JPH09170084A - Galvanized steel sheet excellent in press formability and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a galvanized steel sheet, having superior press formability and excellent in spot weldability, chemical conversion treating property, and electrodeposition coating property, or a galvanized steel sheet, having superior press formability and excellent in adhesion, and their production. SOLUTION: This steel sheet is a steel sheet, having an amorphous reaction product of phosphoric acid and zinc on the plating surface of a galvanized steel sheet (e.g. galvannealed steel sheet, Zn-Ni alloy electroplated steel sheet, etc.) by (20 to 350)mg/m<2> expressed in terms of phosphorus, or a steel sheet having a film consisting of a mixture in which (15 to 100)mg/m<2> of alumina is dispersed in an amorphous phosphoric acid compound in the amount of (5 to 350)mg/m<2> expressed in terms of phosphorus. These steel sheets can be produced by applying an aqueous solution of phosphoric acid of 2-30wt.% concentration or an aqueous solution of phosphoric acid of 0.5-30wt.% concentration, where feather-like alumina sol is added so that 0.15-10wt.% concentration is reached, to the plating surface of a galvanized steel sheet by (1 to 10)ml/m<2> , respectively, and then carrying out drying at >=40 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a zinc-based plated steel sheet which is excellent in press formability and is particularly suitable as a material for automobiles.

[0002]

2. Description of the Related Art Since zinc-based plated steel sheets have excellent corrosion resistance, various zinc-based plated steel sheets are used as automobile steel sheets. However, it has been conventionally known that the press formability of galvanized steel sheets is inferior to that of cold-rolled steel sheets. Therefore, various surface treatment methods have been proposed to improve the press formability of galvanized steel sheets. Has been done.

For example, in JP-A-58-15554, a hard coating such as iron flash plating is formed on the surface of a zinc-based plated steel sheet to prevent galling between the plated surface and the die during pressing, A technique for improving the lubricity in time is described.

Japanese Patent Laid-Open No. 4-88196 discloses that
The surface of zinc-based plated steel sheet is P (phosphorus) oxide 1 to 500
Disclosed is a zinc-based plated steel sheet coated with mg / m ² and having excellent press formability and chemical conversion treatability. Japanese Patent Examination 6-35
According to Japanese Patent Publication No. 678 and Japanese Patent Publication No. 6-96781, the surface of a zinc-based plated steel sheet is converted to Mn of 5 to 500 mg.
Steel sheet coated with Mn oxide / m ² or a mixture of the above Mn oxide with phosphoric acid and one or more of colloidal SiO ₂ , colloidal TiO ₂ and colloidal Al ₂ O _3. A coated steel sheet has been proposed,
Both of them are said to improve the lubricity during pressing.

Further, 1 to 1000 mg of an anhydrous alkali metal salt of an oxide of one or more semimetals selected from boron, phosphorus, silicon and the like is applied to the surface of the plating layer of the zinc-based plated steel sheet.
A zinc-based plated steel sheet having an excellent press formability of 1 / m ² has also been proposed (Japanese Patent Publication No. 7-13306).

By the way, the press formability required for zinc-based plated steel sheets for automobiles is not sufficient to enable forming with a small amount of die maintenance in an actual assembly line, and high-speed press forming is continuously performed. High moldability is required. For this purpose, it is necessary to carry out a surface treatment that not only prevents mold galling during pressing but also prevents powdering.

In addition to press formability, it is also required to have excellent continuous spot weldability, chemical conversion treatment property, electrodeposition coating property and the like. In addition, in the joining process of the assembly line, adhesive joining may be applied instead of welding joining by using an adhesive. In that case, in addition to press formability, excellent adhesiveness Is required.

From this point of view, in the above-mentioned prior art, all of the spot weldability, chemical conversion treatment property and electrodeposition coating property are satisfied, including high press formability including powdering resistance. It cannot be said that a surface treatment method for a zinc-based plated steel sheet or a surface treatment method for a zinc-based plated steel sheet, which has excellent adhesiveness in addition to press-formability, has yet been realized.

