JPS6250497A - Plated steel sheet having superior workability and formability and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a Zn-Ti alloy plated steel sheet having superior workability, formability and corrosion resistance by adding a soluble molybdate to a plating soln. used to form a Zn-Ni alloy film on the surface of a steel sheet by electroplating so as to disperse Mo oxide in the resulting Zn-Ni alloy film. CONSTITUTION:When a Zn-Ni alloy film contg. 5-25wt% Ni is formed on the surface of a steel sheet by electroplating, 1-10g/l soluble molybdate such as Na2MoO4 or (NH4)2MoO4 is added to a plating soln. used so as to dipserse 1.0-10wt% Mo oxide in the resulting Zn-Ni alloy film. Thus, the workability, formability and corrosion resistance of the Zn-Ni alloy plated steel sheet are further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a Zn-Ni alloy electroplated steel sheet that has excellent workability and formability, and also exhibits high performance in terms of corrosion resistance, and a method for manufacturing the same.

[Problems to be solved by conventional technology/inventions] Recently,
Surface-treated steel sheets for automobiles are now required to have high corrosion resistance to withstand severe corrosive conditions, especially in consideration of the spraying of salts (anti-freezing agents) on roads in cold regions.

In response to such requirements, the basic Zn that has been known for a long time
Plated steel sheets do not have satisfactory corrosion resistance, and against this background, various Zn alloy-based electroplated steel sheets have been developed in recent years and their practical use has been progressing. A Zn--Ni alloy plated steel sheet is one of the typical examples, and it exhibits much better corrosion resistance than ordinary Zn-plated steel sheets.

However, even this Zn--Ni alloy plated steel sheet is often still insufficient for the above-mentioned severe usage conditions.

By the way, the corrosion resistance of plated steel sheets is generally largely controlled by the amount of plating deposited, and therefore, effective improvement can be achieved by increasing the amount of plating deposited. However, the amount of plating deposited cannot be determined solely from the viewpoint of corrosion resistance. In other words, in the case of alloy electroplated steel sheets such as Zn-Ni, there are problems with workability (powdering resistance) and formability, and these properties cannot be ignored in applications that involve pressing, such as automobiles. This is because workability refers to the phenomenon in which the plating film peels off into powder during press molding (powdering), and those with a strong tendency to powder are considered to have poor workability.Poor workability In addition to being disadvantageous to the corrosion resistance after processing, the press-plated steel sheet may be damaged through adhesion of peeled pieces of the plating film to the press mold.

Furthermore, formability refers to whether or not the base material breaks during pressing.

This workability and formability tend to deteriorate as the amount of plating increases, and in the case of Ni-Zn alloy electroplated steel sheets, in order to satisfy both of these characteristics, the amount of plating must be adjusted depending on the plating composition. It is necessary to limit the amount to approximately 30 g Al or less.

That is, in the case of Zn-Ni alloy electroplated steel sheet,
The amount of plating deposited can only be about 30 g/rrl at maximum, which is why it cannot meet the requirements for automotive use.

As a countermeasure for the corrosion resistance of this Zn--Ni alloy electroplated steel sheet, a so-called dispersion plating method, in which fine particles are dispersed and contained in the plating film, can be considered. Regarding this dispersion plating, there have been many proposals in recent years, and it seems that some results have been achieved in terms of corrosion resistance as well. For example, dispersion of titanium, titanium oxide, silica, etc. is effective for corrosion resistance. (Unexamined Japanese Patent Publication No. 58-210195,
No. 60-52592, Special Publication No. 56-49999, etc.).

However, even if such conventional dispersion plating is introduced,
Although a certain degree of improvement in corrosion resistance is certainly expected, the aforementioned problem of restricting the amount of plating deposited due to workability and moldability still remains, and in the end, a dramatic improvement in corrosion resistance cannot be expected.

Here, the present invention provides a Zn-Ni alloy electroplated steel sheet and a method for manufacturing the same, which effectively alleviates restrictions on the coating amount by improving workability and formability, and makes it possible to achieve extremely high corrosion resistance. This is what we provide.

[Means/effects for solving the problem] The present inventors
As a result of conducting extensive experiments and research on methods to improve the workability and formability of Zn-Ni alloy electroplated steel sheets and to effectively expand the practical range of the coating amount, we found that molybdenum metal was found in the plating film. It has been discovered that by dispersing and containing an appropriate amount of oxides, it is possible to significantly improve workability and formability, and to significantly increase the amount of plating deposited than before. And such molybdenum/
It was also discovered at the same time that the dispersed content of the metal oxide can be stably ensured by adding molybdenum in the form of a soluble salt to the plating bath.

That is, the gist of the present invention is as follows: 1) Ni is 5
A Zn-Ni alloy plated steel sheet, characterized in that 1.0 to 10 wt% of a molybdenum metal oxide is dispersed and contained in a Zn-Ni alloy plating film containing a total of 25 wt%.

11) When electroplating a steel plate with Zn-Ni alloy,
As a plating bath, 1 to 10 g of soluble molybdate
A method for manufacturing a Zn-Ni alloy electroplated steel sheet, characterized by using a 1Nk-Zn-Ni alloy electroplating bath containing 1 Nk-Zn-Ni alloy electroplating bath.

