JPH0770795A - Composite zinc plating metallic sheet and production therof - Google Patents

Abstract

PURPOSE:To remarkably improve a molding work property and a spot welding while keeping the excellent corrosion resistance of a zinc plating steel sheet. CONSTITUTION:The steel sheet is subjected to electroplating using the acidic plating liq. adding 0.001-10wt.% lignin sulfonic acid (salt) and 0.001--10wt.% higher alcohol or >=100mol.wt. ether or ester, and composite zinc plating film coprecipitating the carbon of 0.001-10wt.% average carbon content and 5-200g/m<2> deposit is formed. The plating film has a carbon concentrated layer on a surface, and its thickness is >=0.1mum and <=10mum and occupies 10-50% of the thickness of the plating film. And, the orientation property index of the (00.2) face of the zinc phase (eta) of the plating film is <=0.6 and the orientation property index of the (10.1) face is >=0.2.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention is suitable as a material for automobiles, home electric appliances, building materials and the like, has good corrosion resistance and formability, and has a markedly improved resistance spot weldability, particularly continuous spotting property during resistance spot welding. In addition, the present invention relates to a composite galvanized metal plate and a method for manufacturing the same.

[0002]

2. Description of the Related Art Various surface-treated metal sheets, particularly surface-treated steel sheets, are used in various fields such as automobiles, home electric appliances, and building materials. With the increase in the amount used, the demand for improving the rust prevention ability of these surface-treated steel sheets is increasing. For example, as surface-treated steel sheets for automobiles, 10-year puncture corrosion resistance in salt-damaged areas and 5-year outer surface rust resistance High corrosion resistance with the goal of corrosion resistance is required.

For automobile bodies, especially for automobile bodies for cold regions used in severe corrosive environments, the application of rust-preventing steel plates having various surface treatments for rust-prevention has been actively promoted. It was The most common rustproof steel sheet is a galvanized steel sheet by hot dipping or electroplating. To further improve the corrosion resistance of galvanized steel, Zn is replaced by Fe, N
Various zinc-based alloy-plated steel sheets alloyed with at least one metal such as i, Co, Mn, Cr and Al have also been proposed, and some of them (eg, Zn-Ni alloy-plated steel sheets) have already been put to practical use. Has been done.

[0004] Such a galvanized steel sheet and a zinc-based alloy-plated steel sheet (hereinafter, both are collectively referred to as a zinc-based plated steel sheet) have improved corrosion resistance due to the plating film, but are often used in the assembly process by consumers. The bondability by resistance spot welding (resistance spot weldability, hereinafter also simply referred to as spot weldability) is not improved and may be lowered in some cases, and has not reached the level satisfying the demand of customers. In addition, the zinc alloy plating with Ni or Co, which is particularly effective for improving the corrosion resistance, is expensive because Ni and Co are expensive.

In order to improve the corrosion resistance, a multi-layer plated steel sheet provided with two or more plating films has also been proposed. For example, in JP-A-60-215789, an adhesion amount of 10 to 300 g / m ²
A zinc-plated layer as a lower layer, one or both of Ni and Co in a total amount of 15 to 30% by weight, and a multi-layer plated steel sheet having a zinc-based alloy plating layer having an adhesion amount of 1 to 20 g / m ² as an upper layer is Have been described. The double-layer plated steel sheet described in JP-B-58-15554 has Fe-based flash plating on the upper layer for the purpose of improving the phosphate chemical conversion treatment property and electrodeposition coating property, and the effect of improving the coating film adhesion This is intended to indirectly improve the corrosion resistance. Even with these multi-layer plated steel sheets, in order to achieve the high corrosion resistance required by customers, it is necessary to increase the amount of the Zn coating layer below, which causes problems in formability, corrosion resistance after work coating, spot weldability, etc. Occurs. Moreover, since the plating process is repeated twice, the manufacturing apparatus becomes complicated. Furthermore, JP-A-60
The one described in Japanese Patent Laid-Open No. 215789 is also disadvantageous in terms of cost because the upper layer plating contains a large amount of Ni and Co.

[0006]

Therefore, while maintaining the corrosion resistance capable of withstanding the harsh environment of use, it has a high level of formability and resistance spot weldability required for the assembly process at the customer's side, and can be manufactured at low cost. The emergence of a surface-treated metal plate that can be done is required. Especially for automobiles, since it is painted after processing, it is necessary to have excellent coating adhesion and to secure corrosion resistance (corrosion resistance after painting) at the scratches and end faces after painting.

In response to this demand, the present invention is excellent in corrosion resistance, moldability and coating adhesion, and at the same time, resistance spot weldability,
In particular, it is an object of the present invention to provide a surface-treated metal sheet and a method for producing the same, in which continuous spotting property during resistance spot welding is remarkably improved.

