JPS63203797A - Production of composite electroplated metallic material having high corrosion resistance - Google Patents

Abstract

PURPOSE:To produce a composite galvanized metallic material having high corrosion resistance, excellent paintability, etc., by executing electrolysis in a galvanizing bath which contains a prescribed amt. of phosphoric acid ions and is specified in pH value to form a plating layer co-deposited with a phosphorus compd. and metal Zn. CONSTITUTION:A metallic material to be plated such as steel sheet as a cathode is electrolyzed in the galvanizing bath which contains the phosphoric acid ions at 0.05-200g/l terms of PO4 and is adjusted to pH1-5.5. The phosphorus compd. and metal Zn are co-deposited at the boundary face by utilizing the phenomenon by which the pH is increased at the cathode boundary face at the time of electrodeposition of Zn to form the combined plating layer. The above-mentioned co-deposition is preferably executed in the above-mentioned plating bath contg. 2-500ppm Fe<3+> ion. The titled material which has excellent corrosion resistance and corrosion resistance after painting, good paint adhesiveness and permits omission of a phosphate treatment prior to painting is obtd. by such method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrolytic zinc composite plated metal material having excellent corrosion resistance, and mainly to a method for producing the electrolytic zinc composite plated metal material.

[Conventional technology]

Conventionally, steel sheets with electrogalvanized coating were mainly
It has a high corrosion protection effect due to the sacrificial corrosion protection effect of zinc, the basis weight can be easily adjusted, and it is also excellent in processability.
It has been widely used as a material for coating products, mainly for automobiles and home appliances. However, in recent years, there has been a demand for metal materials with even higher corrosion resistance and quality, mainly for use in automobiles.

Technological developments that have been carried out in the field of steel sheet manufacturing technology to meet such demands can be roughly divided into two methods. In other words, one method is Zn-based alloy plating, in which Zn is alloyed and precipitated with metals that are electrochemically more sensitive than Zn, such as Ni and Co. Another method is Zn-based dispersion composite plating using a suspended or dispersed Zn plating bath.

Furthermore, alloy-plated steel sheets are already being put into practical use.

By the way, in ordinary Zn-plated steel sheets, because the potential difference between the Zn coating layer and the iron material is large, the sacrificial corrosion protection effect of the coating layer is excellent, but conversely, the dissolution rate of the galvanized layer is fast, so it will not last long. When the purpose is to prevent rust, it is necessary to form an extremely thick plating layer. On the other hand, the zinc-based alloy coated steel sheets currently in practical use are made of Ni.

The dissolution rate of the plating layer is suppressed by coexisting metals such as Co and Fe that are more harmful than Zn as alloying components, controlling the potential difference between the material and the plating layer to an appropriate level, and adjusting the sacrificial corrosion current within an appropriate range. There is.

Therefore, zinc-based alloy coated steel sheets are said to have a longer-term rust prevention effect than conventional galvanized steel sheets at the same basis weight. However, in reality, in the sacrificial anticorrosion action of zinc-based alloy coated steel sheets, uniform dissolution of the plating components does not occur, and Zn, which is less noble in potential, is preferentially eluted. For this reason, the plating layer gradually loses its negative alloying components and eventually reaches the potential of the alloying components, which has the drawback of losing its sacrificial anticorrosion effect on the iron material.

In addition, in dispersion plating, in which fine particles such as alumina and silica are added to the Zn plating solution, Zn and fine particles are difficult to eutectoid unless a sufficient positive charge is given to the fine particles.
It is not economical as it requires the addition of high concentration of fine particles into the plating bath, and it is difficult to maintain and manage the bath, so it has not yet been put to practical use. Disclosures are made in Nos. 61-52321 and 60-125395.

[Problem that the invention seeks to solve]

As mentioned above, alloy plating has Z
There is an inherent tendency that the sacrificial anticorrosion effect of n is weakened.

In dispersion plating of fine particles, fine particles with a diameter of 5 to 50 mμ, which are positively charged by a cationic surfactant or the like or due to the properties of the fine particles themselves, migrate to the cathode surface due to the charge, and lose charge on the electrode surface. Precipitate.

The precipitated plating metal is bonded to the electrode through a metallic bond, whereas the particles deposited on the electrode surface are only physically adsorbed by van der Waals forces with the electrode surface, so the particles are half the particle size. The fine particles are in a state where they can be easily detached from the electrode surface until they are embedded in the precipitated matrix metal. therefore,
In the conventional dispersion plating method, 1. Eutectoid plating cannot be obtained with a plating thickness of 1/2 or less of the eutectoid particle diameter, and 2. It is difficult to obtain a high eutectoid rate because the probability of eutectoid particle detachment is high. Therefore, in order to obtain a constant eutectoid rate, it is necessary to significantly increase the content of eutectoid components in the bath. 3. Strong stirring is required under high-speed plating conditions (high current density conditions). 4. The larger the particle size, the more influenced by gravity; for example, when an electrode is plated in a horizontal state, when comparing the plating layers on the top and bottom surfaces, the eutectoid rate of the particles on the bottom surface decreases. There were disadvantages such as non-uniform plating, such as 5 solids, and maintenance of uniformity of bath components and maintenance of the equipment became complicated due to the solid content.

