Inspection method of surface film

Abstract

To provide a testing method that can obtain an inspection result in a shorter time than a conventional salt water spraying method, timely give feedback to a manufacturing process when a test piece is determined to be a nonconforming item, and promptly prevent the nonconforming item from being continuously manufactured.SOLUTION: An inspection method of a surface film comprises a first step of wetting a surface film of a test piece in which the surface film is formed with a test liquid containing a metal indicator and a second step of keeping the support of the metal indicator on the surface film only for a predetermined period. The test piece is a metallic member in which the surface film is formed, the test liquid contains the metal indicator and halogen ion, and the metal indicator is active to a main metallic element of the metallic member.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method for inspecting a surface film that is suitable for inspecting the quality of a chemical conversion film applied to, for example, an aluminum alloy. [Background technology]

[0002] To increase the corrosion resistance of metal materials such as aluminum alloys, a chemical conversion coating is sometimes applied to the surface. For example, chromate-treated aluminum alloys are widely used in the aircraft industry. Inspection is sometimes required to ensure the quality and integrity of such chemical conversion coatings. Salt spray testing (JIS Z2371) is often carried out as a quality inspection of chemical conversion coatings. In salt spray testing, a test piece is placed in a salt spray testing device that is kept at a constant temperature, and a mist of sodium chloride solution is sprayed onto it. The surface condition of the test piece is observed after a specified period of time has passed since the spraying, but the test period generally requires more than several days.

[0003] Patent Document 1 proposes a test method in which the test liquid is an aqueous solution containing sodium ions, chloride ions, and sulfate ions in order to simulate a real environment more accurately than the salt spray test. Patent Document 1 also discloses that in addition to the above three types of ions, the test liquid may further contain magnesium ions and calcium ions, and may further contain potassium ions, strontium ions, bromine ions, bicarbonate ions, fluoride ions, and boric acid. However, according to the examples in Patent Document 1, a 240-hour combined cycle test CCT-N2 (Non-Patent Document 1) is required, which is the same in that a test period of more than several days is required. The objects inspected in the examples in Patent Document 1 are steel sheets and zinc sheets. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6713972 Summary of the Invention [Problem to be solved by the invention]

[0005] Corrosion resistance testing methods such as the salt spray method generally require a test period of more than several days. Therefore, even if the results of the salt spray method indicate that the product is non-conforming, it is difficult to provide timely feedback to the manufacturing process. The manufacturing process referred to here is, for example, the process related to chemical conversion coating. Based on the above, the present disclosure proposes a testing method that can obtain inspection results in a shorter time than the conventional salt spray method, and that can provide timely feedback to the manufacturing process when non-conforming products are identified, quickly correcting the continued production of non-conforming products. [Means for solving the problem]

[0006] The method for inspecting a surface film according to the present disclosure includes: A first step of wetting the surface film of the test piece on which the surface film has been formed with a test liquid containing a metal indicator; A second step of maintaining the metal indicator supported on the surface film for a predetermined period of time; The test specimen is A metal member having a surface coating formed thereon, The test solution is The metal indicator comprises a metal indicator and a halide ion, the metal indicator being active towards the predominant metal element of the metal component. Effect of the Invention

[0007] According to the present disclosure, by using a metal indicator that is active against the main metal element, it is possible to grasp the metal ions that are eluted due to the influence of halogen ions. Therefore, the inspection results can be obtained in a shorter time than the conventional salt spray method, and when a non-conforming product is found, the information can be fed back to the manufacturing process in a timely manner, and the continuous production of non-conforming products can be promptly corrected. [Brief description of the drawings]

[0008] [Figure 1]FIG. 2 is a flow chart showing the procedure of the inspection method according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing an inspection procedure according to the first embodiment. [Diagram 3] FIG. 1 is a diagram showing the test results in Example 1. [Figure 4] FIG. 13 is a diagram showing the test results in Example 2. [Diagram 5] FIG. 13 is a diagram showing the test results in Example 3. [Figure 6] FIG. 11 is a flow chart showing the procedure of an inspection method according to a second embodiment. [Figure 7] FIG. 13 is a diagram showing the test results in Example 4. [Figure 8] FIG. 13 is a diagram showing the test results in Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments will be described with reference to the accompanying drawings. [Summary of the inspection method] In the inspection method according to the present embodiment, the surface of a test piece is wetted with a color-developing test liquid containing a metal indicator suitable for the metal member constituting the object to be inspected, and the metal ions eluted through the pits, which are defects in the chemical conversion coating, are caused to develop color, thereby detecting the presence of pits, which enables the rapid evaluation of surface coatings such as chemical conversion coatings.

