Method for testing corrosion resistance of coated metal material, corrosion resistance testing device, program for corrosion resistance testing, and recording medium

Abstract

Disclosed is a corrosion resistance test method for a coated metal material (1) formed by providing an electrophoretic coating film (4) on a steel sheet (2). The corrosion resistance test method includes an electric current application step (S2) in which the temporal change in electric current and / or voltage is measured, the electric current and / or voltage being generated between the surface of the electrophoretic coating film (4) and the steel sheet (2) by applying voltage and / or electric current to the surface of the electrophoretic coating film (4) and the steel sheet (2) in a state in which a corrosion factor is in contact with the surface of the electrophoretic coating film (4), and an evaluation step (S3) in which the occurrence of defects in the electrophoretic coating film (4) is evaluated based on the waveform of the temporal change.

Description

Technical Field

[0001] This disclosure relates to a method for testing the corrosion resistance of coated metallic materials, a corrosion resistance testing apparatus, a procedure for testing corrosion resistance, and a recording medium. Background Technology

[0002] To date, accelerated corrosion tests such as composite cycle tests and salt spray tests have been used as methods to evaluate coating performance.

[0003] However, the evaluation in the aforementioned accelerated corrosion tests takes several months, making it difficult to easily assess the state of the coating under different constituent materials or baking conditions of the coated steel sheet, and difficult to quickly optimize coating conditions. Therefore, in the fields of material development, process management in coating plants, and quality management related to vehicle rust prevention, there is a need to establish a quantitative evaluation method that can quickly and easily assess the corrosion resistance of coated steel sheets.

[0004] In contrast, in Patent Document 1, as a method for predicting the lifetime of the coated metal, the following method is described: applying a DC voltage between the coated metal and the counter electrode in actual use or test condition, measuring the current flowing at this time, calculating the change of current over time in advance, extrapolating to a current value equivalent to any opening area of ​​the coated film, and taking this time as the lifetime.

[0005] Patent document 2 describes a method for evaluating the corrosion resistance of a film formed on the surface of a metal component as follows: the metal component and the counter electrode component are immersed in water or an electrolyte solution, the negative terminal of a measuring power supply is electrically connected to the metal component, the positive terminal of the measuring power supply is electrically connected to the counter electrode component, and the corrosion resistance of the film is evaluated based on the oxygen-limited diffusion current flowing from the counter electrode component through the film to the metal component.

[0006] Patent document 3 describes the following evaluation method: an electrode is placed on the surface of the coating of the coated metal material with an electrolyte material between it, a voltage is applied between the substrate of the coated metal material and the surface of the coating, and the corrosion resistance of the coated metal material is evaluated based on the voltage value when the insulation of the coating is damaged.

[0007] Patent Document 1: Japanese Patent Publication No. 61-54437

[0008] Patent Document 2: Japanese Patent Publication No. 2007-271501

[0009] Patent Document 3: Japanese Patent Publication No. 2016-50915 Summary of the Invention

[0010] -The technical problem the invention aims to solve-

[0011] While the technologies described in Patent Documents 1 to 3 can predict the lifespan of the membrane and evaluate the overall corrosion resistance of the membrane, there is still room for improvement from the perspective of evaluating the condition of the membrane more specifically.

[0012] Therefore, this disclosure provides a method, apparatus, procedure and recording medium for testing the corrosion resistance of coated metal materials, which can evaluate the state of the film in the surface-treated film more specifically, with high precision and simplicity.

[0013] - Technical solutions for solving technical problems -

[0014] To address the aforementioned technical problems, one embodiment of this disclosure discloses a corrosion resistance testing method for coated metal materials formed by depositing a surface treatment film on a metal substrate. The method is characterized by including an energizing step and an evaluation step. In the energizing step, the time-dependent changes in current and / or voltage are measured. The current and / or voltage are generated between the surface of the surface treatment film and the metal substrate by applying voltage and / or current between the surface of the surface treatment film and the metal substrate while the corrosive agent is in contact with the surface of the surface treatment film. In the evaluation step, the occurrence of defects in the surface treatment film is evaluated based on the waveform of the time-dependent changes.

[0015] Generally, in coated metal materials including surface-treated films, corrosive agents such as brine or electrolyte-containing mud penetrate the surface-treated film and reach the metal substrate, thus initiating corrosion. That is, the corrosion process of coated metal materials is divided into a pre-corrosion phase and a corrosion progression phase. By separately determining the pre-corrosion period (corrosion inhibition period) and the corrosion progression rate (corrosion progression rate), the corrosion process of the coated metal material can be evaluated.

[0016] For example, in Patent Document 3, a corrosion inhibitor is brought into contact with the surface of a surface-treated film, and a voltage is applied between the surface of the surface-treated film and the metal substrate. The corrosion inhibition period in the corrosion resistance of the coated metal material is evaluated based on the voltage value at which the insulation of the coating is compromised. Specifically, when the surface-treated film is a normal coating, if a voltage that gradually increases over time is applied, initially almost no current flows between the surface of the surface-treated film and the metal substrate, but the current value increases sharply when the voltage exceeds a certain value. This sharp increase in the detected current value indicates that the penetration of the corrosion inhibitor into the surface-treated film is promoted as the voltage is applied, and the corrosion inhibitor reaches the surface of the metal substrate. That is, if the applied voltage value at which the detected current value reaches a predetermined threshold is taken as the insulation voltage, the time until this insulation voltage is reached corresponds to the period until the corrosion inhibitor reaches the steel plate, i.e., the corrosion inhibition period of the coated metal material.

[0017] However, when localized defects exist in the surface-treated film, the waveform predicting the time-varying change of the detected current value differs from the waveform described above. Specifically, it is assumed that the effective film thickness is smaller at locations with defects compared to locations without defects. Consequently, when voltage and / or current are applied, corrosive agents can easily reach the metal substrate at the defect location, resulting in easy conduction. Furthermore, if corrosive agents reach the metal substrate, electrochemical reactions such as water electrolysis may occur on the substrate surface. Due to the resulting gases or electrolysis products, the defect location may be blocked, potentially disrupting conduction. In other words, with the presence of localized defects, the waveform of the time-varying change of current and / or voltage will exhibit uneven shapes representing the rise and fall of current and / or voltage values, accompanied by the conduction and interruption at the defect location. Therefore, by analyzing the time-varying waveform, the defect occurrence status in the surface-treated film, such as the presence or absence of defects, the effective film thickness at defect locations, and the number of defects per unit area, can be evaluated simply and with high precision. This improves the reliability of corrosion resistance testing. Furthermore, according to this disclosure, information related to the corrosion resistance of the surface treatment film in the coated metal material can be quantitatively presented as digital data.

