JPS5852492A - Plating method for iron-zinc solid solution alloy - Google Patents

Abstract

PURPOSE:To obtain plated layers permitting high degrees of chemical conversion in mass production by specifying the titled plating conditions by high current density for steel materials for automobiles, houshold electrical appliances, etc. CONSTITUTION:Metals are plated on steel materials by using a sulfate bath of 0.02-0.15 Zn<++>/Fe<++> weight ratio in the plating bath, >=100g/l total and within solubility limit in sulfate concon. of both metals and 0.8-2.3pH and using an insoluble anode at 60-200A/dm<2> current density and 40-80 deg.C bath temp. Here, if the ion ratios of both metals are in excess of the upper limit, no solid soln. alloy of iron and zic is formed, and the water resistance and alkali resistance of the phosphated film are not enough. If below the lower limit, the plated film is vulnerable to formation of rust. If the sulfate conc. of both metals is below the lower limit, it is difficult to obtain the balance in said ion ratios and impossible to maintain high current density. When the pH is too low, the results are similar to those when the above-described ion ratios are similar to those when the above-described ion ratios are in excess of the upper limit, and conversely, if it is in excess of 2.3, high speed plating is difficult. If the current density is below the lower limit, it hinders devices and mass productivity and if in excess of the upper limit, continuous high speed plating is difficult.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plating method for forming an iron-zinc solid solution alloy plating layer on a steel material.

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. It is used. However, it has the drawback of being easily rusted and corroded, and more advanced 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 typically involve galvanizing the steel, applying chemical conversion treatment on top of that, and then painting with paint such as electrodeposition paint. It was done. Regarding zinc plating, attempts have recently been made to further improve corrosion resistance, weldability, paintability, etc. by applying Fe--Zn alloy plating on steel materials by electroplating. For automobiles, home appliances,
In order to be suitable for large-scale applications such as building materials, the plating process must also be mass-producible. Therefore, F・− due to high current density
Zn alloy plating was considered, but the conditions for this were not yet clear.

The present inventor has discovered that when a chemical conversion treatment is performed on a plating layer, a chemical conversion treatment layer with good adhesion and corrosion resistance is formed, and as a result, it is possible to form a chemical conversion treatment layer with good adhesion and corrosion resistance. We conducted research on plating methods to enhance corrosion resistance and paint corrosion resistance, and also conducted detailed studies on methods for mass-producing iron (Fe)-zinc (z!0 solid solution alloy plating layers) on steel surfaces under high current density. As a result of this progress, we have completed the present invention.

The method of the present invention will be described in detail below.
．． 02 to 0.15, the total sulfate concentration of both metals is 100
g/1 or more and within the solubility limit, using a sulfate bath with a pH of 0.8 to 2.3, and a current density of 60 to 200 A/dm.
It is characterized by electroplating on steel materials using an insoluble anode at a bath temperature of 40 to 80°C.

First of all, it is necessary to set the zr+F/F@-1-1-weight ratio in the sulfate bath to a ratio of 0.02 to 0.15. For this purpose, appropriate amounts of zinc sulfate and ferrous sulfate are supplied into the plating bath, and the ratio is controlled to be within this range.

If the weight ratio (zn+l-7Fe+) exceeds 0.15, the amount of zinc in the plating layer will be too large, and no iron-zinc solid solution alloy will be formed. For this reason, the water resistance and alkali resistance of the phosphate film obtained when phosphate treatment is performed are insufficient. The reason for this is that the elution of Fs+ from the surface to be treated does not occur sufficiently during phosphorus salt treatment.
We believe that this is because it becomes difficult to generate phosphohyrite-based phosphate crystals (Fs!5la(pot)t) that have excellent water resistance and alkali resistance.

If the weight ratio of Zn+4-/F@'' does not reach 0.02, the F content in the plating layer becomes excessive, rusting is likely to occur, and the anticorrosion effect decreases, which is not preferable.

The sulfate concentration of both metals should be at least 100 g/1 in total and within the solubility limit. When it is less than log/1, the above Zn"/F-
In addition to making it difficult to balance the weight ratio, the conductivity of the plating bath decreases, making it impossible to maintain a high current density.

