JP2010090401A - Zn-Al-BASED PLATED STEEL SHEET, AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Zn-Al-based plated steel sheet having excellent corrosion resistance and excellent press formability. <P>SOLUTION: A surface activation treatment with alkaline solution is applied on a surface of the Zn-Al-based plated steel sheet, and the surface is brought into contact with acid solution containing fluorine (for example, hydrofluoric acid of the predetermined amount is added) and having pH value of 0.5-3.0 and having the pH buffering action. Then, after such a state is kept for 1-60 seconds, water rinsing and drying are performed. An oxide layer containing Zn and Al is formed on the surface of the plated steel sheet. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a Zn-Al-based plated steel sheet having excellent corrosion resistance, low sliding resistance during press molding and having excellent press formability, and a Zn-Al-based plated steel sheet excellent in corrosion resistance and press formability. Is.

In the automotive industry field, Zn-based plated steel sheets have been conventionally used for the purpose of enhancing rust prevention. In particular, in recent years, there has been a movement to further extend the antirust life of automobiles, and there is a need to further strengthen the antirust ability of steel sheets for automobiles.
It is known that the corrosion resistance when using Zn-plated steel sheets as automotive steel sheets is greatly dependent on the amount of Zn deposited (Non-patent Document 1). Is effective. However, increasing the amount of Zn deposited due to the increase in Zn demand due to the increase in Zn demand and the depletion of Zn resources leads to an increase in steel prices. At the same time, there may be problems with stable supply. Moreover, it is thought that it has a bad influence on weldability, press formability, etc.
On the other hand, as another means for improving the corrosion resistance, there is a method of preventing the steel sheet from being directly exposed to the corrosive environment by applying a wax or sealer, which is called a secondary material, to a corrosive portion. This method is used particularly in areas where corrosion is severe. However, the method of applying wax or the like is often performed manually, which increases costs. In addition, since organic solvents are often used for wax and the like, there are problems in terms of health of the installer and high environmental burden. From such a point, it is preferable to omit as much as possible.
Shinzo Sasai, CAMP-ISIJ, 9 (1996), 474.

In view of the above, it is desired to develop a rust-proof steel sheet having high corrosion resistance that has a low zinc adhesion amount and omits the application of wax or the like as much as possible.
On the other hand, since the steel plate for automobile body use is subjected to press forming and used, it is also desired that the steel plate is excellent in press formability.

  In view of such circumstances, the present invention aims to provide a method for producing a Zn-Al-based plated steel sheet having excellent corrosion resistance and press formability, and a Zn-Al-based plated steel sheet having excellent corrosion resistance and press formability. And

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, the following knowledge was obtained.

First, as a highly corrosion-resistant steel plate used for automobile body applications, not a Zn-based plated steel plate, but a steel plate provided with plating containing Zn and Al (hereinafter referred to as a Zn-Al-based plated steel plate) was focused. Then, the possibility of applying Zn-Al-based plated steel sheets to automobile bodies was examined by a method that can simulate the real environment.
As a result, it was found that high corrosion resistance can be obtained when a Zn-Al-based plated steel sheet is applied to an automobile.
On the other hand, as a result of examining the press formability, it became clear that sufficient characteristics for application to automobiles were not obtained. The press formability of this Zn-Al-based plated steel sheet has been hardly studied because Zn-Al-based plated steel sheets are mainly used in the field of building materials and press formability is not so much required.
Based on these results, in the present invention, it was decided to use a Zn-Al-based plated steel sheet as a highly corrosion-resistant steel sheet used for automobile body applications, and then examined improvement of press formability, which is a problem.
The press formability that becomes a problem when used as an automobile body is slidability during press forming. This slidability is considered to be deteriorated by causing local adhesion between the press mold and the steel plate surface and increasing the friction coefficient.

Therefore, as a technique to improve the slidability, it is considered effective to suppress the adhesion between the press die and the steel sheet surface by applying an oxide to the surface of the Zn-Al plated steel sheet. We proceeded with the examination.
First, an oxide application experiment was performed on a Zn-Al-based plated steel sheet by a method of applying an oxide to a Zn-based plated steel sheet disclosed in JP-A-2002-256448. As a result, an oxide sufficient for improving the slidability could not be provided, and the effect of improving the press formability could not be obtained.