[0018] It should be noted that, in this specification, "time variation (data)" can be data plotted as a curve of the detected current value and / or detected voltage value relative to time, or, in the case of applying a gradually increasing voltage and / or current, data plotted as a curve of the detected current value and / or detected voltage value relative to the applied current value and / or applied voltage value.

[0019] Preferably, in the evaluation process, the occurrence of the defect is evaluated based on the peak value of the waveform.

[0020] If the defect is sufficiently localized, peaks representing sharp rises and falls in current and / or voltage values ​​may appear in the waveform of time-varying current and / or voltage. Providing the applied voltage and / or applied current values ​​for these peaks reflects the effective film thickness at the defect location. In other words, in the presence of multiple localized defects, multiple peaks corresponding to each defect will appear in the waveform at the applied voltage and / or applied current values ​​corresponding to each effective film thickness. Therefore, by analyzing the number of peaks, providing the applied voltage and / or applied current values ​​for the peaks, and the detected peak current and / or voltage values, the defect occurrence can be evaluated more specifically.

[0021] Preferably, in the energizing process, the voltage and / or current are applied in a manner that increases gradually over time, or the voltage and / or current are applied in a manner that increases proportionally over time.

[0022] By applying a voltage and / or current that increases gradually over time, preferably a voltage and / or current that increases proportionally over time, the defect status of the surface treatment film can be evaluated with high precision in a shorter time.

[0023] Preferably, the metal substrate includes a chemical conversion film formed on its surface, and the surface treatment film is disposed on the surface of the metal substrate through the chemical conversion film.

[0024] The metal substrate is preferably a steel plate used for automotive parts.

[0025] The surface treatment film is preferably an electrophoretic coating formed using resin-based coatings.

[0026] One embodiment of this disclosure relates to a corrosion resistance testing apparatus for coated metal materials, which is formed by depositing a surface treatment film on a metal substrate. The apparatus is characterized by comprising an electrode, a power supply unit, a detection unit, and an evaluation unit. The electrode is disposed on the surface treatment film side of the coated metal material. The power supply unit applies a voltage and / or current between the electrode and the metal substrate when a corrosion factor is disposed between the surface treatment film and the electrode in contact with the surface treatment film and the electrode. The detection unit detects the current and / or voltage generated between the electrode and the metal substrate accompanying the application of the voltage and / or current by the power supply unit. The evaluation unit evaluates the defect occurrence status of the surface treatment film based on the waveform of the time-varying current and / or voltage detected by the detection unit.

[0027] According to this configuration, by analyzing the waveform of the time-varying current and / or voltage, the defect occurrence status in the surface-treated film, such as the presence or absence of defects, the effective film thickness at defect locations, and the number of defects per unit area, can be evaluated simply and with high precision, thus improving the reliability of corrosion resistance testing. Furthermore, according to this disclosure, information related to the corrosion resistance of the surface-treated film in the coated metal material can be quantitatively presented as digital data.

[0028] Preferably, the evaluation unit evaluates the occurrence of the defect based on the peak value of the waveform.

[0029] According to this configuration, by analyzing the number of peaks, providing the applied voltage and / or applied current values ​​of the peaks, and the detected peak values ​​of current and / or voltage, the occurrence of defects can be evaluated more specifically.

[0030] Preferably, the power supply applies a voltage and / or current that increases gradually over time, or applies a voltage and / or current that increases proportionally over time.

[0031] By applying a voltage and / or current that increases gradually over time, preferably a voltage and / or current that increases proportionally over time, the defect status of the surface treatment film can be evaluated with high precision in a shorter time.

[0032] At least one of the above-described evaluation steps is programmed as a corrosion resistance test procedure. That is, one embodiment of this disclosure discloses a corrosion resistance test procedure for coated metal materials formed by depositing a surface treatment film on a metal substrate. The procedure is characterized by: a computer executing a step to evaluate the defect occurrence of the surface treatment film based on a waveform showing a time-varying change in current and / or voltage, wherein the current and / or voltage are generated between the surface treatment film surface and the metal substrate by applying voltage and / or current between the surface treatment film surface and the metal substrate while a corrosive agent is in contact with the surface of the surface treatment film.

[0033] An embodiment of this disclosure relates to a recording medium that can be read by a computer and records a procedure for testing the corrosion resistance of the aforementioned coated metal material.

[0034] -The effects of the invention-

[0035] As described above, according to this disclosure, by analyzing the waveform of the time-varying current and / or voltage, the defect occurrence status in the surface-treated film, such as the presence or absence of defects, the effective film thickness at the defect location, and the number of defects per unit area, can be evaluated simply and with high precision. This improves the reliability of corrosion resistance testing. Furthermore, according to this disclosure, information related to the corrosion resistance of the surface-treated film in the coated metal material can be quantitatively presented as digital data. Attached Figure Description

[0036] Figure 1 This is a diagram illustrating an example of a corrosion resistance testing apparatus for a coated metal material according to the first embodiment;

[0037] Figure 2 This is a flowchart illustrating the steps of the corrosion resistance testing method according to the first embodiment;

[0038] Figure 3 This is a diagram illustrating an example of the variation in applied voltage (dashed line) and the variation in current flowing between the electrode and the steel plate (solid line) accompanying the applied voltage in a corrosion resistance test of a coated metallic material, including a normal electrophoretic coating.

[0039] Figure 4 This is a diagram illustrating an example of the conduction mechanism of a coated metallic material, including a normal electrophoretic coating.

[0040] Figure 5 These are digital microscope photographs illustrating examples of localized defects;

[0041] Figure 6 This is a diagram illustrating an example of the conduction mechanism of a coated metal material having an electrophoretic coating, which includes pores.

[0042] Figure 7 This is a diagram illustrating an example of the conduction mechanism of a coated metal material with foreign matter on the surface of a steel plate;

[0043] Figure 8 This is a diagram illustrating an example of the conduction mechanism of a coated metal material with uneven surfaces on a steel plate.

[0044] Figure 9 This is a diagram illustrating the concept of the corrosion resistance testing method involved in the first embodiment;

[0045] Figure 10 It is a graph showing the results of corrosion resistance tests on experimental examples;

[0046] Figure 11 It is a graph showing the results of corrosion resistance tests on experimental examples;

[0047] Figure 12This is a diagram illustrating an example of a corrosion resistance testing apparatus for the coated metal material according to the second embodiment.