[0008] Another object of the present invention is to provide a zinc-plated metal sheet with a single coating layer and / or a thick zinc coating layer, while maintaining corrosion resistance, coating adhesion and formability. (EN) An inexpensive galvanized metal sheet having markedly improved resistance spot weldability and a method for producing the same.

[0009]

According to the present invention, corrosion resistance,
Provided is a composite galvanized metal sheet having excellent formability and coating adhesion, and remarkably improved resistance spot weldability.

This composite galvanized metal sheet has, on one side, a carbon content of 0.001 to 10 on at least one side of the metal sheet.
It has a carbon-containing composite zinc plating film with wt% and an adhesion amount of 5 to ²⁰⁰ g / m ² , and this plating film has C concentrated on the surface layer.
The thickened layer has a thickness of 0.1 μm or more and 10 μm or less and occupies 5 to 50% of the thickness of the plating film.

From another aspect, the composite galvanized metal sheet has a carbon content of 0.001 to 0.001 on at least one side of the metal sheet.
It has a carbon-containing composite zinc plating film of 10 wt% and an adhesion amount of 5-200 g / m ² , and the orientation index of the (00 ・ 2) plane of the η phase in this plating film is 0.6 or less, (10 ・ 1) The feature is that the orientation index of the surface is 0.2 or more.

The above composite galvanized metal plate has 0.001 to 10 wt.% Of ligninsulfonic acid or its salt on the metal plate.
%, Higher alcohols, ethers having a molecular weight of 100 or more and esters having a molecular weight of 100 or more, or 0.002 to 10% by weight in total, and electroplating is performed in an acidic zinc plating solution. It can be manufactured by the method.

[0013]

As described above, many zinc-based alloy-plated steel sheets have been developed as rustproof steel sheets for automobiles. These are generally superior in terms of bare corrosion resistance compared to zinc (pure Zn) plated steel sheets when compared with the same amount of coating. However, even with a galvanized steel sheet, the bare corrosion resistance is improved to the same degree by increasing the amount of adhesion and increasing the thickness. Moreover, such a galvanized steel sheet with a thick plating is supposed to be used in an actual environment.
In the end face corrosion resistance test after coating and the corrosion test with flaws, it shows much more stable and superior corrosion resistance than the alloy-plated steel sheet. This is because, in many cases, alloy plating often sacrifices some of its sacrificial anticorrosion ability in order to improve the corrosion resistance of the plating film, whereas thick zinc plating has the sacrificial anticorrosion effect of zinc. This is because the

Therefore, in practical use, the galvanized steel sheet is never inferior in corrosion resistance, and is advantageous over the alloy-plated steel sheet in terms of cost. Rather, the problems with galvanized steel sheets are the formability and resistance spot weldability. Zinc has a high ductility and powdering of the plating film is unlikely to occur during processing, but due to its large coefficient of friction, it is easily seized in the mold during press molding, and defects are likely to occur on the surface of the processed material. In addition, during resistance spot welding, Zn is applied to the Cu-based electrode.
As a result of diffusing and wear of the electrodes, continuous dot performance is greatly reduced. The phenomenon leading to the deterioration of the formability and the spot weldability becomes more remarkable as the amount of zinc plating attached increases.

In view of this point, the present invention improves corrosion resistance and formability by improving the formability and resistance spot weldability of galvanized steel sheets, especially thickly galvanized steel sheets without sacrificing corrosion resistance. The present invention enables a galvanized steel sheet having a satisfactory level of both spot weldability and a rust preventive steel sheet for automobiles.

As a result of repeated studies on electrogalvanizing conditions, the present inventors perform electrogalvanizing by adding ligninsulfonic acid and a specific organic compound together in a plating solution in an amount within a certain range. Then, it was found that the formability and spot weldability of the galvanized steel sheet were improved while maintaining the corrosion resistance. When the plating film at that time was examined, it was found that 0.001 to 10 wt% of carbon was a co-deposited carbon-containing composite zinc-based plating film.

When a carbon-containing composite galvanized coating having improved formability and spot weldability was examined from the chemical structure, this galvanized coating was found to have a carbon-enriched carbon-rich layer on the surface of the galvanized coating. Was formed, and the thickness of the C-enriched layer was within the range of 0.1 to 10 μm and was less than half of the thickness of the entire plating film (specifically 5 to 50%).

The reason why the C-enriched layer is formed on the surface of the plating film is not clear, but it is presumed as follows at present.
Carbon is produced by decomposition of an organic compound in a plating solution by an electrode reaction, and is co-deposited with a plating metal. However, since the metal electrodeposition reaction rate is higher than the electrode reaction of the organic compound, it is considered that carbon eutectoid is delayed and carbon is relatively concentrated on the plating surface layer. As a result, despite the fact that it is a single-layer plating, the cross section of the plating film differentiates into a lower layer with a low carbon content and a surface layer with a high carbon content (C-enriched layer), similar to the two-layer plating. The effect of can be obtained.