  Therefore, as a result of further intensive studies by the inventors, the Zn-Al-based plated steel sheet after the plating treatment was subjected to a surface activation treatment with an alkaline solution, and then contacted with an acidic solution containing fluorine and having a pH buffering action. Then, it was found that an oxide was formed on the surface of the Zn—Al-based plated steel sheet by holding it in the air, and good press formability was obtained.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A Zn-Al-based plated steel sheet is subjected to a surface activation treatment with an alkaline solution, then contacted with an acidic solution, held for 1 to 60 seconds after completion of the contact treatment, and then washed with water and dried to obtain Zn- In the manufacturing method of the Zn-Al system plated steel sheet that forms an oxide layer on the surface of the Al system plated steel sheet,
The acidic solution is a method for producing a Zn—Al-based plated steel sheet, containing fluorine, having a pH buffering action, and having a pH of 0.5 to 3.0.
[2] In the above [1], the Zn-Al-based plated steel sheet preferably contains 20 to 95 mass% Al.
[3] A Zn-Al-based plated steel sheet produced by the method for producing a Zn-Al-based plated steel sheet according to [1] or [2], wherein an oxide layer containing Zn and Al is formed on the surface of the steel sheet. It is. s
In the present invention, regardless of whether or not alloying treatment is performed, a steel plate obtained by plating Zn—Al on a steel plate by a plating method is collectively referred to as a Zn—Al-based plated steel plate. That is, the Zn-Al-based plated steel sheet in the present invention includes both a Zn-Al-plated steel sheet that has not been subjected to alloying treatment and an alloyed Zn-Al-plated steel sheet that has undergone alloying treatment.

  According to the present invention, a Zn-Al-based plated steel sheet having excellent corrosion resistance and press formability can be obtained. By applying the highly corrosion-resistant automotive plated steel sheet of the present invention, it is possible to reduce the steel material cost and the cost by reducing the auxiliary materials.

In the present invention, the Zn-Al-based plated steel sheet is subjected to a surface activation treatment with an alkaline solution, then brought into contact with an acidic solution, held for 1 to 60 seconds after completion of the contact treatment, and then washed with water and dried to obtain Zn. -When forming an oxide layer on the surface of an Al-based plated steel sheet,
An acidic solution containing fluorine, having a pH buffering action, and having a pH of 0.5 to 3.0 is used. Thus, it is an important requirement and a feature in the present invention that a solution containing fluorine and having a defined pH is used as a solution for contacting a steel sheet. As a result, a sufficient oxide layer can be formed on the steel sheet surface to ensure good press formability.
The term “after contact treatment” means that after the immersion process is completed in the case of immersion treatment, after the spray process is completed in the case of spray treatment, and after the application step is completed in the case of roll coating. is there.

The Zn-Al-based plated steel sheet used in the present invention preferably contains 20 to 95 mass% Al. More preferably, it is 40-70 mass%. By containing Al in the above range, corrosion resistance is improved.
Further, the plating adhesion amount is preferably 20 g / m ² or more per one surface. When it is 20 g / m ² or more, sufficient corrosion resistance is obtained as a steel sheet for automobiles regardless of the corrosive environment. Moreover, since it does not increase cost when it is 70 g / m < ² > or less, it is more preferable.

  Al oxide is formed on the surface of the Zn—Al-based plated steel sheet before contact with the acidic solution. However, when this Al oxide was observed by EPMA (Electron Probe Micro-Analysis), it was found that there were a portion with a lot of Al component and a portion with a little Al, resulting in a non-uniform oxide form. And since the oxide layer of the plating layer surface exists nonuniformly, it is thought that favorable slidability cannot be obtained stably.

  Therefore, after the Zn-Al-based plated steel sheet after the plating treatment is subjected to a surface activation treatment with an alkaline solution, it is brought into contact with an acidic solution, and then held for a predetermined time with an acidic solution film formed on the steel plate surface. A new oxide layer was formed on the plating surface layer by washing with water and drying. As a result, the new oxide formed at this time was a uniform oxide layer containing Zn and Al, and was formed mainly in the portion that was in direct contact with the press die during press forming of the surface of the plated steel sheet. By newly forming a uniform oxide layer on the surface of the plating layer in this way, adhesion between the mold and the plating is suppressed, and good press formability can be obtained.

  In the present invention, it is necessary to perform a surface activation treatment with an alkaline solution before contacting with the acidic solution. And it is preferable that the chemical | medical solution used for a surface activation process is an alkaline solution which is pH11 or more. The purpose of this treatment is to remove the Al-based oxide formed on the surface of the Zn-Al-based plated steel sheet and expose the new surface on the surface, thereby activating the reaction in the exposed portion of the new surface, Zn and Al This is for facilitating the formation of an oxide containing as an essential component.

