KR20200063837A - Alloyed aluminium coated steel sheet having excellent weldability and phosphating properties and method of manufacturing the same - Google Patents

Abstract

The present invention relates to an alloyed aluminum plated steel sheet with excellent weldability and phosphate treating property and a manufacturing method thereof. To this end, the alloyed aluminum plated steel sheet according to an embodiment of the present invention comprises: a base steel sheet; and an alloyed aluminum plated layer provided on the base steel sheet. Here, the alloyed aluminum plated layer comprises an upper plated layer and a lower plated layer. The upper plated layer contains, based on wt%, 30% or more to less than 40% of Fe, 53-65% of Al and 10% or less of Zn (excluding 0%). The lower plated layer contains, based on wt%, 40% or more to 50% or less of Fe, 47-55% of Al and 10% or less of Zn (excluding 0%).

Description

ALLOYED ALUMINIUM COATED STEEL SHEET HAVING EXCELLENT WELDABILITY AND PHOSPHATING PROPERTIES AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to an alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment, and a method for manufacturing the same.

Conventionally, it has been widely known that Zn plating is performed to improve the corrosion resistance of steel materials, and Al is added to the plating bath to further secure insufficient corrosion resistance. For example, in Patent Document 1, molten Al- in which the Al content in the plating film is 20 to 95% by weight, the Si content in the plating film is 5% by weight or more with respect to the Al content, and the thickness of the interfacial alloy phase is 5 µm or less. A Zn-based plated steel sheet is disclosed.

However, in the component system of the hot-dip plating layer, as the Al content is high, the Al reacts with the welding rod to form an Al-Cu alloy, resulting in non-uniformity of the welding current, reducing the welding rod life, and also due to the surface oxidation layer of aluminum. In the case of phosphate treatment, there is a problem that the phosphate structure is not well formed. In addition, when alloying to make the Al-based hot-dip galvanizing layer having the above-described component system into a Fe-Al alloy phase, it must be heated to a very high temperature of 750°C or higher, which is very difficult to manufacture in a continuous line.

Japanese Patent Application Publication No. 2010-070784

One aspect of the present invention is to provide an alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment and a method for manufacturing the same.

One embodiment of the present invention is a steel sheet; And an alloyed aluminum plated steel sheet having an alloyed aluminum plated layer on the steel plate, wherein the alloyed aluminum plated layer is composed of an upper plated layer and a lower plated layer, wherein the upper plated layer is in weight percent, Fe: 30% or more to less than 40%, Al : 53~65% and Zn: 10% or less (excluding 0%), the lower plating layer is in weight%, Fe: 40% to 50%, Al: 47 to 55% and Zn: 10% It provides an alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment, including the following (excluding 0%).

Another embodiment of the present invention comprises the steps of immersing the plated steel sheet in weight percent, Zn: 10 to 30%, immersed in a plating bath containing the remaining Al and other inevitable impurities; And it provides a method of manufacturing an alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment, comprising the step of alloying heat treatment of the plated base steel sheet at 600 ~ 700 ℃.

According to one aspect of the present invention, it is possible not only to manufacture an alloyed aluminum plated steel sheet, which is usually not easy to manufacture, but also to improve the lifespan of a welding electrode during welding, and thus has excellent weldability and excellent phosphate treatment. And a method of manufacturing the same.

1 is a schematic view showing a cross section of a molten aluminum plated steel sheet.
2 is a schematic view showing a cross section of an alloyed aluminum plated steel sheet according to an embodiment of the present invention.
3 is a photograph of a cross-section of Comparative Example 1 according to an embodiment of the present invention observed by SEM.
4 is a photograph of a cross-section of Inventive Example 1 according to an embodiment of the present invention observed by SEM.

1 is a schematic view showing a cross section of a molten aluminum plated steel sheet. As shown in FIG. 1, in the case of the existing molten aluminum plated steel sheet 100, when the plated steel plate 1 is immersed in a plating bath, it is formed between the plated steel sheet 1 and the molten aluminum plated layer 3, , The Al-Fe alloy phase (2) that prevents the diffusion of Fe into the plating layer is formed thick, and thus, even if alloying heat treatment is performed, there is a disadvantage in that alloying occurs only when the alloying heat treatment temperature is heated to a high temperature of 750°C or higher.