In the present invention, the "C-enriched layer" means the C concentration profile in the cross-sectional depth direction of the plating film.
It means a portion where the C concentration is higher than the average C concentration. The C concentration in the depth direction of the plating film is, for example, glow discharge emission (GDS).
It can be measured by analysis. Based on this measurement result, the average value of the C concentration in the depth direction of the plating film was obtained,
The thickness of the high concentration portion is defined as the thickness of the C-enriched layer. The thickness of the C-enriched layer in the present invention is a value measured as described above based on the result of glow discharge emission analysis.

This C-enriched layer has a higher electric resistance than the conventional zinc-based plating film in which carbon is not co-deposited, so that the amount of heat generated by resistance during spot welding is significantly increased.
A joint called a nugget is easily formed. By forming the C-enriched layer only on the surface layer of the plating film, the spot weldability is remarkably improved without sacrificing the corrosion resistance. This is because the C concentration in the C-enriched layer is only about 2 to 3 times the average C concentration of the plating film, and the Zn with a low C concentration occupies more than half the thickness of the plating film below it.
Since the layer is present, even if the C-enriched layer is formed, the corrosion resistance of the plating film does not decrease, but may even become good. Further, in this plating film, the C-concentrated layer on the surface layer is harder than the pure Zn film and has a low friction coefficient, so that seizure on the mold hardly occurs and the press formability is good. Since the C-enriched layer is hard, powdering may occur. However, the C-enriched layer exists only on the surface layer and the ductile Zn layer exists on the lower side, so that powdering can be avoided.

In the galvanized coating of the present invention, the thickness of the surface C concentrated layer is 0.1 μm or more and 10 μm or less, and the C concentrated layer occupies 5 to 50% of the thickness of the plated coating. When the thickness of the C-enriched layer is less than 0.1 μm or less than 5% of the thickness of the plating film, the spot weldability is insufficiently improved due to the increase in the amount of resistance heat generated by C eutectoid. On the other hand, when the thickness of the C-enriched layer is more than 10 μm or exceeds 50% of the thickness of the plating film, electrode contamination due to a large amount of carbon adhering to the center of the electrode becomes worse when continuous spot welding is performed by spot welding. However, this becomes an electrical insulator and the nugget is no longer formed, and contrary to the purpose, the spot weldability deteriorates again. The thickness of the surface layer C concentrated layer is preferably 0.1 to 5 μm, more preferably 0.5 to 3 μm.
The thickness of the C-enriched layer preferably accounts for 5 to 40%, more preferably 10 to 30% of the thickness of the plating film.

Further, the present inventors have conducted a crystallographic study on the above-mentioned carbon-containing composite galvanized coating.
In this galvanized film, the metal matrix excluding the co-deposited carbon phase is composed of a Zn phase called η phase except for the portion close to the underlying metal plate. The η phase has a close-packed hexagonal crystal form extending in the c-axis direction and has orientation. When the present inventors investigated the crystallographic characteristics of the η phase in the plating film by X-ray diffraction measurement, regarding the carbon-containing composite zinc plating film excellent in formability and spot weldability,
The orientation index of the (00 ・ 2) plane of the η phase is 0.6 or less.
It was found that the 1) plane had an orientation index of 0.2 or more.

Here, the "orientation index" of each surface [eg, (00 · 2) surface] is an index indicating the degree of orientation relative to the degree of orientation of the same surface of the zinc standard substance registered in ASTM. Based on the measured value of the diffraction intensity of each surface in the X-ray diffraction measurement, for example, the (00 · 2) surface is calculated by the following equation.

[0024]

[Equation 1]

[0025] In the above formula, I _{XX · X} is the test materials X-ray diffraction peak intensity of (XX · X) plane, IR _{XX · X} is the zinc standard registered in ASTM (XX · X) surface of It represents the X-ray diffraction peak intensity. Here, the diffraction angle (Co 2 θ) of each plane is 42.4 for the (00.2) plane.
°, (10.0) plane is 45.6, (10.1) plane is 50.7 °, (10.2)
Surface is 64.0 °, (10.3) surface is 83.6 °, (11.0) surface is 84.4 °
°.

Therefore, when the orientation index of a surface is 1, it means that the orientation degree of the surface is the same as that of the standard substance. The smaller the orientation index, the smaller the orientation degree of the surface. In the composite galvanized film of the present invention, the η phase (00 ・ 2)
Since the orientation index of the surface is 0.6 or less, the orientation degree of this surface is considerably smaller than that of the standard substance.
In addition, the orientation index of the (10 ・ 1) plane must be 0.2 or more.
If the orientation index of the (00 ・ 2) plane exceeds 0.6 or the orientation index of the (10 ・ 1) plane becomes smaller than 0.2, the resistance spot weldability remarkably deteriorates.

