JP2022001833A - Corrosion resistance testing method for coated metal material - Google Patents

Abstract

To provide a corrosion resistance testing method capable of evaluating, with a simple configuration and high reliability, corrosive environment strength under a surface treatment film in a coated metal material obtained by providing the surface treatment film on a metal substrate.SOLUTION: There is provided a corrosion resistance testing method for a coated metal material 1 having an electro-deposition coating film 4 provided on a steel plate 2 and a chemical conversion coating 3. The corrosion resistance testing method includes: a preparation step S1 of arranging, on a surface of the electro-deposition coating film 4, a conductive part 13 composed of a material having a standard electrode potential higher than that of the steel plate 2 in a state in which the steel plate 2 and the chemical conversion coating 3 are not in contact with each other; a connection step S2 of connecting the steel plate 2 and the conductive part 13 with each other through wiring 17 including an ammeter 19; and a testing step S4 of bringing a corrosion factor 6 into contact with the coated metal material 1 to test the corrosion resistance of the coated metal material 1. In the testing step S4, a corrosion progress speed as the corrosion resistance of the coated metal material 1 is evaluated based on a corrosion current 18 that flows due to electrical short circuit between the steel plate 2 and the conductive part 13 caused by the corrosion factor 6 impregnated in the electro-deposition coating film 4.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a corrosion resistance test method for a coated metal material.

As a corrosion test sensor, an ACM type corrosion sensor is known. In this method, an insulating paste is screen-printed on a target metal (Fe, galvanized steel sheet, etc.) to be a substrate, and a conductive paste (Ag, etc.) is laminated on the insulating paste so as to maintain insulation with the substrate. It is printed. When this is exposed to the atmosphere, a thin water film is formed between the metal of the conductive paste and the substrate due to rainfall or dew condensation, and a corrosion current flows. Since this current correlates with the corrosion rate, the corrosiveness of the atmospheric environment can be monitored.

Further, another example of the corrosion test method is described in Patent Document 1. This uses a corrosion sensor in which conductive portions are provided at a plurality of locations on the surface of the substrate via insulating portions. In this corrosion sensor, the substrate is formed of the same material as the constituent members of the structure exposed to the atmosphere, and the surface of the substrate is covered with the same coating film as the coating film applied to the constituent members. When the corrosion sensor is exposed to the atmosphere and cracks occur in the coating film due to the action of corrosion factors, rainwater invades from the cracks, short-circuits the conductive part and the substrate, and a corrosion current flows. By measuring this with an ammeter, deterioration of the coating film is determined.

Further, Patent Document 2 describes a moisture sensor that detects moisture and corrosion factors by alternately laminating dissimilar metal materials and sandwiching an electrical insulating material between the dissimilar metal materials and using the outcrops of the laminated body as a sensor surface. It has been disclosed. This humidity sensor can be used as a corrosion sensor by forming a coating film on the sensor surface.

Japanese Unexamined Patent Publication No. 2010-133748 Japanese Unexamined Patent Publication No. 2019-200141

The ACM type corrosion sensor is used for monitoring the strength of the corrosive environment when the target metal is exposed to the atmosphere. That is, it is used unpainted. However, where corrosion progresses under the coating film, the corrosion environmental strength does not always match under the coating film and outside the coating film. That is, the ACM type corrosion sensor cannot evaluate the corrosive environment strength under the coating film.

On the other hand, in the corrosion test method of Patent Document 1, the corrosion current is detected with the surface of the sensor covered with a coating film, but if the coating film is cracked and rainwater does not infiltrate, the corrosion current will flow. No. That is, in the coated material, the corrosion factor permeates the coating film and reaches the bottom of the coating film, or repeatedly escapes from under the coating film to the outside of the coating film. It is not possible to monitor the entry and exit of various corrosive factors.

Moreover, since the surface of the sensor is uneven due to the lamination of the insulating part and the conductive part, the coating film cannot be formed with a constant thickness, and the influence of the thickness of the coating film on the corrosion resistance should be evaluated. Is difficult.

Further, the moisture sensor of Patent Document 2 can be used as a corrosion sensor by forming a coating film on the sensor surface, but evaluates the corrosion environment strength under the coating film provided on a metal base material such as a steel plate. That is difficult.

Therefore, it is an object of the present disclosure to provide a corrosion resistance test method capable of highly reliable evaluation of the corrosion environment strength under a surface-treated film in a coated metal material in which a surface-treated film is provided on a metal substrate with a simple configuration. And.

In order to solve the above problems, the technique disclosed herein is a corrosion resistance test method for a coated metal material in which a surface-treated film is provided on a metal base material, and the above-mentioned is described on the surface of the surface-treated film. A preparatory step for arranging a conductive portion made of a material having a standard electrode potential higher than that of the metal substrate in a non-contact state with the metal substrate, and a current detecting means for the metal substrate and the conductive portion. A connection step of connecting via an external circuit provided and a test step of testing the corrosion resistance of the coated metal material by contacting the coating metal material with a corrosive factor are provided, and the surface treatment is performed in the test step. It is characterized in that the corrosion progress rate as the corrosion resistance of the coated metal material is evaluated based on the corrosion current flowing by electrically short-circuiting the metal base material and the conductive portion due to the corrosion factor permeating into the film. And.

Generally, in a coated metal material provided with a surface-treated film, corrosion factors such as moisture and salt water permeate the surface-treated film and reach the metal substrate to initiate corrosion. Therefore, the corrosion process of the coated metal material is divided into a process until corrosion occurs and a process in which corrosion progresses. The process until corrosion occurs can be evaluated by determining the period until corrosion starts (corrosion suppression period). Further, the process in which corrosion progresses can be evaluated by determining the rate at which corrosion progresses (corrosion progress rate).