Further, for example, JP-A-58-15554.
The technique of forming a hard coating such as iron flash plating on the surface of a zinc-based plated steel sheet disclosed in Japanese Patent Laid-Open Publication No. 2003-242242 has a problem that the number of steps is increased and the manufacturing cost is increased. Tokuhei 6
In the technique of coating the surface of a zinc-based plated steel sheet with Mn oxide, which is disclosed in JP-A-35678 or JP-B-6-96781, a solution containing a permanganate ion which is a strong oxidant is used, and therefore the treatment is performed. However, the processing cost is added to the manufacturing cost. Further, the method of coating the surface with P oxide disclosed in Japanese Patent Application Laid-Open No. 4-88196 enhances the adhesiveness, particularly the oil surface adhesiveness when the adhesive joining is performed with the cleaning oil adhered to the steel sheet. Above, it is said to be unfavorable.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances and has excellent press formability,
Moreover, spot-weldability, chemical conversion treatability, zinc-plated steel sheet excellent in electrodeposition paintability, or zinc-plated steel sheet having excellent press formability and adhesiveness, and those steel sheets at low cost It is intended to provide a method for easy production.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the inventors have found that a phosphoric acid-based compound formed on the surface of a plating layer of a zinc-based plated steel sheet has a press formability of that steel sheet, The following findings were obtained as a result of examining the effects on weldability, chemical conversion treatability, and electrodeposition paintability by various model experiments.

The phosphoric acid-based compound formed on the surface of the plating layer of the zinc-based plated steel sheet has a boundary lubrication action when oil is applied to the surface of the steel sheet and the steel sheet is press-formed. That is, the phosphoric acid-based compound reacts with the oil component, and the reaction product prevents the metal from coming into contact with the tool and the zinc-based plating layer.

Among the phosphoric acid type compounds, particularly the compound of phosphoric acid and zinc improves all the press moldability, chemical conversion treatment property and electrodeposition coating property.

When a soluble alkali metal or alkaline earth metal is mixed in the phosphoric acid compound, the chemical conversion treatment property and the electrodeposition coating property, especially the water-resistant adhesion property are deteriorated.

The crystalline phosphoric acid compound is inferior in powdering resistance and chemical conversion treatment property to the amorphous phosphoric acid compound.

Amorphous phosphoric acid and zinc compounds are produced by applying a specific concentration of phosphoric acid to the surface of the plating layer of a zinc-based plated steel sheet and drying.

After that, as a result of further examination of an inexpensive and simple surface treatment method for imparting excellent press formability and adhesiveness to a zinc-based plated steel sheet, the following facts were found.

When a phosphoric acid aqueous solution containing feather-like alumina sol is applied to the surface of a zinc-based plated steel sheet and dried at 40 ° C. or higher, a film composed of a mixture of a phosphoric acid compound and alumina is formed on the surface. The press formability is synergistically improved.

The coexistence of the phosphoric acid compound and the feather-like alumina sol lowers the lower limit of the amount of the phosphoric acid compound deposited on the surface of the steel sheet for maintaining excellent press formability.

When the amount of the phosphoric acid compound is reduced, the adhesive property, particularly the oil surface adhesive property is improved regardless of whether or not the feathery alumina sol is added.

When the amount of the phosphoric acid compound is reduced and the feather-like alumina sol is added, the adhesiveness, especially the oil surface adhesiveness is further improved.

As described above, by coating the surface of the galvanized steel sheet with the compound of phosphoric acid and zinc (reaction product), the press formability of the steel sheet, the chemical conversion treatment property, and the electrodeposition coating property are improved. It has been found that the press formability can be synergistically improved and the adhesiveness can be improved by coating the surface of the steel sheet with a hard film made of a mixture of alumina and a phosphoric acid compound.

The inventors of the present invention have further studied the processing conditions and the like based on these findings and have completed the present invention. The gist thereof lies in the following zinc-plated steel sheets (1) and (2), and their manufacturing methods (3) and (4).

(1) An amorphous reaction product of phosphoric acid and zinc is converted into phosphorus in the range of 20 mg / m ² or more and 350 mg / m ² or less on the surface of the plating layer of the zinc-based plated steel sheet. A zinc-based plated steel sheet having excellent press formability, which is characterized by having.

[0025] (2) on the surface of the plating layer of the galvanized steel sheet, in terms of phosphorus 5 mg / m ² or more 350 mg / m ²
15 mg / m ² or more in the following amorphous phosphate compounds 10
A zinc-based plated steel sheet having excellent press formability, which has a coating formed of a mixture in which 0 mg / m ² or less of alumina is dispersed.

