JPS58210191A - Production of steel plate plated with zn-fe alloy - Google Patents

Abstract

PURPOSE:To enable the plating with high workability and at a stable and high content of iron, by adding Na2SO4 in place of (NH4)2SO4 and further K2TiF6 or Na2TiF6 and Al2(SO4)3 or MgSO4 to a plating bath contg. respective ions of zinc and iron. CONSTITUTION:A steel plate is plated in an electric Zn-Fe alloy plating bath of 0-15pH which contains 5-32g/l Zn<2+>, 27-60g/l Fe<2+>, 40-152g/l Na2SO4 in terms of anhydrous salt, 2X10<-3>-0.13mol/l K2 (or Na2) SiF6 and 8X10<-4>-9X 10<-2>mol/l Al2 (SO4)3 or MgSO4 and is controlled to 0.6-1.4 Na2SO4 molar concn./Fe<2+> molar concn., 0.5-0.8 Fe<2+> molar concn./(Fe<2+>+Zn) molar concn. Even if the bath temp. is <=20 deg.C here, the formation of crystals is prevented and the content of iron in the plating layer is increased by Na2SO4, and the fluctuation in the compsn. of the plating layer according to plating conditions is suppressed by K2SiF6, Al2 (SO4)3, etc.

Description

[Detailed Description of the Invention] The present invention provides a method for manufacturing Zn-Fe@gold-plated steel sheets by electroplating, which has excellent workability and allows stable and high Fe content in the edge and groin layers. Regarding.

For zinc alloy plated steel sheets, the entire coating layer or Zn −
1. Excellent in pre-painting treatment (chemical conversion treatment) and paint film adhesion than Zn-Fe alloy coated steel sheets made of Fe alloy or galvanized steel sheets whose entire coating layer is made of pure zinc. Because of this, it has been widely used in fields such as building materials.

In recent years, the characteristics of this Zn-Fe alloy plated steel sheet have become widely recognized in the automobile and home appliance industries, and it has become important as a base plate for painting.
Most of Fe alloy plated steel sheets are made by hot-dipping zinc onto the steel sheet and then heat-treating the steel sheet to reduce the entire plating layer to 52nm.
-Since it is alloyed with Fe, conventionally used (・
There were the following problems when using it in place of electrogalvanized steel sheets.

(1) The workability of the Zn-Fe alloy pot for the plating layer is inferior to that of pure zinc, and it is difficult to thin the plate with hot-dip plating, so even with light processing, the matte layer will not crack or crack, and the workability will be poor. It lacks.

(2) Zn-Fe alloyed plating layer surface pressure addition element Al is enriched and becomes inactive Al 203, and chemical conversion treatment of that part is not necessarily sufficient (.

(3) The plated original sheet undergoes thermal distortion during alloying treatment, and its workability is inferior to that of cold-rolled steel sheet.

Therefore, as Zn-Fe@gold-plated steel sheet without the above-mentioned problems, it is possible to coat Zn-Fe on the steel sheet (C directly) by electroplating.
The electric Zn -Fe @Kinmetsugi steel plate that has been used in -Fe alloys is attracting attention (・ru).

Conventionally, this electric Zn-Fe alloy mating steel plate was used as a mating bath by adding Na25Oa, K2SO4 or (NH4)2SO as a conductive agent to a bath containing Zn and Fe2+.
Each time a steel plate is electroplated, a small amount of one of the following salts is added (hereinafter referred to as a simple salt bath). , ill flow density, jet velocity of plating solution, etc.), the composition of the metal layer changes significantly.
It was difficult to obtain Fe alloy mating steel plates.

The Fe content in this predetermined plating layer is always stable.
-Fe @ As a method for producing gold-plated steel sheets, Fe
``: A method of electroplating steel sheets using a Kushita mating bath (hereinafter referred to as improved bath) similar to IK was proposed.

However, in the case of using this improved bath, there were various problems in bath management, such as poor workability, and there were limits to the types of products manufactured.

(1) When the bath temperature is below 20C, ammonium sulfate
Since a large amount of iron double salt crystals are formed, it is necessary to keep the plating solution at a low level (at least 20 tll') including the circulation process.
The temperature may drop below Or, causing clogging of pipes, etc.