  Moreover, you may perform temper rolling before this surface activation process. Furthermore, after the plating treatment, surface activation treatment may be performed, temper rolling may be performed, and then contacted with an acidic solution. This is because it is possible to destroy part of the Al-based oxide layer present on the surface of the plated steel sheet with a pressure-control roll used during temper rolling, and by combining surface activation treatment, the Al-based oxide The layer can be removed effectively.

The aqueous solution used for the surface activation treatment preferably has a pH of 11 or more, a bath temperature of 30 ° C. or more, and a contact time with the solution of 1 to 30 seconds. In the case of 1 second or less, since the Al oxide cannot be sufficiently dissolved, the reactivity with the subsequent acidic solution cannot be increased, and the oxide does not form sufficiently and may be longer than 30 seconds. Long-term treatment is not preferable because it reduces productivity. More preferably, the pH is 11 or more and the bath temperature is 50 ° C. or more. If it is pH in the said range, there will be no restriction | limiting in the kind of solution, Sodium hydroxide, a sodium hydroxide type | system | group degreasing agent, etc. can be used.
The surface activation treatment needs to be performed before contact with the acidic solution, but may be performed either before or after temper rolling performed after galvanization performed as necessary. However, if the surface activation treatment is performed after temper rolling, the Al-based oxide is mechanically destroyed at the portion that has been crushed by the rolling roll and becomes a convex portion. There is a tendency for the amount of removal to be different. For this reason, the amount of Al oxide after the surface activation treatment becomes non-uniform in the surface, and the subsequent oxidation treatment becomes non-uniform so that sufficient characteristics may not be obtained. For this reason, it is more preferable to perform a surface activation treatment after plating, remove the appropriate amount of Al oxide uniformly in the surface, perform temper rolling, and subsequently contact with an acidic solution.
The method for the surface activation treatment is not particularly limited. Examples of the method include a dipping method, a spray method, and a roll coating method.

Next, the acidic solution brought into contact with the Zn—Al-based plated steel sheet will be described.
In the present invention, the acidic solution contains fluorine. By using a fluorine-containing solution as a solution for contact-treating the steel sheet, it is possible to dissolve the Al oxide formed on the steel sheet surface before contact with the acidic solution. At this time, the fluorine content is preferably in the range of 50 to 10,000 mass ppm. When the fluorine content is less than 50 mass ppm, it is insufficient to dissolve the Al oxide without supplying sufficient fluorine. On the other hand, if the concentration exceeds 10,000 mass ppm, the concentration of fluorine contained in the formed oxide layer becomes high, and there is a concern that the treatment liquid is contaminated when the oxide is dissolved in the chemical conversion treatment step performed thereafter.
Fluorine can be added to the acidic treatment liquid as hydrofluoric acid or fluoride.

  Moreover, the acidic solution to be used shall have a pH buffer action in the range of pH 2.0-6.0. This is because when an acidic solution having a pH buffering action in the above pH range is used, it is maintained for a predetermined time after contact with the acidic solution, so that the dissolution of Zn and the Zn-Al oxide are caused by the reaction between the acidic solution and the plating layer. This is because the formation reaction sufficiently occurs and the oxide layer can be stably obtained on the surface of the steel sheet. In addition, as an index of such pH buffering action, evaluated by the degree of pH increase defined by the amount of 1.0 mol / l sodium hydroxide aqueous solution (liter) required to raise the pH of 1 liter acidic solution to 2.0-5.0 This value is preferably in the range of 0.05 to 0.5. If the pH increase is 0.05 or more, the pH will rise rapidly and there will be no sufficient dissolution of zinc for the formation of oxide, resulting in the formation of a sufficient oxide layer, while 0.5% If the following, the dissolution of Zn is promoted, the formation of the oxide layer has a long time, the damage of the plating layer is not significant, and the original role as a rust-proof steel sheet is not lost. is there. Here, the pH buffering action is evaluated by adding an inorganic acid having almost no buffering property within the pH range of 2.0 to 5.0 to an acidic solution having a pH value exceeding 2.0, and once reducing the pH to 2.0. .