(3) An aqueous phosphoric acid solution having a concentration of 2% by weight or more and 30% by weight or less is applied to the surface of the coating layer of the zinc-based plated steel sheet within a range of 1 ml (milliliter) / m ² or more and 10 ml / m ² or less. And then drying at 40 ° C. or higher, a method for producing a zinc-based plated steel sheet having excellent press formability.

(4) Feather-like alumina sol was added to the surface of the plating layer of the zinc-based plated steel sheet to a concentration of 0.15% by weight or more and 10% by weight or less, and 0.5% by weight or more and 30% by weight or less of phosphoric acid aqueous solution of concentration is applied in the range of 1 ml / m ² or more 10 ml / m ² or less, the production method excellent galvanized steel sheet in press formability, which comprises drying at 40 ° C. or higher.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The zinc-based plated steel sheet as the base material used in the present invention (the inventions of (1) to (4) above) is not particularly limited. Representative examples include hot-dip galvanized steel sheets and hot-dip galvanized steel sheets, and electroplating systems include zinc-nickel alloy-plated steel sheets.

Amorphous reaction product of phosphoric acid and zinc which the zinc-based plated steel sheet of (1) has on the surface of the plated layer (a compound of phosphoric acid and zinc, hereinafter also referred to as "coating")
Is required to be an amorphous film formed by a reaction between phosphoric acid contained in the phosphoric acid water-soluble and applied to the surface of the plating layer and zinc forming the plating layer.

When the coating is crystalline, such as hopite, which is clearly observed by a microscope, the lubricity is good, but powdering is likely to occur, so that the zinc-based plated steel sheet having such coating is Continuous high-speed press formability is not always good. If the film is crystalline,
Even if the chemical conversion treatment is performed, there is a problem that the crystals of the underlayer interfere and the crystals of the chemical conversion treatment film are not formed uniformly.

Such a film which is a reaction product of phosphoric acid and zinc should not be formed by using an aqueous phosphoric acid solution containing an alkali metal salt or an alkaline earth metal salt. When an aqueous solution of phosphoric acid containing an alkali metal salt or an alkaline earth metal salt is used to form a film defined in the present invention, a water-soluble alkali metal salt or an alkaline earth metal salt is incorporated into the film to form a film. This significantly reduces the water resistance of. This tendency is remarkable especially when a film is formed by a coating type treatment without washing with water. When the water resistance of the film is lowered, the water resistance adhesion after electrodeposition coating becomes insufficient. Further, the presence of a water-soluble component in the film also does not give good results with respect to rust resistance during steel sheet storage (rust resistance evaluated by a stack test or the like).

The amount of coating adhered should be 20 mg / m ² or more and 350 mg / m ² or less in terms of phosphorus, that is, when the amount of coating adhered is represented by the amount of phosphorus contained therein. Is. If the adhesion amount is less than 20 mg / m ² , press formability is insufficient, while the adhesion amount is 350 m.
If it exceeds g / m ² , the chemical conversion treatment property is deteriorated.

In order to clarify the morphology and composition of the above film, field emission type electron microscope observation and
Measurements were made by X-ray photoelectron spectroscopy and Auger electron spectroscopy. As a result, it was found that the film had an element ratio of zinc and phosphorus (zinc / phosphorus) of 1.3 to 1.9 and was an amorphous uniform film that could not be observed by a microscope. However, when the adhered amount was large, spherical adherents were observed on the surface of the film.

FIG. 1 and FIG. 2 are views showing the crystal structure of the surface of a film which is a reaction product of phosphoric acid and zinc, which is observed by a field emission type scanning electron microscope (FE-SEM). FIG. 1 shows Example 3 of the present invention, which will be described later.
Fig. 2 shows the crystal structure of the film formed on the surface of the plating layer of the zinc-based plated steel sheet (phosphorus deposition amount: 25 mg / m ² ).
Is the same as Example 6 of the present invention (phosphorus adhesion amount: 100 mg / m
² ) Corresponding to that. In both figures, (a) is a magnification of 3000 and (b) is a magnification of 20000. As shown in these figures, the film is amorphous, and in Example 6 of the present invention in which the amount of adhesion is large, spherical deposits are recognized (indicated by an arrow in FIG. 2B).