[0048] - Symbol Explanation -

[0049] 1 – Coated metal material; 2 – Steel plate (metal substrate); 3 – Chemical conversion film (metal substrate); 4 – Electrophoretic coating (surface treatment film); 6 – Corrosion agent; 7 – External circuit; 8 – Power supply unit (power supply section, detection section); 9 – Control device (evaluation section); 12 – Electrode; 100 – Corrosion resistance testing device; S1 – Preparation process; S2 – Power supply process; S3 – Evaluation process. Detailed Implementation

[0050] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings. The preferred embodiments described below are merely examples and are not intended to limit the scope of this disclosure, its application, or its uses.

[0051] (First Implementation)

[0052] <Coated metal material>

[0053] In the corrosion resistance test of this embodiment, the coated metal material 1, which is the test object, is formed by setting a surface treatment film on a metal substrate.

[0054] The metal substrate is, for example, steel used in household appliances, building materials, and automotive parts, such as cold-rolled steel sheet (SPC), alloyed hot-dip galvanized steel sheet (GA), high-tensile steel sheet, or hot-stamped materials, or it can be a light alloy material. The preferred metal substrate is steel sheet for automotive parts. The metal substrate can also be a material with a chemical conversion film (phosphate film (e.g., zinc phosphate film), chromate film, etc.) formed on its surface.

[0055] The surface treatment film is preferably a coating film formed using resin-based coatings, i.e., a resin coating film, and more preferably an electrophoretic coating film. Specifically, as a resin coating film, there are, for example, cationic electrophoretic coating films (primer films) such as epoxy resin and acrylic resin.

[0056] The coated metal material may also include two or more multilayer films as surface treatment films. Specifically, for example, when the surface treatment film is a resin coating, it may also be a multilayer coating with a top coating layered on an electrophoretic coating, or a multilayer coating with a middle coating and a top coating layered on an electrophoretic coating, etc.

[0057] The intermediate coating film ensures the finishability and crack resistance of the coated metal material and improves the adhesion between the electrophoretic coating and the topcoat film. The topcoat film is used to ensure the color, finishability, and weather resistance of the coated metal material. Specifically, these coatings can be formed, for example, by coatings made from base resins such as polyester resins, acrylic resins, and alkyd resins, and crosslinking agents such as melamine resins, urea resins, and polyisocyanate compounds (including block copolymers).

[0058] In the following description, we will take the following coated metal material 1 as an example. The coated metal material 1 is formed by setting an electrophoretic coating 4 (resin coating) as a surface treatment film on a metal substrate. The metal substrate is formed by forming a chemical conversion film 3 on the surface of a steel plate 2.

[0059] <Corrosion Factor>

[0060] Corrosion factor 6 is an electrolyte material containing at least water and a supporting electrolyte, and functions as a conductive material. In the market, salt water, mud containing electrolyte components, etc., may be the main causes of corrosion. By bringing corrosion factor 6, which simulates a substance that is the main cause of corrosion, into contact with the surface of the electrophoretic coating 4, the penetration of corrosion factor 6 into the electrophoretic coating 4 is promoted when voltage and / or current are applied in the subsequent energizing step S2, thus shortening the time required for corrosion resistance testing. Corrosion factor 6 can also be a mud-like substance further containing clay minerals. By including clay minerals in corrosion factor 6, ions and water in corrosion factor 6 easily penetrate into the electrophoretic coating 4 in the subsequent energizing step S2.

[0061] The supporting electrolyte is a salt, which is a substance used to impart sufficient conductivity to the corrosion factor 6. 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 used as the supporting electrolyte. It is particularly preferred to use at least one salt selected from sodium chloride, sodium sulfate, and calcium chloride as the supporting electrolyte. 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.

[0062] Clay minerals are used to make the corrosion agent 6 into a mud-like state and to promote the movement of ions into the electrophoretic coating 4 and the penetration of water into the electrophoretic coating 4. Layered silicate minerals or zeolites can be used as clay minerals, for example. Layered silicate minerals can be selected from at least one of kaolinite, montmorillonite, sericite, illite, glauconite, chlorite, and talc, and kaolinite is particularly preferred. The content of clay minerals in the corrosion agent is preferably 1% to 70% by mass, more preferably 10% to 50% by mass, and particularly preferably 20% to 30% by mass. It should be noted that by making the corrosion agent 6 into a mud-like state, the corrosion agent 6 can be placed on the surface of the electrophoretic coating 4 even when the electrophoretic coating 4 is not horizontal.

[0063] The corrosion factor 6 may further contain additives other than water, supporting electrolytes, and clay minerals. Examples of such additives include organic solvents such as acetone, ethanol, toluene, and methanol, as well as substances that improve the wettability of the coating film. These organic solvents and substances can also promote the penetration of water into the electrophoretic coating film 4. These organic solvents and substances can be added to the corrosion factor 6 instead of clay minerals. When the corrosion factor 6 contains organic solvents, the volume ratio of the organic solvent to water is preferably 5% to 60%. This volume ratio is more preferably 10% to 40%, and even more preferably 20% to 30%.

[0064] <Corrosion Resistance Testing Apparatus for Coated Metal Materials>

[0065] Figure 1 This illustrates an example of the corrosion resistance testing apparatus 100 for coated metal materials according to this embodiment.

[0066] like Figure 1 As shown, the corrosion resistance testing apparatus 100 according to this embodiment includes a container 30, an electrode 12, an external circuit 7, an energizing unit 8 (power supply unit, detection unit) and a control device 9 (evaluation unit).

[0067] -container-

[0068] The container 30 is placed on the electrophoretic coating 4 of the coated metal material 1 through a seal 32 for preventing liquid leakage. The corrosive agent 6 is in contact with the surface of the electrophoretic coating 4 while contained in the container 30.

[0069] The shape of container 30 is not particularly limited; it can be cylindrical, polygonal, or other cylindrical shapes. Container 30 can be made of resin materials such as acrylic resin, epoxy resin, or polyetheretherketone (PEEK), or ceramic, with acrylic resin, epoxy resin, or PEEK being particularly preferred. This ensures insulation between container 30 and the outside environment and allows for a lighter and lower-cost corrosion resistance testing apparatus 100.

[0070] The seal 32, for example, is a sheet-like seal made of silicone resin. When the container 30 is placed on the coated metal material 1, the seal 32 improves the adhesion between the container 30 and the electrophoretic coating 4 and fills the gap between them. Therefore, it effectively inhibits the leakage of corrosive agents 6 from between the container 30 and the electrophoretic coating 4. A structure without the seal 32 can also be used, but from the viewpoint of sufficiently inhibiting the leakage of corrosive agents 6, it is preferable to include the seal 32.