[0010] [Test piece: object to be inspected] The test piece, which is the object to be inspected according to this embodiment, is typically a metal member having a chemical conversion coating formed on its surface. Metal materials are classified into ferrous metals and non-ferrous metals, and the present embodiment is applicable to both. However, in the case of chromate treatment of ferrous metals, it is applied on a plating film made of a non-ferrous metal such as zinc.

[0011] Chemical conversion coating is a general term for inorganic coatings that are chemically deposited on metal surfaces by immersion in a treatment solution. Phosphate treatment and chromate treatment are well-known methods for forming chemical conversion coatings, and the present disclosure can be applied to the inspection of both types of chemical conversion coatings, but is preferably applied to chemical conversion coatings formed by chromate treatment. The inspection method of the present disclosure is applied to ensure the soundness of the chemical conversion coating.

[0012] [Phosphate Salt Treatment] Phosphating is a process in which the surface of a metal base material is corroded and dissolved while a phosphate film is deposited on the surface through a chemical reaction. Phosphating is a technology that was originally established for iron-based metal materials. Among the various types of phosphate treatment, zinc phosphate treatment is applied to zinc materials such as zinc-plated steel sheets and zinc die castings, as well as aluminum materials such as aluminum alloy sheets and aluminum die castings.

[0013] [Chromate Treatment] Chromate treatment is an example of a chemical conversion treatment used for non-ferrous metals such as aluminum alloys, zinc alloys, and magnesium alloys. In this disclosure, for example, when referring to an aluminum alloy, it means not only aluminum alloys but also pure aluminum. The same applies to zinc, magnesium, etc. After chromate treatment, the surface of the metal is covered with an oxide film (chromate film) that contains chromium, which has a barrier effect that prevents corrosion and can extend the life of the metal component.

[0014] [Test procedure: See Figure 1] The testing procedure according to this embodiment starts with determining the components and concentrations of the test liquid (FIG. 1, S101). Each step will be described below in order.

[0015] [Test solution determination and preparation steps (Fig. 1 S101, S103)] In a preferred embodiment of the present invention, the method includes two steps, an activation step and a color development step, and therefore requires a test solution corresponding to each step.

[0016] <Activation process> The test solution used in the activation process (hereinafter, activation test solution) is an aqueous solution containing halogen ions that promote the growth of pits (weak corrosion-resistant areas that are the starting point for pitting and corrosion in real environments, hereinafter sometimes simply referred to as pits) as initial defects present in the chemical conversion film. This activation process promotes the elution of metal ions that make up the base material through the pits. A halogen ion is an ion of a negatively charged halogen atom, and is called a fluoride ion, F - , chloride ion Cl - , bromide ion Br - , iodide ion I - The corresponding fluoride ion is F - Compounds that exhibit this include hydrogen fluoride (HF) and potassium fluoride (KF), which have chloride ions Cl - The compound that exhibits this is sodium chloride (NaCl). - Sodium bromide (NaBr) is a compound that exhibits the iodide ion I - An example of a compound that exhibits this property is sodium iodide (NaI).

[0017] The concentration of halogen ions contained in the activation test liquid is selected from the range of 0.1 to 30 wt%, preferably from the range of 1 to 10 wt%, and more preferably from the range of 3 to 7 wt%. Ions that may be contained other than halogen ions are permitted to be contained in a total amount of 5 wt% or less.

[0018] <Color development process> The test liquid (color-developing test liquid) used in the color-developing process is an aqueous solution containing a metal indicator and halogen ions, and some of the water in the aqueous solution can be replaced with ethanol. The metal indicator is usually provided as a powder, and dissolves in water or other solvents to form the color-developing test liquid.