It is presumed that the mechanism of improving the lubricity during press forming due to the presence of such a film on the surface of the plated steel sheet is similar to the extreme pressure additive added to forming oil or the like. In other words, the phosphoric acid-based compound that constitutes the film reacts with the oil component when oil is applied and press-molded, and the reaction product prevents boundary metal contact between the tool and the plating layer. It is considered to show an effect.

As shown in Examples described later, this coating is also very good in spot weldability, chemical conversion treatment property and electrodeposition coating property.

As described above, the zinc-based plated steel sheet of (1) has a coating which is an amorphous reaction product of phosphoric acid and zinc on the surface of the plating layer, and is continuously high-speed press-formed. It has a high level of press formability to withstand, and is also excellent in spot weldability, chemical conversion treatment and electrodeposition coating.

The film (2) that the zinc-based plated steel sheet has on the surface of the plated layer is a film made of a mixture of an amorphous phosphoric acid compound and alumina dispersed therein.

The phosphoric acid-based compound in this coating is an amorphous coating formed by the reaction between phosphoric acid and zinc forming the plating layer, as in the case of the coating on the surface of the plated steel sheet of (1). It is necessary to be. If it is crystalline, the lubricity during pressing is good, but powdering tends to occur. Similarly, the amorphous film should not be formed by using a phosphate of alkali metal or alkaline earth metal. This is because a large amount of alkali metal or alkaline earth metal is taken into the coating, the water resistance of the coating is reduced, and the water-resistant adhesion after electrodeposition coating is reduced.

In the case of the zinc-based plated steel sheet of (2), the phosphoric acid-based compound contained in the film is converted into phosphorus and is 5 mg /
it is necessary that m is ² or more 350 mg / m ² or less.

As described above, in the zinc-based plated steel sheet of (1), the phosphoric acid-based compound contained in the film is
It is necessary to be 20 mg / m ² or more in terms of phosphorus, but the coexistence of the alumina sol with the phosphoric acid-based compound results in a deposition amount of the phosphoric acid-based compound of 20 mg / m ²
Good press moldability is ensured even if the amount is less than the range. This is because the contact area between the steel plate and the mold is reduced by the formation of the hard alumina film in addition to the boundary lubrication action of the phosphoric acid compound, and the lubricity is improved.

However, the amount of the phosphoric acid compound attached is 5 mg.
If it is less than / m ² , the press moldability is not sufficient, while if it exceeds 350 mg / m ² , good adhesiveness cannot be secured. Preferably, 10 mg / m ² or more and 200 mg /
m ² or less.

The alumina contained in the above-mentioned amorphous film, which will be described in detail later, is formed by drying feather-like alumina sol dispersed in an aqueous phosphoric acid solution at a temperature of 40 ° C. or higher. It is necessary to be.

The amount of alumina contained in the film was 15 mg.
/ M ² or more and 100 mg / m ² or less.
When it is less than 15 mg / m ² , synergistic improvement in press moldability due to the phosphoric acid compound and alumina is not seen, and
Almost no improvement in adhesion is observed. On the other hand, when the amount of alumina exceeds 100 mg / m ² , "roughness" occurs on the surface of the steel sheet during press forming, the appearance after press forming is significantly impaired, and powdering occurs. Therefore,
The amount of alumina in the coating is 15 mg / m ² or more and 100 m
It was limited to g / m ² or less. More preferable range is 20 m
It is g / m ² or more and 80 mg / m ² or less.

The zinc-plated steel sheet (2) has excellent press formability as described above and also excellent adhesiveness.

The invention of (3) is the method for producing a zinc-based plated steel sheet according to (1). Zinc-based plating of (1) by applying a predetermined amount of an aqueous phosphoric acid solution having a concentration of 2% by weight or more and 30% by weight or less on the surface of the plating layer of the zinc-based plated steel sheet that is the base material, and drying at 40 ° C or more Steel sheets can be manufactured.

When the concentration of the phosphoric acid aqueous solution is less than 2% by weight, the precipitation of zinc phosphate crystals is partially observed in the formed film. Further, when a phosphoric acid aqueous solution having a concentration of more than 30% by weight is applied, hydrogen is intensely generated, etching of the plating surface is remarkable, and many pit-like etching marks are observed on the plating surface even after drying.