In this configuration, when the coating metal material is exposed to a corrosive environment containing a corrosion factor, or the corrosion factor is directly supplied to the coating metal material, the corrosion factor is brought into contact with the coating metal material, and the surface treatment film is corroded. Factors penetrate. Then, when the corrosion factor permeating the surface treatment film reaches both the conductive portion and the metal base material, both are electrically short-circuited, the dissolution reaction of the metal base material starts, and the corrosion current starts to flow. That is, it is considered that the time when the corrosion current starts to flow is the time when the corrosion occurs, that is, the time when the corrosion suppression period ends. Then, the corrosive factor further penetrates into the surface treatment film and spreads. The dissolution reaction of the metal substrate also proceeds further. Then, the amount of corrosion current increases. It can be said that these phenomena simulate the process of corrosion progress. Therefore, the corrosion progress rate can be evaluated by observing the process of increasing the amount of current. Then, a highly reliable corrosion resistance test can be performed with a simple configuration.

In one embodiment, in the preparatory step, a thin film having a predetermined width and having a plurality of linear patterns arranged side by side at predetermined intervals as the conductive portion is formed on the surface of the surface-treated film. Form.

According to this configuration, since the conductive portion is a thin film having a plurality of linear patterns, when the corrosion progresses around the position where the corrosion occurs, a current is sequentially applied to the linear pattern reached by the corrosion factor. It will flow. Then, each time the corrosion factor reaches each of the plurality of linear patterns, the current that has begun to flow in the linear pattern is detected by the current detecting means, so that the corrosion progress rate can be accurately evaluated with a simple configuration.

In one embodiment, the predetermined width is 0.5 mm or more and 5 mm or less, and the predetermined interval is 0.5 mm or more and 5 mm or less.

For example, while an automobile is traveling on a highway, snowmelt salt or the like may adhere to the vehicle body to form water droplets. As described above, when salt or the like adheres to the surface of an object to form water droplets, it is known that the diameter of the water droplets is generally about 300 μm.

According to this configuration, by setting the predetermined width of a plurality of linear patterns and the lower limit of the predetermined interval to the above values, even if the above-mentioned water droplets adhere as a corrosion factor, the adjacent linear patterns are formed. It is possible to prevent water droplets from adhering to the pattern at the same time. Further, by setting the upper limit values of the predetermined width and the predetermined interval to the above values, the process of increasing the amount of the corrosion current can be detected in more detail. Then, a highly reliable corrosion resistance test becomes possible.

In one embodiment, the conductive portion includes a pad portion that connects the plurality of linear patterns, and in the connection step, the external circuit is connected to the pad portion in the conductive portion.

According to this configuration, it is not necessary to connect each of the plurality of linear patterns and the metal base material by an external circuit, so that the connection process can be simplified.

In one embodiment, in the test step, the corrosion progress rate is calculated based on the time change of the current value detected by the current detection means, the predetermined width and the predetermined interval.

Since a plurality of linear patterns are conducting each other through the pad portion, the current value detected by the ammeter is detected as an integrated value of the current values detected so far as the corrosion progresses. It increases in steps. The corrosion progress rate can be calculated based on the time change of the current value and the predetermined width and predetermined interval of the linear pattern.

In one embodiment, the plurality of linear patterns are formed in a non-conducting state on the surface of the surface-treated film, and the external circuit comprises each of the plurality of linear patterns and the metal substrate. , Equipped with multiple wires to connect.

According to this configuration, since the plurality of linear patterns are in a non-conducting state with each other, corrosion progresses and the current flowing through each of the linear patterns can be detected individually. As a result, the current value flowing through each of the linear patterns can be accurately measured, so that the calculation accuracy of the corrosion progress rate is improved.

In one embodiment, the external circuit comprises wiring and a metal plate soldered to the tip of the wiring, and the metal plate and the conductive portion are fixed via a conductive bond in the connection step. By doing so, the conductive portion and the external circuit are connected.

It is necessary to ensure sufficient continuity at the connection portion between the conductive portion and the external circuit. However, soldering the tip end side of the wiring directly to the conductive portion causes damage to the conductive portion, and there is a possibility that continuity cannot be ensured. According to this configuration, since the metal plate soldered to the tip side of the wiring and the conductive portion are adhered and fixed by using a conductive bond, sufficient conduction at the connection portion can be ensured while suppressing damage to the conductive portion. ..

In one embodiment, the coated metal material is further provided with an artificial scratch forming step of forming an artificial scratch that penetrates the surface treatment film and reaches the metal substrate.

When an artificial wound is formed that penetrates the surface treatment membrane and reaches the metal substrate, the corrosive factor invades the artificial wound and reaches the metal substrate. As a result, the penetration of the corrosive factor from the artificially scratched portion into the surface treatment membrane is promoted. In addition, since the metal base material also comes into contact with the corrosive factor, the dissolution reaction of the metal base material also starts. This means that corrosion started from the part of the artificial wound. That is, by forming an artificial wound, it is possible to simulate the state at the end of the corrosion suppression period. Then, the corrosion progress rate can be evaluated accurately in a shorter time.

In one embodiment, the artificial scratch is formed in the central portion of the region where the conductive portion is formed on the surface of the surface treatment film.

According to this configuration, since the artificial scratch that is the starting point of corrosion is provided in the central portion of the region where the conductive portion is formed, the entire region where the conductive portion is formed can be used for the corrosion resistance test.

In one embodiment, the corrosive factor is supplied to the portion where the artificial wound is formed in the test step.

According to this configuration, by directly supplying the corrosion factor to the portion where the artificial wound is formed, it is possible to more reliably promote the progress of corrosion starting from the artificial wound. Then, a highly reliable corrosion resistance test can be performed in a shorter time.

In one embodiment, the conductive portion is formed by screen printing in the preparation step.

