JPS5852493A - Plating method for iron-zinc intermetallic compound alloy - Google Patents

Abstract

PURPOSE:To obtain high speed plating which is highly resistant to corrosion and forms no eta phase by specifying the titled plating conditions by high current density for steel materials for automobiles, household electrical appliances, etc. CONSTITUTION:Metals are plated on steel materials by sing a sulfate bath of 0.4-0.9 Zn<++>/Fe<++> weight ratio in the plating bath, >=100g/l and within solutibility limit in sulfate (as hydrate) conc., and 0.8-2.3pH and by using an insoluble electrode at 60- 200A/dm<2> current density and 40-80 deg.C bath temp. Thus >=1 kind of plating layers of GAMMA, LAMBDA1, zeta phases having excellent corrosion resistance are obtained. Here, if said ion ratios are in excess of the upper limit, the adhesiveness to the chemically converted layer and corrosion resistance are degraded. If below the lower limit, no intermetallic compds. are formed, and the compsn. contg. more iron than GAMMA phase is resulted, with correspondingly degraded adhesiveness of the plating layers and no improvement in corrosion resistance. If the sulfate concn. is below the lower limit, it is difficult to obtain the balance of said ions and impossible to maintain high current density. If the pH is too low, the results are similar to those when the ion ratios are in excess of the upper limit, and conversely if it is in excess of 2.3., stable high speed plating is difficult.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention forms an iron-zinc intermetallic compound layer having excellent anti-corrosion properties and consisting of at least one of r-phase, δl-phase and ζ-phase on a steel material. This invention relates to a method for high-speed plating of iron-zinc alloys in which there is no phase difference.

Steel materials (including copper strips, steel plates, steel pipes, steel sections, etc.) are important metal materials because they are strong, highly workable, and can be supplied in large quantities, and are used in large quantities for automobiles, home appliances, etc. has been done. However, in addition to having the disadvantage of being easily rusted and corroded, higher q# properties are being required in terms of weldability, processability, chemical conversion treatment properties, paintability, etc. For this reason, surface treatment of steel is extremely important, but conventional methods have typically involved galvanizing the steel, applying chemical conversion treatment on top of that, and then painting with paint such as electrodeposition paint. I was worried. Regarding galvanizing, recently,
Attempts have been made to further improve corrosion resistance, weldability, paintability, etc. by applying Fe-zn alloy plating to steel materials by electroplating. For example, %Fe80.
・FH202501/It, Zn80. -7H202
20ri/2, (NH,), 80.120ri/2, KcQ
pH 2.9, temperature 50°C, current density 40 μm/d using a bath consisting of 10R/2 and citric acid α5P/1.
If a zinc-iron plating coating of 2097 m'' is carried out under conditions of 2097 m'', a coating of 70% by weight zinc and 30% by weight iron is obtained. The corrosion resistance of this coating is no different from that of electrogalvanized steel made of pure zinc, and its performance is extremely inferior.
This result is significantly inferior to that of so-called alloyed galvanized steel containing 10% by weight of iron.

This seems to be because the plating layer mainly consists of the V (eta) phase, and the Fe-
It has been desired to develop a method for plating Zn alloys.

On the other hand, in order to be suitable for mass-scale applications such as automobiles, home appliances, and building materials, the plating process must also be mass-producible. For this reason, Fe--Zn alloy plating using high current density was considered, but the conditions for this failure were not clear.

Based on this knowledge, the present inventor has conducted extensive research and has found that the F (gamma) phase, which has excellent anti-corrosion properties, can be applied to steel materials.
High-speed plating of iron (Fe)-zinc (Zn) intermetallic compound alloy consisting of one or more types of δl (delta) phase and ζ (zeta) phase, and which does not substantially form η phase This led to the development of a method.

That is, in the present invention, as a plating bath, zn++/
Fθ0 weight ratio is α4 to α9, sulfate (as hydrated substance) concentration is 1ooy7tt or more, within the solubility limit at the working temperature,
Using a sulfate bath with a pg of 08-2.3, a current density of 6
0~200 A/(L!11", bath temperature 40~80℃
It is characterized by electroplating on steel materials using an insoluble anode under the following conditions.