The pH of the plating bath is in the range of 0.8 to 2.3. If the pH is too low, the zinc content in the plating layer will increase, causing the same disadvantages as when the above-mentioned Rakuchu Zn''/F1++ weight ratio exceeds 0.15.On the contrary, if the pH is 2.3 If it exceeds , the plating bath is likely to deteriorate, such as iron hydroxide precipitating when the pH increases near the cathode during plating, making it difficult to perform stable, high-speed plating.Normally, the pH decreases during plating, Replenishment of metal ions will return the pH to its original value, so the bath pH will be maintained at a constant value; however, if necessary, the pH should be adjusted by replenishing sulfuric acid, ammonia, or 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 -p of the plating bath is low.
The degree of consumption and replenishment of metal components can also be estimated from slight fluctuations in H.

Next, regarding the plating conditions, the current density is 60 to 200.
The current density should be in the range of A/(11!l"). For high-speed plating, it is important that the current density is at least 60 A/(1!!1'). If the current density is less than this, the plating time will be longer and continuous The marking device also becomes extremely long, which poses a problem in mass production.If it exceeds 200A/dm,
In particular, the amount of hydrogen gas generated from the cathode surface is significant, making it difficult to perform continuous high-speed plating.The bath temperature must also be controlled within the range of 40 to 80"C to ensure plating stability. If the temperature is less than 40"C, it is difficult to control the plating bath temperature at a constant temperature, and disadvantages such as poor adhesion of the plating layer occur, which is not preferable. Also, 80
If the temperature exceeds ℃, evaporation of the liquid will be large and selection of equipment material will be difficult, 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 made of, for example, a lead alloy, a noble metal such as platinum, rhodium, or iridium, or a melt of these metals. When such an insoluble melt electrode is used, a stable threshold current can be ensured under high current density, and therefore the control of plating and coating becomes extremely easy. The formed solid solution alloy plating layer has a Zn content of 35% by weight or less.

1. In the present invention, the pH is kept low and the sulfate concentration is increased to provide as much bath conductivity as possible, with the aim of preventing plating burn when applying high current density and reducing bath voltage. In the plating bath, conductivity imparting agents such as ammonium sulfate, sodium sulfate, and aluminum sulfate are added to an amount that does not impair the solubility of iron ions and zinc ions, for example, 5 to 50%.
There is no problem in adding 80 g/l.

When steel materials are used in fields that require a particularly high degree of corrosion resistance, such as automobile steel materials, salt damage from melting salt sprinkled on roads in snow-covered areas and chipping damage from flying pebbles can occur. be. The damage caused by salt is particularly severe, and in severe cases, it can cause holes in the steel itself, which poses a serious problem from a safety standpoint.

In such a case, a plating layer may be further provided below the solid solution alloy plating layer to enhance anticorrosion and rust prevention. For example, a layer of about 5 to 25 g/layer consisting of one or more of δ, phase, ζ phase, and ζ phase and substantially free of η phase is formed by electroplating as a lower layer on a steel material. A F.-Zn based intermetallic compound alloy layer is formed, this is used as a steel material, and the solid solution alloy plating of the present invention is applied as an upper layer on the steel material to a thickness of, for example, 0.5 to 7 g/m'. The compound layer can be formed, for example, as a plating bath with a z,,+t-/F@-)4-weight ratio of 0.4 to 0.
9. Use a sulfate bath in which the sulfate concentration of both metals is 100 g/J or more within the solubility limit, the pH is 0.8 to 0.3, the current density is 60 to 200 A/mu'', and the bath temperature is 4 to 80. It can be formed by electroplating using an insoluble anode under plating conditions at °C.δ, the phase is mainly Fe.
Has a composition of Zn 7, Zn 8B, 6-93% by weight
The ζ phase mainly contains TeFθIIznII and (J
It is a mixed crystal of FeH'ZXX10, contains 72 to 80% by weight of Zn, and the ζ phase has a composition mainly of FeZnu, and is said to contain 93.8 to 94.5% by weight of Zn, and has excellent corrosion resistance. ing. However, if the thickness is less than 5 g/m', the corrosion resistance effect cannot be achieved, and if the thickness exceeds 25 g/m', not only will the merits of manufacturing by electroplating decrease from the viewpoint of productivity, but also the processability will be reduced. On the contrary, weldability deteriorates.

Compared to conventional electrogalvanizing and iron-zinc alloy hot-dip plating, the solid solution alloy plating of the present invention is less likely to cause coating defects such as blisters on the coating during electrodeposition, and the coating layer is thinner. Therefore, the moldability is good.

When applying the solid solution alloy plating of the present invention on the above-mentioned intermetallic alloy plated steel material, the thickness should be 0.5 to 7 g/W? , preferably in the range of 1 to 3 g/-.

