JPH0718040B2 - Composite plated steel sheet excellent in spot weldability and corrosion resistance and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention provides an electric Zn excellent in spot weldability and corrosion resistance.
TECHNICAL FIELD The present invention relates to a system alloy plated steel sheet, particularly a composite plated steel sheet and a method for producing the same.

<Prior Art and Problems Thereof> Zn-plated steel sheets are widely used as rust-prevented steel sheets in automobiles, home appliances and the like, which require corrosion resistance. This is because the pure Zn plating layer has a base electric potential with respect to the iron of the steel plate.
This is to prevent the occurrence of red rust on the steel sheet due to the sacrificial anticorrosion effect that Zn is corroded first in the plating defects such as pinholes and in the exposed portion of the base metal generated during processing.

However, since Zn itself is active only with Zn, there is a drawback that corrosion of the Zn plating layer itself remarkably progresses in a corrosive environment. In addition, pure Zn is a conductive ZnO as a corrosion product.
It is considered that one of the reasons is that the corrosion resistance existing on the surface is poor and that the corrosion resistance is not sufficient because the corrosion resistance is insufficient.

Therefore, in order to improve the corrosion resistance of Zn-plated steel sheet, (1) increase the plating amount of Zn.

(2) A method of applying alloy or composite plating to control the dissolution of the plating layer itself has been proposed. However, increasing the Zn plating amount is not preferable in terms of resource saving, weldability, and workability. Therefore, alloy composite plating is currently being actively developed.

For example, the following technologies are known.

(1) In a Zn plating bath, nickel ions and chromium ions are mixedly contained and electroplated, so that the plating layer has a Zn-Ni alloy composition to improve corrosion resistance (JP-A-55).
-50484).

(2) Main component is Zn, and contains two components of Co, Ni, Mg, Mn, Si, Sn, and Fe, and the amount of the two components deposited is 5 to 30 wt% (Japanese Patent Publication No. 50-29821). .

(3) Zn-Ni alloy plating layer in which Cr hydrate is dispersed in a range of 0.3 μm or more from the surface layer by using a Zn-Ni alloy plating bath or a zinc plating bath containing Cr ⁶⁺ of 0.05 to 1.0 g / l , Zn plating layer is formed (JP-A-56-123395).

(4) An electrozinc alloy plating layer containing 10 to 20 wt% nickel and 0.01 to 1.0 wt% chromium is formed (JP-A-57).
-67188).

(5) A surface-treated steel sheet having an oxide (Al ₂ O ₃ , SiO ₂ , TiO ₂ ) coating on a zinc-plated layer or a zinc alloy-plated layer and having excellent spot weldability (JP-A-55-110783).

These electroplated steel sheets have improved bare corrosion resistance as compared with pure Zn plating, but with respect to corrosion resistance after coating, there is a drawback that blisters are likely to occur when cationic electrodeposition coating is performed after phosphate treatment.

In addition, since Zn is the main plating layer, the melting temperature of Zn is lower than that of cold-rolled steel sheet, so the electrode contact area is increased to form an alloy layer of electrode tip and Zn, which requires an excessive welding current. To do. In addition, the electrode tip is severely worn and the continuous weldability is poor.

In (5), an oxide film is formed in order to improve spot weldability of Zn and Zn-based alloy plating, but since it is formed on the plating layer, it is difficult to form a phosphate film,
It has the drawback of poor corrosion resistance after painting.

As described above, a high corrosion-resistant galvanized steel sheet having excellent properties such as a bare material and corrosion resistance after coating and spot weldability has not yet been obtained.

<Object of the Invention> The object of the present invention is to elute a predetermined amount of Ni, Cr and a predetermined amount of Al and Si as an oxide or a hydroxide in a plated layer to obtain bare corrosion resistance and corrosion resistance after coating and High corrosion resistance electric Zn with excellent properties such as spot weldability
To provide a system-based composite plated steel sheet and a method for manufacturing the same.