[0071] -electrode-

[0072] Electrode 12 is used to apply a voltage between the surfaces of the steel plate 2 and the electrophoretic coating 4. Electrode 12 is arranged on the side of the electrophoretic coating 4 of the coated metal material 1. Corrosion agent 6 is arranged between the electrophoretic coating 4 and the electrode 12 in such a way that it is in contact with both the electrophoretic coating 4 and the electrode 12. Specifically, electrode 12 is arranged such that at least its front end is embedded in the corrosion agent 6 and is in contact with the corrosion agent 6.

[0073] As electrode 12, electrodes commonly used in electrochemical measurements can be used, specifically, carbon electrodes, platinum electrodes, etc.

[0074] The shape of electrode 12 can be any shape commonly used in electrochemical measurements, such as rod or plate. For example, a porous electrode with at least one hole at the front end can also be used as electrode 12. For example, if a porous electrode with a ring-shaped front end is used, it is sufficient to arrange the porous electrode so that the ring is approximately parallel to the electrophoretic coating 4. Alternatively, a mesh electrode can be used as the porous electrode, and the mesh electrode can be arranged so that it is embedded in the corrosion factor 6 and approximately parallel to the electrophoretic coating 4.

[0075] -External Circuit-

[0076] The external circuit 7 includes wiring 71 and energizing units 8 arranged on wiring 71. Wiring 71 electrically connects electrode 12 to steel plate 2. Known wiring can be appropriately used as wiring 71.

[0077] -Power-on unit-

[0078] The energizing unit 8 is connected to the electrode 12 and the steel plate 2 via wiring 71, serving as a power source that applies voltage and / or current between the electrode 12 and the steel plate 2. Simultaneously, the energizing unit 8 also functions as a current detection unit / voltage detection unit (detection section), which detects the current and / or voltage flowing between the electrode 12 and the steel plate 2 in conjunction with the application of voltage and / or current. Specifically, for example, a potentiostat / galvanostat capable of controlling the application of voltage / current can be used as the energizing unit 8.

[0079] The power-on unit 8 is electrically or wirelessly connected to the control device 9 (described later), and is controlled by the control device 9. Power-on information, such as the actual voltage and / or current values ​​applied by the power-on unit 8 (also referred to as "applied voltage values ​​and / or applied current values"), the current and / or voltage values ​​detected by the power-on unit 8 (also referred to as "detected current values ​​and / or detected voltage values"), and the power-on time, is sent to the control device 9.

[0080] It should be noted that the energizing unit 8 applies a voltage and / or current that gradually increases with time between the electrode 12 and the steel plate 2, preferably applying a voltage and / or current that increases proportionally with time between the electrode 12 and the steel plate 2. This allows for a more precise evaluation of the defect occurrence status of the electrophoretic coating 4 in a shorter time.

[0081] -Control device-

[0082] The control device 9 is, for example, a device based on a known microcomputer, and includes a control unit 91, a storage unit 92, and an arithmetic unit 93. The control device 9 also includes, for example, an input unit 94 composed of a keyboard, and an output unit 95 composed of a display screen, etc. The storage unit 92 stores various data and arithmetic processing programs. The arithmetic unit 93 performs various arithmetic operations based on the information stored in the storage unit 92 and the information input via the input unit 94. The control unit 91 outputs control signals to the power supply unit 8 based on the data stored in the storage unit 92 and the calculation results of the arithmetic unit 93, controlling the voltage and / or current applied to the external circuit 7 by the power supply unit 8.

[0083] It should be noted that the control device 9 functions as an evaluation unit, which evaluates the defect occurrence status of the electrophoretic coating 4 based on the waveform of the time-varying current and / or voltage detected by the energizing unit 8, as detailed later. In particular, the control device 9 preferably evaluates the defect occurrence status of the surface treatment film based on the peak value of the waveform.

[0084] <Test Methods for Corrosion Resistance of Coated Metallic Materials>

[0085] Figure 2 This is a flowchart illustrating the steps of the corrosion resistance testing method involved in this embodiment. Figure 3 This is a diagram illustrating an example of the variation in applied voltage (dashed line) and the variation in current flowing between the electrode and the steel plate (solid line) accompanying the applied voltage in a corrosion resistance test of a coated metallic material, including a normal electrophoretic coating. Figure 4 This is a diagram illustrating an example of the conduction mechanism of a coated metallic material, including a normal electrophoretic coating. Figure 5 These are digital microscope photographs showing examples of localized defects. Figure 6 This is a diagram illustrating an example of the conduction mechanism of a coated metallic material having an electrophoretic coating, which includes pores. Figure 7 This is a diagram illustrating an example of the conduction mechanism of a coated metal material with foreign matter on the surface of a steel plate. Figure 8 This is a diagram illustrating an example of the conduction mechanism of a coated metal material with uneven surfaces on a steel plate. Figure 9 This diagram illustrates the concept behind the corrosion resistance testing method described in this embodiment. Hereinafter, refer to... Figures 2-9 The corrosion resistance test method involved in this embodiment will be described.

[0086] like Figure 2 As shown, the corrosion resistance test method involved in this embodiment includes a preparation step S1, an energizing step S2, and an evaluation step S3.

[0087] -Preparation Process-

[0088] Preparation step S1 is a step of arranging corrosion agent 6 and electrode 12 in contact with the surface of electrophoretic coating 4 on the side of the coated metal material 1.

[0089] Specifically, for example, firstly, a container 30 is placed over a seal 32 on the surface of the electrophoretic coating 4 of the sample coated with metal material 1, and the container 30 is filled with a corrosion agent 6. This brings the corrosion agent into contact with the surface of the electrophoretic coating 4. Furthermore, an electrode 12 connected to an external circuit 7 is immersed in the corrosion agent 6.

[0090] -Power-on process-

[0091] The energizing process S2 is a process of applying voltage and / or current between electrode 12 and steel plate 2, and measuring the time-dependent changes in current and / or voltage generated between electrode 12 and steel plate 2.

[0092] Specifically, for example, under the control of the control device 9, a voltage and / or current is applied between the electrode 12 and the steel plate 2 through the energizing unit 8. At this time, the applied voltage and / or current increases gradually over time, preferably proportionally over time. This allows for a more accurate evaluation of the defect occurrence status of the electrophoretic coating 4 in a shorter time. When applying voltage, the scanning speed of the applied voltage is specifically, for example, in the range of 0.1 to 10 V / s, more preferably 0.5 to 2 V / s. When applying current, the scanning speed of the applied current is specifically, for example, in the range of 0.1 to 2 mA / s, more preferably 0.5 to 1 mA / s. It should be noted that the applied voltage and / or current can be direct current (DC) or alternating current (AC).

