Preparation method of chromic acid anodized film layer capable of resisting damp-heat test

Abstract

The invention discloses a preparation method of a chromic acid anodized film layer for resisting a damp-heat test, which comprises the following steps: (1) carrying out chromic acid anodizing treatment on an aluminum alloy part, and controlling the technological parameters as follows: the voltage is 45-50V, the time is 53-58 minutes, and the thickness of the film layer reaches 4-5 microns; and (2) the part subjected to chromic acid anodizing is clamped in a suspension mode in a damp-heat test, and direct contact between the part and a contact surface is avoided. The two parameters of voltage and time required in the chromic acid anodizing process are controlled through a control variable method, the optimal chromic acid anodizing parameter is explored, and a chromic acid anodizing film layer meeting the requirement of a damp-heat test is achieved. The optimal clamping mode is obtained by further changing the clamping mode of the part in the damp heat test process.

Description

Technical Field

[0001] The invention relates to the technical field of chromic acid anodizing, and in particular to a method for preparing a chromic acid anodizing film layer resistant to wet heat test. Background Art

[0002] In the actual production of chromic acid anodizing, the corrosion resistance of the chromic acid anodizing oxide film is reduced due to the influence of various factors such as chromic acid anodizing electrolyte, process parameters, and sealing components. If these problems are not solved in time, the corrosion resistance of components and the whole machine will be reduced, and the service life of the whole machine will be shortened.

[0003] Most aluminum alloy chromic acid anodizing film resistance tests usually conduct salt spray tests, and there are very few experiments to verify the chromic acid anodizing film's resistance to moisture and heat. However, moisture and heat conditions are a harsh environment that often exists, so they cannot be ignored. By exploring new chromic acid anodizing parameters, the thickness of the chromic acid anodizing film that can resist moisture and heat conditions has been achieved. Summary of the invention

[0004] In order to solve the over-corrosion phenomenon of the film layer after chromic acid anodizing of aluminum alloy during the wet heat test, the present invention provides a method for preparing a chromic acid anodizing film layer resistant to wet heat test. Through the test, the qualified rate of chromic acid anodizing production of aluminum alloy reaches 100%.

[0005] The technical solution adopted by the present invention is a method for preparing a chromic acid anodized film layer resistant to wet heat test, comprising the following steps: (1) Aluminum alloy parts are anodized with chromic acid, and the process parameters are controlled as follows: voltage 45-50V, time 53-58 minutes, so that the film thickness reaches 4-5μm; (2) The chromic acid anodized parts should be mounted in a hanging manner during the wet heat test to avoid direct contact between the parts and the contact surface. Preferably, in step (1), the process parameters of chromic acid anodizing are preferably a voltage of 45 V and a time of 55 minutes.

[0006] Preferably, the hanging method in step (2) is to hang the parts by perforating cotton thread so that the parts are in a non-contact state in the wet heat test chamber.

[0007] Preferably, the thickness of the film layer is determined by taking an average value after multiple thickness gauge measurements, the thickness of the film layer after repair is 4-5 μm, and the film layer loss after the damp heat test is 1-2 μm.

[0008] Preferably, the damp heat test condition is a temperature of 30-60°C, a test cycle of 24 hours, and 10 cycles.

[0009] An aluminum alloy part prepared by a method for preparing a chromic acid anodized film layer resistant to a wet heat test, wherein the chromic acid anodized film layer has no corrosion, blistering or cracking after the wet heat test.

[0010] The beneficial effects of the present invention are: by controlling the two parameters of voltage and time required in the chromic acid anodizing process through the control variable method, the optimal chromic acid anodizing parameters are explored, and the chromic acid anodizing film layer that meets the requirements of the wet heat test is achieved. Further, by changing the clamping method of the parts during the wet heat test, the most effective clamping method is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a diagram of the damp heat test conditions.

[0012] Figure 2 Schematic diagram of the hanging position of the test piece during the wet heat test.

[0013] Figure 3 It is the thickness of chromic acid anodizing film before rework, after rework and after wet heat test. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0015] The above object of the present invention is achieved by the following technical solution, comprising the following steps: Step (a), measuring the film thickness before rework.

[0016] Step (ii): designing chromic acid anodizing test parameters and conducting chromic acid anodizing test.

[0017] Step (iii), measuring the chromic acid anodizing parameters after repair.

[0018] Step (iv) placing the repaired parts into the wet heat test chamber using different mounting methods.

[0019] Step (V): Conduct a damp heat test.

[0020] Step (six): observe the chromic acid anodized film after the wet heat test and draw conclusions.

[0021] Embodiment: The electric explosion valve of a certain product with an aluminum alloy grade of 2A12 is measured for size and film thickness according to the final inspection. The part numbers are 2304228, 2304229, 2304230, and 2304231 respectively; the parts are subjected to film removal treatment until the film layer is completely removed; the parts are re-anodized with chromic acid, and different parameters are used for production. It is tentatively determined to use 45V and (50-60)min for production, and the test is divided into 3 groups. Group 1, 45V 50min, part number 2304228; Group 2, 45V 55min, part number 2304229; Group 3, 45V 60min, part numbers 2304230 and 2304231.

[0022] This test was mainly conducted on Electric Explosion Valve 1 and Electric Explosion Valve 2. Both products showed different degrees of corrosion. There were corrosion spots on the appearance of the parts after the wet heat test of Electric Explosion Valve 1 and the appearance of the parts after the wet heat test of Electric Explosion Valve 2. The initial judgment was that the film layer of the parts had problems, resulting in failure of the wet heat test.

[0023] The test piece was subjected to a damp heat test. The test was conducted on all four test pieces. Among them, test pieces No. 2304228, 2304229, and 2304230 were tested in a hanging manner, and product No. 2304231 was tested in a flat manner. During the test, it was necessary to mark them properly and avoid confusion. The damp heat test conditions are shown in Figure 1 , 0-2h temperature rises from 30℃ to 60℃, during this process, the relative humidity is maintained at ≥85%; 2-8h temperature is maintained at 60℃, during this process, the relative humidity is maintained at 95%; 8-16h temperature drops from 60℃ to 30℃, during this process, the relative humidity is maintained at ≥85%; 16-24h temperature is maintained at 30℃, during this process, the relative humidity is maintained at 95%. This process is one cycle, and the damp heat test is completed after ten cycles. The test piece is considered to have passed the test if there is no coating bulge, cracking, blistering, or corrosion. After the parts entered the damp heat test, the appearance of the 4 test pieces met the requirements after the damp heat test, and the damp heat test was passed.

[0024] From the above, it can be seen that the chromic acid anodizing film of aluminum alloy showed no corrosion phenomenon after 10 days of wet heat test under the conditions of 45V, 50min, 45V, 55min and 45V, 60min. According to the selection principle of chromic acid anodizing process parameters in QJ450B "Metal Coating Thickness Series and Selection Principles", the lower limit of parameters can be selected, and the chromic acid anodizing parameters of aluminum alloy can be controlled at (45~50)V, (53~58)min.

[0025] When the parts are placed flat for wet heat test, it can be clearly seen that obvious marks appear on the surface, indicating that the parts are beginning to show obvious film loss. Compared with the parts with the same chromic acid anodizing parameters, the effect of the wet heat test by hanging is better than the horizontal test. The parts are hung in the wet heat box by perforating cotton thread. The specific hanging method is as follows: Figure 2 As shown. In the subsequent damp heat test, it is best to suspend the parts in the damp heat box to ensure that the parts are in the damp heat environment of the damp heat box and at the same time, minimize contact with other objects. Avoid using a horizontal tray for damp heat testing. Under high humidity conditions, after a certain period of time, the contact surface between the part and the tray will be equivalent to being immersed in water, which will increase the severity of the damp heat test. The standard only requires a damp heat environment, and the parts can be suspended to meet the requirements. The film thickness of the test piece is measured. The thickness of the film on the surface of the part is measured with a thickness gauge before rework, after rework and after the damp heat test. The measurement results are shown in Table 1 and Figure 3 shown.

[0026] From Table 1, it can be seen that before the parts are repaired, the film thickness after the original process parameters are basically about 3μm, while the film thickness after the refined process parameters is basically (4~5)μm. The test piece is subjected to a 10-day damp heat test, and the film layer of the parts is basically consumed between (1~2)μm after the damp heat test. If the original process parameters are used, the film thickness of individual parts may be about 2μm due to current distribution and other reasons. During the damp heat test, corrosion will occur at the local points where the film is weak.

[0027] Table 1 Thickness of chromic acid anodized film before rework, after rework and after wet heat test (μm) The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a chromic acid anodized film layer resistant to wet heat test, characterized in that: The following steps are involved: (1) Aluminum alloy parts are anodized with chromic acid, and the process parameters are controlled as follows: voltage 45-50V, time 53-58 minutes, so that the film thickness reaches 4-5μm; (2) The chromic acid anodized parts should be mounted in a hanging manner during the wet heat test to avoid direct contact between the parts and the contact surface.

2. The preparation method according to claim 1, characterized in that: In the step (1), the process parameters of chromic acid anodizing are preferably a voltage of 45 V and a time of 55 minutes.

3. The preparation method according to claim 1, characterized in that: The hanging method in step (2) is to hang the parts by perforating cotton threads so that the parts are in a non-contact state in the wet heat test chamber.

4. The preparation method according to claim 1, characterized in that: The thickness of the film layer is determined by taking an average value after multiple thickness gauge measurements. The thickness of the film layer after repair is 4-5 μm, and the film layer loss after the wet heat test is 1-2 μm.

5. The preparation method according to claim 1, characterized in that: The damp heat test conditions are a temperature of 30-60°C, a test cycle of 24 hours, and 10 cycles.

6. An aluminum alloy part prepared according to any one of claims 1 to 5, characterized in that: The chromate anodized film showed no corrosion, blistering or cracking after the wet heat test.

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