[0019] The color-developing test liquid contains a metal indicator. The metal indicator reacts with metal ions to produce any one of color development, color change, and turbidity. Color development, color change, and turbidity are hereinafter abbreviated as color development, etc. Depending on the type of metal ion, some metal indicators develop color, etc., and some do not. In this disclosure, a metal indicator that develops color, etc. is said to be active with respect to the metal ion. An appropriate metal indicator is selected depending on the material of the metal member constituting the test object. For example, when the metal member is made of an aluminum alloy, a metal indicator that reacts with aluminum ions to develop color or the like is used. Metal indicators that detect aluminum ions include Chrome Azurol S, Eriochrome Cyanine R, Aluminon, Hematoxylin, Alizarin, Alizarin Red, Alizarin S, Morin, and 8-Quinolinol. These metal indicators are active against aluminum ions.

[0020] The color-developing test solution contains halogen ions in addition to the metal indicator. The halogen ions can be the same as those used in the test solution for the activation process and for the same purpose.

[0021] The color-developing test liquid is brought into contact with and wets the test piece while the test piece is impregnated in a support medium, such as cellulose filter paper, glass filter paper, porous filter, printing paper, gel, agar, or polymer. It is also advisable to add a pH buffer to the color test solution and maintain a constant pH during testing.

[0022] [Immersion of the test piece, activation process, and color development process (Fig. 1 S105-S111)] Once the test solution has been prepared, the test piece is immersed in the activation test solution and held there for a predetermined period of time. Immersion in the activation test liquid is a preferred form of this embodiment, and it may be possible to determine the presence of the conversion coating based on the color development process alone. Therefore, there is no particular limit to the immersion time in the activation test liquid, but a time similar to the immersion time in the color development process may be used.

[0023] A method for accelerating damage to the chemical conversion coating can be taken for the test liquid in which the test piece is immersed. Typically, this involves heating the test liquid to a temperature above room temperature. Since the test liquid is an aqueous solution, specific methods for heating the test liquid include a method using a liquid that has been heated to a temperature above room temperature in advance, a method using a water bath with a temperature control function, and a method using a thermostatic bath.

[0024] After immersing the test piece in the activation test liquid for a specified time, the test piece is removed from the activation test liquid, the surface of the test piece is washed with water, etc., and then the test piece is wetted with the color-developing test liquid. Specifically, a support medium impregnated with the color-developing test liquid is placed on the test piece, etc., to wet the chemical film of the test piece with the color-developing test liquid (first step). The entire support medium is impregnated with the color-developing test liquid, and the color-developing test liquid wets the entire area of ​​the test piece that is in contact with the support medium.

[0025] This contact state is maintained for a predetermined period of time. The holding time should be 48 hours or less. Preferably, it should be within 12 hours, and more preferably, within 2 hours. The optimum holding time varies depending on the material, quality, and surface condition.

[0026] [Visualization of pits using a color-developing test solution: see Figure 2] After a predetermined retention time has elapsed, the support medium develops color or the like depending on the location of defects (pits P) that were present in the chemical conversion coating. In FIG. 2, a test piece TP1 having a chemical conversion coating C1 of low quality with multiple pits P and a test piece TP2 having a chemical conversion coating C2 of high quality with no pits P are prepared. A support medium SM impregnated with a color development test liquid is placed on each of the chemical conversion coating C1 of the test piece TP1 and the chemical conversion coating C2 of the test piece TP2, and left for a predetermined time (second step).

[0027] In the test piece TP1 with a low quality coating, metal ions of the metal member of the test piece TP1 are eluted from pits P where the chemical conversion coating C1 is insufficiently formed. Therefore, localized discoloration or CL of the metal indicator occurs at a plurality of positions corresponding to the pits P. The lower the quality of the coating, the more CL such as discoloration is detected. Therefore, it is possible to quantitatively evaluate the quality of the coating by, for example, photographing the support medium SM with a digital camera.