By developing a new composite electrolytic Zn plating technology, the present invention does not, in principle, have the problems of conventional zinc plating technology, and is particularly suitable for manufacturing galvanized steel sheets for which high-speed plating is an essential condition. Another object of the present invention is to provide a method for producing a composite galvanized metal material having excellent corrosion resistance and paintability.

[Means for solving problems]

The present inventors have succeeded in developing a previously unknown composite plating method in which metallic Zn, which is deposited on a steel sheet by galvanizing, and phosphorus are uniformly dispersed within the electrogalvanized film. Conventionally, even when using a plating bath containing zinc phosphate and zinc ions, metallic Zn and
It was not possible to disperse phosphorus uniformly.The present inventors previously dissolved phosphoric acid and zinc, which are components of a composite plating bath, in the plating bath as ions, and when the zinc was electrolytically deposited, they were dissolved at the cathode interface. By actively utilizing the phenomenon in which the pH increases in Zn and eutectoiding a phosphorus compound with Zn at the interface to form a composite, we succeeded in developing a composite electrogalvanizing method.

That is, in the method for producing an electrolytic zinc composite plated metal material with excellent corrosion resistance according to the present invention, the plating conditions are specified so as to cause the above-mentioned eutectoid, and the phosphate ion is 0.05 in terms of P04. ~200g/l, preferably 1
A Zn plating bath containing ~50 gzl and having a pH of 1 to 5.5, preferably 2 to 4 is used.

A phosphate ion content of less than 0.05 g/J is insufficient to bring out the effects of the present invention. Also, phosphate ion is 200
If it exceeds g/l, the adhesion of the plating film to the substrate will decrease. As the Zn plating bath, an acidic bath containing Zn sulfate, chloride, or others as a main component can be used.
It is preferable that the amount of Zn'' is 2 to 150 g/l. In addition, various ammonium salts, fluorides, sodium salts, etc. may be added as pH stabilizers and conductivity imparting components to improve the eutectoid effect. can.

Furthermore, by containing 2 to 500 pp+w of Fe' ions, the eutectoid state of phosphate becomes fine and uniform, which has the effect of significantly improving corrosion resistance.

If the content is less than 2pp+w, the effect is small, and 500%
If it exceeds ppm, the precipitation of Zn will be inhibited. Fe3
It is relatively desirable to add + as a soluble salt such as nitrate or hydrochloride.

In the Zn plating bath in the present invention, Li1M+b Aj!
+Ca, Ti, V, Cr+ Mn, Fe”
+ Co, Ni, Cu, Ge, As, Sr,
Zr, Nb.

Mo, Te, 8g, Cd, Sn, Sb, Cs,
One or more types of Ba, -, Pb, Bi, and Ce ions can be added.

[For production]

The production process of the composite electrogalvanized film according to the present invention is considered to be as follows.

Electrolysis is carried out using a Zn plating bath containing phosphate ions and a steel plate as a cathode. At this time, at the cathode interface, 2 H" + 26−−Hz ↑ −・・−・−
The reaction (1) occurs, some hydrogen ions are consumed, and the pH
rises. When the pH exceeds the dissolution pH of zinc phosphate in the bath, phosphorus compounds begin to precipitate on the surface of the steel sheet.

The main reaction at this time is considered to be expressed by the following formula.

3 Zn(HzPOa)z-Zns(POn)!
+ 4H" + 4HzPOt-... (2) As the current continues, the precipitation of phosphorous compounds continues, but of course at the same time Zn" + 2 e--Zn ・"... (3
), the precipitated phosphorus compound and metal Zn repeat the precipitation while simultaneously forming a Zn plating layer, resulting in a composite plating in which metal Zn and phosphorus compound are almost uniformly dispersed. form a structure.

Further, if Fe'' is present in the bath at this time, crystal nucleation of phosphate tends to occur, and the eutectoid rate and uniform dispersibility are greatly improved.

In addition, as in equation (2), there is a possibility that the bath components form a film due to adsorption of phosphorus, adsorption of metal hydroxides, etc. in the bath.

In the present invention, there is no need for solid matter to be present in the plating bath, and po, 3-, which is a composite component of composite plating, exists in the form of ions, and with the discharge of H''' at the cathode, the phosphorus compound Since this is a mechanism in which phosphorus is precipitated, this precipitation state occurs only within the extremely thin diffusion layer on the electrode surface, and while the precipitated phosphorus compound is embedded in the galvanized layer on the electrode surface,
Since it is thought that epitaxial crystal growth is performed on the substrate, and it is strongly bonded to the electrode surface, it is understood that the probability of detachment due to physical force such as stirring is extremely low. The plating method of the present invention does not have the drawbacks of conventional dispersion plating, and is particularly excellent because high-speed plating is possible.