Acidic solutions with such pH buffering action include acetates such as sodium acetate (CH ₃ COONa), phthalates such as potassium hydrogen phthalate ((KOOC) ₂ C ₆ H ₄ ), sodium citrate (Na Citrates such as ₃ C ₆ H ₅ O ₇ ) and potassium dihydrogen citrate (KH ₂ C ₆ H ₅ O ₇ ), succinates such as sodium succinate (Na ₂ C ₄ H ₄ O ₄ ), and lactic acid Examples thereof include lactate salts such as sodium (NaCH ₃ CHOHCO ₂ ), tartrate salts such as sodium tartrate (Na ₂ C ₄ H ₄ O ₆ ), borate salts, and phosphate salts. An aqueous solution containing each component content in the range of 5 to 50 g / l can be used. When the concentration is less than 5 g / l, the pH of the solution rises relatively quickly with dissolution of Zn, so that an oxide layer sufficient for improving the sliding property cannot be formed, and 50 g / l is reduced. If it exceeds, dissolution of Zn is promoted and not only it takes a long time to form the oxide layer, but also the plating layer is severely damaged, and it is considered that the original role as a rust-proof steel sheet is lost.

In the present invention, the pH needs to be 0.5 to 3.0. When the pH is less than 0.5, the plating layer is frequently dissolved and is not productive. On the other hand, if the pH exceeds 3.0, the plating layer does not dissolve, so that no oxide film is formed.
The method for adjusting the pH within the above range is not particularly limited, but for example, sulfuric acid, nitric acid, hydrochloric acid and the like can be used.

  About the temperature of a solution, 20-70 degreeC is preferable. Since the formation reaction of the oxide layer occurs when it is held for a predetermined time after contact with the solution, it is effective to control the temperature of the steel sheet during the holding to a range of 20 to 70 ° C. If it is lower than 20 ° C., the reaction for forming the oxide layer takes a long time, resulting in a decrease in productivity. On the other hand, when it exceeds 70 ° C., the reaction proceeds relatively quickly, but conversely, processing unevenness tends to occur on the surface of the steel sheet.

  In the present invention, if fluorine is contained in the solution in contact with the surface of the Zn-Al-based plated steel sheet, an oxide layer excellent in slidability can be stably formed. Even if a compound or the like is intentionally contained as an impurity, the effect of the present invention is not impaired. Even if N, P, B, Cl, Na, Mn, Ca, Mg, Ba, Sr, Si, or the like is incorporated into the oxide layer, it is applicable as long as the effect of the present invention is not impaired.

  In addition, there is no restriction | limiting in particular in the method of making a Zn-Al type plated steel plate contact-treat with the said acidic solution, the method of immersing a plated steel plate in a solution, the method of spraying a solution to a plated steel plate, and plating a solution via a coating roll There is a method of applying to a steel plate, and it is desirable that it is finally in the form of a thin liquid film on the steel plate surface.

After the galvanized steel sheet is brought into contact with the acidic solution composed of the above, it is desirable that the solution exists in the form of a thin liquid film on the steel sheet surface. This is because if the amount of the solution existing on the surface of the steel plate is large, the pH of the solution hardly rises even if Zn is dissolved, and it takes a long time to form the oxide layer. On the other hand, if the amount is small, the amount of oxide formation decreases, and the press formability does not improve. From this viewpoint, it is preferable and effective to adjust the amount of the solution film formed on the steel sheet surface to 1 to 10 g / m ² . Moreover, in order to prevent drying of a liquid film, it is more preferable to set it as 2-5 g / m < ² >. The amount of the solution film can be adjusted by a squeeze roll, air wiping or the like.

After contacting the Zn—Al-based plated steel sheet with the acidic solution, the time until the water washing (the holding time until the water washing) is 1 to 60 seconds. If the time until washing with water is less than 1 second, the solution is washed out before a sufficient oxide layer is formed, so that the effect of improving the slidability cannot be obtained. Alternatively, since the pH is not sufficiently increased, less oxide is formed. On the other hand, productivity is reduced in the holding time when it exceeds 60 seconds.
After holding for 1 to 60 seconds, washing and drying are performed.
Without washing with water, acidic substances remain on the surface of the steel sheet, so that it corrodes and is washed with water.

  As described above, an oxide layer containing Zn and Al is formed on the surface of the plated steel sheet of the present invention. The oxide layer formed on the Zn-Al plating surface prevents direct contact between the metal mold and the plating during press molding and prevents adhesion of the plating film to the mold. It is possible to significantly reduce the resistance at the time, that is, the friction coefficient.