[0028] [Judgment: Figure 1 S115, S117, S119, S121] After the test piece has been held on the support medium for a predetermined time, it is visually inspected. Based on the results of the visual inspection, it is determined whether the conversion coating meets the quality standards (third step). The appearance inspection and judgment may be performed by one or both of a method based on human visual inspection and a method other than human visual inspection. For example, in the former case, the judgment can be performed by comparing the discoloration state of the discolored sample with that of the test piece. In the latter case, the surface of the test piece is photographed with a digital camera as described above, and the number of discolorations is counted, and a quantitative judgment can be performed by comparing the counted number of discolorations with a discoloration number threshold value that serves as the judgment criterion.

[0029] If the test piece is determined to conform to the quality standard, the result of the determination is stored, for example. If the test piece is judged as not meeting the quality standard as a result of the judgment, the judgment result is fed back to improve the manufacturing process that has been carried out up to that point, in this case the process of forming the chemical conversion coating.

[0030] [Example 1: See Figure 3] Example 1 illustrates the evaluation of test strips to which a color development process was applied after an activation process. The effect of five test pieces made of aluminum alloy (JIS A2024) on which a chromate film was formed was confirmed by placing a support medium impregnated with the color development test liquid according to this embodiment on the surface on which the chromate film was formed. Cellulose filter paper was used as the support medium. The results are shown in Figure 3. The five test pieces had different qualities of chromate film before being subjected to the color development test liquid, and the "average number of SST pits" in Figure 3 represents these differences. The "average number of SST pits" is the number of pits counted after a conventional salt spray test was performed on the same test pieces as the five test pieces, and the higher the "average number of SST pits", the lower the quality of the chromate film. Color test solution (aqueous solution): Ingredients / Concentrations; Metal Indicators; Chrome Azurol S Chloride ion 5wt% Holding time: 30 minutes

[0031] Figure 3 shows the results of an actual visual inspection using the color-developing test liquid. In Figure 3, the discolored areas are the areas discolored by the color-developing test liquid. Note that the test piece used in this visual inspection did not undergo an activation process.

[0032] [Example 2: See Figure 4] Example 2 shows an example of evaluation of a test piece that was subjected to an activation process and then a coloring process. The test piece was made of an aluminum alloy having the same chromate film formed thereon as in Example 1.

[0033] Activation test solution: Ingredients / concentration: Chloride ion (NaCl) 5wt% (aqueous solution) Temperature; 25℃ Holding time: 30 minutes

[0034] Color test solution (aqueous solution): Ingredients / Concentration; Metal indicators; Eriochrome Cyanine R, Chrome Azurol S Chloride ion (NaCl) 5wt% Holding time: 30 minutes

[0035] The results are shown in Figure 4. Both metal indicators make it possible to visually identify pits, which are initial defects that are the starting point of pitting corrosion or corrosion, but it can be seen that visibility differs depending on the type of metal indicator. This shows that it is possible to select appropriate inspection conditions, including the type of metal indicator, depending on the quality requirements of the product being inspected and the inspection environment.

[0036] [Example 3: See Figure 5] This is an example in which a test strip was evaluated by performing an activation process and then a color development process, and shows an example of the combination of the following factors different from Example 2.

[0037] Activation test solution (aqueous solution): Ingredients / concentration: Chloride ion (NaCl) 5wt% Temperature; 25℃ Holding time: 30 minutes

[0038] Color test solution (aqueous solution): Ingredients / Concentration; Metal Indicator; Chrome Azurol S, Aluminon Chloride ion (NaCl) 5wt% Holding time: 30 minutes Support media: cellulose filter paper, porous filter

[0039] The results are shown in Figure 5. It can be seen that the detectability and visibility of pits as initial defects that are the starting point of pitting and corrosion varies depending on the combination of elements. In other words, pits can be visually recognized whether Chrome Azurol S or Aluminon is used as the metal ion indicator. However, in this embodiment, the difference in color tone between the metal ion detection area and the non-detection area is larger in Chrome Azurol S than in Aluminon. Therefore, it is desirable to select an appropriate combination of elements in the manufacturing process including the actual formation of the chemical conversion film. It is possible to improve the visibility of the pits to be detected and detect them with reduced bleeding.