The orientation of the (00 ・ 2) plane of the η phase is small, and (10.
1) If the orientation of the surface is large, it is presumed that the resistance spot weldability is improved because the contact resistance with the electrode increases due to electrical anisotropy and the diffusion of Zn to the electrode is suppressed. .

The orientation index of the (00 · 2) plane is preferably 0.
It is 5 or less, more preferably 0.4 or less. On the other hand, (10
The orientation index of the 1) plane is preferably 0.3 or more, more preferably 0.5 or more. Most preferably, the orientation index of the (00 · 2) plane is 3.0 or less, and the orientation index of the (10 · 1) plane is 1.0 or more, whereby a marked improvement in spot weldability is achieved.

Regarding the plating film of the composite galvanized metal sheet of the present invention, the above-mentioned crystallographic characteristics are compatible with the chemical structural characteristics defined by the surface layer C concentrated layer, but both of them are not necessarily required. It is not necessary to check that it has the characteristics of. That is, in order to obtain a galvanized metal sheet with improved formability and spot weldability, it is sufficient to investigate only the chemical structure of the plating film and have the above C-enriched layer, or the crystal of the plating film. It is only necessary to investigate the structure and have the above-mentioned characteristics of the orientation index. Further, as described later, when the base material is a plated metal plate, it may not be possible to investigate the above crystallographic orientation of the plating film, so only the chemical structure of the plating film will be investigated. .

Corrosion resistance basically depends largely on the amount of zinc plating deposited. If the amount of the composite galvanized coating of the present invention deposited is 5 g / m ² or less, the rust-preventive effect will be insufficient and this plating will be insufficient. It becomes difficult to form a C-concentrated layer of 0.1 μm or more on the surface layer of the film. On the other hand, when the coating amount of the plating film exceeds 200 g / m ² , the cost is high, there is a problem in practical use, and the formability and spot weldability also deteriorate.
Therefore, the adhesion amount of the composite galvanized film of the present invention is 5 to
200 g / m ²

As described above, the composite galvanized metal sheet of the present invention is excellent in formability and resistance spot weldability even with thick plating, so that the adhesion amount of 40 g / m ² or more is sufficient. In the case of plating, the advantage can be exhibited particularly.
In that sense, the preferable adhesion amount is 40 to 100 g / m ² , and more preferably 40 to 80 g / m ² . Further, as described later, the metal plate of the base material may be a plated material, in which case the composite galvanized coating of the present invention is a thin plating necessary for improving spot weldability (eg, 5 to 50 g). / m ² , preferably 10-40 g / m
² ) is sufficient, and if the amount of adhesion is too large, the formability and spot weldability may rather deteriorate.

The carbon content of this composite galvanized coating is 0.001 to 10 wt% as described above. When the carbon content is less than 0.001 wt%, the above-mentioned C-enriched layer or η
Since the plating film having the phase orientation cannot be formed, the spot weldability cannot be sufficiently improved. If the carbon content in the plating film exceeds 10 wt%, the ductility of the plating film will decrease, powdering will likely occur during molding, and the appearance of the plating surface will also deteriorate. The carbon content of the galvanized film is preferably 0.05 to 5 wt%, more preferably 0.5 to 3 wt%.

Next, a method for manufacturing the composite galvanized metal sheet of the present invention will be described. Base metal plate The base material of the composite galvanized metal plate of the present invention is usually a normal steel plate, especially a cold-rolled steel plate, but an aluminum plate is used for weight reduction, depending on the purpose of use and the site of use. A suitable metal plate can be selected.

Further, in order to further improve the corrosion resistance, as a base metal plate, a plated metal plate that has been appropriately plated in advance by a conventional method (eg, zinc-plated steel plate, zinc-based alloy-plated steel plate, aluminum-plated steel plate, Aluminum alloy plated steel sheet, etc.) may be used. Preferred as the plated metal plate is a galvanized steel plate in terms of cost,
This may be an electrogalvanized steel sheet, a hot-dip galvanized steel sheet, or an alloyed hot-dip galvanized steel sheet. The amount of the plating film deposited on the base material is not particularly limited, but it is preferable that the coating weight is about 50 g / m ² or less because the composite zinc plating film of the present invention is further formed thereon.

When the base material is a plated steel sheet having a coating film having a zinc phase (η phase) (eg, galvanized steel sheet), the η in the coating film of the base material is measured by X-ray diffraction.
Phase diffraction is also included. Therefore, since it is not possible to know the orientation state of the η phase of the composite galvanized coating of the present invention from this X-ray diffraction measurement, in this case, the thickness of the C-enriched layer in the composite galvanized coating is investigated, and this is It only has to meet the conditions.

