KR920010777B1 - Electroplating steel sheet with two layer being of alloy metal and process for making - Google Patents

Abstract

An alloy electroplated steel plate consists of (1) the lower electroplated surface layer comprising Zn-Ni-Cr alloy which contains 5-20 wt.% of nickel, 0.1-0.5 wt.% chromium and the residual iron, having the thickness of at least 10 g/m2 on one side of steel plate and (2) the upper layer comprising Fe-Zn-Mn alloy electroplating layer which contains 5-30 wt.% zinc, 0.1-10 wt.% manganese and the residual iron, having a thickness of more than 0.5 g/m2. The bilayered alloy steel plate is electroplated by controlling and applying to the following conditions: (a) the total metallic concentration has the range from 0.5 mol/l to the critical solubility, (b) the amount of zinc ion and manganese ion in this concentration is 1-40 mol.%, (c) the ionic concentration of chloride is 5.0-1.0 mol, and the pH of chloride is 1.0-4.0, (d) the current density in the chloride bath is 250 or 20-150 A/dm2 and the relative flow velocity is 20-200 or 30-120 m/min.

Description

Double layer alloy plated steel sheet and manufacturing method

The present invention relates to a two-alloy plated steel sheet in which a zinc-based alloy is plated on a surface of a steel sheet and an iron-zinc-manganese alloy is plated thereon, and more particularly, to a zinc-nickel-chromium alloy comprising a first plating layer. The present invention relates to a two-alloy plated steel sheet and a method of manufacturing the same, which are easy to process with an iron-zinc-manganese alloy as a second plating layer and have excellent plating appearance as well as excellent phosphate treatment property, water resistance and corrosion resistance after coating. Galvanized steel sheet is widely used as automotive material because of its rust resistance. There is a demand for a plating layer that can improve product quality characteristics such as phosphate treatment, paint adhesion, and corrosion resistance after painting to adopt steel sheets and minimize plating deposition amount and to satisfy high rust resistance. Representative methods for producing two-layer plated steel sheet having excellent plating properties as automotive materials have been disclosed in Japanese Patent Laid-Open Publication Nos. 58-77591, 59-177391, 59-177392, 59-182987, 59-211592 and Japanese Patent. The methods listed in Announcements 58-15554, 63-24080, etc. may be mentioned.

Japanese Patent Laid-Open Publication Nos. 58-77591, 58-177391, 59-177392 and Japanese Patent Publication Nos. 58-15554, 63-24080 are mainly used as the lower layers of Zn-Fe, Zn- and Zn-based alloys, The iron-zinc alloy was plated on the Zn-Ni alloy plating layer, and the method disclosed in Japanese Patent Laid-Open Publication No. 59-182987 was used to plate the iron-zinc alloy on the Zn and Zn-based alloy plating layers and then contain a small amount of Sn. The method proposed in Japanese Patent Laid-Open No. 59-211592 is a method of plating iron-phosphorus alloys on the Zn and Zn alloy plating layers by substituting the iron-zinc alloy plating layers. In the production method, most of them use a sulfate bath, and a chloride bath is used in the iron-phosphorus plating of JP-A-59-211592. The second plating layer (surface layer) of zinc alloy containing 16 to 30wt% (weight ratio, used as weight ratio below) shown in Japanese Patent Publication No. 63-24080 is deteriorated in phosphate treatment property due to low iron content. Improvements in water resistance and paintability cannot be expected. In addition, as the second plating layer (surface layer) shown in Japanese Patent Laid-Open Publication Nos. 58-77591, 59-177391, 59-177392 and 58-1554, in the case of a zinc alloy plated steel sheet having an iron content of 60% or more, the plating adhesion amount of the surface layer and Fe Phosphate treatment, paintability and corrosion resistance after painting, depending on the content is a big problem.

In other words, when the amount of plating adhesion on the surface layer is small and the Fe content is 60 to 70%, the non-uniformity of the phosphate coating and the phosphophyllite (Phospohphyllite, Zn ₂ Fe (PO ₄ ) ₂ 4H ₂ O, hereinafter referred to as “P-type”) during phosphate treatment Due to the low crystal formation, deterioration of phosphate treatment property, resulting in poor paintability and poor adhesion of coating film, etc. On the other hand, when the amount of plating adhesion on the surface layer is high and grooves or defects occur on the coating film, the red iron is promoted due to the high iron content of the surface layer, which leads to deterioration of corrosion resistance after coating, and the unpainted corrosion resistance of the entire coating layer is lower than that of the single layer plated only. Deterioration occurs. In the case of the iron-phosphorus system disclosed in Japanese Patent Laid-Open Publication No. 59-182987, the increase in brittleness of the plating layer by phosphorus and the Fe and phosphorus (P) ions in the plating bath are not limited to the electrolytic reaction in the initial process of upper plating, There is a problem that the upper plating layer is peeled off due to the adhesion deterioration of the trace amount of Fe and P precipitates due to the electroless substitution reaction.