According to this configuration, the conductive portion can be reliably formed by a simple method.

As a coating metal material suitable for subject to the corrosion resistance test, for example, there is a coated metal material in which a resin coating film is provided as a surface treatment film on a metal base material.

The metal base material is, for example, a steel material constituting home appliances, building materials, automobile parts, etc., for example, a cold rolled steel sheet (SPC), an alloyed hot-dip galvanized steel sheet (GA), a high-strength steel sheet, a hot stamping material, or the like. Yes, or it may be a light alloy material. The metal base material may have a chemical conversion film (a phosphate film (for example, a zinc phosphate film), a chromate film, etc.) formed on the surface thereof.

Specific examples of the resin coating film include a cationic electrodeposition coating film (undercoat coating film) such as an epoxy resin-based or acrylic resin-based coating film, and a laminated coating film in which a topcoat coating film is superimposed on the electrodeposition coating film. It may be a laminated coating film in which an intermediate coating film and a top coating film are superimposed on an electrodeposition coating film.

The painted metal material is used as a material for, for example, home appliances, building materials, automobile parts, and the like.

In one embodiment, a test piece having the conductive portion and the external circuit provided on a coated metal material having the same specifications as the coated metal material constituting the portion is arranged at a test target portion of the automobile, and the automobile is exposed. The corrosion resistance of the coated metal material to the environment is tested.

According to this configuration, it is possible to evaluate the corrosive environment strength under the coating film of each part of the automobile due to the use of the automobile, which is advantageous for the design of the rust preventive structure and the design of the coating film.

In one embodiment, the conductive portion is a probe provided on one end side of the external circuit and capable of contacting the surface of the surface treatment membrane, and in the preparation step, the probe is placed on the tip end side of the probe. It is a step of abutting on the surface of the surface treatment film via the corrosion factor arranged in.

When the probe position is changed around the position where corrosion has occurred, the current value increases or the resistance value decreases at the position where corrosion has progressed, while the amount of current decreases or decreases at the position where corrosion has not progressed. The resistance value increases. Therefore, by changing the probe position around the position where corrosion has occurred, the degree of corrosion progress can be observed and the corrosion progress rate can be calculated. Then, a highly reliable corrosion resistance test can be performed with a simple configuration.

As described above, according to the present disclosure, when the corrosive factor is brought into contact with the coated metal material, the corrosive factor permeates into the surface-treated membrane. Then, when the corrosion factor permeating the surface treatment film reaches both the conductive portion and the metal base material, both are electrically short-circuited, the dissolution reaction of the metal base material starts, and the corrosion current starts to flow. That is, it is considered that the time when the corrosion current starts to flow is the time when the corrosion occurs, that is, the time when the corrosion suppression period ends. Then, the corrosive factor further penetrates into the surface treatment film and spreads. The dissolution reaction of the metal substrate also proceeds further. Then, the amount of corrosion current increases. It can be said that these phenomena simulate the process of corrosion progress. Therefore, the corrosion progress rate can be evaluated by observing the process of increasing the amount of current. Then, a highly reliable corrosion resistance test can be performed with a simple configuration.

It is a top view of the test piece used in the corrosion resistance test method which concerns on Embodiment 1. FIG. FIG. 3 is a cross-sectional view taken along the line AA of FIG. It is a flow for demonstrating the corrosion resistance test method which concerns on Embodiment 1. It is sectional drawing for demonstrating the connection process. It is a figure which shows an example of the corrosion resistance test of an automobile. It is a digital microscope image of the surface of a test piece in the corrosion resistance test of an experimental example. It is a graph which shows the time-dependent change of the current value in the corrosion resistance test of an experimental example. It is a figure corresponding to FIG. 1 of the test piece in Embodiment 2. FIG. It is a figure corresponding to FIG. 1 of the test piece in Embodiment 3. FIG. It is a figure for demonstrating the corrosion resistance test method which concerns on Embodiment 4, FIG. It is a graph which shows the change of a resistance value.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The following description of preferred embodiments is merely exemplary and is not intended to limit the disclosure, its application or its use at all.

(Embodiment 1)
<Test piece>
FIG. 1 is a plan view of a test piece 10 used in the corrosion resistance test according to the first embodiment of the present disclosure. FIG. 2 is a cross-sectional view taken along the line AA of the test piece 10.

As shown in FIGS. 1 and 2, the test piece 10 includes a coated metal material 1, a conductive portion 13, a metal plate 15 (external circuit), wiring 17 (external circuit), and an ammeter 19 (current detecting means). ) And.

The coated metal material 1 in the test piece 10 has the same specifications as the coated metal material for automobile parts to be tested. The coated metal material 1 includes a metal base material in which a chemical conversion film 3 is formed on the surface of a steel plate 2, and an electrodeposition coating film 4 (resin coating film) provided on the metal base material. The coated metal material 1 in the test piece 10 is, for example, a sample obtained by cutting out a part of the coated metal material constituting the test target portion.

The conductive portion 13 is a thin film provided on the surface of the electrodeposition coating film 4 in a non-contact state with the steel plate 2 and the chemical conversion film 3. The conductive portion 13 is made of a material having a higher standard electrode potential than Fe, which is the main component of the steel plate 2, that is, a material more noble than Fe. The material constituting the conductive portion 13 is preferably a material that does not form a compound with Fe. Specific examples of such a material include Ag, C (carbon), Ti, Pt, Au and the like, and it is desirable to use Ag, C (carbon) from the viewpoint of cost and handleability. ..

The steel plate 2 and the conductive portion 13 are separated by an electrodeposition coating film 4, and while they are not in direct contact with each other, they are connected by a wiring 17 provided with an ammeter 19. The tip of the wiring 17 on the steel plate 2 side is soldered to the steel plate 2. A metal plate 15 made of, for example, a steel plate, a copper plate, or the like is soldered to the tip of the wiring 17 on the conductive portion 13 side, and the metal plate 15 is fixed to the conductive portion 13.