<Structure of Invention> That is, according to the present invention, Ni is contained in the electric Zn-based composite plating layer.
〜20wt%, Cr 0.005〜5wt%, Al or Si 0.001〜8wt% as Al or Si as oxide or hydroxide
Disclosed is a composite plated steel sheet excellent in spot weldability and corrosion resistance, which is characterized by being dispersed.

The present invention also provides 0.5-2 mol / l zinc ion and 0.04-2.0
mol / l nickel ion, 0.005-0.15 mol / l trivalent chromium ion, 0.5-20g in terms of alumina and silica
Zn containing 1 / l alumina sol and silica sol
Provided is a method for producing a composite plated steel sheet having excellent spot weldability and corrosion resistance, which is characterized by performing electroplating while maintaining a pH of a system plating bath at 1.0 to 4.0.

The present invention will be described in more detail below.

As conventionally known, the inclusion of Ni in the galvanized layer improves bare corrosion resistance. This is Zn in the plating layer
This is because Ni ²⁺ is generated in the process of corroding Ni and Ni, a corrosion product film having an excellent protective effect is formed, and dissolution of the plating layer is suppressed.

In the present invention, the Ni content is defined as 5 to 20 wt%. However, if the Ni content is less than 5 wt%, the effect of improving bare corrosion resistance is not observed, and if it exceeds 20 wt%, it may become rather difficult, and plating This is because the hardness of the layer itself becomes high, resulting in deterioration in workability and plating adhesion.

Coexistence with Al has the effect of improving the bare corrosion resistance of the plating film itself. Further, Cr has the effect of improving the adhesion of the coating film, and therefore contributes greatly to the improvement of corrosion resistance after coating. In the present invention, the Cr content is 0.005 to 5 wt%
However, if Cr is less than 0.005 wt%, no improvement in bare corrosion resistance is seen even when coexisting with Al, and if it exceeds 5 wt%, the above effect is saturated and the plating layer itself becomes black and the plating adheres. This is because the sex is slightly reduced.

Al is considered to be co-deposited in the form of oxide or hydroxide in the plating layer, and promotes co-deposition of Cr in the plating layer. Al forms a dense and stable corrosion product film in a corrosive environment together with Ni and Cr, and suppresses elution of the plating layer. Also Al
By the presence of the oxide of dispersed in the plating layer,
Improve spot weldability. That is, since the electric resistance of the plating film is increased, heat generation is concentrated on the contact portion of the electrode tip with a small current, and reliable welding can be performed.

In the present invention, the content of Al is set to 0.001 to 8 wt%,
The reason is that when Al is less than 0.001 wt%, the corrosion resistance improving effect and spot weldability are not sufficiently improved, and when it exceeds 8 wt%, not only the plating adhesion is slightly deteriorated, but also the spot weldability is deteriorated.

It is considered that Si is also codeposited in the form of an oxide or a hydroxide in the plating layer like Al, and improves spot weldability like Al. The reason for this is considered to be the same as in the case of Al. Furthermore, the presence of Si dispersed in the plating layer contributes to the lubricity during processing and has the effect of improving the workability. In the present invention, the content of Si is 0.
001 to 8 wt% was set because the reason is that if Si is less than 0.001 wt%, sufficient effect for improving workability and spot weldability cannot be obtained, and if it exceeds 8 wt%, the workability improving effect is saturated. In addition, the spot weldability, plating adhesion, and corrosion resistance are adversely affected, which is not preferable.

The manufacturing method of the electric Zn-based composite plated steel sheet according to the present invention is 0.
5 to 2 mol / l zinc ion, 0.04 to 2.0 mol / l nickel ion, 0.005 to 0.15 mol / l trivalent chromium ion and 0.5 to 20 g / l alumina sol and silica sol in terms of alumina and silica The pH of the electric Zn plating bath containing 1.0
By carrying out electroplating while maintaining at ~ 4.0, a composite plated steel sheet having a Zn-based alloy plating layer having the above composition can be obtained.

Electric Zn plating baths are sulfuric acid bath, chloride bath, pyrophosphoric acid bath,
A sulfamic acid bath, a fluoride bath, a borofluoride bath, or a mixture bath thereof can be used.

Nickel ions and kuromuion are added to the plating bath as chlorides and other water-soluble compounds according to the plating bath. The amount is 0.04 to 2.0 mol / l as Ni ^{2+ and} 0 as Cr ³⁺ .
It is 005 to 0.15 mol / l. For Al and Si, water-dispersible colloid (average particle size 10 ^-7 to 10 ^-4 cm) is added to the plating bath in an amount of 0.5 to 20 g / l in terms of alumina and silica.

It is easily inferred that the positively charged Al and Si oxide or hydroxide colloidal particles migrate to the cathode part in the electroplating bath and co-deposit. The mechanism of eutectoid in the plating layer is considered to be that particles carried near the cathode are entrained during the reduction precipitation of zinc. The amount of eutectoid is greater than the amount of oxide sol added, and when it reaches a certain concentration, it is no longer co-deposited.

The present invention is to perform Zn-based electroplating by adding an oxide sol of Al and Si, and also by adding nickel ions and trivalent chromium ions, and to add these additives in the Zn-based composite plating layer. The amount of eutectoid is within a predetermined range.

The particle diameter of the added alumina sol and silica sol is preferably 100 nm or less. If the particle size exceeds 100 nm, sedimentation in the colloid solution is likely to occur, and uniform plating cannot be obtained, which is not preferable.

Furthermore, as plating aids, conductive materials such as ammonium chloride and potassium chloride, pH buffering agents such as boric acid and phosphate, complexing agents such as citric acid, tartaric acid, EDTA, brightening agents such as acrylamide and dextrin, and tungsten. An auxiliary agent such as an acid can be added, and the type and concentration thereof are not particularly limited.

Chloride bath allows electrolysis at high current densities of 10 to 180A
/ dm ² is appropriate. When the pH is lower than 1.0 and 4.0
If it exceeds, chromium ions are not co-deposited in the plating layer, which is not preferable. If the plating bath temperature is lower than 30 ° C, the current efficiency of chromium precipitation is low and the corrosion resistance is not improved, so it is preferable to keep the temperature at 30 ° C or higher.

<Examples> Examples of the present invention will be specifically described below.

A 0.7 mm cold rolled steel plate (SPCC) was degreased with alkali, pickled with 5% hydrochloric acid, washed with water, and plated under the following conditions.

Stirring is performed by a pump, and the liquid flow is about 60 m / min and Zn is applied to the anode.
A plate was used, the distance between the electrodes was 20 mm, and the bath temperature was 50 ° C.

The basis weight was 20 g / m ² .

Al and Si were added to the plating solution in the form of a water-dispersible colloidal sol made by Nissan Chemical Industries, Alumina sol # 520, Snowtex-O (silica sol), and Snowtex-AK (silica sol).

<Example 1> chloride bath _{ZnCl 2 1.5mol / l KCl 4mol /} l NiCl 2 · 6H 2 O 0.03~0.8mol / l CrCl 3 · 6H 2 O 0.005~0.15mol / l alumina sol # 520 Al ₂ O ₃ in terms of in 0.5 to 20 g / l Snowtex -O or Snowtex -ak SiO ₂ converted at 0.5 to 20 g / l pH 1 to 4 a current density of 100A / dm ² <example 2> sulfate bath _{ZnSO 4 · 7H 2 O 1mol /} l NiSO ₄・ 6H ₂ O 0.5 to 2.0mol / l K ₂ Cr ₂ (SO ₄ ) ₄・ 24H ₂ O 0.005 to 0.15mol / l Alumina sol # 520 0.5 to 20g / l in terms of Al ₂ O ₃ Snowtex-O or Snowtex-AK SiO ₂ conversion 0.5 to 20 g / l pH 1 to 4 Current density 30 A / dm ² <Comparative example 1> Chloride bath ZnCl ₂ 1.5 mol / l KCl 4 mol / l NiCl ₂ 6H ₂ O 0 to 0.25 _{mol / l CrCl 3 · 6H 2} O 0~0.2mol / l alumina sol # 520Al ₂ O ₃ converted at 0 to 5 g / l Snowtex -O or Snowtex -AK 0~30g / l pH 1~4 in terms of SiO ₂ current density 100A / dm ² <Comparative example 2> sulfate bath _{ZnSO 4 1mol / l NiSO 4 ·} 6H 2 O 0~0.25mo l / l K ₂ Cr ₂ (SO ₄ ) ₄・ 24H ₂ O 0-0.2 mol / l Alumina sol # 520 0-30 g / l in terms of Al ₂ O ₃ Snowtex-O or Snowtex-AK 0 in terms of SiO ₂ 5g / l pH 1 to 4 Current density 30A / dm ^{2 The} steel sheets prepared by these plating baths are No. 8 to 13 in Table 1.
Is. In Nos. 1 to 7 and 14 to 16 shown as comparative examples, the added amounts of zinc ions, nickel ions and trivalent chromium ions are out of the range of the production method of the present invention.