Zinc and zinc-based alloy plating layer can protect the cold-rolled steel sheet, which is a metal, by its excellent sacrificial anticorrosion, but when zinc is damaged in the corrosive environment of the vehicle under the harsh corrosion environment, it contains a large amount of zinc. Because of this, the water penetrated under the coating and zinc react to form corrosion products such as powdered zinc hydroxide, and at the same time, hydroxide ions are generated and converted into an alkaline atmosphere to dissolve the phosphate coating. Penetration is facilitated. This is considered to be a big factor in deteriorating the water-resistant adhesiveness of a coating film, water-resistant adhesiveness of a coating film, and corrosion resistance after coating.

Therefore, there is a need to improve the corrosion resistance of the zinc and zinc-based alloy plating layer and also in terms of the coating quality performance as a steel plate for automobile body panels. Among the coating quality performances of steel plate for vehicle body, paint adhesion is one of them and there is water resistance test as a method of evaluating secondary adhesion of paint. Water resistance adhesion test is performed by chemical treatment (phosphate treatment), electrodeposition coating, middle coating, and top coating on the material corresponding to the outside of the car body, and then immersed in distilled water at 40 ° C for 10 days and then taken out. Coating adhesiveness was evaluated to the extent of the coating film peeled off the tape when the vinyl tape is attached and peeled off. In general, phosphophyllite or hopitite (Hopeite: Zn ₃ (PO ₄ ) ₂ · 4H which may be present in the phosphate treated film) is evaluated. ₂ O, hereinafter referred to as “H type”) The presence of many P-type crystals improves the water-adhesion resistance, and the better the phosphate treatment, the better the cationic electrodeposition coating after phosphate treatment. It is known that the surface appearance after coating and improvement of the corrosion resistance after painting are improved in terms of performance and usability.

According to the findings of the present inventors, a cold rolled steel sheet generally known to have excellent phosphate treatment property forms a phosphate-treated local battery due to an appropriate amount of Fe, C, Mn, Cr oxides, etc. being distributed on the surface thereof. It was evaluated to promote. On the other hand, in pure railway gold by electroplating, the initial reaction is slow and the phosphate grains are coarsened due to the formation of stable oxide film on the surface.

Therefore, in view of the above problems and findings, the inventors of the present invention provide a surface-treated steel sheet excellent in chemical resistance (phosphate treatment), paintability, and workability required for corrosion resistance, film adhesion, and other steel sheet for automobile body shell. Many experiments and studies were conducted for the purpose. As a result, the iron-zinc-manganese alloy plating containing a small amount of manganese in the iron-zinc alloy plating having a high iron content lacks the ability to corrode a cold-rolled steel sheet, which is a metal, in the single layer plating, but contains a large amount of zinc in the lower layer. After plating the metal coating layer, it was confirmed that the desired purpose can be achieved by electroplating iron-zinc-manganese and alloy on the upper layer.

In the present invention, the upper plating layer has a surface state similar to that of a cold rolled steel sheet, and the iron concentration is high in the plating layer composition, so that the phosphate treatment is excellent, and in the case of a metal in which the hydroxide is not easily powdered in the alloying element of the upper plating system, corrosion resistance after coating It is proposed that the metal ions in the plating bath are excellent in plating adhesion by adding ions which are less likely to precipitate due to electroless reaction with zinc, that is, metal ions rather than zinc. The present invention is to provide a high corrosion-resistant two-layer alloy plated steel sheet excellent in plating adhesion, phosphate treatment and water resistance by plating the iron-zinc-manganese alloy on a plated steel sheet of zinc-nickel-chromium alloy, and a manufacturing method thereof. , Its purpose is.

Hereinafter, the present invention will be described. The present invention is a two-layer plated steel sheet having a first plating layer and a second plating layer, the first plating layer is 5 to 20% by weight (hereinafter referred to as "%") nickel, 0.1 to 1.5% chromium and the balance zinc A zinc-nickel-chromium alloy layer made up of at least 10 g / m 2 per sheet steel sheet; The second plating layer is an iron-zinc-manganese alloy electroplating layer composed of 5 to 30% zinc, 0.1 to 10% manganese and residual iron (Fe), and the plating layer has a thickness of 0.5 g / m 2 or more. will be.