Hereinafter, each of the inventions 1) and tl) above will be explained in detail.

- Item 1) Invention This invention incorporates 1.0 to 10 wt of molybdenum metal oxide into a Zn-Ni alloy plating film containing a specific amount of Ni.
% dispersed content. The inclusion of this molybdenum oxide greatly improves workability and formability, and as a result, it becomes possible to significantly increase the amount of plating deposited compared to conventional methods while maintaining these properties at a practical level. Specifically, it is possible to deposit plating at a maximum of about 100 g/rrl, and the effect of improving corrosion resistance is extremely large.

Workability is improved by dispersing the molybdenum metal oxide mentioned above.
The reason why the moldability is improved is considered as follows. In other words, when a Zn-Ni alloy electroplated film is processed due to the inherent brittleness of the intermetallic compound that forms the film, countless microscopic cracks (which cause powdering) occur, but at this time, the plating film This is thought to be because the presence of metal oxides acts as a barrier to crack propagation.

In addition to the above-mentioned effects on workability and formability, molybdenum metal oxides can also be expected to have the effect of directly increasing corrosion resistance, and will contribute to improving corrosion resistance from this perspective as well.

In this invention, the matrix of the Zn-Ni alloy plating film has a Ni content of 5 to 25 wt%.
If it is less than wt%, a ductile zinc-rich precipitate phase appears in the plating film and its brittleness is lost, which reduces the lubricating effect of powdering during dancing, causing problems with base material breakage during pressing, and reducing formability. becomes worse. On the other hand, this is 25
This is because, in a range exceeding wt%, the effect of improving workability due to the inclusion of a metal oxide of molybdenum is not recognized.

The reason why the amount of molybdenum metal oxide dispersed in this matrix was set to 1.0 to 10 wt% is that 1. If Owt is less than 1, the effect of improving workability will not be exhibited, and if it exceeds 10 wt%, bondability between the matrix and the base material will deteriorate, and conversely, deterioration of workability will be observed.

In the present invention, the amount of plating of the above-mentioned film is not limited in principle, and may be determined as appropriate depending on the purpose of use. However, if the plating adhesion exceeds 100 g/m2, the workability and moldability tend to deteriorate, so it is preferable to set it within the range below.

- Item II) Invention The plating method according to the present invention is characterized in that in Zn-Ni alloy electroplating, plating is performed by adding soluble molybdate in the prohibited plating bath in a range of 1 to log/l. According to such a method, it is possible to obtain a Zn--Ni alloy plating film in which molybdenum metal oxide is uniformly dispersed. In the plating bath, the molybdate salt exists in an ionized state, but during plating, molybdenum ions are eutectoid in the form of oxides and are contained in the plating film in a uniformly dispersed state. It becomes. The mechanism by which molybdenum in an ionic state eutectoids as an oxide is still not fully understood, but it is believed that a combination of hydrolysis in an acidic aqueous solution (plating solution) and an oxidation reaction at the anode are involved. It is thought that the

Incidentally, the fact that molybdenum ions in the plating bath are eutectoid as oxides is due to the fact that when X-ray diffraction measurements are performed on the film obtained by the plating operation, molybdenum oxides are This can be confirmed by establishing a town.

A generally well-known method for dispersing and containing fine particles in an electroplated film is to add and disperse insoluble particles in a plating bath. This is a well-known method for dispersing materials such as glue, alumina, and silicon carbide, but this method requires special techniques to maintain a uniformly dispersed state of insoluble particles in the plating bath, and is not practical. It is extremely difficult to obtain stable dispersion plating.

In the method of the present invention, molybdenum as a base material of the material to be dispersed is present in the plating bath in the form of ions, so that the molybdenum base material can be uniformly distributed in the plating bath without any special measures. Dispersion retention is achieved, and dispersion plating with high stability and uniformity, which is difficult to obtain with the above-mentioned conventional methods, is realized.

The plating bath used in the method of this invention may be either an acidic bath or a basic bath.

The basic composition of this plating bath is as follows:
The amount of NL in the film of the plated steel sheet of the present invention is 5 to 25 wt%, as mentioned above, and in order to obtain a Zn-Ni alloy plating film that satisfies this condition, the amount of NL in the coating of the plated steel sheet of the present invention may be determined as appropriate depending on the amount of i. In the case, ZnSO4・7H20: 1
30-250g//NiSO4・6H20: 200~
250 g/1Na2SO4: A composition of about 75 to 100 g// is preferable.

The amount of soluble molybdate to be contained in the above plating bath is 1 to 10 g/l, but this is based on the relationship with the amount of molybdenum oxide in the coating of the plated steel sheet of the present invention, and within this range. By setting this, an amount of molybdenum oxide in the film can be obtained in the range of 0 to 10 g/l. There is a correlation between the amount of molybdate in the plating bath and the amount of molybdenum oxide in the film, as shown in Figure 2. Therefore, the amount of molybdate in the film can be controlled by adjusting the amount of molybdate in the plating bath. It is possible.