In forming the film, the phosphoric acid aqueous solution having the above-mentioned concentration is applied to the surface of the plating layer within the range of 1 ml / m ^{2 to} 10 ml / m ² and dried at 40 ° C. or higher.
Do not wash with water after application. Application amount of phosphoric acid aqueous solution is 1m
When it is less than 1 / m ² , the evaporation of water is too fast and the reaction between phosphoric acid and zinc is not sufficient. On the contrary, the coating amount is 10
When it exceeds ml / m ² , not only is the drying time consuming and impractical, but also the plating surface may be overetched by the time the treatment liquid dries.

The drying temperature (maximum ultimate temperature of steel sheet) is 40
When the temperature is lower than 0 ° C, not only drying takes time but also the reaction between phosphoric acid and zinc becomes insufficient, so the temperature is set to 40 ° C or higher. The upper limit of the drying temperature is not particularly specified, but it is preferably 150 ° C or lower. If the drying temperature exceeds 150 ° C., the coating film may be cracked and the press formability may be reduced.

The method of applying the phosphoric acid aqueous solution is not particularly limited. Conventional methods such as roll drawing after dip coating, roll drawing after spray coating, and roll coater method can be used.
Also for drying, the hot air oven, which is usually used,
An infrared oven or the like may be used.

As described above, by applying the method of (3), the galvanized steel sheet of (1) can be manufactured inexpensively and easily without requiring any special means.

The invention of (4) is the method of manufacturing a zinc-based plated steel sheet according to (2). This zinc-based plated steel sheet was prepared by adding feather-like alumina sol to the surface of the plated layer of the zinc-based plated steel sheet, which is a base material, so as to have a concentration of 0.15% by weight or more and 10% by weight or less. 30% by weight or more
A phosphoric acid aqueous solution having the following concentration (hereinafter, a phosphoric acid aqueous solution to which alumina sol is added is referred to as a "treatment liquid") is applied in a predetermined amount and dried at 40 [deg.] C. or higher to produce the composition.

The feather-like alumina sol is used as the alumina added to the phosphoric acid aqueous solution because the drying can be carried out at a low temperature to shorten the time required for forming a film and to form a hard film. The feather-like alumina sol used at this time is 0.5 μm to 10 μ in which an alumina colloid having a particle diameter in the range of 5 to 200 nm is polymerized.
The size of m is preferable. When such an alumina sol is used, it can be stably and uniformly dispersed in the phosphoric acid aqueous solution, and the stable and uniform coating on the surface of the steel sheet is facilitated.

The concentration of alumina sol in the treatment liquid was 0.1.
It is from 5% by weight to 10% by weight. If the concentration of alumina sol exceeds 10% by weight, the viscosity of the treatment liquid increases,
The coatability and the uniformity of the surface after coating are impaired. If the amount is less than 0.15% by weight, the required amount of the treatment liquid, which will be described later, cannot adhere the required amount of alumina of 15 mg / m ² or more to the surface of the steel sheet.

The concentration of phosphoric acid in the treatment liquid is 0.5% by weight or more and 30% by weight or less. When it is less than 0.5% by weight,
The required phosphate compound of 5 mg / m ² or more cannot be adhered to the surface of the steel sheet, and if the concentration exceeds 30% by weight, the reaction becomes too vigorous, which is not practical.

The amount of treatment liquid applied to the surface of the steel sheet is 1 ml.
/ M ² or more and 10 ml / m ² or less. If it is less than 1 ml / m ² , the reaction between phosphoric acid in the treatment liquid and zinc on the surface of the steel sheet is not sufficient because the drying is too fast, and 10 ml / m 2
^If it exceeds ² , it takes too long to dry, which is not practical.

Drying after applying the treatment liquid to the steel plate is 40
It is necessary to carry out at above ℃. If the drying temperature is lower than 40 ° C., the polymerization / crosslinking between the feather-like alumina sol particles does not proceed sufficiently and a hard alumina film is not formed, so that it is impossible to impart sufficient press formability to the steel sheet. Although the upper limit of the drying temperature is not particularly specified, it is preferably 150 ° C. or lower as in the case of the above method (3). Drying temperature is 15
If the temperature exceeds 0 ° C, the coating film may be cracked and press formability may be deteriorated.

The method of applying the treatment liquid to the steel sheet is the same as the method of applying the phosphoric acid aqueous solution in the above method (3), and is not particularly limited. After soaking, roll squeezing,
After spraying, a method such as roll squeezing or a roll coater method may be used. The same applies to the drying, and a hot air oven, an infrared oven or the like which is usually used may be used.