Hereinafter, an alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment according to an embodiment of the present invention for solving this problem will be described.

2 is a schematic view showing a cross section of an alloyed aluminum plated steel sheet according to an embodiment of the present invention. As shown in Figure 2, the alloyed aluminum plated steel sheet 200 of the present invention is a steel sheet (10); And an alloyed aluminum plating layer 20 on the holding steel plate 10. At this time, the alloyed aluminum plating layer 20 is preferably composed of a lower plating layer 24 formed on the base steel plate 10 and an upper plating layer 22 formed on the lower plating layer 24.

On the other hand, in the present invention, the type of the steel sheet applicable to the alloyed aluminum plated steel sheet is not particularly limited, and any steel sheet commonly used as a plated steel sheet in the art may be applied.

The upper plating layer is weight%, Fe: 30% or more to less than 40%, Al: 53 to 65% and Zn: 10% or less (preferably 0% is excluded). By having the alloy composition as described above, the upper plating layer of the present invention may have the same composition as FeAl ₃ . If the Fe of the upper plating layer is less than 30%, there is a possibility of seizure and cracking due to plating layer melting upon heating, and when it is 40% or more, there may be disadvantages such as peeling of the plating layer during processing. When the Al of the upper plating layer is less than 53%, there may be disadvantages such as peeling on the plating side during processing, and when it is more than 65%, there is a possibility of seizure and cracking due to melting of the plating layer during heating. Zn of the upper plating layer serves to suppress the formation of the Al-Fe alloy phase formed between the steel plate and the plating layer during hot dipping. However, if the content exceeds 10%, liquefied metal embrittlement (LME) may occur during welding.

In addition, the lower plating layer is preferably in the weight%, Fe: 40% or more to 50% or less, Al: 47 to 55% and Zn: 10% or less (excluding 0%). By having the alloy composition as described above, the upper plating layer of the present invention may have the same composition as Fe ₂ Al ₅ . If the Fe of the upper plating layer is less than 40%, the formation of Fe-Al intermetallic compound is suppressed, and there is a disadvantage that liquefaction odor may occur during high-temperature heating, and if it is more than 50%, the plating adhesion may be deteriorated. have. If the Al of the upper plating layer is less than 47%, there may be a disadvantage that the plating adhesion is deteriorated, and if it is more than 55%, the formation of Fe-Al intermetallic compound is suppressed, and thus, a liquefied embrittlement may occur during high temperature heating. have. Zn of the upper plating layer serves to suppress the formation of the Al-Fe alloy phase formed between the steel plate and the plating layer during hot dipping. However, when the content exceeds 10%, liquefied metal embrittlement (LME) may occur during welding, and the life of the welding rod may be shortened by forming an alloy phase of Cu-Zn during welding.

In the present invention, it is preferable that the alloyed aluminum plating layer has a thickness of more than 5 μm to 30 μm or less. When the thickness of the alloyed aluminum plating layer is 5 μm or less, it may be difficult to secure sufficient corrosion resistance, and when it exceeds 30 μm, there may be a disadvantage such as peeling of the plating layer during processing. The lower limit of the thickness of the alloyed aluminum plating layer is more preferably 10 μm, and even more preferably 15 μm. The upper limit of the thickness of the alloyed aluminum plating layer is more preferably 25 μm, and even more preferably 20 μm.

The upper plating layer of the present invention preferably has a thickness of 20 to 80% of the total thickness of the alloyed aluminum plating layer. If, when the thickness ratio of the upper plating layer is less than 20%, there is a disadvantage that the plating adhesion is deteriorated due to excessive formation of the brittle Fe ₂ Al ₅ layer, and when it exceeds 80%, the hardness is higher than that of the Fe ₂ Al ₅ layer. It has the disadvantage of shortening the welding life.

Meanwhile, the alloyed aluminum plating layer may further include at least one selected from the group consisting of Si: 2.5% or less, Mg: 2.5% or less, and Ni: 2.5% or less.