In addition, the present invention is a method for producing a two-alloy plated steel sheet to form a zinc-nickel-chromium alloy plating layer of 10g / ㎡ or more per sheet steel sheet with a first plating layer on the surface of the steel sheet, and to form a second plating layer on the first plating layer. In the hydrochloric acid electric railway bath, hydrochloric acid containing zinc and manganese ions was added to the total concentration of ferrous ions, zinc ions, and manganese ions, ranging from 0.5 mol / l to solubility limit, and zinc and manganese in the total metal ion concentration. The amount of ions is 1 to 40 mol% in molar ratio, the concentration of molar chloride ion is formed at least 5.0 mol / l, and a chloride bath having a pH of 1.0 to 4.0 is formed, in which the current density is 20 to 250 A / d. Manufacture of a two-layer alloy plated steel sheet in which an iron-zinc-manganese alloy electroplating layer having a plating adhesion amount of at least 0.5 g / m 2 is formed as a second plating layer by electroplating under electrolytic conditions having a relative flow rate of 20-200 m / min. Relate to.

EMBODIMENT OF THE INVENTION Hereinafter, the reason for numerical limitation of this invention is demonstrated. In the first plating layer of the present invention, when the plating deposition amount of the zinc-nickel-chromium alloy is less than 10 g / m 2, it is difficult to secure sufficient corrosion resistance, and therefore, it is preferable to limit the content to 10 g / m 2 or more.

According to the confirmation of the inventors, the zinc-nickel alloy electroplated steel sheet having a nickel content of 5 to 20% showed superior surface rust and perforation resistance on the blister side than the zinc high-metal steel sheet. It was evaluated that zinc-nickel-chromium alloy electroplated steel sheets having a nickel content of 5 to 20% and a chromium content of 0.1 to 1.5% have better corrosion resistance such as surface rust and hole rust.

The reason for limiting the zinc content to 5 to 30% in the iron-zinc-manganese alloy electroplating layer of the second plating layer is that when the zinc content is less than 5%, the plating adhesion amount that strongly indicates the iron characteristics of the plating layer is increased. This is because the improvement effect of corrosion resistance is not confirmed, and in the case of zinc content of more than 30%, it is difficult to secure the phosphate treatment property and water adhesion of the cold rolled steel level.

The iron-zinc-manganese alloy electroplating layer, which is the second plating layer, is limited in the range of 0.1 to 10% of manganese due to the improvement of plating adhesion, phosphate treatment resistance and water adhesion. In other words, when the manganese content is less than 0.1% in the vicinity of the zinc content 30% can not be expected to improve the phosphate treatment properties, when the manganese is added to 0.1% or more improves the phosphate treatment properties and water adhesion. However, when 10% or more of manganese is contained, problems such as deterioration of processing due to poor adhesion of the second plating layer and discoloration of surface appearance due to oxygen present in the plating layer are likely to occur.

On the other hand, in the method for producing a two-alloy plated steel sheet according to the present invention, the electroplating layer of zinc-nickel-chromium alloy which is the first plating layer may be formed by a conventional vacuum deposition method or an electroplating method, more preferably. , 150-210 g / l ZnCl ₂ , 20-50 g / l NiCl ₂ , 350-400 g / l KCl and 1.0-3 g / l CrCl ₃ to form a plating bath having a pH of 2.0-4.0 In this plating bath, zinc-nickel-chromium is more than 10g / m2 per plate by electroplating under the electrolytic conditions of plating solution temperature of 55-65 ℃, relative flow rate of 30-120m / min and current density of 20-150A / dm2. The alloy plating layer is formed as the first plating layer. It is preferable to limit the pH of the preferred chloride-based zinc-nickel-chromium plating bath to form the first plating layer to 2.0-4.0, because the precipitation of the cathode due to the increase of the hydrogen ion concentration in the plating bath when the pH is below 2.0 This is because not only the efficiency is lowered, but also the productivity is lowered, and the dissolution of the steel sheet Fe, which is a base metal, is promoted.

In addition, it is preferable to limit the temperature of the plating bath to 55-65 ° C. The reason is that when the temperature of the plating bath is 55 ° C or less, the liquid resistance of the plating bath is increased to cause an increase in the plating voltage. This is because vacancies are difficult, and when the temperature is 65 ° C. or higher, there are problems such as a change in solution amount and a change in plating bath due to evaporation of the plating liquid.