(2) In the case of plating with an insoluble anode, even if an antioxidant such as citric acid is added to the bath, the oxidation of Fe2+ to Fe3+ will not be reduced, and if the bath pH exceeds 15Y, a large amount of the Fe3+ compound will be produced. Precipitation occurs, making it difficult to continue plating. It is necessary to always adjust this fixed bath pH to a low value (lower than L5), but if the bath pH is lower than L5, the Fe content in the agate layer is at most 30% or lower,
If the Zn-Fe alloy exceeds 0%, no effect will be observed.

(3) In the range 4Cj6 of the bath PHLo~L5, the Fe content in the plating layer is as shown in Fig. 1. It is easily influenced by pH (...) The Fe content in the plating layer is In order to stabilize it, it was necessary to test it in the vicinity of PHLO, which is an area where PH fluctuations are relatively small in practical terms. When plating in the vicinity of 1=LPHLO, the Fe content in the plating layer decreases to 10%, resulting in satisfactory paint film adhesion and post-painting corrosion resistance.

The inventors of the present invention found that conventional simple salt baths, improved baths, etc. have various drawbacks, such as luck. We have succeeded in developing a method for manufacturing a Zn--Fe alloy mating steel sheet by an electric mating method that is excellent and also stabilizes the Fe content in the mating layer.

The present invention prevents crystal growth when the bath temperature drops to 20C or less by adding sodium sulfate to the bath containing zinc 3 and iron ions instead of ammonium sulfate, and reduces the Fe content in the abutment layer. Potassium titanium fluoride or sodium titanium fluoride and aluminum sulfate or magnosilicon sulfate were used to increase the bulk and suppress fluctuations in the composition of the plating layer due to changes in plating conditions.
By adding each of the 7 ml (Zuneka), it solves the drawbacks of conventional baths (
Zinc ionone 5 to 3
2νJ, iron ion) k27~60yβ, sodium sulfate as anhydrous salt 40~152 dino, titanium potassium fluoride or titanium fly [sodium 2 x 10-3
~o, 13 mo broken,? and aluminum sulfate or magnesium sulfate Y8xl □ -4 to -9
In addition, the molar concentration ratio (iron ion molar concentration / iron ion molar concentration /
Accounting molar concentration of iron ions and zinc ions) 0.5 to 0
．． Acid electrolytic zinc of PHQ~L5 adjusted to 8-
The process involves electroplating steel plates in a steel metal plating bath.

The present invention will be described in detail below.

As mentioned above (in the conventional improved bath, when ammonium sulfate was added to a bath containing Zn2+ and Fe2+, Fe2+ turned into ammonium sulfate ferrous double salt, and a large amount of crystals thereof precipitated. By adding sodium sulfate, Fe 2+ > Fe SO4
ferrous sulfanate (double salt) consisting of

This salt has a high solubility even when added to the amount of sodium sulfate, so the precipitation of the crystals will not occur (for example, 5tE
II In the case of ammonium @o, if more than 4 s mol (6 (19)) is added, 0.45 mol or more of ferrous ammonium sulfate will be produced, if it is less than 200, crystals will be mainly 1, but in the case of sodium sulfate, 1 mol of ammonium sulfate will be produced. (152, F/-6),
Even if it is added, the crystals of ferrous sulfanate will not form (・.

Therefore, in the case of sodium sulfate, by keeping the Fejly concentration in the bath high, even if the plating conditions change, fluctuations in the Fe content in the plating layer are suppressed;
-Fe alloys can be used.

Figure 2 shows a process in which sodium sulfate is added to a plating bath containing Zn''s and PE2+V, and a steel plate is electroplated in the bath.
This shows the Fe content in the metal layer in this case, which is higher even at the same pH and current density than in the case of aluminum sulfate addition shown in FIG.

With the addition of one layer of sodium sulfate, the Fe content in the inlay layer is P) within 30% in ILO, or P
There is also a large variation in Fe content due to variation in H. This σ,・
As a result of various researches for Tameko I et al.
I have found that adding only 10,000 to 90% is extremely effective.