Plating Method The above-mentioned composite zinc plating film can be formed by electrogalvanizing using an acidic zinc plating solution containing the following two kinds of organic compounds: ligninsulfonic acid or a salt thereof in an amount of 0.001 to 10wt%;
0.001 to 10 wt% of one or more selected from higher alcohols, ethers having a molecular weight of 100 or more and esters having a molecular weight of 100 or more.

Lignin sulfonic acid is a substance produced when wood or other lignin-containing raw material is treated with sulfurous acid or its derivative, and is a large amount of by-produced from pulp manufacturing waste liquor in the paper manufacturing industry. Therefore, lignin recovered from this by-product. Sulfonic acid or its salt can be obtained at low cost. The lignin sulfonic acid may be in the free acid or salt form. As the salt, alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt and magnesium salt, and various heavy metal salts can be used.

Among the organic compounds mentioned above, the higher alcohol means a chain alcohol having 6 or more carbon atoms, such as a polyhydric alcohol such as glycol, an unsaturated alcohol having a double bond or a triple bond, or a branched side chain. It may be a branched chain alcohol having. Examples of useful higher alcohols include 1-hexanol, 1-octanol, 2-
Ethyl-1-hexanol, nonyl alcohol, decyl alcohol, 1-octen-3-ol, 1-hexyne-3-ol, 1,6-hexanediol and the like can be mentioned.

As the ether, one having a molecular weight of 100 or more is used. This ether may be either a monoether having only one ether bond in the molecule or a polymerized ether having two or more ether bonds. Examples of polymerized ethers are polymers of lower alkylene glycols such as ethylene glycol and propylene glycol, that is,
Polymerized glycol. Further, the ether molecular chain may have an unsaturated bond or a branched chain. Useful ethers include monoethers such as di-n-butyl ether, di-n-amyl ether and di-n-hexyl ether,
And polyethylene glycol (molecular weight about 1000),
Polymerized ethers such as polypropylene glycol (molecular weight of about 1000) are exemplified.

The ester also has a molecular weight of 100 or more,
Either a monoester having only one ester bond in the molecule or a polymerized ester having two or more ester bonds may be used. Examples of useful esters include monoesters such as acetylsalicylic acid, and polymerized esters of methyl lactate polymerized ester (molecular weight of about 10,000) and ethyl tartrate polymerized ester (molecular weight of about 10,000).

When the compound of (1) is a lower alcohol, or an ether or ester having a molecular weight of less than 100, a sufficient C-enriched layer cannot be formed in the plating film, or the η layer is oriented as described above. Cannot be controlled.
The upper limit of the carbon number of the compound is not particularly specified, but in the case of alcohol or monoether or monoester,
When the molecular weight becomes large, it becomes difficult to dissolve the required amount in the acidic plating solution, so that the one having a molecular weight within the range in which the required amount is soluble in the plating solution is used.

The amount of ligninsulfonic acid (salt) added to the plating solution is 0.001 to 10 wt% of alcohol, ether or ester (hereinafter, also referred to as a second organic compound).
Is still 0.001-10 wt%. The preferred addition amount is 0.05 to 5 wt% of lignin sulfonic acid (salt), especially 0.1 to 3 wt.
%, The second organic compound is 0.02 to 2 wt%, especially 0.05 to
It is 1 wt%. More preferably, at least one of these is 0.5 wt%. It should be noted that any of the above can use one kind or two or more kinds of compounds.

As the acidic plating solution used for electroplating, a sulfate type or hydrochloride type zinc plating solution can be used. The electrogalvanization can be carried out by cathodic electrolysis by energizing the base metal plate as a cathode according to a conventional method except that the above organic compound is added to the acidic plating solution. Typical plating conditions using the sulfate type plating solution are as follows.

[0044] _{ZnSO 4 · 7H 2 O: 10~60} wt% Na 2 SO 4 + (NH 4) 2 SO 4: 5~20 wt% pH: 1~4 Bath temperature: 40 to 65 ° C. Current density: 40 150 A / dm ² liquid flow rate: 0.01 to 3 m / sec In a preferred embodiment of the present invention, the above electroplating is carried out,
(a) Off time is 1 ms or more, 1 s or less, and the duty ratio is
Pulse current with a current waveform of 0.5 or more, or (b) DC current with alternating current having a frequency of 1 Hz or more and 100 Hz or less and current fluctuation width of ± 1% or more and ± 50% or less, or this AC Is performed by energizing a pulsed current that is superimposed. As a result, organic compounds in the plating solution
Even if the addition amount of (lignin sulfonic acid or its salt and the above-mentioned second organic compound) is the same, it is possible to form a composite galvanized film in which the C content is remarkably increased as compared with ordinary direct current electrolysis, Since the thickness of the C concentrated layer on the surface layer becomes large and the orientation of the η phase becomes more preferable, the resistance spot weldability is further improved. The reason for this is that when the pulse current is turned off or when the superposed alternating current is low, the organic compound added to the plating solution is effectively not disturbed by the polarity due to the voltage applied to the base metal It is speculated that a larger amount of carbon may be co-deposited in the plating film by being adsorbed by.