[0093] The energizing unit 8 detects the current and / or voltage generated between the steel plate 2 and the electrophoretic coating 4 as a result of the application of voltage and / or current. The detected current and / or voltage values ​​are stored in the storage unit 92 as data that changes over time.

[0094] It should be noted that a threshold can also be set for at least one of the applied voltage and / or applied current, and the detected current and / or detected voltage. When the threshold is reached, the applied voltage and / or applied current are fixed, or the power supply is terminated. This can suppress the application of excessive voltage and / or current and ensure measurement accuracy.

[0095] -Evaluation Process-

[0096] Evaluation step S3 is a process that evaluates the defect occurrence status of the electrophoretic coating 4 based on the waveform of the time-varying data of the detected current value and / or detected voltage value obtained in the energizing step S2. The following explanation, using the case of applying voltage and detecting current as an example, illustrates the correspondence between the waveform of the time-varying data and the defect occurrence status of the electrophoretic coating 4.

[0097] like Figure 3 As shown, when the electrophoretic coating 4 is a normal coating, for example, when a proportionally increasing DC voltage is applied between the electrode 12 and the steel plate 2 ( Figure 3 When the dotted line in the diagram is visible, the time-varying data of the current value flowing between electrode 12 and steel plate 2 becomes... Figure 3 The waveform is shown by the solid line. That is, even if the applied voltage is increased, the current hardly flows before the voltage reaches voltage value V1 at time t1. However, if the voltage exceeds voltage value V1, the current increases sharply, reaching the threshold A1 at voltage value V2 (time t2). This change in current over time first indicates that the electrophoretic coating 4 maintains its blocking performance against corrosion factor 6 up to voltage value V1. Then, when voltage value V2 is reached, as... Figure 4As shown, with the application of voltage, the penetration of corrosion agent 6 into the electrophoretic coating 4 is promoted. Even at the weakest points of the electrophoretic coating 4, which are not defects but are, for example, areas with relatively few resin cross-linking structures, corrosion agent 6 reaches the surface of the steel plate 2. In other words, Figure 3 The sharp increase in the detection current value indicates that the electrophoretic coating 4 has lost its insulating properties, i.e., blocking performance, due to the corrosion factor 6 reaching the surface of the steel plate 2. Furthermore, if the applied voltage value V2 when the detection current value reaches the threshold A1 is set as the insulation voltage, then the time t2 for reaching the insulation voltage V2 corresponds to the period until the corrosion factor 6 reaches the steel plate 2, i.e., the corrosion inhibition period of the coated metal material 1.

[0098] On the other hand, in the case of local defects in the electrophoretic coating 4, the waveform of the time-dependent change in the predicted detection current value is compared with... Figure 3 The waveforms shown are different.

[0099] As a localized defect, an example is a defect that promotes the penetration of corrosion factor 6, that is, a defect in which the actual film thickness, i.e., the effective film thickness, is locally reduced. Specifically, for example, besides Figure 5 In addition to the pores, splashes, and slag shown, other examples include foreign matter such as iron powder, pits, contamination from chemically converted sludge, and unevenness on the surface of steel plate 2.

[0100] Figure 5 The digital microscope image shows the electrophoretic coating 4 as viewed from directly above. Pores are pinholes formed during the formation of the electrophoretic coating 4, accompanying the generation of gas within the coating. Specifically, pores are formed, for example, by gases generated when excessively high coating voltage is applied during electrophoretic coating. More specifically, if gases such as hydrogen are generated during coating, holes that serve as gas venting channels will form on the electrophoretic coating 4 immediately after coating. During baking, sufficiently small holes are blocked by the flow phenomenon accompanying the decrease in coating viscosity. However, larger holes cannot be completely blocked, leaving holes on the surface side of the electrophoretic coating 4, creating a well-like appearance. These holes are called pores. Therefore, although pores exist at locations that open on the surface of the electrophoretic coating 4, since the electrophoretic coating 4 is present on the steel plate 2 side, it can be said that the effective film thickness of the electrophoretic coating 4 is less than the film thickness of the electrophoretic coating 4 at locations where pores are not present.

[0101] like Figure 6 As shown, when pores 41 exist in the electrophoretic coating 4, the deeper the pores 41 are in the thickness direction of the electrophoretic coating 4, the smaller the effective film thickness of the electrophoretic coating 4. Considering that the corrosive agent 6 can penetrate into the pores 41 and further penetrate into the electrophoretic coating 4 below the pores 41, it can be imagined that the conduction will start sequentially from the position of the pore with the smallest effective film thickness, i.e., the position of the deepest pore.

[0102] Next, as Figure 5 As shown, the spatter formed on the steel plate 2, such as at welded sections, is a metallic granular foreign object. Since the spatter is conductive, paint will accumulate on it during electrophoretic coating. However, due to the flow phenomenon that occurs as the paint viscosity decreases during baking, the paint accumulated on the spatter will flow to areas where there is no spatter. Therefore, the effective film thickness of the electrophoretic coating 4 on the spatter is less than the film thickness of the electrophoretic coating 4 in areas where there is no spatter. In other words, although the spatter is not a defect formed within the electrophoretic coating 4, from the viewpoint of reducing the effective film thickness of the electrophoretic coating 4, it can be considered a local defect of the electrophoretic coating 4. Examples of foreign objects similar to spatter include iron powder that accumulates on the surface of the steel plate 2 during coating. Furthermore, in cases where the steel plate 2 is made of a material with an uneven surface, such as hot-stamped material, the convex portion on the surface of the steel plate 2 also corresponds to a foreign object similar to spatter.

[0103] Furthermore, the slag formed on the steel plate 2, such as in the welded areas, is a glassy granular substance. While the slag is a type of foreign matter formed on the surface of the steel plate 2, it is non-conductive, so the coating does not accumulate on the surface of the steel plate 2 where the slag is present during electrophoretic coating. Due to the flow phenomenon that occurs during baking as the viscosity of the coating decreases, the coating on the surface of the steel plate 2 surrounding the slag also flows onto the slag to form a coating film. Therefore, the effective film thickness of the electrophoretic coating 4 formed on the slag is less than the film thickness of the electrophoretic coating 4 in areas where there is no slag. In other words, although the slag is not a defect formed within the electrophoretic coating 4, from the viewpoint of reducing the effective film thickness of the electrophoretic coating 4, it can be considered a local defect of the electrophoretic coating 4, similar to spatter. Besides slag, other examples of such non-conductive foreign matter include pollution from chemical conversion sludge such as ferric phosphate produced during chemical conversion treatment.