The conductive portion 13 includes a plurality of linear patterns 13A having a predetermined width W and arranged side by side at predetermined intervals D, and a pad portion 13C connecting the plurality of linear patterns 13A. In FIG. 1, the gap portion between the adjacent linear patterns 13A is indicated by reference numeral 13B.

According to this configuration, in the test step S4 described later, when the corrosion progresses centering on the position where the corrosion occurs, the current sequentially flows through the linear pattern 13A to which the corrosion factor has reached. That is, each time the corrosion factor reaches each of the plurality of linear patterns 13A, the current that has begun to flow in the linear pattern is detected by the ammeter 19, so that the corrosion progress rate can be calculated accurately with a simple configuration. ..

The predetermined width W of the linear pattern 13A is preferably 0.5 mm or more and 5 mm or less, and more preferably 0.5 mm or more and 3 mm or less. The predetermined interval D is 0.5 mm or more and 5 mm or less, and more preferably 0.5 mm or more and 3 mm or less. The predetermined width W and the predetermined interval D may be the same size or may be different sizes.

When the predetermined width W and the predetermined interval D are less than 0.5 mm, when the corrosive factor is supplied, the corrosive factor adheres to the adjacent linear pattern 13A at the same time, and in the test step S4, the change with time of the current value is detected and It may be difficult to calculate the corrosion progress rate. Further, if the predetermined width W and the predetermined interval D exceed 5 mm, it takes time to detect the change with time of the current value, and the corrosion resistance test in a short time may be difficult.

<Corrosion resistance test method>
As shown in FIG. 3, the corrosion resistance test method according to the present embodiment includes a preparation step S1, a connection step S2, an artificial scratch forming step S3, and a test step S4. Hereinafter, each step will be described.

-Preparation process-
In the preparation step S1, the conductive portion 13 is formed on the surface of the electrodeposition coating film 4 in a non-contact state with the steel plate 2 and the chemical conversion film 3.

The method for forming the conductive portion 13 is not particularly limited, and examples thereof include known techniques such as an inkjet method, a screen printing method, a spray method, a vacuum vapor deposition method, a sputtering method, and a plating method. From the viewpoint of reliably forming the conductive portion 13 by a simple method, it is desirable to form the conductive portion 13 by screen printing.

-Connection process-
In the connection step S2, the steel plate 2 and the conductive portion 13 are connected by a wiring 17 provided with an ammeter 19. The ammeter 19 is for detecting the current value flowing between the steel plate 2 and the conductive portion 13.

For example, as shown in FIG. 4, a metal plate 15 is fixed to the tip of the wiring 17 on the conductive portion 13 side by a solder 23. A conductive bond 21 is applied to the pad portion 13C of the conductive portion 13, and a metal plate 15 is placed on the conductive bond 21. Then, the conductive bond 21 is cured by performing treatments such as heating and drying according to the curing conditions of the conductive bond 21. Then, the metal plate 15 is fixed to the pad portion 13C of the conductive portion 13, and the wiring 17 is connected to the conductive portion 13.

It is necessary to ensure sufficient continuity at the connection portion between the conductive portion 13 and the wiring 17. However, soldering the tip of the wiring 17 directly to the conductive portion 13 causes damage to the conductive portion 13 and may not ensure continuity. In this configuration, the metal plate 15 having a certain area and the conductive portion 13 are bonded and fixed by using the conductive bond 21. Further, the metal plate 15 is fixed to the pad portion 13C connecting the plurality of linear patterns 13A. As a result, it is possible to secure sufficient conduction at the connecting portion while suppressing damage to the conductive portion 13.

The conductive bond 21 is a conductive adhesive containing a conductive powder such as Ag or C (carbon) in a resin such as a silicone resin or an epoxy resin, and can be cured at room temperature to about 120 ° C. desirable.

Further, in the example of FIG. 4, the conductive bond 21 is applied to the conductive portion 13, but it may be applied to the metal plate 15 or both.

-Artificial wound formation process-
In the artificial scratch forming step S3, as shown in FIGS. 1 and 2, an artificial scratch 5 that penetrates the conductive portion 13, the electrodeposition coating film 4 and the chemical conversion film 3 and reaches the steel plate 2 is formed on the coated metal material 1. .. As will be described later, by forming the artificial scratch 5, the state at or near the end of the corrosion suppression period can be simulated and the corrosion progress rate can be easily calculated.

The artificial scratch 5 may be formed at any position as long as it is in the region where the conductive portion 13 is formed, but is formed in the central portion of the region where the conductive portion 13 is formed on the surface of the electrodeposition coating film 4. Is more desirable. Specifically, for example, in FIG. 1, among a plurality of linear patterns 13A, the artificial scratch 5 is formed on the central linear pattern 130 in the width direction and near the center in the length direction. .. As described above, when the artificial scratch 5 which is the starting point of corrosion is provided in the central portion of the region where the conductive portion 13 is formed, the entire region where the conductive portion 13 is formed can be used for the corrosion resistance test. In the present specification, the "central portion of the region where the conductive portion 13 is formed" is a concept including a completely central position and a vicinity thereof in a range of about 10 mm in radius.

It is desirable that the artificial wound 5 is formed in a dot shape. The "dot-like" means a shape such as a circle or a polygon in a plan view, and the ratio of the maximum width to the minimum width is 2 or less.

The type of tool for making the artificial scratch 5 is not particularly limited, but for example, an automatic scratch punch is used so that the size and depth of the artificial scratch 5 do not vary from test to test, that is, from the viewpoint of quantitatively scratching. The method to be used, a method of scratching with a predetermined load by the indenter using a Vickers hardness tester, and the like are preferable.