Si is formed between the plated steel plate and the plating layer during plating, and serves to suppress the formation of an Al-Fe alloy phase that prevents the diffusion of Fe into the plating layer, and when it exceeds 2.5%, it is difficult to sufficiently obtain the above effect. There are disadvantages. Mg is an element that plays a role similar to Zn, and when it exceeds 2.5%, the alloying heat treatment temperature increases. Ni is an element that serves to promote alloying, and when it exceeds 2.5%, there is a disadvantage that the Fe ₂ Al ₅ layer is excessively formed. On the other hand, the Si, Mg, and Ni are included in each of the plating bath composition at 2% or less, but the elements are picked up for the same reason as the preferential reaction with the iron during plating, and the content in the plating layer is higher than that of the plating bath composition. Can be.

Hereinafter, a method of manufacturing an alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment according to an embodiment of the present invention will be described.

In the case of the existing molten aluminum plated steel sheet, when the steel sheet is immersed in a plating bath to be plated, it is formed between the steel sheet and the plating layer, and the Al-Fe alloy phase that prevents the diffusion of Fe into the plating layer is formed thick, thereby alloying Even if heat treatment is performed, there is a disadvantage in that alloying occurs only when the alloying heat treatment temperature is heated to 750° C. or higher.

In order to solve this, the present invention is plated by immersing the steel sheet in weight percent, Zn: 10 to 30%, the remaining Al and other inevitable impurities in a plating bath. When the content of Zn is less than 10% by weight, it is formed between the steel plate and the plating layer during plating, and it is difficult to sufficiently inhibit the formation of the Al-Fe alloy phase that prevents the diffusion of Fe into the plating layer, making it difficult to alloy the entire plating layer. If it exceeds 30% by weight, liquefied metal embrittlement (LME) may occur during welding, and the life of the welding rod may be shortened by forming an alloy phase of Cu-Zn during welding. Meanwhile, the Zn is mostly evaporated during an alloying heat treatment process, and accordingly, the Zn content in the plating layer may be lower than the Zn content in the plating bath.

The plating bath may further include at least one selected from the group consisting of Si: 2% or less, Mg: 2% or less, and Ni: 2% or less in weight%. The Si, Mg, and Ni are included in the plating bath composition at 2% or less, respectively, but are picked up for the same reason as the preferential reaction with the base iron during plating, and the content in the plating layer may be higher than the plating bath composition.

Meanwhile, a process of air wiping may be further included to control the thickness of the plating layer formed on the steel sheet.

It is preferable that the plating adhesion amount during the plating is 70 g/m ² or less. When the plating adhesion amount exceeds 70 g/m ² , there is a disadvantage that an alloying heat treatment temperature must be increased in order to alloy the plating layer due to a plating layer that is too thick. In addition, due to the high alloying heat treatment temperature, the cooling is not sufficiently performed during the moving of the steel sheet after the alloying heat treatment, so that the plating layer is detached from the steel plate in the top roll, and a problem of adsorbing to the top roll occurs.

Thereafter, the plated steel sheet is subjected to an alloying heat treatment at 600 to 700°C. When the temperature of the alloying heat treatment is less than 600°C, alloying of the plating layer is not sufficiently achieved, and when it exceeds 700°C, cooling is not sufficiently performed during moving the steel sheet after the alloying heat treatment due to an excessively high temperature, so that the steel sheet is held in the top roll. There is a problem that the plating layer is detached from the adsorption on the top roll, and the ratio of the upper plating layer is increased.

Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by matters described in the claims and reasonably inferred therefrom.

(Example)

AHSS steel sheet containing C: 0.18% by weight, Mn: 1.6% by weight, and Si: 1.5% by weight was plated by immersion in a plating bath having the composition shown in Table 1 below. At this time, the temperature of the plating bath was maintained at 570°C. Thereafter, the AHSS steel sheet was alloyed and heat-treated for 30 seconds at an alloying heat treatment temperature shown in Table 1 to prepare an alloyed aluminum plated steel sheet, and then alloy composition of the upper and lower plating layers and alloyed aluminum plated layer thickness of the alloyed aluminum plated steel sheet. And the thickness ratio of the upper plating layer to the total thickness of the alloyed aluminum plating layer is shown in Table 2 below. In addition, after evaluating the phosphate treatment properties, welding life and plating adhesion, the results are shown in Table 2 below.

Phosphate treatment was evaluated by the following criteria by measuring the phosphate coating rate and coating amount by performing a phosphate solution at 45°C for 120 seconds.