As described above, if the method (4) is applied, the galvanized steel sheet (2) can be easily manufactured.

[0060]

EXAMPLES The present invention will be described below based on examples.

Example 1 A zinc-based plated steel sheet as a sample preparation base material was an alloyed hot-dip galvanized steel sheet (plate thickness: 0.8 mm, coating weight: 60 g / m ^{2 on} both sides, hereinafter referred to as GA. (Abbreviated) was used. As a reference material for the evaluation of powdering resistance, a steel sheet (GA with a basis weight of 2 g / m ² on which iron plating was applied to the upper layer of GA)
/ M).

When the phosphoric acid aqueous solution was applied to the surface of the GA, alkali spray degreasing was performed as a pretreatment.

The application of the phosphoric acid aqueous solution was performed using a Ringer roll squeeze or a roll coater method after spray application. For comparison, an aqueous phosphoric acid solution having various concentrations out of the concentrations specified in the present invention and various aqueous phosphate solutions were also used. Drying after coating was performed in a hot air oven set at 100 ° C.

In Table 1, the phosphoric acid aqueous solution and the like (indicated as a treatment liquid) used, the concentration thereof, the coating method, the coating amount, and the drying temperature (a steel plate heated while passing through a hot stove set at 100 ° C., that is, The temperature of the coating film) and the adhesion amount of the coating film converted to phosphorus are shown.

The following tests were conducted on the samples prepared as described above to evaluate the performance.

Evaluation Method [Press Formability] Using a cylindrical drawing tester, a test was conducted under the following conditions.

Blank diameter: 69 mmφ Forming speed: 60 mm / min Blank holding load: 1.5 tonf Maximum forming height: 17.8 mm Lubricating oil: Washing oil (oil amount 5-6 g / m ² ) The formability evaluation is as follows. It was carried out in four stages, and when it was ⊚, it was considered good.

◎: No break ○: Breaking at a molding height of 15 mm or more △: Breaking at a molding height of 11 mm or more and less than 15 mm ×: Breaking at a molding height of less than 11 mm Further, breaking to the maximum molding height (17.8 mm) For the samples that did not exist (the evaluation of press moldability was ⊚), the molded product was subjected to solvent degreasing, and then the tape was peeled off from the diaphragm wall to examine the powdering amount. The powdering resistance was evaluated in the following two stages using the above GA / M as a reference material, and a good result was evaluated.

○: The amount of powdering is equal to or less than GA / M ×: The amount of powdering is larger than GA / M [Spot weldability] Sample (300 mm × 300 mm) 2
The sheets were overlapped and continuous spot welding was performed under the following conditions using an AC single spot welding machine equipped with a Cu-Cr alloy electrode having a tip diameter of 6 mm.

Pressurization force: 200 kgf Energization time: 12 cycles Holding time: 5 cycles Welding current: 11 kA Weldability was evaluated in the following 3 stages according to the welding point (continuous welding point) until welding peeling occurred by shear tension. If so, it was considered good.

◯: Continuous RBI is 5000 points or more B: Continuous RBI is 3000 points or more and less than 5000 X: Continuous RBI is less than 3000 points [Chemical conversion treatment] After degreasing and surface conditioning the sample surface,
Chemical conversion treatment was performed. As the treatment liquid, PB-L3080 (trade name) manufactured by Nippon Parkerizing Co., Ltd. was used.

The chemical conversion treatment was evaluated in the following four stages according to the result of observing the chemical conversion coating with an electron microscope (magnification: 1000).

⊚: Uniform conversion crystal ○: Some scale (part without formation crystal) or crystal grain size part △: Scale or crystal grain size ×: Crystal grain size or no crystal formation [Electrodeposition coating Property] Using a cationic electrodeposition coating U-600 (trade name) manufactured by Nippon Paint Co., Ltd. on the sample subjected to the chemical conversion treatment,
A 20 μm thick electrodeposition coating was applied.

The sample after this coating was put in warm water at 40 ° C. for 500 times.
After dipping for a period of time, 100 squares of a grid having a side of 1 mm were cut on the surface, and the tape was peeled off from this to determine the residual coating film rate. The evaluation of the electrodeposition coatability was carried out in the following three stages according to the residual coating film rate, and when the result was ◯, it was considered good.