Assuming that the maximum width of the artificial wound 5 is the diameter of the artificial wound 5, the diameter of the artificial wound 5 is preferably 0.1 mm or more and 5 mm or less (the surface area of the artificial wound 5 is 0.01 mm ² or more and 25 mm ² or less), more preferably. It can be 0.15 mm or more and 2.0 mm or less, and particularly preferably 0.2 mm or more and 1.5 mm or less. If the diameter of the artificial scratch 5 is reduced to less than 0.1 mm, the artificial scratch 5 may be blocked by the rust generated by the corrosion, and the corrosion may not proceed. If the diameter of the artificial scratch 5 exceeds 5 mm, the exposed portion of the steel plate 2 becomes too large, so that the melting reaction of the steel plate 2 becomes the main, and the penetration of the corrosion factor 6 into the electrodeposition coating film 4 may not proceed. ..

-Test process-
The test step S4 is a step of testing the corrosion resistance of the coated metal material 1 by bringing the corrosion factor 6 into contact with the coated metal material 1. Specifically, for example, the corrosion factor 6 is supplied to the portion of the coated metal material 1 in which the artificial scratch 5 is formed.

The corrosion factor 6 used in the corrosion resistance test according to the present embodiment is specifically a water-containing electrolyte material containing, for example, water and a supporting electrolyte.

As the supporting electrolyte, specifically, for example, at least one salt selected from sodium chloride, sodium sulfate, calcium chloride, calcium phosphate, potassium chloride, potassium nitrate, potassium hydrogen tartrate and magnesium sulfate can be adopted. As the supporting electrolyte, at least one salt selected from sodium chloride, sodium sulfate and calcium chloride can be particularly preferably adopted. The content of the supporting electrolyte in the corrosion factor 6 is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, and particularly preferably 5% by mass or more and 10% by mass or less. ..

Corrosion factor 6 may be a muddy substance containing clay minerals in addition to water and supporting electrolyte. The clay mineral makes the corrosion factor 6 muddy, promotes the movement of ions to the electrodeposition coating film 4 and the permeation of water, and promotes the progress of corrosion. As the clay mineral, for example, a layered silicate mineral or a zeolite can be adopted. As the layered silicate mineral, for example, at least one selected from kaolinite, montmorillonite, sericite, illite, gloconite, chlorite and talc can be adopted, and kaolinite is particularly preferably adopted. be able to. The content of the clay mineral in the corrosion factor is preferably 1% by mass or more and 70% by mass or less, more preferably 10% by mass or more and 50% by mass or less, and particularly preferably 20% by mass or more and 30% by mass or less. Since the corrosion factor 6 is a muddy substance, the corrosion factor 6 can be arranged on the surface of the electrodeposition coating film 4 even when the electrodeposition coating film 4 is not horizontal.

Corrosion factor 6 may contain additives other than water, supporting electrolyte and clay minerals. Specific examples of such additives include organic solvents such as acetone, ethanol, toluene and methanol. When the corrosion factor 6 contains an organic solvent, the content of the organic solvent is preferably 5% or more and 60% or less by volume with respect to water. The volume ratio is more preferably 10% or more and 40% or less, and more preferably 20% or more and 30% or less.

As shown in FIGS. 1 and 2, when the corrosion factor 6 is supplied to the portion of the linear pattern 130 in which the artificial scratch 5 is formed, corrosion starts from the portion in which the artificial scratch 5 is formed. Specifically, in this example, since the artificial scratch 5 penetrates the electrodeposition coating film 4 and the chemical conversion film 3 and reaches the steel sheet 2, the corrosion factor 6 invades the artificial scratch 5 and the steel sheet 2 To reach. Then, as shown by the arrow 6B, the permeation of the corrosive factor 6 from the portion of the artificial scratch 5 into the electrodeposition coating film 4 is promoted. Further, when the corrosion factor 6 comes into contact with the steel sheet 2, the melting reaction (Fe → Fe ^{2 +} + 2e ⁻ ) of the steel sheet 2 also starts and the corrosion current 18 starts to flow. In this way, by forming the artificial scratch 5 and directly supplying the corrosion factor 6 to the portion where the artificial scratch 5 is formed, the state of the corrosion process of the coated metal material 1 at the end of the corrosion suppression period is simulated. Can be created as a target.

Then, when the permeation of the corrosive factor 6 proceeds from the position of the artificial scratch 5 of the linear pattern 130, the corrosive factor 6 reaches the linear pattern 131 adjacent to the linear pattern 130 (reference numeral 61 in FIG. 2). Then, the corrosion factor 6 electrically short-circuits the steel plate 2 and the linear pattern 131, and the melting reaction of the steel plate 2 also proceeds, so that the current amount of the corrosion current 18 increases. Since the linear pattern 130 and the linear pattern 131 are connected by the pad portion 13C, the current value detected by the ammeter 19 when the corrosion factor 6 reaches the linear pattern 131 is the current value before the arrival. Is detected as an integrated value for. Similarly, as the permeation of the corrosion factor 6 progresses and reaches the linear patterns 132 to 135 in order (reference numerals 62 to 65 in FIG. 2), the current amount of the corrosion current 18 increases sequentially accordingly. Then, since the current value detected by the ammeter 19 is detected as an integrated value of the current values detected so far, a current waveform that increases stepwise is finally obtained.

It can be said that the spread of the permeation of the corrosion factor 6 into the electrodeposition coating film 4 and the progress of the dissolution reaction of the steel sheet 2 simulate the process of progress of corrosion. Therefore, the corrosion progress rate can be calculated accurately based on the time change of the current value and the predetermined width W and the predetermined interval D of the linear pattern 13A.