○: Excellent (phosphate coating rate 100%, coating amount: 3.0 g/m 2 or more to 5.0 g/m 2 or less)

△: Inferiority (Phosphate coating rate exceeded 70%~90%, coating amount: exceeded 2.0g/㎡~3.0g/㎡)

×: Poor (phosphate coating rate of 70% or less, coating amount: 2.0 g/m 2 or less)

The welding life was evaluated by measuring the number of welds to the point where the average size of the button diameter formed by spot welding (pressing force: 4.0 kN, electrode diameter: 6 mm, applied current: 8.0 kA) became smaller than the lower limit diameter of 5 mm. .

○: Over 700 to 1,000 times

△: Over 500 to over 700 times

×: 500 times or less

Plating adhesion was evaluated by the following criteria by measuring the rate at which the sealer dropped the plating layer after a 90° bending test using a sealer.

○: Excellent (no plating peeling)

△: Inferiority (10% or less plating peeling)

×: Bad (more than 10% plating peeling)

division Plating bath composition (% by weight) Alloying
Heat treatment
Temperature
(℃) Lower plating layer composition (% by weight) Al Zn Si Mg Ni Al Zn Si Mg Ni Fe Comparative Example 1 91 - 9 - - 750 51 - 7 - - 42 Comparative Example 2 90 5 5 - - 700 52 - 5 - - 43 Comparative Example 3 90 5 5 - - 720 50 - 5 - - 45 Inventive Example 1 90 10 - - - 700 47 3 - - - 50 Comparative Example 4 90 10 - - - 580 57 2 - - - 41 Comparative Example 5 80 20 - - - 580 52 6 - - - 42 Inventive Example 2 80 20 - - - 600 53 7 - - - 40 Inventive Example 3 80 20 - - - 650 54 5 - - - 41 Inventive Example 4 80 20 - - - 700 55 3 - - - 42 Comparative Example 6 80 20 - - - 750 56 One - - - 43 Inventive Example 5 70 30 - - - 600 57 10 - - - 42 Comparative Example 7 65 35 - - - 740 55 3 - - - 42 Inventive Example 6 78.5 20 1.5 - - 700 53 3 2 - - 42 Comparative Example 8 78 20 2 - - 700 50.5 2.5 3 - - 44 Inventive Example 7 78.5 20 - 1.5 - 700 54 3 - One - 42 Comparative Example 9 78 20 - 2 - 740 53.8 3 - 1.2 - 42 Inventive Example 8 78.5 20 - - 1.5 700 53.5 3 - - 1.5 42 Comparative Example 10 78 20 - - 2 730 53 3 - - 2 42

division Upper plating layer composition (% by weight) Top
Plating layer
ratio(%) phosphate
Processability welding
life span Plated
Adhesion Al Zn Si Mg Ni Fe Comparative Example 1 82 - 13 - - 5 70 × × ○ Comparative Example 2 89.5 1.5 7 - - 2 60 × × ○ Comparative Example 3 85 One 7 - - 7 50 × × ○ Inventive Example 1 57.7 2.3 - - - 40 80 ○ ○ ○ Comparative Example 4 95.4 2.6 - - - 2 15 × × ○ Comparative Example 5 89.2 7.8 - - - 3 20 × × ○ Inventive Example 2 59.6 5.4 - - - 35 20 ○ ○ ○ Inventive Example 3 60.2 3.8 - - - 36 50 ○ ○ ○ Inventive Example 4 59.7 2.3 - - - 38 70 ○ ○ ○ Comparative Example 6 60.5 0.5 - - - 39 85 ○ ○ × Inventive Example 5 56.3 7.7 - - - 36 40 ○ ○ ○ Comparative Example 7 61.3 2.8 - - - 36 90 ○ × × Inventive Example 6 53.0 10 2.5 - - 34.5 60 ○ ○ ○ Comparative Example 8 60.8 2.1 3.1 - - 34 82 ○ ○ × Inventive Example 7 59.7 2.3 - One - 37 50 ○ ○ ○ Comparative Example 9 61.5 2.3 - 1.2 - 35 83 ○ ○ × Inventive Example 8 59.2 2.3 - - 1.5 37 70 ○ ○ ○ Comparative Example 10 58.7 2.3 - - 2 37 85 ○ ○ ×

As can be seen through Tables 1 and 2, in the case of Inventive Examples 1 to 8 satisfying the composition of the upper plating layer and the lower plating layer proposed by the present invention and the thickness ratio of the upper plating layer to the total thickness of the alloyed aluminum plating layer, excellent phosphate It can be confirmed that the processability, the welding life, and the plating adhesion are secured.