The titanium fluoride and sulfate of γL et al.
c) In plating bath pH and addition amount range 4, it is chemically extremely stable even if it coexists in the plating bath.

and ζ These compounds reduce F in the plating layer during electroplating.
The e content is increased to reduce and stabilize fluctuations in Fe content in the plating layer due to P)I fluctuations in pHLo~L5. This is generally P at the cathode interface during electroplating.
As H increases, a film is formed on the surface of the plating layer by hydrolysis consisting of the titanium fluoride and aluminum sulfate or magnesium salt, and this film is Zn2+.
It is thought that this is because the barrier layer acts as a barrier layer to allow only Fe2+ to pass through preferentially.

This is also supported by the fact that eutectoids of Ti, Al, and Mg are observed in the Zn--Fe alloy plating layer according to the present invention.

Next, the reason for limiting the plating bath component concentration in the present invention will be described.

Zn2+:F6. Nibi Fe2+ has 5 to 32 sides and 27 to 60 sides, respectively! /J and KaFe2n (Zn2+
10 pe2. ＋ N.

Make the molar concentration ratio 05 to 08. This is each III! Every time〃
If the temperature is less than the lower limit of 1, the ratio of the amount removed by electrodeposition to the concentration in the bath increases, resulting in large changes in the a degree in the bath, making it difficult to perform plating with uniform string removal. To become. On the other hand, if each concentration exceeds the upper limit, a large amount will adhere to the surface of the plating layer and be carried out, resulting in an increase in the step-up cost, an increase in the viscosity of the plating bath, an increase in the occurrence of pin-poles, etc. (If KFe2+ exceeds the upper limit, as will be described later, in the present invention, 17 cm of sodium sulfate is added depending on the amount of Fe2+, so the amount added increases, and the viscosity of the plating bath decreases. This increases the amount of removal due to adhesion of the steel plate, and also increases the number of pinholes.

Fe”/(Zn”10Fe”) 17) If the molar concentration ratio is less than 0.5, the amount of Zn deposited increases and the Fe content in the plating layer becomes small (it is recommended to set it to 10% or more). On the other hand, if it exceeds 0.8, the amount of Fe deposited increases, and the Fe content in the metsa layer exceeds 70%.

However, the chemical conversion treatment and paintability of the mesh layer are limited to Fe content of 70.
%, so there is no point in increasing the Fe content too much.

Sodium sulfate is used as described above (Fe in the plating bath
(+' This is to make ferrous sulfate, but in the case of the present invention, it is not necessary to make all Fe2+ ferrous sulfates, and Nas+ SO
If the molar concentration ratio of 4/Fe is in the range of 0.6 to L4, it is possible to make a Zn-Fe alloy with a sufficiently stable Fe content.However, if the molar concentration ratio is large and the However, since the Fe content in the mesh layer is high, F
If a high e-content is desired, the molar concentration ratio is preferably set at the upper limit of the above range.

Even if the molar concentration ratio of Na2SO4/Fe2+ is made larger than L4, it is difficult to increase the Fe content in the interlocking layer, and the limit has been reached (...), so there is no point in increasing it.On the other hand, 0, If it is less than 6, the Fe content in the plating layer will follow the changes in the plating conditions, but will remain stable.7, zFe
The content of Zn-Fe alloys is 5 or more difficult.

In the case of the present invention, since the lower limit of Fe2+ content is 27 sides, the lower limit of the amount of sodium sulfate added is 0.6, which is the lower limit of the molar concentration ratio.
The upper limit is calculated in the same way and becomes 409A for anhydrous salt, but the upper limit is 213ν for anhydrous salt, but 152
If it exceeds El/-e, the viscosity of the potting bath will increase and the occurrence of pinholes in the plating layer will increase, so it should be 152u or less.

The appropriate amount of potassium titanium fluoride or titanium fluoride/sodium fluoride is 2 x 10-3 to 0.13 moV.
2 X 10-37V! If the amount is less than 13 mol, even if aluminum sulfate or magnesium sulfate is added, there is no effect of increasing the Fe content in the mating layer.
If it exceeds b/, 13'Y, the amount of titanium deposited will increase too much due to the addition of one of the sulfates, and the plating layer will also become brittle.

The amount of aluminum sulfate or magnesium sulfate added is 8
X 10-' to 9 X 10-2 mo V2 is appropriate.