[0040] [Example 4: See Figures 6, 7, and 8] Next, the determination using image processing will be described. This determination is performed by a determination system 1 shown in FIG. The judgment system 1 includes an image acquisition unit 10 and a control unit 20 that controls the operation of the image acquisition unit 10 and acquires image data acquired by the image acquisition unit 10 to perform judgment processing. The judgment procedure in the judgment system 1 is performed according to the flow diagram shown in Fig. 6. For example, a digital camera is applied to the image acquisition unit 10, and a computer device is applied to the control unit 20. This computer device includes a memory that stores setting information such as threshold values ​​and programs, and a processor that executes judgment processing and the like based on the setting information and programs stored in the memory.

[0041] <Setting the pit threshold Pt: Fig. 6 S201> A threshold value for the pits to be counted is stored and set in the control unit 20, particularly in the memory. This pit threshold value Pt is set, for example, in terms of hue, saturation, and pixel count, and pits that are recognized in an image acquired of the test piece and that satisfy this threshold value are counted. This number of pits to be counted is called the number of counted pits Pc. Hue refers to the difference in color tone, such as red, blue, and green. Hues vary depending on the classification method, but the main hues are red, yellow, green, blue, purple, etc. When these are arranged in a circle and intermediate colors are placed between each color, it is called a color wheel. Saturation is the degree of vividness of an image or video. Vividness varies depending on the amount of white, gray, black, etc. mixed into each color, and pure colors without any impurities are considered to be the most saturated colors. A pixel is the smallest unit or element that has color information when handling images on a computer device, and is also called a picture element.

[0042] <Setting the standard number of pits Ps for pass / fail judgment: Fig. 6 S203> Next, the number of pits serving as the pass / fail judgment criterion (reference pit number Ps) is stored and set in the memory of the control unit 20. The reference pit number Ps is compared with the counted pit number Pc.

[0043] In the present embodiment, steps S201 and S203 are collectively referred to as a setting step. The setting step is not always performed in pairs with the subsequent determination step. After the setting is performed by the setting step, only the determination step can be repeated. When it is necessary to change the setting, the setting step is performed again, and thereafter, the determination step can be repeated.

[0044] <Image data acquisition: FIG. 6 S205> Now, it is shifted to the determination step. In the determination step, the image acquisition unit 10 photographs the surface of the support medium SM placed on the test piece TP to acquire image data. The acquired image data is provided to the control unit 20.

[0045] <Acquisition and comparison of the counted pit number Pc: FIG. 6 S207, S209> When the control unit 20 acquires the image data, it counts and acquires the counted pit number Pc by image analysis based on the pit threshold Pt. The control unit 20 compares the acquired counted pit number Pc with the reference pit number Ps. This comparison is determined as whether the counted pit number Pc and the reference pit number Ps satisfy Pc < Ps.

[0046] <Determination: FIG. 6 S211, S213, S215> When Pc < Ps is satisfied, the control unit 20 determines that the test piece passes the quality standard. The fact of the pass determination is displayed to that effect on, for example, a display device provided in the determination system 1 and stored in the memory. When Pc < Ps is not satisfied (Pc ≥ Ps), the control unit 20 determines that the test piece fails to meet the quality standard. The determination of failure is, for example, displayed to that effect on the display device provided in the determination system 1. The operator who refers to the display feeds back the determination result to the improvement of the manufacturing process being carried out so far, in this case, the formation process of the chemical conversion film.

[0047] FIG. 7 shows an example of the acquired image data, the result of image analysis, and the counted number of pits Pc. From FIG. 7, regarding the result of the pit detection test, by taking the local color tone change and discolored part of the metal ion indicator as pits as the initial defects that are the starting points of pitting corrosion and corrosion, and counting the number thereof, it can be seen that it is possible to evaluate the quality of the chemical conversion film. Further, by performing image processing on the acquired image data, by setting threshold values for hue and saturation and extracting and counting the local color tone change and discolored parts, it is possible to quickly perform a pass / fail determination of the chemical conversion film.