Solid solution alloy layer is 0.5g/rr? If it is less than that, the chemical conversion treatment property is not good and coating film defects such as blisters are likely to occur. Moreover, even if it exceeds 7 g/-, the chemical conversion treatment property will not improve much.

Further, when it is used as a single layer on a cold rolled steel plate, for example, the thickness is preferably in the range of 0.5 to 7 g/m', preferably 1 to 3 g/m'. Fs+ from the treated surface during phosphate treatment
It has been confirmed that when the present invention is applied to a certain type of high-strength cold-rolled steel sheet that is unlikely to be leached, a good 7-Osphophyllite phosphate film is formed.

Next, an example will be given and explained.

Example The following materials A, B, and C were used as steel materials.

Material A: Fe content content 15 凰20 20g/- Fe-Zn alloy electroplated steel sheet.

Material B: F, content approximately 12% by weight, plating amount 30g/-
Fe-Zn alloy hot dip coated steel sheet.

Material C: SPC Note that the plate thicknesses of materials A to C are all 0.8-0.The plating bath composition is Fe50, , 'yH,0 and znSO.
The total amount of 4.7H10 is approximately 500 g/lN. ), So. 3.

The weight ratio of .Z,++/Fe+ was varied in g/l. bath p
H1, 2, bath temperature 60°C, current density 100 A/d
m”, and a titanium substrate plated with platinum was used as an insoluble anode.The amount of plating was 3 g/m.
” was adjusted by changing the plating time.

The following evaluations were performed on the obtained samples.

A9 Adhesion of plating layer A white vinyl tape was attached to the plating surface, OT bending was performed with the surface facing inside, and peeling of the plating layer adhering to the tape was measured (powdering test).

B. Phosphate treatment Phosphate treatment is 7 male 7 ophylite (Phospho
-phyllite % Zn1Fe(PO,)t) based immersion treatment type chemical Gr S-D manufactured by Nippon Paint Co., Ltd.
-2000, TA16-18, AR1
8-20, zn++1000±200ppmSFs”
The sample was immersed for 120 seconds in a solution adjusted to 50 to 1100 pp.

(η Film Amount The phosphate film amount was determined by dissolving the film in a 2% by weight CrOs solution.

(Odor P ratio It was calculated by

Corrosion resistance after C9 coating The sample plate after the above phosphate treatment was air baked at 120°C for 10 minutes, and Power Top U-30 manufactured by Nippon Paint Co., Ltd. was applied by cationic electrodeposition.

3 during cross-cut peeling, red rust resistance, and red rust generation time
Two evaluations used samples at this stage.

In addition, regarding water-resistant adhesion, on the painted plate which had been subjected to the above cationic electrodeposition coating to a dry film thickness of 20 μm, Amirac TP-16R manufactured by Nippon Paint ■ was applied to a dry film thickness of 25 μm, and baked with 140 μm. 20 minutes at 140 degrees Celsius), and then baked (140 degrees Celsius for 20 minutes) with Amylac 030 manufactured by Nippon Paint ■ to a dry film thickness of 30 μm as a top coat.

(1) Water-resistant adhesion A top-coated plate is immersed in hot water at 40°C for 240 hours, and after the immersion is finished, 100 2W square base lines reach the steel substrate.
Each piece was peeled off with cellophane tape, and the peeled area ratio was evaluated.

(2) During cross-cut peeling A board coated with 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, JIS2371) was performed, and during the peeling process (one side ->It's q.

, 11 (3) Red Rust Resistance On a plate coated with a cationic electrodeposition paint having 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, JIS 2371).

(4) Time for occurrence of red rust A salt spray test (JIS 2731) was conducted on a board coated with a cationic electrodeposition paint with a dry film thickness of 5 μm without cross-cutting, and the time until the appearance of red rust was measured.

The above results are shown in Table 1.

Claims (1)

[Claims] 1. As a polishing bath, the weight ratio of Z, +1-/F, -H- in Rakuchu is 0.02 to 0.15, and the sulfate concentration of both metals is 1.
00g/1 or more and within the solubility limit, using a sulfuric acid salt bath with a pH of 0.8 to 2.3, a current density of 60 to 20OA/mu3,
A method for plating an iron-zinc solid solution alloy, which comprises electroplating onto a steel material using an insoluble anode at a bath temperature of 40 to 80°C.