Further, in this configuration, since the corrosion factor 6 is directly supplied to the portion where the artificial scratch 5 is formed, the progress of corrosion starting from the artificial scratch 5 can be promoted more reliably. Then, a highly reliable corrosion resistance test can be performed in a shorter time.

The following tests may be performed as the test step S4. That is, for example, as shown in FIG. 5, one or a plurality of test target parts (in the figure, the fender 26, the floor lower surface 27, and the rear wheel house 28) of the automobile 25 are the same as the painted metal materials constituting the parts. A test piece 10 having a conductive portion 13, a wiring 17, and an artificial scratch 5 provided on the coated metal material 1 of the specifications by the above method is installed. Then, the corrosion resistance of the coated metal material 1 to the environment to which the automobile 25 is exposed may be tested. According to this configuration, it is possible to evaluate the corrosive environment strength under the coating film of each part of the automobile due to the use of the automobile 25, which is advantageous for the design of the rust preventive structure and the design of the coating film.

<Experimental example>
Hereinafter, specific experimental examples will be described.

First, a test piece 10 used in the corrosion resistance test of the experimental example was prepared.

The specifications of the coated metal material 1 are as follows. That is, as the metal base material, a metal substrate in which a zinc phosphate film as a chemical conversion film 3 was formed on the surface of GA as a steel sheet 2 was used. The chemical conversion treatment time for forming the zinc phosphate film was 120 seconds. As the surface treatment film, a film provided with an electrodeposition coating film 4 made of an epoxy resin was used. The electrodeposition baking conditions were 150 ° C. for 20 minutes, and the thickness of the electrodeposition coating film 4 was 10 μm.

On the surface of the electrodeposition coating film 4 of the coating metal material 1, the conductive portion 13 shown in FIG. 1 was formed by screen printing using Ag paste. The predetermined width W and the predetermined interval D were both 2 mm. The thickness of the conductive portion 13 was 50 μm.

Next, the wiring 17 was connected to the steel plate 2 and the conductive portion 13. One end of the wiring 17 was fixed to the steel plate 2 by soldering. A metal plate 15 of GA was soldered to the other end of the wiring 17. A commercially available carbon-based conductive bond 21 was applied to the pad portion 13C of the conductive portion 13, a metal plate 15 was placed on the pad portion 13C, and the metal plate 15 was cured at room temperature to fix both.

Then, using a Vickers hardness tester, an artificial scratch 5 reaching the steel plate 2 was applied. The diameter of the artificial wound 5 was 1 mm.

A simulated mud as a corrosion factor 6 was placed at a position where an artificial wound 5 was formed on the test piece 10, and a corrosion resistance test was conducted under the conditions of a temperature of 50 ° C. and a humidity of 98%. The simulated mud is obtained by mixing 50 g of sodium chloride, 50 g of calcium chloride, and 50 g of sodium sulfate as supporting electrolytes, and 1000 g of kaolinite as a clay mineral with 1.2 L of water.

FIG. 6 is a digital microscope image of the surface of the test piece 10 after the corrosion resistance test. Further, FIG. 7 is a graph showing the result of the current value in the corrosion resistance test of the experimental example. The images of E1 to E5 shown in FIG. 6 are all the same image, and the surface of the test piece 10 in a state where the simulated mud is removed after the corrosion resistance test is taken. In these images, the white lines show the process of corrosion progress, and the reference numerals E1 to E5 correspond to the reference numerals E1 to E5 shown in FIG. 7.

As shown in E1 of FIG. 6, when an artificial scratch 5 is formed in the central portion of the region where the conductive portion 13 is formed and simulated mud is supplied, the current value increases as shown in E1 of FIG. This indicates that corrosion occurred in the portion where the artificial scratch 5 was formed, and a current flowed in the linear pattern of the portion.

Next, as shown in E2 of FIG. 6, when the corrosion progresses to the linear pattern located next to the linear pattern of the portion where the corrosion has occurred, the current value further increases as shown in E2 of FIG. do. Similarly, as shown in E3 to E5 of FIG. 6, when the corrosion further progresses and the corrosion reaches the outer linear pattern, the current value increases stepwise as shown in E3 to E5 of FIG. I will do it.

For example, the corrosion progress rate is calculated based on the data of E3 of FIGS. 6 and 7. From FIG. 6, E3 shows that corrosion has reached the linear pattern 13A two adjacent to the linear pattern 13A on which the artificial scratch 5 was formed. Then, since the predetermined width D and the predetermined interval D are both 2 mm, the distance from the artificial scratch 5 in E3 to the position where the corrosion has reached can be calculated to be about 8 mm. Then, from the time of E1 (about 200 minutes) and the time of E3 (about 1100 minutes) when the current value first increased, the time required from the occurrence of corrosion to the arrival of corrosion at the position of E3 is about. It can be calculated as 15 hours (1100 minutes-200 minutes = 900 minutes). From this information, the corrosion progress rate can be calculated to be about 0.5 mm / hour. In this way, the corrosion progress rate is determined based on the time change of the current value when the corrosion reaches an arbitrary linear pattern from the start of the corrosion, and the predetermined width W and the predetermined interval D of the linear pattern 13A. Can be calculated.

(Embodiment 2)
Hereinafter, other embodiments according to the present disclosure will be described in detail. In the description of these embodiments, the same parts as those of the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

In the first embodiment, the plurality of linear patterns 13A of the conductive portion 13 are connected to each other by the pad portion 13C, but the configuration is not limited to this. As shown in FIG. 8, the plurality of linear patterns 13A may be formed in a non-conducting state on the surface of the electrodeposition coating film 4.

Specifically, in the example of FIG. 8, four linear patterns 13A are formed. The test piece 10 has four wirings 17 connecting each of the linear patterns 13A and the steel plate 2. A metal plate 15 is soldered to the tip of each of the four wirings 17 on the conductive portion 13 side, and each of the metal plates 15 is connected to each of the linear patterns 13A.