  The oxide layer in the present invention is a layer made of an oxide and / or hydroxide containing Zn and Al. The average thickness of this oxide layer is preferably 20 nm to 80 nm in terms of silica thickness determined using a calibration curve prepared from the fluorescent X-ray intensity of O (oxygen) of a silica film having a known thickness. Preferably it is 30-60 nm. When the average thickness of the oxide layer is reduced to less than 20 nm, the effect of reducing the sliding resistance becomes insufficient. On the other hand, if the average thickness of the oxide layer exceeds 80 nm, the oxide layer breaks during press molding, the sliding resistance increases, and the weldability tends to decrease.

  Moreover, regarding the production of the Zn—Al-based plated steel sheet according to the present invention, it is necessary that Zn and Al be added to the plating bath, but the additive element components other than Zn and Al are not particularly limited. That is, even if Pb, Sb, Si, Sn, Mg, Mn, Ni, Ti, Li, Cu, etc. are contained or added in addition to Zn and Al, they are applicable as long as the effects of the present invention are not impaired. .

Next, the present invention will be described in more detail with reference to examples.
A cold-rolled steel sheet having a thickness of 0.8 mm was subjected to hot-dip Zn-Al plating with an adhesion amount per side of 45 g / m ² and an Al concentration of 0 to 100% by mass to produce a Zn-Al-based plated steel sheet. Next, an alkaline solution treatment was performed by dipping treatment as a surface activation treatment on both sides of the obtained Zn-Al-based plated steel sheet.
Subsequently, an oxide layer was formed using a processing facility having the configuration shown in FIG. First, the Zn—Al-based plated steel sheet obtained as described above was immersed in a solution bath 2 at 30 ° C. having different treatment solution compositions and pH values shown in Table 1. Next, the amount of liquid film on the steel sheet surface was adjusted with the drawing roll 3. The liquid film amount was adjusted by changing the pressure of the squeeze roll. Next, the cleaning tank 5 and the cleaning tank 6 are evacuated, the hot water of 50 ° C. is sprayed on the steel sheet in the cleaning tank 7 and washed with a dryer 8, and an oxide layer containing Zn and Al is formed on the plated steel sheet surface. Formed.
The solution to be dipped in the solution tank 2 was a solution to which a predetermined amount of hydrofluoric acid was added for the purpose of adding fluorine. For comparison, in part, a sample with a plating layer that is not a Zn-Al plating layer, a sample that does not undergo surface activation treatment with an alkaline solution, a sample that does not contain fluorine and / or a buffer solution in an acidic solution A sample with no holding time was also prepared.
The holding time until water washing is the time until the liquid film amount is adjusted with the squeezing roll 3 and the cleaning is started in the cleaning tank 7, and is adjusted by changing the line speed. What washed the steel plate immediately after squeezing using the shower water washing apparatus 4 of the side was also produced.

  Next, with respect to the steel sheet produced as described above, the friction coefficient was measured as a method for simply evaluating the press formability as an automobile outer sheet, and the area ratio of red rust was measured for the purpose of evaluating corrosion resistance. . The measuring method is as follows.

(1) Press formability evaluation test (Friction coefficient measurement test)
In order to evaluate the press formability, the friction coefficient of each test material was measured as follows.
FIG. 2 is a schematic front view showing the friction coefficient measuring apparatus. As shown in the figure, a friction coefficient measurement sample 11 collected from a sample is fixed to a sample table 12, and the sample table 12 is fixed to the upper surface of a slide table 13 that can move horizontally. On the lower surface of the slide table 13, there is provided a slide table support base 15 having a roller 14 in contact with the slide table 13 and capable of moving up and down. By pushing up the slide table support base 15, a pressing load N applied to the friction coefficient measurement sample 11 by the bead 16 is measured. A first load cell 17 is attached to the slide table support base 15. A second load cell 18 is attached to one end of the slide table 13 in order to measure the sliding resistance force F for moving the slide table 13 in the horizontal direction with the pressing force applied. In addition, the cleaning oil Preton R352L for press manufactured by Sugimura Chemical Co., Ltd. was applied to the surface of the friction coefficient measurement sample 11 as a lubricant, and the test was performed.
FIG. 3 is a schematic perspective view showing the shape and dimensions of the beads used. The bottom surface of the bead 16 slides while being pressed against the surface of the sample 11. The bead 16 shown in FIG. 3 has a width of 10 mm, a length of 69 mm in the sliding direction of the sample, and a lower portion at both ends of the sliding direction is formed by a curved surface having a curvature of 4.5 mm. It has a plane with a direction length of 60 mm.
The friction coefficient measurement test was conducted under the conditions shown below.
The bead shown in FIG. 3 was used, the pressing load N was 3923N (400 kgf), and the sample drawing speed (horizontal moving speed of the slide table 13) was 20 cm / min.
The coefficient of friction μ between the specimen and the bead was calculated by the formula: μ = F / N.
The evaluation criteria for press formability are shown below.
○: μ is less than 0.15 Δ: μ is 0.15 or more and less than 0.2 ×: μ is 0.2 or more
(2) Corrosion resistance evaluation test (red rust occurrence area ratio measurement test)
Corrosion resistance was obtained by simulating a laminated structure part that is a severely corroded part in an automotive steel sheet, preparing test pieces with two samples facing each other, and subjecting them to a corrosion test, and evaluating the combined interior. Each sample was sheared to a size of 100 × 50 mm to remove edge burrs caused by shearing. Thereafter, two samples of the same type were joined by spot welding to produce a laminated structure test piece for corrosion resistance evaluation. Since this evaluation method is intended to evaluate the corrosion resistance inside the laminated structure, the outer side of the test piece, which is not evaluated, was sealed with a polyester adhesive tape (Nitto Denko's Livic (registered trademark)).
The corrosion test was performed for 60 cycles using a corrosion test cycle defined in SAE J-2334, which is an American Automobile Engineers Association standard. After the corrosion test, the spot welded portion was drilled and the internal red rust occurrence area rate was evaluated.
The evaluation criteria for corrosion resistance are shown below.
○: Red rust generation area ratio is less than 30% △: Red rust generation area ratio is 30% or more and less than 70% ×: Red rust generation area ratio is 70% or more Table 1 shows the test results together with the experimental conditions. Shown in