[0104] like Figure 7 and Figure 8 As shown, when a foreign object 21 or a protrusion 22 is present on the surface of the steel plate 2, the effective film thickness of the electrophoretic coating 4 on the upper side of the foreign object 21 or the upper side of the protrusion 22 is less than the film thickness of the electrophoretic coating 4 at locations where the foreign object 21 is absent or other than the protrusion 22. Therefore, similar to the case where pores are present, conductivity is easily caused at defect locations with smaller effective film thicknesses. It should be noted that, as... Figure 7 As shown, it is assumed that when a foreign object 21 is present on the surface of the steel plate 2, conduction will occur through the surface of the foreign object 21. It should be noted that the ease of conduction will vary depending on whether the foreign object 21 is conductive or non-conductive.

[0105] In other words, it is assumed that: in the case of local defects in the electrophoretic coating 4, i.e., areas with a small effective film thickness, the waveform of the time-varying data obtained in the energizing process S2 is as follows: Figure 9 As shown. It should be noted that, in Figure 9 In the image, using the leftmost cell as an example, the illustration shows the situation where pores exist as a localized defect. That is to say, as... Figure 9 As shown in the left cell, when there are local defects in the electrophoretic coating 4, the corrosive agent 6 penetrates into the entire electrophoretic coating 4, and localized infiltration of the corrosive agent 6 occurs at the defect location. When the corrosive agent 6 penetrates into the electrophoretic coating 4 at a certain defect location and reaches the steel plate 2, the detection current value increases slightly. Assuming that a voltage greater than the voltage that causes water electrolysis is applied between the electrode 12 and the steel plate 2 at this moment, electrochemical reactions such as water electrolysis occur on the surface of the steel plate 2 through conduction. The resulting gas and electrolysis products accumulate in the defect, and the conduction is blocked, causing the slightly increased detection current value to decrease. That is, when there are local defects, with the conduction and blockage at the defect location, peaks representing sharp increases and decreases in the waveform of the time-varying data of the detection current value will be generated. Since it is believed that conduction is caused by a lower applied voltage value in areas with smaller effective film thickness, it is assumed that the applied voltage value that gives the peak value is related to the effective film thickness. Moreover, it is assumed that in the case of multiple defects, a number of peaks corresponding to the number of defects will be generated.

[0106] It should be noted that, as Figure 9 As shown in (1), it is believed that when a gradually increasing voltage (DC) is applied, a peak value corresponding to the number of local defects will appear as the detection current value gradually increases. Figure 9 As shown in (2), it is believed that when a constant voltage (DC) is applied, a peak value corresponding to the number of local defects will appear, and the baseline of the current value will also rise in a stepwise manner. Figure 9 As shown in (3), it is believed that when an increasing voltage (AC) is applied, the amplitude of the current value gradually increases, and a peak value appears on the positive or negative side corresponding to the number of local defects. Figure 9 As shown in (4), it is assumed that when a constant voltage (AC) is applied, the amplitude of the current value is roughly constant, but peaks appear on the positive or negative side corresponding to the number of local defects.

[0107] Therefore, based on the waveform of the time-varying data of the detected current and / or detected voltage values, preferably based on the peak value of the waveform, the defect occurrence status of the electrophoretic coating 4, such as the presence or absence of defects, the effective film thickness at the defect location, and the number of defects per unit area, can be evaluated simply and with high precision. Furthermore, by analyzing, for example, the shape and number of peaks in the waveform, the applied voltage and / or applied current values ​​that give the peak values, the peak values ​​of the detected current and / or voltage, and the shape of the waveform baseline, the defect occurrence status can be evaluated more specifically. This improves the reliability of the corrosion resistance test. It should be noted that, for the coated metal material 1 with localized defects, the time until the initial peak value is observed can be considered the corrosion inhibition period.

[0108] It should be noted that in the analysis of waveforms of time-varying data, including processing such as peak detection, image processing techniques such as machine learning can be used, as well as mathematical methods such as differential calculus. Alternatively, a combination of these methods can be employed.

[0109] Based on the waveform analysis results of time-varying data, it is possible to detect defects in the electrophoretic coating 4 of the coated metal material 1, speculate on the causes, and manage the process.

[0110] Specifically, for example, by periodically taking parts from the production line and analyzing the waveform of time-varying data, or periodically analyzing the waveform of time-varying data of market products, it is possible to monitor the occurrence and increase or decrease of local defects in the coated metal material 1. This helps to confirm the quality of the electrophoretic coating 4, detect signs of quality decline, and confirm the impact of the market environment on the electrophoretic coating 4.

[0111] For example, the manufacturing process of the coated metal material 1 is mainly divided into the following four steps: forming and processing of steel plate 2; degreasing; chemical conversion treatment; and electrophoretic coating. Spatter and slag are generated due to welding conditions during the forming and processing of steel plate 2. Iron powder is generated due to the cleanliness of steel plate 2 and deterioration of processing tools during the forming and processing of steel plate 2. Cavities are generated based on the degree of oil residue during the degreasing process. Sludge is generated during the chemical conversion treatment process based on the degree of water washing after chemical conversion treatment, such as water pressure or the spraying condition of the washing water. Pores are generated during the electrophoretic coating process due to coating conditions such as voltage or paint balance. Therefore, by preferably combining the analysis of waveforms of time-varying data with the results of surface observation, it is possible to determine the type of defect, the process leading to the defect, etc.

[0112] Furthermore, at the manufacturing site of the coated metal material 1, by databases of time variation data from the same production line, the same factory, other factories, and other manufacturers' factories, the defect occurrence status of the electrophoretic coating 4 can be evaluated with higher precision based on comparisons with these data.

[0113] Furthermore, by identifying the processes that cause the impact or analyzing performance differences between plants, the quality of the electrophoretic coating 4 can be ensured or the causes of quality degradation can be inferred. Moreover, by linking it to production management conditions, process-based quality management can be achieved in the rust-preventing area. In addition, by combining this evaluation technique with other analytical techniques, unified management can be achieved from coating component management to rust-preventing function and its manifestation process.

[0114] It should be noted that, regarding the coated metal material 1 with an electrophoretic coating 4 containing various local defects, if the correspondence between waveform and type of local defects is clarified by collecting and analyzing multiple of the above-mentioned time-varying data, it is possible to determine the type of local defects, the conductivity / non-conductivity of foreign objects, etc., based solely on waveform analysis.

[0115] <Experimental Example>

[0116] Next, an experimental example will be described to represent a specific example of data changing over time.

[0117] First, test pieces (also known as "TP") were prepared for use in the corrosion resistance test of the experimental examples.