Further, by carrying out electrolysis with a pulse current or a direct current or a pulse current superposed with an alternating current, a composite galvanized film with less internal stress and reduced cracks and pinholes is formed. as a result,
The adhesion of plating film, coating adhesion, bare corrosion resistance, and moldability are also improved.

A metal plate whose base material is a composite galvanized film in which 0.001 to 10 wt% of carbon is co-deposited by electroplating in an acidic plating solution containing ligninsulfonic acid (salt) and the second organic compound described above. Formed on the surface. This plating film has the aforementioned C-enriched layer on the surface layer, and its η phase exhibits the above-mentioned orientation. Since the composite galvanized metal sheet of the present invention exhibits excellent formability and spot weldability in addition to corrosion resistance even in thick plating, it can be used as it is as an anticorrosive metal sheet for automobiles in the manufacture of automobile bodies.

In the production of an automobile body, generally, after being formed into a desired shape, a chemical conversion treatment (usually a phosphate treatment) is applied and then coating is carried out. However, the composite galvanized metal sheet of the present invention has a corrosion resistance after coating. Since the (corrosion resistance and the end surface corrosion resistance in the case where a coating film has a flaw) is improved, it is possible to satisfy the high corrosion resistance performance required for an automobile body.

The composite galvanized metal sheet of the present invention is useful not only for automobiles but also for home electric appliances and building materials. In addition,
As described above, the composite galvanized metal sheet of the present invention can be used as it is for various purposes, but depending on the application and environment of use, a chemical conversion treatment in which only the chromate treatment is further applied onto the composite galvanized film. It can also be used as a plated metal plate or an organic composite-coated metal plate which has been subjected to a chromate treatment and an organic thin film coating (eg, an epoxy resin coating having a film thickness of 2 μm or less). Further, the composite galvanized film may be formed on only one surface of the base material or may be formed on both surfaces depending on the application and the required rust preventive property.

[0049]

【Example】

The cold-rolled steel sheet Production of coated steel sheet (thickness 0.8 mm) or galvanized steel sheet (0.8 mm in both sides of the cold-rolled steel plate having a thickness in the coating weight 30 g / m ² per surface that has been subjected to electro-galvanized) Mother As a material, the base material is electrolyzed on one side of the base material in a sulfate type acidic plating solution in which sodium ligninsulfonate and a second organic compound are added as shown in Table 2 under the following basic plating conditions. It was galvanized.

The plating _{solution: ZnSO 4 · 7H 2 O 80~160} g / L Na 2 SO 4 65 g / L pH 1.6 ~2.6 Bath temperature: 50 ± 10 ° C. solution flow rate: 0.06~1.40 m / sec anode: Pb- The 1% Ag electrolysis was carried out by applying a direct current, a pulse current, or a direct current or a pulse current in which alternating current is superposed as shown in Table 1 below. In Table 1, electrolysis method number 0 is direct current electrolysis, 1 to 3 are pulse current electrolysis, 4 to 5 are direct current electrolysis in which alternating current is superposed, and 6 is pulse current electrolysis in which alternating current is superposed. For example, in 4, the alternating current having a current fluctuation width of ± 1.0% = ± 0.6 A is superimposed on the direct current having a current density of 60 A / dm ² . Similarly, at 5, a direct current with a current density of 90 A / dm ² ,
An alternating current having a current fluctuation width of ± 50% = ± 45 A was superimposed. The adhesion amount of the plating film was controlled by the energization time.

[0051]

[Table 1]

[Chemical and Crystallographic Properties of Plating Film]
The carbon content of the plating film of the obtained electrogalvanized steel sheet (when the base material is a galvanized steel sheet, does not include the plating layer of the base material, the plating film formed in this example) is It was mechanically peeled from the steel sheet and measured by gas analysis by the combustion method.

Further, the change in C concentration in the depth direction of the cross section of this galvanized film was measured using a glow discharge emission spectrometer (GDLS-5017) manufactured by Shimadzu Corporation. With this analyzer, the concentration profile of each element of Fe, Zn, and C in the cross-sectional direction of the plated steel sheet was measured. An example of the measurement result is shown in FIG. For comparison, a plating film having a carbon content of 0% formed by using a plating solution containing neither sodium ligninsulfonate nor a second organic compound (test in Table 2
Figure 2 shows an example of the concentration profile of No. 37). From the measured data of the C concentration, the average C content in the plating film, the thickness of the surface C-enriched layer, and the thickness of the plating film (in the case where the base material is a galvanized steel sheet, the plating film formed in this example is The ratio (%) of the thickness of the C-enriched layer to the thickness was calculated.