In addition, when the first plating layer is formed by electroplating, the relative flow rate is preferably limited to a range of 30-120 m / min. When the relative flow rate is 30 m / min or less, the plating is performed at a low current density, thereby decreasing productivity. This is because the plating layer grains are unstable, and the upper limit thereof is limited to 120 m / min in relation to the current density.

In addition, it is preferable to limit the current density in the range of 20-150 A / dm 2, because the vacancy of chromium in the zinc-nickel-chromium alloy intermediate layer is difficult at current densities of 20 A / dm 2 or less. This is because it is not possible to form a zinc-nickel-chromium alloy plating layer composed of 5-20% nickel, 0.1-1.5% chromium and the balance zinc. When the current density is 150 A / dm 2 or more, the ternary alloy also This is because a tanning phenomenon occurs in which the surface of the plated layer becomes black due to exceeding the limit current density of the abstinence, and coarse grains are formed.

On the other hand, in the case where the iron-zinc-manganese alloy layer having a plating deposition amount of 0.5 g / m 2 or more on the first plating layer is electroplated to form the second plating layer, the total metal ion concentration of ferrous ions, zinc ions, and manganese ions is 0.5 mol / l. It is maintained in the solubility limit range, if the total metal ion concentration is 0.5 mol / L or less, the negative electrode precipitation efficiency is lowered, while the productivity is lowered, while if the solubility limit is exceeded, there is a problem that a solid precipitate is formed. In the plating bath of the second plating layer, ferrous ions, zinc ions, and manganese ions may be introduced in the form of chloride, sulfate, etc., and the zinc and manganese contents of the second layer plating film are zinc in the total metal ion concentration in the plating bath. And manganese ion concentration ratio can be appropriately selected. In other words, zinc and manganese ions in the total metal ion concentration in the plating bath in order to stably deposit the iron-zinc-manganese alloy coating film having a zinc content of 5 to 30% and manganese content of 0.1 to 10% in the plating layer. The concentration should be maintained in the range of 1 to 40 mol% in molar ratio.

In addition, the total chloride ion concentration in the plating bath of the second plating layer is maintained at 5.0 mol / l, preferably 6.0 mol / l, to a solubility limit. When the total chloride ion concentration is less than 5.0 mol / l, the electrical conductivity of the plating bath is low. The alloy composition of the plating layer is nonuniform and hardly causes precipitation of manganese.

In the plating bath of the present invention, as an addition method of chloride ions, inorganic plating bath conductivity aids such as potassium chloride, ammonium chloride, sodium chloride, and calcium chloride may be added alone or in a mixture. However, the addition of organic compounds such as sodium acetate (CH ₃ COONa), citric acid (C ₆ H ₈ O ₇ ), tartaric acid, etc. is not limited to the increase in the internal stress of the plating layer, that is, the deterioration of workability, and its type and amount of addition. This should be limited.

Relative flow rate used in the present invention is a relative moving speed of the steel through the plating bath, it should be maintained in the range of 20 to 200mpm. If the relative flow rate is less than 20mpm, the alloy composition of the iron-zinc-manganese alloy plating layer by the low current density plating is unstable, and the surface contamination is a problem due to the low speed. The reason for limiting the current density to 20 to 250 A / dm 2 is that vacancies of manganese are difficult at current densities of 20 A / dm 2 or less. If the current density is 250 A / dm 2 or more, the limit current density range is exceeded. This is because a kind of tanning (Burning) occurs in which the plating surface becomes black and coarse grains are generated, thereby degrading the plating adhesion of the second plating layer. If the plating liquid pH is less than 1.0, the plating liquid is strongly acidic, so it is inadequate in terms of dissolution of the lower first plating layer and reduction of the negative electrode deposition efficiency, and at pH 4.0 or higher, oxidation of ferrous ions (Fe ²⁺ ), which is present in a large amount in the plating liquid, is difficult. Hydrogen precipitates of F (eOH) ₃ are formed by the production of ferric ions (Fe ³⁺ ), and thus problems such as corrosion and surface contamination of the facility are generated, and thus a pH range of 1.0 to 4.0 is preferable. In addition, even in the relationship between the pH of the plating solution and the ferric ion concentration, if the ferric ion concentration and the pH of the plating solution are high, defects such as precipitation alloy composition of the plating layer, surface streaks, and stains occur, so that the plating solution pH is within the above range. . The plating liquid temperature is not particularly limited, but plating is possible in a range of 30 to 70 ° C. which is a temperature used for ordinary electroplating. Hereinafter, the present invention will be described in detail through examples.