[0118] The specifications of the coated metal material 1 are as follows. That is, it is a substrate on which a zinc phosphate film, as a chemical conversion film 3, is formed on the surface of GA (Experimental Examples 1, 2-1, 2-2, 3, 4-1, 4-2, 6) or hot-stamped material (Experimental Example 5) as a steel plate 2. It should be noted that the chemical conversion treatment time required to form the zinc phosphate film is 120 seconds. As a surface treatment film, an electrophoretic coating 4 formed of epoxy resin is formed. The electrophoretic baking conditions and the thickness of the electrophoretic coating 4 are as follows. Figure 10 and Figure 11 As shown.

[0119] As corrosion factor 6, a 5% (w / w) sodium chloride aqueous solution was used. At 25°C, a voltage was applied while increasing the voltage by 1V / s until the detected current reached the threshold current of 10mA. Then, the current generated between electrode 12 and steel plate 2 was detected every second. Data showing the time-varying changes of the detected current relative to the applied voltage, and digital microscopic photographs of the surface after TP coating or after the composite cycle test (CCT test) are shown below. Figure 10 and Figure 11.

[0120] It should be noted that the test conditions for CCT are as follows: for TP, the processes of salt spraying (6 hours), drying (3 hours), wetting (14 hours), and air supply (1 hour) are carried out in a 24-hour cycle for a specified period.

[0121] like Figure 10 As shown, in the case of TP including the normal electrophoretic coating 4 in Experimental Example 1, the waveform of the time-varying data shows a pattern of a sharp increase in current when the applied voltage exceeds 250V. When the TP of Experimental Example 1 was subjected to CCT testing, no corrosion of the electrophoretic coating 4 was observed after 30 days and 60 days.

[0122] Regarding the TP films with pores, including the electrophoretic coating 4, in Examples 2-1 and 2-2, the waveforms of the time-varying data differ from those in Example 1, and peak values ​​of the detected current can be observed. In Example 2-1, which has a higher number of pores, the waveform shows more peaks compared to Example 2-2, which has fewer pores. When the TP films in Examples 2-1 and 2-2 underwent CCT testing, corrosion progress was observed after 30 days. The corrosion initiation point is considered to be the location of the pores. In Example 2-1, more corrosion initiation points were observed compared to Example 2-2.

[0123] In the TP contaminated with chemically converted sludge in Experiment Example 3, multiple peaks can be seen in the waveform of the time-varying data.

[0124] like Figure 11 As shown, for the TPs with welding spatter in Experiments 4-1 and 4-2, multiple peaks appeared in the waveform of the time-varying data. In Experiment 4-1, where there were more areas with welding spatter, the number of peaks in the waveform was greater than in Experiment 4-2, where there were fewer areas with welding spatter. It should be noted that when observing the surface of the TPs in Experiments 4-1 and 4-2 after electrophoretic coating, it can be seen that the electrophoretic coating 4 is raised due to the welding spatter.

[0125] Taking the hot-stamped material of Experimental Example 5 as the TP of steel plate 2, multiple peaks appeared in the waveform of the time-varying data. When the TP of Experimental Example 5 was subjected to CCT testing, corrosion progress was observed at multiple corrosion initiation points after 30 days. It is assumed that the locations of these corrosion initiation points are the convex portions of steel plate 2.

[0126] Regarding TP in Experimental Example 6, although the type of local defects was unclear, multiple peaks appeared in the waveform of the time-varying data. When TP in Experimental Example 6 underwent CCT testing, corrosion progress was observed at multiple corrosion initiation points after 30 days.

[0127] <Procedures and Recording Media for Corrosion Resistance Testing>

[0128] At least a portion of the steps in the above-described corrosion resistance testing method are programmed as a corrosion resistance testing program. Specifically, the corrosion resistance testing program according to this embodiment is a program that causes a computer to execute at least the evaluation step S3 of each of the above-described steps, preferably the power-on step S2 and the evaluation step S3. This corrosion resistance testing program can be executed by the control unit 91 and the arithmetic unit 93 while stored in the storage unit 92. The corrosion resistance testing program is not limited to being stored in the storage unit 92; for example, it can also be recorded on various known recording media that can be read by a computer, such as optical disc media or magnetic tape media. Moreover, the program can be executed by installing such a recording medium on the reading device (not shown) of the control device 9 and reading out the corrosion resistance testing program.

[0129] (Second Implementation)

[0130] The following describes in detail other embodiments involved in this disclosure. It should be noted that in the description of these embodiments, the same symbols are used to denote the parts that are the same as in the first embodiment, and detailed descriptions are omitted.

[0131] The corrosion resistance testing apparatus 100 of the first embodiment has a structure that houses the corrosion factor 6 in the container 30, but is not limited to this structure, for example, Figure 12 As shown, probe-type electrodes such as 12 can also be used.

[0132] In this embodiment, in the preparation step S1, the corrosion agent 6 is arranged on the surface of the electrophoretic coating 4. If the corrosion agent 6 is a mud-like or highly viscous material, it can be directly arranged on the surface of the electrophoretic coating 4. If it is a low-viscosity aqueous solution or similar material, it can be allowed to permeate into a porous material such as a sponge before being arranged on the surface of the electrophoretic coating 4. Then, the tip of the electrode 12 is brought into contact with the corrosion agent 6 arranged on the surface of the electrophoretic coating 4. Preferably, the tip of the electrode 12 is brought into contact with the corrosion agent 6 while the corrosion agent 6 is attached to the tip of the electrode 12. By attaching the corrosion agent 6 to the tip of the electrode 12, the contact resistance at the interfaces of the electrode 12, the corrosion agent 6, and the surface of the electrophoretic coating 4 can be reduced.

[0133] According to the above structure, the shape of the test piece is not limited, and it becomes easy to measure test pieces that do not have a flat surface, the edge of the test piece, the curved surface of the test piece, etc.

[0134] It should be noted that the surface treatment film can be insulating.

[0135] The location where the defect exists can be a region where the surface treatment film exists, and the thickness of the surface treatment film at the location where the defect exists is less than the thickness of the surface treatment film at the location where the defect does not exist. In other words, in this structure, the location of the "defect" to be evaluated can be a region where, in the state before power is applied, the thickness of the surface treatment film is not 0, but is less than the thickness of the film at the location where the defect does not exist. That is to say, in the state before power is applied, the "defect" may not include a through-hole penetrating the surface treatment film along the thickness direction.