Further, the orientation indices of the (00 · 2) plane and the (10 · 1) plane of the η phase of the galvanized coating were calculated based on the X-ray diffraction measurement values by the method described above. The X-ray diffraction measurement was performed using a strong X-ray diffractometer with Co as a target. For Test Nos. 21 to 24 in which the base material was a Zn-plated steel sheet, this measurement was not performed because the orientation index could not be measured accurately as described above.

[Test of galvanized steel sheet] As the performance of the electrogalvanized steel sheet obtained in this example, the corrosion resistance after coating (corrosion resistance at the flaws and the end surface after coating), forming workability, and resistance spot weldability were as follows. It was evaluated by the method.

Corrosion resistance after coating (corrosion resistance of flaws after coating) 70 mm x 150 mm from galvanized steel sheet
mm test piece was cut out, the plated surface of this unprocessed flat plate was degreased with the degreasing agent FC4336 (manufactured by Nippon Parkerizing Co., Ltd.), and the surface was adjusted with the adjusting liquid PZT (manufactured by Nippon Parkerizing Co., Ltd.). A chemical conversion treatment was carried out using PB-L3080 (manufactured by Nippon Parkerizing Co., Ltd.), followed by a cationic electrodeposition coating with a thickness of 20 ± 1 μm using U-80 (manufactured by Nippon Paint Co., Ltd.) and baking at 175 ° C. for 25 minutes. After that, an intermediate coating (40 μm) for automobile alkyd paint, baking, and melamine
Top coating (40 μm) of polyester paint and baking were performed to prepare coated samples.

On the evaluation surface (painted surface) side of this coated sample, a cross-cut reaching the steel plate base was put with a cutter knife,
A complex corrosion test with the following cycle settings was performed. Salt spray (5% NaCl, 35 ° C, 7 hours) → dry (50 ° C, 2 hours) → wet (RH 85%, 50 ° C, 15 hours).

The evaluation was carried out in the following five stages based on the measured value of the blister width found in the cross cut portion after the above corrosion test was carried out for 30 cycles. ◎: Blister width <0.5 mm ○: Blister width <1.0 mm △: Blister width <2.0 mm ×: Blister width <3.0 mm × ×: Blister width ≧ 3.0 mm.

(Corrosion resistance of end surface after coating) Test piece of galvanized steel was press-punched by adjusting the clearance of the die so that the burrs on the end surface of the test piece would be 10% of the plate thickness. Then, electrodeposition coating, intermediate coating, and top coating were performed to prepare coated samples. This coated sample was subjected to the complex corrosion test of the above cycle. Evaluation is based on the area ratio of red rust on the end face after 60 cycles of corrosion test
The process was divided into stages. ⊚: No red rust occurred ○: 5% or less △: 10% or less ×: 30% or less XX: more than 30%

[0060] The disk-shaped blank moldability diameter from (processability) galvanized steel sheet 90 mm was taken, diameter 50 mm, and a cylindrical deep drawing depth 28 mm, a plating film of the side wall surface Was peeled off with a transparent adhesive tape, the peeled amount was visually inspected, and the tape area ratio with the peeled pieces adhered was evaluated according to the following criteria. 5: No peeling at all 4: Adhered area ratio of peeled pieces less than 10% 3: Same as 10% or more, less than 30% 2: Same as 30% or more, less than 50% 1: Same as 50% or more (formability) Above deep drawing Presence of blank break during
⊚, None: ×)

Spot Weldability Continuous spot welding was performed under the following conditions using a single-phase AC spot welder.

Current: 10,000 A Pressurization: 200 kgf Energization time: 12 cycles (at 60 Hz) Electrode shape: Dome Welding method: "1 point / 2 seconds, 20 points continuous welding, 40 seconds or more pause" This cycle is repeated. N for every 100 points
= 3 shear test pieces are taken, and the nugget diameter is measured after the tensile test.

Judgment Criteria: Number of consecutive dots (nugget diameter is 3.
The number of spots that were continuously spot welded to 6 mm or more) The test results are shown together with the results of the measurement of the coating amount of the coating film, the C content, the thickness and ratio of the C-enriched layer, and the orientation of the η phase. It is also shown in 2.

[0064]

[Table 2]

As can be seen from Table 2, 0.001 wt% or more of sodium lignin sulfonate and 0.001 wt% of the second organic compound
% Of carbon by 0.001 to 10 wt% of carbon by electroplating from an acidic plating solution containing 0.1% or more and the thickness of the surface layer C concentrated layer is 0.1 μm or more and 10 μm or less and the thickness of the plating film is 5 to 5%. A composite galvanized film, which accounts for 50%, was formed. In addition, this galvanized film has an η phase of (00 ・ 2)
The orientation index of the plane is 0.6 or less, and the orientation index of the (10 ・ 1) plane is
It had a crystallographic property of 0.2 or more.