[0048] Among the pit threshold values Pt, by setting a threshold value for the number of pixels, it is possible to improve the correlation with the result of the salt spray test (SST test). That is, as shown in FIG. 8, compared with the case where no threshold value is set for the number of pixels, the correlation between the number of pits by the salt spray test and the number of pits according to this embodiment is improved, and it is possible to obtain a determination result having a higher correlation with the salt spray test.

[0049] [Appendix] The present disclosure can be grasped as follows. [Appendix 1] The inspection method of the surface film is a first step of supporting a metal indicator on the surface film (C) of a test piece (TP) on which the surface film (C) is formed; a second step of holding the support of the metal indicator on the surface film (C) for a predetermined time. The test piece (TP) is a metal member having a surface film (C) formed on the surface, The test solution is The metal indicator and halide ions are included, and the metal indicator is active to the major metal element of the metal component. [Appendix 2] In the first step in Appendix 1, preferably, The surface coating (C) is wetted with the test liquid by contacting the support medium (SM) impregnated with a metal indicator with the surface coating (C). [Appendix 3] In Appendix 1 or Appendix 2: The preferred metal member is an aluminum alloy. [Appendix 4] In any of Supplementary Note 1 to Supplementary Note 3, A preferred surface coating is a conversion coating. [Appendix 5] In any of Supplementary Note 1 to Supplementary Note 4, The test specimen in the first step is Preferably, the chemical conversion coating is activated with an aqueous solution containing halogen ions. [Appendix 6] In any of Supplementary Note 3 to Supplementary Note 6, In the support medium (SM) that is coated on the test piece that has undergone the second step, It is preferable to have a third step of counting the number of pits activated by the metal indicator and evaluating the quality of the surface coating based on the number of pits counted. [Appendix 7] In the third step in Appendix 6, preferably, The number of pits is counted based on image data obtained by photographing the support medium (SM). [Appendix 8] In the third step in Appendix 7, preferably, The number of pits (Pc) is counted based on a preset pit threshold value (Pt). [Appendix 9] In the third step in Appendix 8, preferably, The number of counted pits (Pc) is compared with a predetermined standard number of pits (Ps) to determine whether the quality of the surface coating is acceptable or not.

[0050] In addition to the above, it is possible to select and discard the configurations given in the above embodiment, or to change them to other configurations as appropriate. The present disclosure can be widely applied to coatings that have pits as initial defects that are the starting points for pitting corrosion or corrosion, regardless of the type of coating. [Explanation of symbols]

[0051] 1 Judgment system 10 Image acquisition section 20 Control section SM support medium TP, TP1, TP2 test pieces

Claims

1. A first step of wetting a surface film of a test piece having a surface film formed thereon with a test liquid containing a metal indicator; A second step of maintaining the metal indicator supported on the surface film for a predetermined period of time, The test piece is a metal member having the surface coating formed thereon, The test solution is The metal indicator and a halogen ion are included, and the metal indicator is active to a major metal element of the metal component. Inspection method for surface coatings.

2. In the first step, wetting the surface coating with the test liquid by contacting a support medium impregnated with the metal indicator with the surface coating; The method for inspecting a surface film according to claim 1.

3. The metal member is an aluminum alloy. The method for inspecting a surface film according to claim 1.

4. The surface coating is a chemical conversion coating. The method for inspecting a surface film according to claim 1.

5. The test piece in the first step is The chemical conversion coating is activated by an aqueous solution containing halogen ions. The method for inspecting a surface film according to claim 4.

6. The support medium coated on the test piece after the second step, a third step of counting the number of pits activated by the metal indicator and evaluating the quality of the surface coating based on the number of pits counted. The method for inspecting a surface film according to claim 2.

7. In the third step, The number of pits is counted based on image data obtained by photographing the support medium. The method for inspecting a surface film according to claim 6.

8. In the third step, The number of pits is counted based on a preset pit threshold value. The method for inspecting a surface film according to claim 7.

9. In the third step, The number of counted pits is compared with a predetermined reference number of pits to determine whether the quality of the surface coating is acceptable or not. The method for inspecting a surface film according to claim 8.

Images