As the soluble molybdate to be added, sodium molybdate, potassium molybdate, etc. can be used.

Other plating conditions for carrying out the method of the present invention may be the same as those for ordinary Zn--Ni alloy electroplating. That is, it is roughly as follows.

・Plating bath pH: 2.0 to 3.0 Fist plating bath temperature: 50 to 60℃ ・Current density = 50 to 120V [Example] Cold rolled steel plate (SPC) is used as the material, and the composition of F ■ to e Zn-Ni alloy electroplating was performed using a plating bath of The plating conditions other than the bath composition were bath 111H2,o.

The bath temperature was 50° C. and the current density was 60 A/d.

・Bath composition ■ZnSO4・7H20130-190 g/l,
NiSO4・66H2O245/e, Na2S0
Based on 475 g//, 3 g/l of Na2MoO4 (sodium molybdate) was added.

@ZnSO4・7Hz0110~170 g/l,
NiSO4・66H2O260/l, Na2SO
Based on 475g/e, (Nf(a) 2Mo04(
ammonium molybdate) 3g//added.

θZnC/z75~130 g//, NiCl2・
6H20225g/l.

Based on 120g/f with NH4C, Na 2M0047
g/j? Or add 10 g/l.

@ZnSO4・7H2080~140 g/l! ,
NiSO4・6H20292g/l, Na2S04
75 g/l.

@ZnSO4・7H20140~200 g/l! ,
N15O+ ・66H2O260/l! , Na2S
Based on 0475g/J, 0.5g/J of Na2MoO4
l! Or add 15 g/l.

θZnSO4・7H2090~240 g/l! ,
NiSO4・66H2O250/e.

Based on Na2S0475 g/e, Na2M0O4
Added 3 g/l.

Corrosion resistance, workability, and formability of each plated steel plate obtained were investigated using the following methods.

(Corrosion resistance) A salt spray test using 5% salt water is conducted, and the evaluation is based on the time (number of days) until red rust appears.

(Workability) A 90mm+/disk-shaped blank was taken from a plated steel plate, deep-drawn into a cylindrical shape of 50mm/28mm+depth, and a test was conducted in which the plating film on the side wall surface was peeled off with adhesive tape. and visually inspect and determine the amount of peeling. The evaluations are: 5: No peeling at all, 4: Tape area with peeling pieces attached is less than 10 inches, 3: Same < less than 30%, 2: Same less than 50 inches, 1: Peeling pieces adhered to the entire surface of the tape. Rank as follows.

(Moldability) Is there any breakage of the base material during the above deep drawing process (Yes: ×).

Evaluate as (No: ○).

The results are summarized in Table 1.

In the above table, Examples 1 to 6 of the present invention, in which the Ni content in the plating film was 5 to 25 wt% and the molybdenum oxide content was 1.0 to 10 wt%, all received high evaluations of 4 or higher in terms of workability. Moreover, moldability is also good. Especially 2,4.6
Regarding the amount of plating deposited is 60g/rr? It shows extremely good performance in terms of corrosion resistance while satisfying workability and moldability.

Regarding comparative examples, 1 has poor corrosion resistance because the amount of molybdenum oxide contained in the film and the amount of plating is as low as 20 g/rrl, and 2 has the same amount of molybdenum oxide as 0, but the amount of plating is 60 g/rrl. Although the corrosion resistance is relatively good, the workability is extremely poor. Sample No. 3 has an amount of molybdenum oxide exceeding the range of the present invention, and Sample No. 4 has a molybdenum oxide amount below the range of the present invention and a coating amount of as much as 60 g/n/, so each has difficulty in workability. Nos. 5 and 6 have a problem with Ni in the plating film, and No. 5, which is below the range of the present invention, has poor formability, and No. 6, which is outside the same range, is significantly inferior in workability and corrosion resistance.

〔Effect of the invention〕

As is clear from the above description, the present invention maintains particularly good workability in Zn-Ni alloy electroplated steel sheets, and also ensures extremely good corrosion resistance by greatly increasing the amount of plating deposited than before. It is possible to
This greatly contributes to improving the durability of automotive steel sheets used under harsh conditions.

[Brief explanation of the drawing]

'fJ1 is a diagram showing an example of the X-ray diffraction measurement results of a Zn-Ni alloy electroplated film containing molybdenum oxide obtained by the method of the present invention, and Figure 2 is a diagram showing an example of the results of X-ray diffraction measurement of a Zn-Ni alloy electroplated film obtained by the method of the present invention. FIG. 3 is a diagram showing the relationship between the amount of molybdate and the amount of molybdenum oxide in the plating film.

Claims (2)

[Claims] (1) 1.0 to 10 wt of molybdenum metal oxide is added to the Zn-Ni alloy plating film containing 5 to 25 wt% of Ni.
A plated steel sheet with excellent workability and formability, characterized by containing % dispersed content. (2) When electroplating a steel plate with Zn-Ni alloy,
As a plating bath, add 1 to 10 g of soluble molybdate/
A method for producing a plated steel sheet with excellent workability and formability, characterized by using a Zn-Ni alloy electroplating bath containing l.