The composite galvanized steel sheet of the present invention having these plating film characteristics was excellent in corrosion resistance both on the flaw portion and the end surface after coating. In addition, despite the thick plating of 60 g / m ² , the forming workability was good, and the resistance spot weldability, which was a continuous improvement of 8,000 or more, was remarkably improved.

Comparing Test Nos. 12 to 15 with Test Nos. 17 to 20, even if the same plating solution composition was used, electrolysis was carried out by superimposing pulsed current or alternating current. The carbon content of the plating film is high, the thickness and ratio of the surface C concentrated layer increase, the orientation index of the (00 ・ 2) plane of the η phase is small, and the orientation index of the (10 ・ 1) plane is opposite. It can be seen that it becomes extremely large. In particular, if the orientation index of the (00 ・ 2) plane of the η phase is 0.4 or less and the orientation index of the (10 ・ 1) plane is 0.5 or more, the number of continuous dots in 60 g / m ² thick plating is If it exceeds 10,000, the former is 0.3 or less, and the latter is 1.0 or more, the continuous welding number is 11,000 to 13,000, and spot welding is remarkably improved.

On the other hand, in Comparative Example, if the addition of sodium lignin sulfonate and one of the second organic compounds to the plating solution was omitted, the carbon content of the plating film was 0.
Even if the thickness of the C-enriched layer was 001 wt% or more and the thickness was 0.1 μm or more, the proportion of the C-enriched layer in the plating film was insufficient. Therefore, the spot weldability was as low as 5000 or less in the number of continuous spots. If neither of these two types of organic compounds is added, or if the amounts of both are very small, a C-enriched layer is not formed, spot weldability is significantly reduced, and press formability is poor (deep draw forming). (Material rupture). Also,
When either one of the organic compounds was added in a large amount exceeding 10 wt% and the C content of the plating film exceeded 10 wt%, the spot weldability was remarkably improved, but the workability deteriorated.
The plating film peeled due to powdering. Further, in the comparative example in which toluenesulfonic acid was used as the sulfonic acid, carbon did not co-deposit in the plating film, and the test results deteriorated in each item. Further, in the comparative example in which methanol was used as the alcohol, the spot weldability was significantly reduced.

[0069]

INDUSTRIAL APPLICABILITY The galvanized metal sheet of the present invention is a composite galvanized coating in which the plated coating has a C-enriched layer on the surface and the η phase is co-deposited with carbon having a specific orientation. Even if the plating layer is a single layer, it retains the high corrosion resistance peculiar to the galvanized coating and has superior formability compared to the conventional galvanized metal sheet, and at the same time, the resistance spot weldability is significantly improved. . Therefore, they are useful for automobiles, home appliances, building materials, etc., and are most suitable for automobile outer panels.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of C, Zn, and Fe concentration change profiles in the cross-sectional direction of the surface of a composite galvanized steel sheet of the present invention.

FIG. 2 is a diagram showing an example of a similar concentration change profile of a conventional galvanized steel sheet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Yoshida 4-53-3 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries, Ltd. (72) Inventor, Kiyoyuki Fukui 4-53, Kitahama, Chuo-ku, Osaka No. Sumitomo Metal Industries Co., Ltd.

Claims (4)

[Claims] 1. A metal-containing composite zinc plating film having a carbon content of 0.001 to 10 wt% and an adhesion amount of 5 to ²⁰⁰ g / m ² is provided on at least one surface of a metal plate, and this plating film has a high concentration of C on the surface layer. A composite galvanized metal plate, characterized in that the thickness of the C-enriched layer is 0.1 μm or more and 10 μm or less and occupies 5 to 50% of the thickness of the plating film. ^2. A carbon-containing composite zinc plating film having a carbon content of 0.001 to 10 wt% and an adhesion amount of 5 to ²⁰⁰ g / m ² is provided on at least one surface of a metal plate, and the η phase of the plating film ( 00
・ A composite galvanized metal sheet having an orientation index of 0.6 or less for the (2) plane and 0.2 or more for the (10-1) plane. 3. A metal plate containing 0.001 to 10 wt% of ligninsulfonic acid or a salt thereof, and one or more kinds selected from higher alcohols, ethers having a molecular weight of 100 or more and esters having a molecular weight of 100 or more in a total of 0.001. ~Ten
A method for producing a composite galvanized metal plate, which comprises performing electroplating in an acidic zinc plating solution containing wt%. 4. The electroplating is performed by (a) an off time of 1 ms.
Pulse current having a current waveform of 1 s or more and a duty ratio of 0.5 or more, or (b) frequency of 1 Hz or more, 10
The method according to claim 3, wherein the method is carried out by energizing a direct current superimposing an alternating current or a pulse current superimposing the alternating current having a current waveform of 0 Hz or less and a current fluctuation width of ± 1% or more and ± 50% or less.