc alloy is reduced to 0.
．． 01 to 0.1% by weight.

In addition, in the present invention, it is preferable to reduce the content of impurities such as Pb, Cd, and Sn in the plating bath as much as possible, which are involved in promoting embrittlement of the molten zinc alloy plating layer.
As mentioned above, by using high-purity zinc metal,
The total content of these impurities is less than 0.01% by weight.

According to the present invention, AI 0.1-0.5M
When a steel plate is plated using a hot-dip galvanizing bath made of a zinc alloy containing 0.01 to 0.1% by weight of Bi, the adhesion of the plating layer to the steel base is good and It is possible to obtain a crystalline hot-dip galvanized steel sheet with spangles and a clear and beautiful appearance without deterioration of the plating.

Furthermore, by changing the content of AI and Bi in the plating bath within the above range, the size of the spangles that appear can be adjusted arbitrarily, so for example, it is possible to adjust the size of the spangles that appear in the plating bath. It is possible to provide a crystalline hot-dip galvanized steel sheet having spangles of an appropriate size depending on the application of the decorative sheet.

The present invention also has the advantage that spangle development can be promoted using a smaller amount of Bi than Pb added to the plating bath used in the production of conventional crystalline hot-dip galvanized steel sheets.

EXAMPLES The present invention and its effects will be specifically explained below with reference to Examples.

A 5S41 steel plate with dimensions of 501, length 10 (1 mm) and thickness 3.2 m and 1 m was degreased by immersing it in an alkaline bath at a temperature of 80°C for 30 minutes, then washed with hot water, and then
Rust was removed by immersing it in a 0% hydrochloric acid solution (at room temperature) for 30 minutes.

After washing the steel plate pretreated as described above with hot water, ZnC1
Flux treatment was performed by immersing in 2-KF melt (80°C) for 30 seconds, and then immersed in each plating bath having the composition shown in Table 1 for 1 minute at a bath temperature of 460°C, and then at a speed of 1 m per minute. I pulled it up. Next, the steel plate pulled up from the plating bath was left to cool in the atmosphere for 5 seconds, and then cooled with 40°C hot water.

Each of the galvanized steel sheets thus obtained was immersed in a 10% hydrochloric acid solution (at room temperature) for 5 seconds to etch the plating film.

Table 1 shows the evaluation of the state of spangles developed in each galvanized steel sheet obtained as described above. As a comparative example, the state of spangles was similarly determined for steel plates plated using a hot-dip galvanizing bath containing only AI and a hot-dip galvanizing bath containing AI and PB in the same procedure as above. The results were also shown in Table 1.

Table 1 Note) ■% in plating bath composition indicates weight.

■Evaluation criteria for spangle size are as follows.

0----No spangles occur.

1----------Minute size.

2----------One small size.

3.---11----Normal size.

! −−−−−−−Slightly large size.

5・------One larger size.

As shown in Table 1, when using the hot-dip galvanizing bath containing AI and Bi according to the present invention (inhibitors 4 to 14
) shows that the size of the spangles produced can be adjusted by changing the amounts of AI and Bi in the bath.

In addition, those using a plating bath containing AI and PB (
-1 to 3), although spangle expression is observed,
The adhesion of the plating layer to the steel substrate was poor, and brittleness of the plating layer was observed over time.

Claims (2)

[Claims] (1) Al0.1 to 0.5% by weight and Bi0.01
A zinc alloy for crystalline hot-dip galvanizing, characterized in that it contains 0.1% by weight. (2) The zinc alloy according to claim (1), wherein the total content of unavoidable impurities is less than 0.01% by weight.