On the other hand, in the case of Comparative Examples 1 to 3, it can be seen that, as Zn is not included in the upper plating layer or the lower plating layer, the plating layer is not alloyed, and an aluminum oxide layer is present on the surface layer, thereby deteriorating phosphate treatment and welding life.

In the case of Comparative Examples 4 and 5, it can be seen that the alloying of the plating layer is not made because the alloying heat treatment temperature is less than 600°C, so that the upper portion of the plating layer is formed of an aluminum layer, resulting in a low level of phosphate treatment and welding life.

In the case of Comparative Examples 6 to 10, as the alloying heat treatment temperature exceeds 700°C, the ratio of the upper plating layer exceeds 80%, and thus it can be confirmed that the adhesion is deteriorated. In particular, in the case of Comparative Example 7, it can be seen that as the Zn content in the plating bath exceeds 30%, liquefied metal embrittlement may occur due to excessive formation of an alloy phase, and a shortening of the welding life.

3 is a photograph of the cross section of Comparative Example 1 observed by SEM. As can be seen through FIG. 3, in the case of Comparative Example 1, the plating layer was not alloyed, and the Al-Fe alloy phase was formed between the base steel plate and the plating layer as in the conventional molten aluminum plated steel plate, and the Al plating layer was formed on the surface layer. You can see that it is.

4 is a photograph of the cross section of Inventive Example 1 observed by SEM. As can be seen through FIG. 4, in the case of Inventive Example 1, it was confirmed that an alloyed aluminum plating layer having an upper alloy layer and a lower alloy layer was formed as the plating layer was sufficiently alloyed.

1: possession steel sheet
2: Al-Fe alloy phase
3: molten aluminum plating layer
100: hot-dip galvanized steel sheet
10: possession steel sheet
20: alloyed aluminum plating layer
22: upper plating layer
24: lower plating layer
200: alloyed aluminum plated steel sheet

Claims (7)

Possession steel sheet; And
An alloyed aluminum plated steel sheet having an alloyed aluminum plated layer on the base steel sheet,
The alloyed aluminum plating layer is composed of an upper plating layer and a lower plating layer,
The upper plating layer is weight%, Fe: 30% or more to less than 40%, Al: 53 to 65% and Zn: 10% or less (excluding 0%),
The lower plating layer is weight%, Fe: 40% or more to 50% or less, Al: 47 to 55% and Zn: 10% or less (excluding 0%), and an alloyed aluminum plated steel sheet with excellent weldability and phosphate treatment .
The method according to claim 1,
The alloyed aluminum plated layer is an alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment with a thickness of more than 5 μm to 30 μm or less.
The method according to claim 1,
The upper plating layer is an alloyed aluminum plated steel sheet having excellent weldability and phosphate treatment, whose thickness accounts for 20 to 80% of the total thickness of the alloyed aluminum plated layer.
The method according to claim 1,
The alloyed aluminum plating layer is weight%, Si: 2.5% or less, Mg: 2.5% or less and Ni: 2.5% or less, further comprising at least one member selected from the group consisting of alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment .
Plating by holding the steel sheet in weight percent, Zn: 10 to 30%, remaining Al and other inevitable impurities in a plating bath; And
Method for manufacturing an alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment, comprising the step of alloying heat treatment of the plated base steel sheet at 600 to 700°C.
The method according to claim 1,
The plating bath, by weight, Si: 2% or less, Mg: 2% or less and Ni: 2% or less of an alloyed aluminum plated steel sheet excellent in weldability and phosphate treatment further comprising one or more selected from the group consisting of: Manufacturing method.
The method according to claim 1,
A method of manufacturing an alloyed aluminum plated steel sheet having excellent weldability and phosphate treatment with a plating adhesion of 70 g/m ² or less during plating.

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