The artificial scratch 5 is formed in the gap portion 13B between the two inner linear patterns 131 among the four linear patterns 13A shown in FIG. In this case, when the corrosion factor 6 is supplied to the portion where the artificial scratch 5 is formed, the current value is hardly detected by the ammeter 19 immediately after the supply. Then, the corrosion progresses from the portion where the artificial scratch 5 is formed, and in a state where the corrosion progresses to the position indicated by the reference numeral 61, a current flows through the linear pattern 131. Further, in a state where corrosion has progressed to the position indicated by reference numeral 62, a current flows through the linear pattern 132.

In the example of FIG. 8, since the four linear patterns 13A are in a non-conducting state with each other, corrosion progresses and the current flowing through each of the linear patterns 13A can be detected individually. As a result, the current value flowing through each of the linear patterns 13A can be accurately measured, so that the calculation accuracy of the corrosion progress rate is improved.

From the viewpoint of simplifying the connection step S2, the configuration of the first embodiment in which it is not necessary to connect each of the plurality of linear patterns 13A and the steel plate 2 by the wiring 17 is desirable.

(Embodiment 3)
In the above embodiment, the conductive portion 13 has a linear pattern as a plurality of linear patterns, but the configuration is not limited to this. As shown in FIG. 9, the plurality of linear patterns may be curved lines. In the example of FIG. 9, an artificial scratch 5 may be formed in the central gap portion 13D of the conductive portion 13 to perform a corrosion resistance test.

(Embodiment 4)
In the above embodiment, the conductive portion 13 is a thin film formed on the surface of the electrodeposition coating film 4, but the configuration is not limited to this.

Specifically, for example, as shown in FIGS. 10A and 10B, the conductive portion 13 of the test piece 10 is provided on the electrodeposition coating film 4 side (one end side) of the wiring 17, and is electrodeposited. The probe 13E may be a probe 13E capable of contacting the surface of the coating film 4. In this case, the wiring 17 includes the energizing means 16 instead of the ammeter 19. The energizing means 16 serves as a power source means for applying a voltage between the surface of the electrodeposited coating film 4 and the steel plate 2, and also serves as a current detecting means for detecting a current flowing between the two. Specifically, as the energizing means 16, for example, a controllable potentiometer / galvanostat or the like can be used as a method of applying voltage / current.

The wiring 17 and the probe 13E may be connected by using the method of the above embodiment or by soldering. In this embodiment, the connection step S2 is performed before the preparation step S1.

In the present embodiment, in the preparation step S1, the probe 13E is brought into contact with the surface of the electrodeposition coating film 4. At this time, it is desirable that the tip of the probe 13E is brought into contact with the surface of the electrodeposition coating film 4 in a state where the corrosion factor 6 is attached. By arranging the corrosion factor 6 at the tip of the probe 13E, the contact resistance between the probe 13E and the electrodeposition coating film 4 can be reduced.

When the artificial scratch 5 is formed and the corrosion factor 6 is supplied to generate corrosion, the corrosion factor 6 that has invaded the artificial scratch 5 permeates into the electrodeposition coating film 4 around the artificial scratch 5 (FIG. 10). (B) Medium reference numeral 60). As shown by the white arrows in FIGS. 10A and 10B while applying a predetermined voltage by the energizing means 16, when the position of the probe 13E is changed around the position where corrosion has occurred, corrosion occurs. At the position where is advanced, the current value increases, that is, the resistance value decreases as shown in the graph of FIG. 10 (c). On the other hand, at the position where corrosion has not progressed, the current value decreases, that is, the resistance value increases. Therefore, by applying a predetermined voltage by the energizing means 16 and changing the probe position around the position where the corrosion has occurred, the degree of corrosion progress can be observed and the corrosion progress rate can be calculated. Then, a highly reliable corrosion resistance test can be performed with a simple configuration.

(Other embodiments)
In the above embodiment, the artificial scratch 5 that penetrates the conductive portion 13, the electrodeposition coating film 4, and the chemical conversion film 3 to reach the steel plate 2 is formed, but the artificial scratch 5 that reaches the steel plate 2 is not required. good. Further, it is not necessary to form the artificial wound 5. In this case, when the corrosion factor 6 permeating the electrodeposition coating film 4 reaches both the conductive portion 13 and the steel plate 2, the two are electrically short-circuited, and the corrosion current 18 starts to flow, when corrosion occurs. That is, it is considered to be the end of the corrosion suppression period. Therefore, the corrosion progresses from the portion where the corrosion first occurs, and the corrosion progress rate is calculated. From the viewpoint of promoting corrosion starting from a desired position, it is desirable to form the artificial scratch 5.

Further, a natural wound may be used instead of the artificial wound 5. In this case, for example, in FIGS. 1, 8 and 9, a natural wound may be used instead of the artificial wound 5. Specifically, the conductive portion 13 may be formed on the surface of the coated metal material 1 provided with natural scratches so that the natural scratches are arranged at the positions of the artificial scratches 5 in these figures. If the corrosion factor 6 is supplied to the natural wound in the test step S4, the increase in the current value due to the progress of the corrosion can be detected, and the corrosion progress rate can be calculated. In the example of FIG. 10, a natural wound may be used instead of the artificial wound 5.

The method of connecting the wiring 17 to the steel plate 2 and the conductive portion 13 is not limited to the configuration of the above embodiment, and other known methods may be used as long as sufficient continuity of the connecting portion can be ensured.

In the above embodiment, the electrodeposition coating film 4 is provided as the surface treatment film, but the coating metal material 1 can be configured to include two or more multilayer films as the surface treatment film. Specifically, for example, in addition to the electrodeposition coating film 4, a configuration in which an intermediate coating film is provided on the surface of the electrodeposition coating film 4, or a configuration in which an intermediate coating film or the like is further provided on the intermediate coating film 4 is provided. It can be a multilayer film.