◯: Residual coating film ratio is 95% or more Δ: Residual coating film ratio is 70% or more and less than 95% ×: Residual coating film ratio is less than 70% Table 1 also shows the evaluation results of each performance. from this result,
Plated steel sheet produced by the method of the present invention (Examples 1 to 1 of the present invention)
It can be seen that 8) is excellent in all of press formability, powdering resistance, spot weldability, chemical conversion treatment property and electrodeposition coating property.

FIGS. 1 and 2 are views showing the crystal structure of the film formed on the surface of the plated layer of the steel sheets of Inventive Examples 3 and 6, respectively, which were observed by FE-SEM. In both figures, (a) is a magnification of 3000 and (b) is a magnification of 20.
000. Inventive Example 3 (FIG. 1) is the case where the coating amount is 25 mg / m ² in terms of phosphorus, and Inventive Example 6 (FIG. 2) is the same 100 mg / m ² ; As is apparent, an amorphous uniform film is formed in each case. In addition, in the steel sheet of Inventive Example 6 with a large amount of adhesion, spherical deposits were observed (indicated by an arrow in FIG. 2B).

On the other hand, in the comparative example which deviates from the conditions specified in the present invention, at least one of the above performances was poor.

[0078]

[Table 1]

(Example 2) GA (sheet thickness: 0.8 mm, coating weight: 60 g / m ^{2 on} both sides) was used as the zinc-based plated steel sheet as the base material. In addition, Fe of the plating film
The content was 11.0% by weight, and the Al content was 0.3% by weight.

The above GA is degreased with an alkali, dipped in a treatment liquid in which a feather-like alumina sol (for comparison, a plate-like alumina sol is also used) is dispersed, and the GA surface is coated with a Ringer roll. The amount of the treatment liquid was adjusted to ² ml / m ² and then dried in a hot air oven. The concentration of alumina sol is in the range of 0 to 15% by weight, and the concentration of phosphoric acid is 0.
Varying within the range of ˜35% by weight.

Table 2 shows the composition of the treatment liquid (concentration of alumina sol and phosphoric acid), the form of alumina sol, the drying temperature, and the amount of alumina contained in the film formed on the surface of the base steel sheet and phosphorus. The amount of the phosphoric acid compound shown (indicated as the amount of adhesion in the table) is shown.

The following tests were conducted on the samples produced as described above to evaluate the performance.

Evaluation Method [Press Formability] Using a cylindrical drawing tester, a test was conducted under the following conditions.

Blank diameter: 69 mmφ Forming speed: 60 mm / min Blank holding load: 1.5 tonf Maximum forming height: 18 mm Lubricating oil: General rust preventive oil (oil amount 5-6 g / m
² ) The moldability was evaluated in the following four stages, and ◎ and ○ were evaluated as good.

◎: No break ○: Break at molding height of 15 mm or more △: Break at molding height of 11 mm or more and less than 15 mm ×: Break at molding height of less than 11 mm [Adhesiveness] Bake-curable polyester adhesive was used. ,
After applying the adhesive to a thickness of 150 μm,
A test piece was prepared by baking and curing under conditions of 0 ° C. × 10 minutes. The application of the adhesive was carried out in the state where the cleaning oil (the amount of applied oil was 5 to 6 g / m ² ) was present on the surface of the sample, assuming the actual usage situation.

The adhesiveness was evaluated by measuring the T-peel strength and observing the adhesive surface to investigate the form of the exfoliation. The evaluation criteria were the following four grades, and ⊚ and ◯ were considered good.

⊚: T peel strength of 100 N / 25 mm or more and cohesive failure on the entire adhesive surface ◯: T peel strength of 100 N / 25 mm or more and 70% or more of adhesive surface on cohesive failure Δ: T peel strength of 50 N / 25 mm or more 100 N / 25
If the T peel strength is less than 50 N / 25 mm and the T-peel strength is less than 50 N / 25 mm, the adhesive surface undergoes interfacial fracture.
The results of evaluation are also shown in Table 2. As is clear from these results, the examples of the present invention have excellent press formability and adhesiveness, whereas the comparative examples deviating from the conditions specified in the present invention have poor press formability and adhesiveness. And some of them caused powdering. Further, the press moldability was poor when the film was composed of only alumina (Comparative Example 35). When the form of the alumina sol was not feathery, a hard alumina film was not formed even when dried at 40 ° C. and the press formability was poor (Comparative Example 36). When dried at high temperature (150 ° C.), alumina And powdering occurred even though the amount of the phosphoric acid compound attached was within the specified range (Comparative Example 37).

Comparing Example 20 of the present invention with Comparative Example 34, it can be seen that the latter has a larger amount of the phosphoric acid compound adhered (indicated as P in the table) than the former.
In the latter case, the press formability was poor. This is because, in the former case (Example 20 of the present invention), the alumina and the phosphoric acid compound coexist in the coating, and the alumina and the phosphoric acid compound have a synergistic effect on the improvement of press moldability. it is conceivable that.

[0089]

[Table 2]

Example 3 The same GA as in Example 2 was used as the base material, this was degreased with alkali, and the surface thereof was coated with a treatment liquid having the composition shown in Table 3 using a roll coater.
Dried in infrared oven. The drying temperature at this time is 4
5 ° C.

Table 3 shows the composition of the treatment liquid (concentrations of alumina sol and phosphoric acid), the coating amount of the treatment liquid, and the amount of alumina contained in the film formed on the surface of the base steel sheet and phosphorus. The amount of the phosphoric acid compound (indicated as the attached amount in the table) is shown. A feather-like alumina sol was used.

With respect to the sample manufactured as described above, press moldability and adhesiveness were evaluated in the same manner as in Example 2.

The evaluation results are also shown in Table 3. As is clear from this result, when the coating amount of the treatment liquid is out of the range specified in the present invention, both press moldability and adhesiveness cannot be maintained well, and the amount of alumina or phosphoric acid compound attached If there were many, powdering occurred.

[0094]

[Table 3]

[0095]

The zinc-plated steel sheet of the present invention has excellent press formability, and is also excellent in spot weldability, chemical conversion treatment property, and electrodeposition coating property, or in addition to excellent press formability. It also has good adhesiveness and is particularly suitable as a material for automobiles. This galvanized steel sheet is
If the method of the present invention is applied, no special means is required,
It can be manufactured inexpensively and easily.

[Brief description of the drawings]

FIG. 1 is a diagram showing a crystal structure of a film (phosphorus deposition amount: 25 mg / m ² ) formed on the surface of a zinc-based plated steel sheet according to the present invention, in which (a) is a magnification of 3000 and (b) is a magnification of 2000.
0.

FIG. 2 is a diagram showing a crystal structure of a coating film (phosphorus deposition amount: 100 mg / m ² ) formed on the surface of a zinc-based plated steel sheet of the present invention, in which (a) is a magnification of 3000 and (b) is a magnification of 200.
00.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C25D 5/48 C25D 5/48 (72) Inventor Tadashi Sakane 4-5 Kitahama, Chuo-ku, Osaka-shi, Osaka No. 33 Sumitomo Metal Industries, Ltd.

Claims (4)

[Claims] 1. An amorphous reaction product of phosphoric acid and zinc is contained in the range of 20 mg / m ² or more and 350 mg / m ² or less in terms of phosphorus on the surface of the plating layer of a zinc-based plated steel sheet. A zinc-based plated steel sheet excellent in press formability, which is characterized in that 2. A surface of a plating layer of a zinc-based plated steel sheet, containing 15 mg / m ² or more and 100 mg or more of an amorphous phosphoric acid compound of 5 mg / m ² or more and 350 mg / m ² or less in terms of phosphorus.
/ M ² or less, a zinc-based plated steel sheet having excellent press formability, which has a coating film made of a mixture in which alumina is dispersed. 3. The surface of the plating layer of a zinc-based plated steel sheet, 2
1m of phosphoric acid aqueous solution with a concentration of more than 30% by weight
Apply within the range of 1 / m ^{2 to} 10 ml / m ² and apply 4
A method for producing a zinc-based plated steel sheet having excellent press formability, which comprises drying at 0 ° C or higher. 4. Feather-like alumina sol is added to the surface of the plating layer of a zinc-based plated steel sheet so as to have a concentration of 0.15% by weight or more and 10% by weight or less, Concentration of phosphoric acid aqueous solution 1 ml / m ² or more 10
A method for producing a zinc-based plated steel sheet having excellent press formability, which comprises coating within a range of ml / m ² or less and drying at 40 ° C. or more.