[0136] In this structure, a corrosive agent is brought into contact with the surface of a surface-treated film. A voltage and / or current are applied between the surface of the surface-treated film and the metal substrate, thereby allowing the corrosive agent to penetrate into the surface-treated film. The occurrence of defects is evaluated based on the changes in current and / or voltage over time. The surface-treated film initially maintains insulation, but as the corrosive agent penetrates and reaches the metal substrate, the insulation is broken, and conductivity occurs, causing the detected current and / or voltage values ​​to rise.

[0137] In this structure, at the location of the defect (the evaluation target), the thickness of the surface-treated film is less than that at the location without defects. Therefore, corrosive agents can easily reach the metal substrate, resulting in easy conduction. Furthermore, if corrosive agents reach the metal substrate, electrochemical reactions such as water electrolysis may occur on the substrate surface. Due to the resulting gases or electrolysis products, the defect location may be blocked, and conduction may be interrupted. In other words, in this structure, the conduction and interruption occurring at the location of the defect are represented by a concave-convex shape in the waveform of the time-varying current and / or voltage, indicating the rise and fall of the current and / or voltage values.

[0138] In this structure, by analyzing the waveforms of the time-varying current and / or voltage values ​​obtained reflecting the above mechanism, the occurrence of defects in the surface-treated film, such as the presence or absence of defects, the effective film thickness at defect locations, and the number of defects per unit area, can be evaluated simply and with high precision. This improves the reliability of corrosion resistance testing and allows for the quantitative presentation of corrosion-resistant information related to the surface-treated film in the coated metal material as digital data.

[0139] -Industry Applicability-

[0140] This disclosure provides a corrosion resistance testing method, corrosion resistance testing apparatus, corrosion resistance testing procedure, and recording medium for coated metal materials that can more specifically, accurately, and simply evaluate the state of the film in a surface-treated film, and is therefore extremely useful.

Claims

1. A method for testing the corrosion resistance of a coated metal material, wherein the coated metal material is formed by depositing a surface treatment film on a metal substrate, characterized in that: This includes the power-on process and the evaluation process. In the energizing process, the time-dependent changes in current and / or voltage are measured. This current and / or voltage are generated between the surface of the surface treatment film and the metal substrate by applying voltage and / or current between the electrode and the metal substrate, with only one electrode disposed on one side of the surface treatment film of the coated metal material in contact with both the electrode and the surface treatment film. In the evaluation process, the occurrence of defects in the surface treatment film is evaluated based on the waveform that changes over time. When the value of the voltage applied in the energizing process is set as the applied voltage value, the value of the current applied in the energizing process is set as the applied current value, the value of the current detected in the energizing process is set as the detected current value, and the value of the voltage detected in the energizing process is set as the detected voltage value, The time-dependent variation is data obtained by plotting the detected current value and / or the detected voltage value relative to time, or by plotting the detected current value and / or the detected voltage value relative to the applied voltage value and / or the applied current value when an increasing voltage and / or current is applied during the energizing process.

2. The corrosion resistance test method for coated metal materials according to claim 1, characterized in that: In the evaluation process, the occurrence of the defect is evaluated based on the peak value of the waveform.

3. The corrosion resistance test method for coated metal materials according to claim 1 or 2, characterized in that: In the energizing process, the voltage and / or current are applied in a manner that increases gradually over time, or the voltage and / or current are applied in a manner that increases proportionally over time.

4. The corrosion resistance test method for coated metallic materials according to any one of claims 1 to 3, characterized in that: The metal substrate includes a chemical conversion film formed on its surface. The surface treatment film is disposed on the surface of the metal substrate through the chemical conversion film.

5. The corrosion resistance test method for coated metallic materials according to any one of claims 1 to 4, characterized in that: The metal substrate is a steel plate used for automotive parts.

6. The corrosion resistance test method for coated metallic materials according to any one of claims 1 to 5, characterized in that: The surface treatment film is an electrophoretic coating formed using resin-based coatings.

7. A corrosion resistance testing apparatus for coated metal materials, wherein the coated metal material is formed by depositing a surface treatment film on a metal substrate, characterized in that: Includes only one electrode, power supply, detection, and evaluation sections. The electrodes are arranged on the side of the surface treatment film of the coated metal material. The power supply unit applies voltage and / or current between the electrode and the metal substrate when the corrosion agent is arranged between the surface treatment film and the electrode in a manner that contacts the surface treatment film and the electrode. The detection unit detects the current and / or voltage generated between the electrode and the metal substrate as the voltage and / or current are applied by the power supply unit. The evaluation unit evaluates the defect occurrence status of the surface treatment film based on the waveform of the time-varying current and / or voltage detected by the detection unit. When the value of the voltage applied by the power supply unit is set as the applied voltage value, the value of the current applied by the power supply unit is set as the applied current value, the value of the current detected by the detection unit is set as the detection current value, and the value of the voltage detected by the detection unit is set as the detection voltage value, The time-varying change is data obtained by plotting the detected current value and / or the detected voltage value relative to time into a curve, or by plotting the detected current value and / or the detected voltage value relative to the applied voltage value and / or the applied current value when the power supply unit applies an increasing voltage and / or current.

8. The corrosion resistance testing apparatus for coated metal materials according to claim 7, characterized in that: The evaluation unit evaluates the occurrence of the defect based on the peak value of the waveform.

9. The corrosion resistance testing apparatus for coated metallic materials according to claim 7 or 8, characterized in that: The power supply applies a voltage and / or current that increases gradually over time, or applies a voltage and / or current that increases proportionally over time.

10. A procedure for testing the corrosion resistance of a coated metal material, wherein the coated metal material is formed by depositing a surface treatment film on a metal substrate, characterized in that: The computer performs a step of evaluating the defect occurrence of the surface treatment film based on the waveform of the time-varying current and / or voltage. The current and / or voltage are generated between the surface of the surface treatment film and the metal substrate by applying voltage and / or current between the electrode and the metal substrate, with the corrosion agent in contact with both the electrode and the surface treatment film on one side of the surface treatment film disposed on the coated metal material. When the applied voltage between the electrode and the metal substrate is set as the applied voltage value, the applied current between the electrode and the metal substrate is set as the applied current value, the current generated between the electrode and the metal substrate is set as the detection current value, and the voltage generated between the electrode and the metal substrate is set as the detection voltage value,... The time-dependent variation is data obtained by plotting the detection current value and / or the detection voltage value relative to time, or by plotting the detection current value and / or the detection voltage value relative to the applied voltage value and / or the applied current value when an increasing voltage and / or current is applied between the electrode and the metal substrate.

11. A recording medium that can be read by a computer and records a procedure for testing the corrosion resistance of the coated metal material as claimed in claim 10.

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