From the test results shown in Table 1, the following matters were clarified.
(1) Nos. 1 to 18 are samples obtained by the method for producing a Zn-Al-based plated steel sheet according to the present invention, and are excellent in press formability and corrosion resistance.
(2) Nos. 19 and 20 are comparative examples in which the plating layer is not a Zn-Al plating layer. In No. 19, which is a plating layer containing 100% Zn, the corrosion resistance is inferior, and in No. 20, which is a plating layer containing 100% Al, an oxide layer is not formed on the surface, so that press formability is inferior.
(3) No. 21 is a comparative example in which treatment with an acidic solution is not performed. An oxide film sufficient to improve slidability is not formed, and press formability is inferior.
(4) No. 22 is a comparative example using an acidic solution having no pH buffering action. Press formability is poor.
(5) No. 23 is a comparative example in which the time (holding time) required for forming a solution film on the steel plate surface and washing with water is 0.4 seconds, which is shorter than the range of the present invention. Since a predetermined oxide layer was not formed, press formability is inferior.
(6) No. 24 is a comparative example which is an untreated Zn—Al-based plated steel sheet. Corrosion resistance is excellent, but press formability is inferior.
(7) No. 25 is a comparative example in which the surface activation treatment with an alkaline solution is not performed. Since a predetermined oxide layer was not formed, press formability is inferior.

  Since it is excellent in press formability, it can be applied in a wide range of fields, mainly for automobile body applications.

The figure which shows the principal part of the oxide layer formation processing equipment used in the Example. The schematic front view which shows a friction coefficient measuring apparatus. The schematic perspective view which shows the bead shape and dimension in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Washing tank 2 Solution tank 3 Squeezing roll 4 Shower water washing apparatus 5 Washing tank 6 Washing tank 7 Washing tank 8 Dryer S Steel plate 11 Friction coefficient measurement sample 12 Sample stand 13 Slide table 14 Roller 15 Slide table support stand 16 Bead 17 First Load cell 18 Second load cell 19 Rail N Pressing load F Sliding resistance

Claims (3)

After surface activation treatment of the Zn-Al-based plated steel sheet with an alkaline solution, it is brought into contact with an acidic solution, held for 1 to 60 seconds after completion of the contact treatment, and then washed with water and dried, thereby performing Zn-Al-based plating. In the method for producing a Zn-Al-based plated steel sheet that forms an oxide layer on the steel sheet surface,
The method for producing a Zn-Al-based plated steel sheet, wherein the acidic solution contains fluorine, has a pH buffering action, and has a pH of 0.5 to 3.0.   2. The method for producing a Zn-Al-based plated steel sheet according to claim 1, wherein the Zn-Al-based plated steel sheet contains 20 to 95 mass% of Al.   A Zn-Al-plated steel sheet produced by the method for producing a Zn-Al-based plated steel sheet according to claim 1 or 2, wherein an oxide layer containing Zn and Al is formed on the steel sheet surface.

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