The method of the present invention will be described in detail below.

First, zn++/1? in a sulfate bath? θ+1 weight ratio α4~
It is necessary to set it to α9. For this, zinc sulfate,
When preparing a plating bath using ferrous sulfate, the ratio is controlled within this range. zn++/Fe in bath
If the ++ weight ratio exceeds α9, free zinc will precipitate, reducing the adhesion to the chemical conversion layer and the corrosion resistance. Also, α4
If the content is less than 10%, no intermetallic compound is formed and the formed plating layer is r-phase (Fe5Z%□, or FosZnzo:
The composition has a higher Fe content than Zn content (72 to 80%), resulting in poor adhesion of the plating layer and no improvement in corrosion resistance.

The sulfate concentration should be 1oOP/41 or more and within the solubility limit.

When it is less than 100 to 71, the above zn++ / Fe+
+ It becomes difficult to balance the weight ratio, and if the conductivity is low, high current density cannot be maintained.

The pH of the plating bath is in the range of 08 to 2.3. If the pH is too low, problems similar to those in the case where the Zn content in the plating layer is 4<9 and the above-mentioned bath zn++ /, e++ weight ratio exceeds α9 will occur. On the other hand, if pE exceeds 2.3, iron hydroxide tends to precipitate, the plating bath tends to deteriorate, and it becomes difficult to perform stable high-speed plating. Normally, plating lowers the pH, and replenishing metal ions returns the pH to its original value, so the bath pH is maintained at a constant value, but if necessary, the pH can be adjusted using sulfuric acid, ammonia,
Alternatively, this can be done by replenishing water. Since the pH of the plating bath of the present invention is low, the plating component metal has a considerably high dissolution rate, so replenishment is easy, and the degree of consumption and replenishment of metal components can be estimated from metal control based on slight fluctuations in the pH of the plating bath. obtain.

Next, the current density is in the range of 60 to 200 A/am2. For high-speed plating, the efficiency of iron-zinc plating is about 80% at most even if the pH, temperature, flow rate, etc. of the solution are set to the optimum conditions, so a current density of at least 60 A is required.
It is important that the plating temperature is at least /cl-, and if it is less than this, the plating time will be long and the continuous plating equipment will be extremely long, which will be too busy and will hinder mass production. 200 A/
am'', the amount of hydrogen gas generated especially from the cathode surface is significant, and these gases may be occluded in the plating layer, reducing the corrosion protection.In addition, high-speed plating is not possible as it increases the current carrying resistance between the two electrodes. It becomes difficult to do it continuously.

It is also necessary to control the bath temperature within the range of 40 to 80°C for the stability of plating. If it is less than 40°C, it is difficult to control the plating bath temperature at a constant temperature, and the adhesion between the plating layer and the steel material is also poor, which is not preferable.

Further, if the temperature exceeds 80°C, evaporation of the liquid will be large and it will also be difficult to select the material of the device, which is not preferable.

Next, in the present invention, high-speed plating is made possible by using an insoluble anode instead of a soluble anode. In the case of a soluble anode, not only is it troublesome to replace the electrode due to wear, but also the electrode becomes passivated under high current density, making high-speed plating impossible. The insoluble anode of the present invention is suitably made of, for example, a lead alloy, or a precious metal such as platinum, rhodium, or iris, or an oxide thereof. When such an insoluble anode is used, a stable plating current can be ensured under high current density, and therefore, the control of the plating film becomes extremely easy.

In the present invention, the pH is kept low and the sulfate concentration is increased to provide bath temperature conductivity as much as possible.

The aim is to prevent plating burn and reduce bath voltage when high current densities are applied, but the plating bath of the present invention contains conductivity imparting agents such as ammonium sulfate, sodium sulfate, and aluminum sulfate, as well as iron ions and zinc ions. It may be added to an extent that does not impair solubility, for example, 5 to 80 y/J2.

The plating layer obtained under the above conditions is an Fa-Zn intermetallic compound consisting of at least one of ζ phase, δl phase, and ζ phase and substantially no η phase.

The δl phase mainly has a composition of FeZn7, with ZnB&
6 to 93% by weight, and the ζ phase is mainly Fe1s Z
%□ and Fe3Zn□. It is a mixed crystal of Zn 7
2 to 80% by weight, and the ζ phase is mainly F'92nz
zn9r5h8-94. ．． It is said to contain 5% by weight, and the η phase corresponds to pure zinc. The Fe thus obtained consists of at least one of the F phase, δl phase and ζ phase, and has substantially no I phase.
-Zn intermetallic compounds have a high degree of corrosion resistance, and for automobiles, they are also effective against salt damage caused by snow melting salt sprayed on roads in cold regions, as well as resistance to punctures from flying pebbles. Excellent @ For example, for such applications, 5 to 25 y/m
It is preferable to form a plating layer with a thickness of about 2 mm, and to apply an upper layer plating on top of the plating layer to enhance adhesion with the chemical conversion treatment layer and coatability with electrodeposition paint or the like. The thickness of the plating layer formed by the method of the present invention is preferably 5 P/m" or more from the viewpoint of corrosion resistance, but
If it exceeds 25P/m'', the merits of manufacturing by electroplating will be reduced from the viewpoint of productivity, and the workability and weldability will also deteriorate.For example, as the upper plating layer,
As a plating bath, Zn++/Fe”+ weight ratio system α02~
α151. Sulfate concentration (as hydrated salt) total 1oo y
/f1 or above and within the rumored solubility limit (working temperature), pH is 08
Using a sulfate bath with a current density of ~2.3 and a current density of 60 to 200
A Fe-Zn solid solution alloy plating layer obtained by electroplating on steel material using an insoluble anode under the conditions of A/4 m2 and bath temperature of 40 to 80 °C is α5 to 7.
Formed with a thickness of f/m2. In the above, Zn
/Fe If the weight ratio exceeds 0.15, no solid solution alloy is formed and chemical conversion treatment properties are insufficient.

Further, if it is less than 002, the corrosion resistance is insufficient. The reasons for setting other conditions are the same as in the case of forming the intermetallic compound of the present invention.

If the thickness of the solid solution alloy plating layer is less than α5y/rn", the chemical conversion treatment property will not be good and coating defects such as blisters will easily occur. If the thickness exceeds γf/m", the chemical conversion treatment property will not improve much. It is preferably in the range of 1 to 3 f/m2.

Even if the above-mentioned solid solution alloy plating layer is multilayer plated on the intermetallic compound alloy plating layer by the method of the present invention, the 5.5 to 32
The thickness is approximately 45 l/m" or more on average in the case of hot-dip galvanized steel sheets, which are made by heating and alloying iron and zinc after conventional galvanizing. Despite the fact that K has a significantly thinner plating layer, it has superior corrosion resistance, weldability, workability, etc.
Demonstrates excellent performance.

The present invention will be explained in more detail with reference to Examples below.

Example 1 Fe--Zn intermetallic compound alloy electroplating was performed on a normal cold-rolled steel sheet under the conditions shown in Table 1. Plating conditions are the first
I changed it as shown in 2. The bath composition is ZnBO, 7
H,0 and Fe50. -7H20 and “total amount te500
p/ft and Naruyo KL, also (NH,)280.3
0 P/I- was used.

As an anode, a titanium substrate plated with platinum was used as an insoluble anode. The amount of plating was adjusted to 20 y/m2 by changing the plating time. The amount of plating and the phase of the plating layer were determined by atomic absorption method and X-ray diffraction method, respectively. The evaluation results are shown in Table 1.

Example 2 Electroplating was performed on a steel material under the experiment No. 30 conditions of Example 1, and then Fe-Zn solid solution electroplating, chemical conversion treatment, and cationic I-layer coating were performed on the steel material under the following conditions.111
Conditions for water side 01Fe-Zn solid solution electroplating for strict comparison: Zn++/IPe++ weight ratio α07 (Zn5O,
・7a, o30p/fi, FsBO, ・7H204'7
0P/i), sulfate concentration 500y/child, bath pH 12, bath temperature 60℃, current density 100 A/am'', using a platinum-plated titanium substrate as the anode, plating amount 5y/day.
mlA.

Comparative Example 1 Fe-Zn was deposited on a normal cold-rolled steel plate under the same conditions as Example 2.
Solid solution electroplating, phosphate treatment, and cationic electrodeposition coating were performed to test the physical properties, and the evaluations are shown in Table 2.

Comparative Examples 2 and 3 Galvanized steel sheet by conventional method (film thickness 60y/m2, Comparative Example 2) and alloyed hot-dip galvanized steel sheet (film thickness 45P)
/ m2, Comparative Example 3) was tested for performance, and the evaluation is shown in Table 2.

Table 2 In addition, in Tables 1 and 2 It was like evaluation after evaluation.

A. Adhesion of the plating layer A white vinyl tape was pasted on the plating surface, the mirror surface was turned inside and 01 bending was performed, and the peeling of the plating layer adhering to the tape was measured. Salt treatment phosphate treatment is 7 osphofluorite (Phospho
Nippon Paint special GrS-D-200, which is a phyllite, Zn2F@(PO4)1)-based immersion treatment chemical.
0, and this was applied to TA16-1B, AR18-20.
Zn++11000900pp%Fe”50~1QO
The sample was immersed in a solution adjusted to ppm for 120 seconds.

(1) Film amount The phosphate film amount was determined from the 0 (2) P ratio determined by dissolving the film in a 2% by weight OrOs solution.

Corrosion resistance after 0% coating The sample plate after the above phosphate treatment was air-baked at 120°C for XIO minutes, and Nokuward Tube U-30, manufactured by Nippon Paint, was cationically electrodeposited thereon. Samples at this stage were used for three evaluations: cross-cut peeling, red rust resistance, and red rust generation time. In addition, regarding water-resistant adhesion, Nippon Paint special Amirac TP-16R was applied to the painted board that had been coated with the above cationic electrodeposition coating to a dry film thickness of 20 μm.
Painted to a dry film thickness of 25 μm and baked at 140°C.
Evaluation was made on a sample which was coated with Amirac 030 manufactured by Nippon Paint ■ for 20 minutes) and baked (140° C. for 20 minutes) to a dry film thickness of 30 μm.

(1) Water resistant adhesion Top coat 9j & plated board is immersed in hot water at 40℃ for 240 hours, and after the immersion is finished, immediately apply one 2 mm square base line to the steel substrate.
The film was peeled off with cellophane tape in 00 pieces, and evaluated based on the peeled area ratio.

(2) During cross-cut peeling A board coated with a cationic electrodeposition paint with a dry film thickness of 20 μm was cross-cut to reach the steel substrate, and a salt spray test (360 hours, J Engineering 82371) was performed.
).

(3) Red Rust Resistance On a plate coated with a cationic electrodeposition paint with a dry film thickness of 20 μm, the occurrence of red rust at the cross-cut portion was observed after a salt spray test (360 hours, J Engineering 82371).

(4) Red rust generation time A salt water spray test (J Engineering 82371) was conducted on a board coated with cationic electrodeposition paint with a dry film thickness of 5μ without cross-cutting.
The time until red rust appeared was measured.

Agent: Patent attorney Masao Inoue

Claims (1)

[Claims] L As a plating bath, the Zn''/Fe++ weight ratio in the bath is α4 to α9, and the sulfate concentration of both metals is 100 in total.
Use a sulfate bath with a pH of 08 to 2.3, F/It or higher and within the solubility limit, and a current density of 60 to 200 A/am.
", an iron-zinc intermetallic compound alloy plating method characterized by electroplating on a steel material using an insoluble anode at a bath temperature of 40 to 80°C.