If it is less than 8 x 10-'moIL-/13, the Fe content in the plating layer will be high within the range of addition of titanium hepta-noide of the present invention, and the Tb effect will be small, which is not sufficient. On the other hand, if the aluminum sulfate exceeds 9×10 moV, a precipitate consisting of titanium fluoride and aluminum sulfate will be formed during bath preparation.
Bath stability decreases. On the other hand, in the case of magnesium sulfate, if the concentration exceeds 9 x 10-2 mo~/-e'l, unplating occurs locally, and Ti and Mg are concentrated in those areas.

When the pH of the plating bath becomes less than zero, it becomes difficult to deposit Fe, and the Fe content in the plating layer decreases to less than 10%, resulting in reverse KL! When In exceeds the oxidation level of re in the aqueous bath, Fe3+ compounds eventually start to precipitate.

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

Example: After degreasing and pickling a cold-rolled steel plate with a thickness of 0.6 cm using a hot method, electrolytic Zn −
Fe alloy plating was applied. The right side of Table 1 shows the Fe content in the plating layer of the obtained product. Furthermore, the plating layer (
・When we confirmed the presence of titanium, aluminum, magnesium, potassium 8, and sodium using fluorescent X-ray analysis, we found that when compounds of the elements were added to the plating bath and the bath composition was 1, the content was confirmed. 1 confirmed.

As is clear from Table 1, according to the present invention, the Fe content in the mating layer can be significantly increased compared to the conventional method, and it is also possible to plate with the same Fe content as the conventional method.
Mainly, by selecting Fe'')7[Zn''+pe2+) in the bath, Zn--Fe alloy abutment steel sheets with a wide range of Fe contents can be produced.

Figure 3 shows the relationship between the plating bath PHX and electric flL\B degree and the Fe content in the plating layer in Table 1 for each of the inventions 5.6.8.9 and 15-8. As can be seen by comparing Figures 1 and 2, as the pH changes, 5F
The fluctuation of e content is small (, stable y, IFe content of Zn
-Fe alloy plating is possible.

As described above, the present invention allows easy management of the potting bath, has excellent workability, and has a stable Fe content.
Fe alloy plating can be performed. In addition, since it is possible to use Zn-Fe alloy steel sheets with a high Fe content, it is possible to obtain products with excellent chemical conversion treatment properties and post-painting corrosion resistance, thereby improving the quality of Zn-Fe alloy steel sheets. 0 that contributes significantly to

[Brief explanation of drawings]

Figure 1 shows the relationship between PH'j6 and current density of a conventional improved bath for Zn-Fe alloy plating, 8-layer metal bath, and Fe content in the plating layer, and Figure 2 shows the relationship between the Fe content in the plating layer. Figure 3 shows the relationship between the metal bath PHg in this case, the metal current density, and the Fe content in the metal layer. For each invention, the relationship between the metal bath PH, the metal metal current density, and the Fe content in the plating layer is shown. Fuji Mitsuru 1st figure, ki kanfl-1 2nd fig.

Claims (3)

[Claims] (1) Zinc ions: 5 to 32 tons, iron ions: 27 tons
~60 i/A, 40 i/A with sodium nitrate as anhydrous salt
~1529/-13, potassium titanium fluoride or sodium titanium fluoride'Y2X10 ~0,13moWI3
S-56 and aluminum sulfate or magnesium sulfate' contain 8X10-(9X10-2 mole), and the amount of sodium sulfate is the molar concentration ratio (molar concentration of sodium sulfate, / molar concentration of iron ion) to the amount of iron + ion. 0.6~L
4, the amount of iron ions is adjusted to 0.5 to 0.8 by the molar concentration ratio (iron ion molar concentration, /total molar concentration of iron ions and zinc ions) to the total i of iron ions and zinc ions. Zn characterized by electroplating a steel plate in an acidic electrolytic zinc-iron alloy potting bath of pH 0-15.
-Fe@Method for producing gold-metal steel plate. (2) By selecting the plating bath set 111'Y, Zn-F containing 10 to 70% iron and trace amounts of titanium 8 and aluminum based on the total weight of the plating layer
The method for manufacturing a Zn--Fe alloy plated steel sheet according to claim 1, characterized in that an e-base metal is electroplated. (3) Plating bath set ['& Depending on the selection, a Zn-Fe alloy containing 910 to 70% iron based on the total weight of the plating layer and trace amounts of titanium 8 and magnesium 4. The method for manufacturing a Zn-Fe@gold-metal steel plate according to claim 1, characterized in that: