A method for testing the adhesion of inorganic coatings on magnesium alloys

Abstract

The application discloses a magnesium alloy inorganic coating adhesion test method and relates to the technical field of surface performance test. The method comprises the following steps: tape sticking: covering a tear tape on the surface of the inorganic coating of a magnesium alloy sample to be tested, and extending one end of the tear tape to form a tear section; sample positioning: fixing the magnesium alloy sample to be tested, so that the surface of the inorganic coating forms an angle of 90 degrees plus or minus 2 degrees with the direction of gravity of the magnesium alloy sample to be tested; dynamic peeling: applying a transient impact load to the tear tape through the tear section, so that the tear tape falls off and the inorganic coating is partially peeled off; and adhesion calculation: based on the percentage of the residual area of the inorganic coating, the adhesion value of the inorganic coating of the magnesium alloy sample to be tested is obtained through a pre-established corresponding relationship model between the percentage of the residual area of the inorganic coating and the adhesion value tested by the pull-out method. The application can realize instant quantification of the adhesion, the result is reliable, and the method can directly guide process adjustment and quality control on the production site.

Description

Technical Field

[0001] This invention relates to the field of surface performance testing technology, and specifically to a method for testing the adhesion of inorganic coatings on magnesium alloys. Background Technology

[0002] Magnesium alloys have poor corrosion resistance, so a protective coating is usually required before use. Chemical conversion and micro-arc oxidation are the most common methods for preparing protective coatings for magnesium alloys. Industrial applications have varying requirements for the adhesion of protective coatings on magnesium alloys, as this not only determines the coating's protective ability but also affects the adhesion of subsequent paints, ultimately determining the quality of the product.

[0003] Current methods for testing coating adhesion include pull-out and scratch methods. The pull-out method uses a high-strength adhesive to bond a special puller for a pull-out device to the coating sample. After a long curing period, the adhesion is tested using the pull-out device. Its advantage is its simplicity, but its disadvantage is the inability to obtain data immediately, as the curing process takes 12 hours or more. In industrial applications, it is often necessary to quickly obtain coating adhesion values ​​on-site to rapidly adjust processes and make appropriate production decisions. The scratch method primarily uses a diamond indenter to apply a certain compressive stress to the coating. As the diamond indenter penetrates the coating until it reaches the substrate, the significant difference in mechanical properties between the coating and the substrate causes a noticeable abrupt change in the acoustic emission signal, ultimately yielding the critical load. The scratch method applies an increasing load to the coating surface using a diamond indenter, and the critical load (unit: N) is determined by the abrupt change in acoustic emission signal or frictional force. Because the coating-substrate contact area is difficult to measure accurately, the critical load is usually used directly to characterize adhesion rather than being converted to strength (MPa). In addition, the scratch test is mainly for coated or thin metal films, and its effect on detecting coatings such as magnesium alloy chemical conversion and micro-arc oxidation, which have large roughness and thickness, is not good.

[0004] Therefore, how to quickly conduct coating adhesion tests and obtain relatively accurate data is an urgent problem to be solved in industrial production. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a rapid and relatively accurate method for testing the adhesion of inorganic coatings on magnesium alloys.

[0006] The technical solution adopted in this invention is a method for testing the adhesion of inorganic coatings on magnesium alloys, comprising the following steps:

[0007] Tape application: A tear-off tape is applied to the inorganic coating surface of the magnesium alloy sample to be tested, with one end of the tear-off tape extending to form a tear section;

[0008] Sample positioning: Fix the magnesium alloy sample to be tested so that the inorganic coating surface and the gravity direction of the magnesium alloy sample are at an angle of 90 degrees ± 2 degrees.

[0009] Dynamic peeling: An instantaneous impact load is applied to the tearing tape through the tearing section, causing the tearing tape to detach and the inorganic coating to partially peel off;

[0010] Adhesion calculation: Based on the percentage of the remaining area of ​​the inorganic coating, the adhesion value of the inorganic coating of the magnesium alloy sample to be tested is calculated by using a pre-established correspondence model between the percentage of the remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method.

[0011] Furthermore, the inorganic coating is a micro-arc oxidation coating or a chemical conversion coating.

[0012] Furthermore, the thickness of the inorganic coating is 5 μm to 50 μm.

[0013] Furthermore, the peel strength of the tear-off tape is 20 N / cm to 50 N / cm.

[0014] Furthermore, the sample positioning includes: fixing the magnesium alloy sample to be tested onto the support frame using clamps and bolts.

[0015] Furthermore, the dynamic peeling includes: connecting the tearing segment to the counterweight via a flexible connecting line, releasing the counterweight to allow it to fall freely, causing the tearing tape to detach, and partially peeling off the inorganic coating through the tearing of the tearing tape.

[0016] Furthermore, the mass of the counterweight is 5kg±12.5g, the initial position of the counterweight is 5cm±1cm away from the magnesium alloy sample to be tested along the direction of gravity, the size of the tear-off tape covering the magnesium alloy sample to be tested is 100mm long × 50mm wide, and the length of the flexible connecting line is 1.5m±0.05m.

[0017] Furthermore, the method for pre-establishing the correspondence model between the percentage of remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method includes:

[0018] By adjusting the preparation process parameters of the inorganic coating, multiple batches of magnesium alloy samples with different inorganic coating adhesion values ​​were obtained.

[0019] Tear tests and pull-out tests were performed on magnesium alloy samples from the same batch with the same preparation process parameters. The percentage of the remaining inorganic coating area was obtained through the tear test, and the adhesion value was obtained through the pull-out test. The tear test included: covering the inorganic coating surface of the magnesium alloy sample with a peel strength of 20 N / cm to 50 N / cm, with one end of the peel tape extending to form a tear segment; fixing the magnesium alloy sample so that the inorganic coating surface and the gravity direction of the magnesium alloy sample were at an angle of 90 degrees ± 2 degrees; applying an instantaneous impact load to the peel tape through the tear segment, causing the peel tape to detach and the inorganic coating to partially peel off, and calculating the percentage of the remaining inorganic coating area after tearing.

[0020] Establish a model relating the percentage of remaining area of ​​the inorganic coating to the adhesion value tested by the pull-out method.

[0021] Furthermore, when the inorganic coating is a chemical conversion coating, the corresponding relationship model between the percentage of the remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method is: Y = 6.25x + 1.8, where Y is the adhesion value in MPa and x is the percentage of the remaining area of ​​the inorganic coating.

[0022] Furthermore, when the inorganic coating is a micro-arc oxidation coating, the corresponding relationship model between the percentage of the remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method is: Y = 12.0x + 5.9, where Y is the adhesion value in MPa and x is the percentage of the remaining area of ​​the inorganic coating.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] The magnesium alloy inorganic coating adhesion test method provided by this invention replaces the traditional pull-out or scratch test with a tear test. It utilizes the correspondence between the percentage of the remaining area of ​​the inorganic coating after tearing and the adhesion value of the pull-out test to achieve real-time quantification of adhesion, significantly improves testing efficiency, and provides reliable results. It can directly guide process adjustment and quality control on the production site. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the design principle for testing the adhesion of inorganic coatings on magnesium alloys according to an embodiment of the present invention; wherein, 1, magnesium alloy substrate; 2, inorganic coating; 3, tear-off tape; 301, tear-off section; 4, tear-off area; 5, flexible connecting line; 6, counterweight; 7, clamp; 8, bolt; 9, support frame.

[0026] Figure 2 This is a comparison diagram of the adhesion test of magnesium alloy samples before and after the test provided in the embodiment of the present invention.

[0027] Figure 3This is a diagram showing the correspondence between the sample data of the magnesium alloy chemical conversion film sample provided in Embodiment 1 of the present invention after tearing and pulling tests.

[0028] Figure 4 This is a diagram showing the correspondence between the sample data of the magnesium alloy micro-arc oxidation coating sample provided in Embodiment 2 of the present invention after tear test and pull-out test. Detailed Implementation

[0029] To better understand the above technical solutions, the technical solutions of the present invention will be described in detail below through specific embodiments.

[0030] This invention provides a method for testing the adhesion of inorganic coatings on magnesium alloys, comprising the following steps:

[0031] Tape application: The tear-off tape 3 is applied to the surface of the inorganic coating 2 of the magnesium alloy sample to be tested, with one end of the tear-off tape 3 extending to form a tear section 301;

[0032] Sample positioning: Fix the magnesium alloy sample to be tested so that the surface of inorganic coating 2 is at an angle of 90 degrees ± 2 degrees to the direction of gravity of the magnesium alloy sample to be tested.

[0033] Dynamic peeling: An instantaneous impact load is applied to the tearing tape 3 through the tearing section 301, causing the tearing tape 3 to fall off and the inorganic coating 2 to partially peel off;

[0034] Adhesion calculation: Based on the percentage of the remaining area of ​​the inorganic coating, the adhesion value of the inorganic coating of the magnesium alloy sample to be tested is calculated by using a pre-established correspondence model between the percentage of the remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method.

[0035] The magnesium alloy inorganic coating adhesion testing method provided in this invention replaces the traditional pull-out or scratch method with a tear test (instant tearing of adhesive tape after application). By utilizing the correlation between the percentage of the remaining inorganic coating area after tearing and the adhesion value (bonding strength) obtained by the pull-out test, the adhesion can be quantified in real time, significantly improving testing efficiency and providing reliable results (verification data dispersion is within the acceptable range for engineering). This method can directly guide process adjustments and quality control on the production site.

[0036] In some embodiments, the inorganic coating 2 is a micro-arc oxidation coating or a chemical conversion coating.

[0037] Specifically, experiments have shown that the magnesium alloy inorganic coating adhesion test method of the present invention can be used for adhesion testing of magnesium alloy micro-arc oxidation coatings, as well as for adhesion testing of magnesium alloy chemical conversion coatings. It is applicable to coating thicknesses of 5μm to 50μm, and is particularly suitable for testing the adhesion of coatings with thicknesses of 8μm to 30μm.

[0038] In some embodiments, the peel strength of the tear-off tape 3 is 20 N / cm to 50 N / cm.

[0039] Specifically, the selection of the tear-resistant tape 3 is independent of the coating thickness and only depends on the tear strength (peel strength). For coatings with expected adhesion below 20 MPa, a tear-resistant tape 3 with a tear strength of 20 N / cm is sufficient to meet the test requirements. If the expected adhesion of the coating reaches or exceeds 20 MPa, a tear-resistant tape 3 with a tear strength higher than 20 N / cm is required.

[0040] In some embodiments, the dynamic peeling method includes: connecting the tearing section 301 to the counterweight 6 via the flexible connecting line 5, releasing the counterweight 6 to allow it to fall freely, causing the tearing tape 3 to fall off, and causing partial peeling of the inorganic coating 2 by tearing the tearing tape 3.

[0041] Specifically, the instantaneous tensile force generated by the free fall of the counterweight 6 can quickly and uniformly peel off the inorganic coating 2 locally. At the same time, the design of the flexible connecting line 5 can precisely control the tearing direction and force, and the operation is simple and inexpensive.

[0042] Example 1: A Method for Testing the Adhesion of Inorganic Coatings on Magnesium Alloys

[0043] See Figure 1 Example 1 presents a rapid detection method for inorganic coatings on magnesium alloys based on the high-strength adhesive tape tearing method, which includes the following steps:

[0044] (1) Prepare a flat magnesium alloy substrate 1, and prepare an inorganic coating 2 on the surface of the magnesium alloy substrate 1 (by micro-arc oxidation or chemical conversion) to obtain a magnesium alloy sample.

[0045] (2) Lay the tear-off tape 3 (high-strength tape) flat on the surface of the inorganic coating 2 of the magnesium alloy sample to be tested, and press it firmly to ensure that there are no air bubbles on the bonding surface between the tear-off tape 3 and the inorganic coating 2. A tear-off section 301 is reserved at one end of the tear-off tape 3 for connecting the counterweight 6. The area of ​​the inorganic coating covered by the tear-off tape 3 is 100mm long × 50mm wide. Optionally, the tear-off tape 3 is JSJ4816 model adhesive tape from Shangrao Dayu Adhesive Products Co., Ltd., with a peel strength of 24.5 N / cm.

[0046] (3) The counterweight 6 and the tear section 301 of the tear-off tape 3 are connected by a flexible connecting line 5 with a length of 1.5m. The counterweight 6 has a mass of 5kg and an allowable mass deviation of ±12.5g. The magnesium alloy sample is fixed to the support frame 9 by clamps 7 and bolts 8. The height of the magnesium alloy sample to be tested from the ground is controlled to be 1.7m by the support frame 9. The initial position of the counterweight 6 is fixed below the magnesium alloy sample. The counterweight 6 maintains a distance of 5cm from the magnesium alloy sample in the direction of gravity of the sample.

[0047] (4) During the test, the counterweight 6 is released. The free fall of the counterweight 6 pulls the tearing tape 3 to move quickly, so that the inorganic coating 2 on the surface of the magnesium alloy sample to be tested is partially peeled off, forming the tear area 4. In this way, the inorganic coating 2 is quickly peeled off.

[0048] (5) Calculate the percentage of the remaining area of ​​the inorganic coating after the magnesium alloy sample is to be tested. The percentage of the remaining area of ​​the inorganic coating after the magnesium alloy sample is to be tested is the ratio of the area of ​​the inorganic coating of the magnesium alloy sample that has not been peeled off to the area of ​​the inorganic coating covered by the peeling tape 3.

[0049] (6) Input the percentage of the remaining area of ​​the inorganic coating of the magnesium alloy sample to be tested after tearing into the correspondence model between the percentage of the remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method, and calculate the adhesion value of the inorganic coating of the magnesium alloy sample to be tested.

[0050] Example 2: Relationship between tear area and pull-out conversion of magnesium alloy chemical conversion film sample

[0051] The relationship between the tear area and the adhesion tested in the pull-out test of magnesium alloy chemical conversion film samples includes the following steps:

[0052] (1) Sample preparation: Magnesium alloy chemical conversion film samples with different structures and adhesion were obtained by controlling the formulation components, pH, and treatment time. In order to ensure the correspondence between the samples, the samples used for pull-out test and the samples used for tear test need to be surface treated in the same batch.

[0053] (2) Tear Test: The sample covered with tear-resistant tape 3 (100mm long × 50mm wide) was tested for coating peeling before and after tearing. Figure 2 As shown, the percentage of remaining coating area after peeling is calculated using the following formula:

[0054]

[0055] Where W is the adhesive width of the tear-off tape 3, L is the adhesive length of the tear-off tape 3, and S... ‘ The remaining unpeeled area of ​​the coating was tested using Image Pro software.

[0056] (3) Pull-out test: The adhesion (bonding strength) of the coating was tested using a Posi-test adhesion tester. The procedure was as follows: An aluminum alloy ingot was bonded to a magnesium alloy chemical conversion film sample using epoxy adhesive. After curing at room temperature for 24 hours, excess adhesive around the ingot was cut off using a cutter. Then, the pull-out equipment sleeve was fitted onto the aluminum alloy ingot, the equipment was turned on, and the pull-out test was performed. After the magnesium alloy chemical conversion film sample detached from the aluminum alloy ingot, the adhesion value was recorded.

[0057] (4) Figure 3 This shows the correlation between tear and pull-out test data for magnesium alloy chemical conversion coating samples. Figure 3 As can be seen, the percentage of the remaining coating area after the sample is peeled off is basically positively correlated with the adhesion value tested by the pull-out method. Considering the fluctuations in the test itself, the degree of dispersion is acceptable. After fitting, the relationship between adhesion and the percentage of the remaining coating area is: Y = 6.25x + 1.8, where Y is the adhesion value (MPa) and x is the percentage of the remaining inorganic coating area.

[0058] Example 3: Relationship between tear area and pull-out test of magnesium alloy micro-arc oxidation coating sample

[0059] The relationship between the tear area and the adhesion tested in the pull-out test of magnesium alloy micro-arc oxidation coating samples includes the following steps:

[0060] (1) Sample preparation: Magnesium alloy micro-arc oxidation film samples with different structures and adhesion were obtained by controlling the formulation components, pH, and treatment time. In order to ensure the correspondence between the samples, the samples used for pull-out test and the samples used for tear test need to be surface treated in the same batch.

[0061] (2) Tear test: The sample covered with a 100mm long × 50mm wide tear-resistant tape 3 was tested. The percentage of the remaining coating area after tearing was calculated according to the following formula:

[0062]

[0063] Where W is the adhesive width of the tear-off tape 3, L is the adhesive length of the tear-off tape 3, and S... ‘ The remaining unpeeled area of ​​the coating was tested using Image Pro software.

[0064] (3) Pull-out test: The adhesion (bonding strength) of the coating was tested using a Posi-test adhesion tester. The procedure was as follows: An aluminum alloy ingot was bonded to the magnesium alloy micro-arc oxidation coating sample using epoxy adhesive. After curing at room temperature for 24 hours, excess adhesive around the ingot was cut off using a cutter. Then, the pull-out equipment sleeve was fitted onto the aluminum alloy ingot, the equipment was turned on, and the pull-out test was performed. After the magnesium alloy micro-arc oxidation coating sample separated from the aluminum alloy ingot, the adhesion value was recorded.

[0065] (4) Figure 4 The correlation between tear and pull-out test data for magnesium alloy micro-arc oxidation coating samples. Figure 4 As can be seen, the percentage of remaining coating area after tearing is basically positively correlated with the adhesion value tested by the pull-out method. Considering the fluctuations in the test itself, the degree of dispersion is acceptable. After fitting, the relationship between adhesion and the percentage of remaining coating area is: Y = 12.0x + 5.9, where Y is the adhesion value (MPa) and x is the percentage of remaining inorganic coating area.

[0066] It will be readily understood by those skilled in the art that the above-described advantageous methods can be freely combined and superimposed without conflict. The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A method for testing the adhesion of inorganic coatings on magnesium alloys, characterized in that, Includes the following steps: Tape application: The tear-off tape (3) is applied to the surface of the inorganic coating (2) of the magnesium alloy sample to be tested, with one end of the tear-off tape (3) extending to form a tear section (301). Sample positioning: Fix the magnesium alloy sample to be tested so that the surface of the inorganic coating (2) is at an angle of 90 degrees ± 2 degrees to the gravity direction of the magnesium alloy sample to be tested; Dynamic peeling: An instantaneous impact load is applied to the tearing tape (3) through the tearing section (301), causing the tearing tape (3) to fall off and the inorganic coating (2) to partially peel off; Adhesion calculation: Based on the percentage of the remaining area of ​​the inorganic coating, the adhesion value of the inorganic coating of the magnesium alloy sample to be tested is calculated by using a pre-established correspondence model between the percentage of the remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method. The dynamic peeling includes: connecting the tearing section (301) to the counterweight (6) through the flexible connecting line (5), releasing the counterweight (6) to allow it to fall freely, causing the tearing tape (3) to fall off, and causing the inorganic coating (2) to be partially peeled off through the tearing of the tearing tape (3). The method for establishing the pre-established correspondence model between the percentage of remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method includes: By adjusting the preparation process parameters of the inorganic coating (2), multiple batches of magnesium alloy samples with different inorganic coating adhesion values ​​were obtained. Tear tests and pull-out tests were performed on magnesium alloy samples from the same batch with the same preparation process parameters. The percentage of the remaining inorganic coating area was obtained through the tear test, and the adhesion value was obtained through the pull-out test. The tear test included: covering the inorganic coating surface of the magnesium alloy sample with a peel strength of 20 N / cm to 50 N / cm, with one end of the peel tape extending to form a tear segment; fixing the magnesium alloy sample so that the inorganic coating surface and the gravity direction of the magnesium alloy sample were at an angle of 90 degrees ± 2 degrees; applying an instantaneous impact load to the peel tape through the tear segment, causing the peel tape to detach and the inorganic coating to partially peel off, and calculating the percentage of the remaining inorganic coating area after tearing. Establish a model relating the percentage of remaining area of ​​the inorganic coating to the adhesion value tested by the pull-out method; When the inorganic coating (2) is a chemical conversion coating, the corresponding relationship model between the percentage of the remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method is: Y = 6.25x + 1.8, where Y is the adhesion value in MPa and x is the percentage of the remaining area of ​​the inorganic coating.

2. The method for testing the adhesion of inorganic coatings on magnesium alloys according to claim 1, characterized in that, The inorganic coating (2) is a micro-arc oxidation coating or a chemical conversion coating.

3. The method for testing the adhesion of inorganic coatings on magnesium alloys according to claim 1 or 2, characterized in that, The thickness of the inorganic coating is 5μm to 50μm.

4. The method for testing the adhesion of inorganic coatings on magnesium alloys according to claim 1 or 2, characterized in that, The peel strength of the tear-off tape (3) is 20N / cm to 50N / cm.

5. The method for testing the adhesion of inorganic coatings on magnesium alloys according to claim 1 or 2, characterized in that, The sample positioning includes fixing the magnesium alloy sample to be tested onto the support frame (9) using clamps (7) and bolts (8).

6. The method for testing the adhesion of inorganic coatings on magnesium alloys according to claim 1 or 2, characterized in that, The mass of the counterweight (6) is 5kg±12.5g. The initial position of the counterweight (6) is 5cm±1cm away from the magnesium alloy sample to be tested along the direction of gravity. The size of the tear-off tape (3) covering the magnesium alloy sample to be tested is 100mm long × 50mm wide. The length of the flexible connecting line (5) is 1.5m±0.05m.

7. The method for testing the adhesion of inorganic coatings on magnesium alloys according to claim 1 or 2, characterized in that, When the inorganic coating (2) is a micro-arc oxidation coating, the corresponding relationship model between the percentage of the remaining area of ​​the inorganic coating and the adhesion value tested by the pull-out method is: Y=12.0x+5.9, where Y is the adhesion value in MPa and x is the percentage of the remaining area of ​​the inorganic coating.

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