The tests described below were conducted on the plated steel sheets obtained in the above examples. The results are shown in Table 1.

The Ni and Cr in the plated layer were quantified by atomic absorption method, Si was measured by absorptiometry using molybdenum blue, and Al was quantified by EPMA.

(1) Plating adhesion evaluation method Dupont impact test (shooting diameter 1/4 inch, weight 1 kg, height 50 cm)
The peeling state of the subsequent plating layer was evaluated.

◎: No peeling ○: Very slight peeling Δ: Slightly peeling ×: Peeling (2) Workability evaluation method Cup squeezing as shown in Fig. 1 was performed, tape was stripped on the squeezed surface, and the amount of weight reduction was measured. Evaluated.

◎: 0 to 2 mg ○: 2 to 5 mg △: 5 mg or more ×: Not squeezed (3) Corrosion resistance evaluation method (3-1) Bare corrosion resistance A salt spray test (JIS Z 2371) was performed and the thickness reduction value after 720 hours Was measured and evaluated.

(3-2) Corrosion resistance after coating About a sample which was subjected to a phosphate treatment (Nippon Parkerizing Co., Ltd., Bonderite # 3030) and then subjected to cation electrodeposition coating (Nippon Paint Co., Ltd., Power Top U-30) 20 μm A cross cut until reaching the base steel sheet was put in, and the blister width after 340 hours of salt spray (JIS Z 2371) was evaluated.

◎: 0 to 1 mm ○: 1 to 3 △: 3 to 6 ×: 6 mm or more (4) Spot Weldability Evaluation Method The welding conditions are as follows.

Current: 7000A Number of cycles: 10 Pressing force: 180kg Welding tip shape: 8000 points were continuously applied as shown in Fig. 1 and the nugget diameter was measured.

As shown in Table 1, the steel sheet obtained by the present invention is excellent in bare corrosion resistance of the plating layer itself as well as in corrosion resistance after coating, and also has good spot weldability. It also has excellent plating adhesion and workability.

<Effects of the Invention> According to the present invention, it is possible to particularly improve spot weldability and corrosion resistance by containing a proper amount of Ni, Cr, Al, and Si in the Zn plating layer. Further, it has excellent plating adhesion and workability, and is suitable as a highly corrosion-resistant steel plate for automobiles, home appliances and the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an electrode tip used in a spot weldability evaluation test of a highly corrosion-resistant electric Zn composite plated steel sheet of the present invention.

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-60-125395 (JP, A) JP-A-60-211095 (JP, A)

Claims (2)

[Claims] 1. Ni to 5 to 20 wt% in an electric Zn based composite plating layer
%, Cr 0.005 to 5 wt%, as oxide or hydroxide
A composite plated steel sheet having excellent spot weldability and corrosion resistance, which is obtained by dispersing Al and Si in an amount of 0.001 to 8 wt% in terms of Al or Si. 2. Zinc ion of 0.5 to 2 mol / l and 0.04 to 2.0 mo
l / l nickel ion, 0.005-0.15mol / l trivalent chromium ion, 0.5-20g / l in terms of alumina and silica
The method for producing a composite plated steel sheet having excellent spot weldability and corrosion resistance, which comprises performing electroplating while maintaining the pH at 1.0 to 4.0 in an electric Zn-based plating bath containing alumina sol and silica sol.