JPH03260087A - Production of galvanized steel sheet having superior spot weldability - Google Patents

Abstract

PURPOSE:To produce a galvanized steel sheet having superior spot weldability and satisfactory workability by adding a prescribed amt. of a complexing agent stable to zinc as well as an oxidizing agent to a galvanizing bath. CONSTITUTION:A prescribed amt. of a complexing agent stable to zinc is added to an acidic galvanizing bath contg. an oxidizing agent and a steel sheet is galvanized with the resulting bath. It is necessary that the complexing agent has ability to form a complex with zinc and ensures >=1.0 stability constant for the formed complex in the case where the pH of the bath is 6. The pref. amt. of the complexing agent in the bath is 1-20g/l and disodium ethylenediaminetetraacetate or sodium citrate is suitable for use as the complexing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a zinc electroplated steel sheet with excellent spot weldability.

[Conventional technology]

When trying to spot weld galvanized steel sheets.

The heat generated during welding causes the galvanized layer on the spot weld to melt and react with the copper of the electrode tip to form a hard alloy layer, resulting in severe wear and tear on the electrode tip and a short lifespan.

As a method for solving such problems and manufacturing plated steel sheets with excellent spot weldability, for example,
In JP-A-205083 and JP-A-1-205090, zinc is applied onto the surface of a steel plate by electroplating using an acidic zinc electroplating bath containing an oxidizing agent such as hydrogen peroxide, and using the steel plate as a cathode. A method of forming an oxide plating layer (hereinafter referred to as "prior art") is disclosed.

In the above-mentioned prior art, let's use the 5# agent.

In addition to hydrogen peroxide, NO2-, Br01. IO,”
, SeO,-, etc., and by performing electroplating using a plating bath containing these oxidizing agents,
Hydrogen is reduced on the surface of the cathode, and the pH of the plating bath at the cathode interface increases. As a result, zinc oxide or hydroxide grows on the surface of the steel plate.

A plating layer made of zinc oxide or hydroxide is formed. A steel plate with such a plating layer.

It is said that zinc oxide or hydroxide has superior weldability to galvanized steel sheets due to its high melting point and high electrical resistance.

[Problem to be solved by the invention]

However, the above-mentioned prior art has the following problems. That is, the pH of the plating bath at the cathode interface increases excessively due to the oxidizing agent contained in the plating bath. For this reason, the amount of deposited plating made of zinc oxide or hydroxide becomes excessive. As a result, the spot weldability is adversely affected, causing problems such as deterioration of workability.

Therefore, an object of the present invention is to solve the above-mentioned problems when forming a plating layer consisting of zinc oxide or hydroxide on the surface of a steel sheet using an acidic zinc electroplating bath containing an oxidizing agent. Another object of the present invention is to provide a method for stably producing zinc electroplated steel sheets having an appropriate coating amount, excellent spot weldability, and good workability.

[Means to solve the problem]

The present inventors have conducted extensive research in order to solve the above-mentioned problems. As a result, if a predetermined amount of a zinc-stable complexing agent is added to an acidic zinc electroplating bath containing an oxidizing agent and electroplating is performed using this plating bath, an excessive increase in pH can be prevented. restrained.

It has been found that it is possible to stably produce a zinc electroplated steel sheet with excellent spot weldability, which is made of an appropriate coating amount of dizinc oxide or hydroxide.

This invention was made based on the above findings, and
By electroplating using an acidic dumbbell electroplating bath containing an oxidizing agent and using a steel plate as a cathode.

In the method for producing a zinc electroplated steel sheet, in which a plating layer made of zinc oxide or hydroxide is formed on the surface of the steel sheet, in the acidic zinc electroplating bath, together with the oxidizing agent, zinc and a stable The method is characterized in that it contains a predetermined amount of a complexing agent, and electroplating is performed using an acidic zinc electroplating bath containing an oxidizing agent and a complexing agent.

In this invention, as mentioned above, since a complexing agent stable with zinc is contained in the acidic zinc electroplating bath containing an oxidizing agent, this complexing agent allows hydrogen to be removed during electroplating. Excessive increase in pH of the plating bath due to reduction is suppressed. Therefore.

The amount of plating made of zinc oxide or hydroxide formed on the surface of the steel sheet is not excessive.