Further, the excellent properties of the composite plated metal material obtained by the method of the present invention are thought to be due to the interaction between zinc and the phosphorus compound finely dispersed in the zinc matrix. That is,
Phosphorus compounds exhibit the action of improving corrosion resistance and acting as a base for painting, and further suppress the corrosion of electroplated metal Zn plating layers, and have a remarkable effect on corrosion resistance, especially on preventing paint film blistering related to post-painting corrosion resistance. On the other hand, metal Zn protects the material by sacrificial corrosion protection.

Furthermore, by using the composite plated steel sheet obtained by the method of the present invention, it is possible to obtain corrosion resistance and coating adhesion that are equivalent or better than that without the need for zinc phosphate treatment as a pre-painting treatment that was previously required. According to the present invention, a surface-treated metal material having coating surface properties that cannot be obtained by conventional methods can be obtained.

Hereinafter, the present invention will be explained in detail with reference to Examples.

〔Example〕

In the Examples and Comparative Examples of the present invention described below, a cold rolled steel plate (SPCC) subjected to alkali degreasing as a pretreatment was
%HtSO and a pickling solution, followed by washing with water, and plating was performed under the conditions described individually below. In addition, plating was carried out by blowing air during plating, and a pure Zn plate was used as an anode, and a cold-rolled steel plate as a test plate was used as a cathode, and the liquid temperature was 30°C.
Electrolysis was performed by applying current for 30 seconds at a current density of 20 A/dIII2.

[Comparative Example 1] Bath composition Zinc sulfate heptahydrate 200 g/1
Sodium sulfate 100 g/1 sulfuric acid
4g/β H3 [Comparative Example 2] Bath composition Zinc sulfate heptahydrate 150g/j! Nickel sulfate hexahydrate 200g/1 sodium sulfate 100g/j! Sulfuric acid 4
g/1 pH2.8 [Examples 1 to 4] Bath composition Zinc sulfate heptahydrate 200 g/1
Sodium sulfate 100 g / 1 phosphoric acid
1-100 g/It (as PO4) (adjusted to pH 3, o with sodium hydroxide) (Example 5-
6] Bath composition Zinc sulfate heptahydrate 200 g/1
Sodium sulfate 100 g/It Phosphoric acid 15 g/1 (as PO4) Citric acid 30 g/L (pHtII adjusted with sodium hydroxide) [Example 7] Bath composition Zinc chloride 100 g/I
l Ammonium chloride 50g/II phosphoric acid
15 g/1 (as PO4) Calcium chloride 25 g/II (adjusted to pH 3, s with aqueous ammonia) [Example 8] Bath composition Zinc chloride 200 g/1
Sodium chloride 100g/It phosphoric acid 38g/j! (As PO4) Titanium tetrachloride (35%) 20 g/l (adjusted to pH 1.5 with sodium hydroxide) [Examples 9-10] Bath composition Zinc sulfate heptahydrate 200 g / β sodium sulfate 100 g / monophosphate
15g/i! (as PO4) Ferric sulfate 0.01-0.1g/1 (as Fe") (Adjusted to pH 3.0 with sodium hydroxide) Below margin i) Corrosion resistance (unpainted) is based on salt spray (JIS-Z- 237
1) shows the time required for red rust to develop.

ii) Corrosion resistance (Plates E and D) is measured by applying cationic electrodeposition paint (Kansai Paint ■) for 15Jna, then inserting cross-cuts, and applying salt water spray test for 480 hours. ).

4...O~1f1 3...2~3 Tsuru2...4~6fi l...7 or more [Effects of the Invention] As explained above, the composite electroplated metal obtained by the method of the present invention Since the material was obtained using a method that is fundamentally new, it has the potential to exhibit performance that has never been seen before. Currently confirmed performances include bare corrosion resistance,
Corrosion resistance after painting, especially corrosion resistance after painting, has the feature that blistering of the paint film, which is a drawback of conventional Zn plating, does not easily occur.

Furthermore, since the surface of the plating layer has fine irregularities, it has good paint adhesion and has the advantage that phosphate treatment before painting is not necessarily required.

Furthermore, it has high lubricity compared to conventional Zn plating, and is expected to be applied as a surface treatment for cold working.

Claims (1)

[Claims] 1. 0.05 to 200 g of phosphate ion in terms of PO_4
/l in a Zn plating bath with a pH of 1 to 5.5,
A method for producing a highly corrosion-resistant composite electroplated metal material, which comprises performing electrolysis using the metal material to be plated as a cathode to form a plating layer in which a phosphorous compound and metal Zn are eutectoid. 2. Z containing 2 to 500 ppm of Fe^3^+ ions
2. The method for producing a highly corrosion-resistant composite electroplated metal material according to claim 1, wherein the eutectoid is carried out in an n-plating bath.