Example 1

A second plating layer was formed on a specimen in which a zinc-nickel-chromium alloy was plated as the first plating layer, using a plating solution composition as shown in Table 1 below.

As described above, the plating adhesion, the phosphate treatment, the water resistance, and the corrosion resistance after coating were measured on the specimens on which the second plating layer was formed, and the results are shown in Table 1 together with the results of the specimens coated by the conventional method and the comparative method. Indicated.

TABLE 1

The plating adhesion in Table 1 was evaluated by the degree of peeling of the plating layer by vinyl tape after bending the sample 180 °, and the phosphate treatment property was the P-type film ratio by X-ray diffraction and the appearance of the phosphate coating after the phosphate treatment by the immersion type phosphate treatment method. And the morphology and density of the coating grains by scanning electron microscopy (SEM). In addition, the water-resistance resistance was applied to the sample by dipping phosphate treatment and cationic electrodeposition coating 20 μm, medium coating about 30 μm, top coating about 30 μm, so that the overall coating thickness was about 80 μm, and then immersed in distilled water at 40 ° C. for 10 days. After taking out and performing a checkered cross-cut at 2 mm intervals, the degree of peeling on the tape was evaluated when the vinyl tape was attached and peeled off. Corrosion resistance test after coating is performed in the same way as the water tightness test, after the phosphate treatment, the middle coating, and the top coating, the salt spray test (JIS Z 2371) and constant temperature (49) ℃) After 100 hours (50 days) of complex corrosion test for 12 hours, such as drying at constant humidity (relative humidity 90-100%) and 49 ℃, 50% or less relative cycle, the corrosion width and Corrosion depth was evaluated.

Each evaluation result was expressed as follows.

⊙: Extremely excellent, ◎: Very good, ○: Excellent, △: Normal, ×: Slightly bad, ××: Bad.

Comparative material of Table 1 is a case where the manganese content, zinc content in the upper layer plating layer which is the second layer is outside the scope of the present invention, in addition, the conventional material 1 is a cold-rolled steel sheet not subjected to plating treatment, the middle material 2 is nickel content 12 % Zinc-nickel alloy electroplated steel sheet.

As shown in Table 1, Inventive materials 1 and 2 in accordance with the present invention can be seen that the superior in plating adhesion, phosphate treatment, water tightness and post-painting corrosion resistance than the comparative materials and conventional materials 1 and 2.

Claims (3)

In a two-layer plated steel sheet having a first plated layer and a second plated layer, the first plated layer is a zinc-nickel-chromium alloy layer composed of 5 to 20% by weight of nickel, 0.1 to 1.5% of chromium and residual zinc, per sheet steel sheet. At least 10 g / m 2; The second plating layer is an iron-zinc-manganese alloy electroplating layer composed of 5 to 30% of zinc, 0.1 to 10% of manganese and residual iron (Fe), and has a plating adhesion amount of 0.5 g / m 2 or more. Plated steel sheet. A method of producing a double-alloy coated steel sheet by forming a zinc-nickel-chromium alloy plated layer having a thickness of 10 g / m 2 or more per sheet steel sheet with a first plated layer on the surface of a steel plate, and forming a second plated layer on the first plated layer. Hydrochloric acid containing zinc and manganese ions added to the electroplating bath, the total concentration of ferrous ions, zinc ions, and manganese ions is 0.5 mol / l to the solubility limit, and the zinc and manganese ions in the total metal ion concentration are 1 To 40 mol%, a chloride ion concentration of at least 5.0 mol / l, a chloride bath having a pH of 1.0 to 4.0, forming a chloride bath having a current density of 20 to 250 A / dm 2 and a relative flow rate. Electroplating under the electrolytic conditions of 20-200m / min to form an iron-zinc-manganese alloy electroplating layer having a plating deposition amount of at least 0.5 g / m 2 as a second plating layer. . The method of claim 2, wherein the first plating layer is composed of 150-210 g / l ZnCl ₂ , 20-50 g / l NiCl ₂ , 350-400 g / l KCL, and 1.0-30 g / l CrCl ₃ , wherein the pH is A plating bath having a thickness of 2.0 to 4.0 is formed, and the plating bath is electroplated under electrolytic conditions with a plating solution temperature of 55-65 ° C., a relative flow rate of 30-120 m / min, and a current density of 20-150 A / dm 2. Method for producing a two-layer alloy plated steel sheet characterized in that the forming.