The intermediate coating film has a role of ensuring the finish and chipping resistance of the coating metal material 1 and improving the adhesion between the electrodeposition coating film 4 and the top coating film. Further, the topcoat coating film ensures the color, finish and weather resistance of the coated metal material 1. Specifically, these coatings are made of, for example, a paint composed of a base resin such as polyester resin, acrylic resin and alkyd, and a cross-linking agent such as melamine resin, urea resin and polyisocyanate compound (including a block). Can be formed.

According to this configuration, for example, in a manufacturing process of an automobile member, parts can be taken out from a manufacturing line in each painting process, and the quality of the coating film can be confirmed.

Further, in the above embodiment, the corrosion factor 6 has a configuration in which a clay mineral can be contained as a component having a function of promoting the permeation of water into the electrodeposition coating film 4, but if it is a component having the same function, the clay mineral can be contained. It may contain substances other than. Specifically, for example, the corrosion factor 6 may contain a solvent such as acetone, ethanol, toluene, and methanol, a substance that improves the wettability of the coating film, and the like.

The present disclosure can provide a corrosion resistance test method capable of highly reliable evaluation of the corrosive environment strength under a surface-treated film in a coated metal material in which a surface-treated film is provided on a metal substrate with a simple configuration. Extremely useful.

1 Coated metal material 2 Steel plate (metal base material)
3 Chemical conversion film (metal base material)
4 Electrodeposition coating film (surface treatment film)
5 Artificial scratch 6 Corrosion factor 10 Test piece 13 Conductive part 13A Multiple linear patterns 13B Gap part 13C Pad part 13E Probe (conductive part)
15 Metal plate (external circuit)
16 Energizing means (current detecting means)
17 Wiring (external circuit)
18 Corrosion current 19 Ammeter (current detection means)
21 Conductive bond 23 Solder 25 Automotive S1 Preparation process S2 Connection process S3 Artificial scratch formation process S4 Test process

Claims (14)

It is a corrosion resistance test method for a coated metal material in which a surface treatment film is provided on a metal base material.
A preparatory step of arranging a conductive portion made of a material having a standard electrode potential higher than that of the metal base material on the surface of the surface treatment film in a non-contact state with the metal base material.
A connection step of connecting the metal base material and the conductive portion via an external circuit provided with a current detecting means.
The coating metal material is provided with a test step of testing the corrosion resistance of the coating metal material by contacting the coating metal material with a corrosion factor.
Corrosion of the coated metal material as corrosion resistance based on the corrosion current flowing by electrically short-circuiting the metal base material and the conductive portion due to the corrosion factor permeated into the surface treatment film in the test step. A method for testing corrosion resistance of a coated metal material, which comprises evaluating the progress rate. In claim 1,
In the preparatory step, a thin film having a predetermined width and having a plurality of linear patterns arranged side by side at predetermined intervals is formed on the surface of the surface-treated film as the conductive portion. Corrosion resistance test method for coated metal materials. In claim 2,
The predetermined width is 0.5 mm or more and 5 mm or less.
A method for testing corrosion resistance of a coated metal material, wherein the predetermined interval is 0.5 mm or more and 5 mm or less. In claim 2 or 3,
The conductive portion includes a pad portion for connecting the plurality of linear patterns.
A method for testing corrosion resistance of a coated metal material, wherein the external circuit is connected to the pad portion in the conductive portion in the connection step. In claim 4,
Corrosion resistance of the coated metal material, which is characterized in that the corrosion progress rate is calculated based on the time change of the current value detected by the current detecting means in the test step, the predetermined width and the predetermined interval. Test method. In claim 2 or 3,
The plurality of linear patterns are formed on the surface of the surface-treated film in a non-conducting state with each other.
A method for testing corrosion resistance of a coated metal material, wherein the external circuit includes a plurality of wirings connecting each of the plurality of linear patterns and the metal base material. In any one of claims 2 to 6,
The external circuit comprises wiring and a metal plate soldered to the tip side of the wiring.
A method for testing corrosion resistance of a coated metal material, which comprises connecting the conductive portion and the external circuit by fixing the metal plate and the conductive portion via a conductive bond in the connection step. In any one of claims 2 to 7,
A method for testing corrosion resistance of a coated metal material, which further comprises an artificial scratch forming step of forming an artificial scratch that penetrates the surface-treated film and reaches the metal substrate. In claim 8,
A method for testing corrosion resistance of a coated metal material, wherein the artificial scratch is formed in a central portion of a region where the conductive portion is formed on the surface of the surface treatment film. In claim 8 or 9,
A method for testing corrosion resistance of a coated metal material, which comprises supplying the corrosion factor to a portion where an artificial scratch is formed in the test step. In any one of claims 2 to 10,
A method for testing corrosion resistance of a coated metal material, which comprises forming the conductive portion by screen printing in the preparation step. In any one of claims 1 to 11,
A method for testing corrosion resistance of a coated metal material, wherein the coated metal material is a coated metal material for an automobile part in which a resin coating film is provided as a surface treatment film on the metal base material. In claim 12,
A test piece having the conductive portion and the external circuit provided on a coated metal material having the same specifications as the coated metal material constituting the portion is arranged at a test target portion of the automobile, and the coated metal for the environment to which the automobile is exposed is provided. A method for testing the corrosion resistance of a coated metal material, which comprises testing the corrosion resistance of the material. In claim 1,
The conductive portion is a probe provided on one end side of the external circuit and capable of contacting the surface of the surface treatment film.
The preparatory step is a step of bringing the probe into contact with the surface of the surface-treated film via a corrosion factor arranged on the tip end side of the probe, which is a corrosion resistance test method for a coated metal material.

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