The complexing agent has the ability to form a complex with dumbbell, and the stability factor of the complex with zinc is required to be 1.0 or more when P)I of the plating bath is 6.

When the stability number is less than 1.0, the ability to suppress the increase in pH is small, and the initial purpose cannot be achieved.

The content of the complexing agent in the plating bath is ~2Or, IQ.

It is preferable to set it within the range of. If the content of the complexing agent is less than Ig/l, it is not possible to appropriately suppress the increase in pl+ of the plating bath. On the other hand, the complexing agent contained in the animal is
If it exceeds 20 g/l, the electrolytic efficiency decreases, 1, plating burn occurs, and quality deteriorates.

An example of a suitable complexing agent for use in this invention is shown below.

EDTA-Na (disodium ethylenediaminetetraacetate) Citric acid ion Oxalate ion Tartrate ion Cy DTA (Trans-1+2-CycLo
hexane-djamjneN, N, N', N'-t
etraacetic Ac1d) D T P A (
Diethylene triamine Penta
acetic acid) G E D T A (Ethylenedioxyb
is(ethylaminer')N, N, N', N'-
tetraacetiCACid)-I-rien As the oxidizing agent to be contained in the plating bath, No2NO
,−,BrO,−,IO,−,Sea,−,It,O,
etc. can be used. The content of the oxidizing agent is determined to be an appropriate amount depending on the oxidizing performance of each oxidizing agent.

Next, the present invention will be explained using Examples while comparing with nine comparative examples outside the scope of the present invention.

〔Example〕

An acidic zinc electroplating bath consisting of the following was used as the base bath.

Zinc sulfate: 300g/Q Sodium sulfate: 30gIQ Sodium acetate: I2gIQ pH: 2 To the above basic bath, the method within the scope of this invention shown in Table 1 (
In accordance with Nαl-27 (hereinafter referred to as the “method of the present invention”), an oxidizing agent and a complexing agent are added, and an acidic zinc electroplating bath is
Made by A. By electroplating using the acidic zinc electroplating bath prepared in this way and using a cold rolled steel sheet as a cathode,
A zinc oxide or hydroxide coating layer was formed on the surface of the steel sheet.

For comparison, electroplating was carried out using an acidic zinc electroplating bath containing only a dioxidizing agent.

Method N shown in Table 1 (hereinafter referred to as “comparative method”)
(on the surface of cold-rolled steel sheet according to 11-25).

A plating layer made of zinc oxide or hydroxide was formed. The spot weldability of the zinc electroplated steel sheets manufactured by the method of the present invention and the comparative method described above was determined by determining the end point of electrode life (predetermined nugget diameter can be ensured, number of spot welding points). As is clear from Table 9 shown in conjunction with Table 1, Comparative Methods Nos. 1 and 2 using a plating bath to which no N-forming agent was added
In No. 5, the plating deposition amount was 1.2 to 3.5 g/m, which was excessive, and as a result, the electrode life end point was determined to be 30
Spot weldability was poor at 0 to 1500 points. Furthermore,
Although not shown in the table, workability was also poor.

On the other hand, in the method of the present invention Na 1 to 27 using a plating bath to which a complexing agent was added, the plating deposition amount was 0.05-1.0 g/rr? As a result, the electrode life end point was determined to be 5000 points or more.

It had extremely excellent spot weldability, and also had good workability.

〔Effect of the invention〕

As described above, according to the present invention, when forming a plating layer made of zinc oxide or hydroxide on the surface of a steel sheet using an acidic zinc electroplating bath containing an oxidizing agent, It is possible to stably produce zinc-electroplated steel sheets with excellent spot weldability and good workability without excessive coating weight. J. You can make it.

Industrially useful effects are produced.

Claims (1)

[Claims] 1. Using an acidic zinc electroplating bath containing an oxidizing agent,
A method for producing a zinc electroplated steel sheet, in which a plating layer made of zinc oxide or hydroxide is formed on the surface of the steel sheet by electroplating using the steel sheet as a cathode, wherein in the acidic zinc electroplating bath, A predetermined amount of a complexing agent that is stable with zinc is contained together with the oxidizing agent, and electroplating is performed using an acidic zinc electroplating bath containing the oxidizing agent and the complexing agent. , a method for producing zinc electroplated steel sheets with excellent spot weldability. 2. The method according to claim 1, wherein the content of the complexing agent is within the range of 1 to 20 g/l.