CN115127886A - Internal stress testing method for aluminum alloy sheet - Google Patents

Abstract

The invention relates to the field of stress testing of aluminum alloy materials, in particular to an internal stress testing method of an aluminum alloy sheet. The method carries out the evaluation of the internal stress by measuring the bending value of the sheet, can accurately reflect the size of the internal stress value of the sheet, is convenient for visually carrying out the transverse comparison of the internal stress size between the aluminum alloy sheets, and thus evaluates the quality of the aluminum alloy sheets.

Description

A kind of internal stress test method of aluminum alloy sheet

technical field

The invention relates to the field of stress testing of aluminum alloy materials, in particular to an internal stress testing method of aluminum alloy sheets.

Background technique

Aluminum alloy sheets have many excellent properties such as easy processing, low density, high corrosion resistance, low thermal expansion coefficient, high specific strength, and outstanding strain capacity, so they are widely used in aerospace, navigation, road transportation, construction and cutting-edge weapons. and other fields.

Internal stress refers to the stress that remains inside the elastic material after the external load is removed. It is characterized by the formation of a balanced force system in the object, that is, it obeys the static conditions. Internal stress is a common inherent stress in the aluminum alloy sheet, which is caused by the uneven volume change of the macroscopic or microscopic structure inside the material. The rolling deformation conditions of the aluminum alloy sheet are symmetrical to the neutral plane, and the farther away from the neutral plane and the part close to the roll, the more serious the deformation occurs. Therefore, the internal stress distribution of the aluminum alloy sheet has the following characteristics: the internal stress of the sheet only changes with the thickness of the sheet. , and is uniformly distributed in any plane parallel to the mid-plane of the plate, and symmetrically distributed along the mid-plane of the plate, parallel to the mid-plane of the plate.

The existence of internal stress has an important influence on the strength, fatigue characteristics and surface strength of the parts, and also causes harmful effects such as dimensional deviation of the parts and deformation during use. Therefore, the study of internal stress is of great significance in controlling machining deformation and ensuring the strength and surface quality of parts.

At present, traditional residual stress measurement methods can be divided into two types: mechanical release measurement method and non-destructive measurement method. The mechanical release measurement method is to separate or cut the components with internal stress from the component to release the stress, and measure the change of the strain to obtain the residual internal stress. This method needs to cause a certain degree of damage to the workpiece, and it is even more difficult for thin plates. operation, and new residual stress will be introduced, mainly including drilling method, ring core method, split cutting method, etc. The peeling method needs to remove the material layer by layer, and measure the residual stress value in combination with other test methods. Since the stress is released in the process of removing the material, the measured value is not accurate. Non-destructive measurement methods are physical detection methods, mainly including X-ray diffraction method, neutron diffraction method, scanning electron acoustic microscopy, electron speckle interferometry, ultrasonic method and magnetic method. These methods have no damage to the tested parts, but the equipment required is expensive. X-ray methods and neutron diffraction methods cannot accurately determine the internal stress of severely textured thin plates and have a shallow detection range. Magnetic methods are only suitable for ferromagnetic materials. s material.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned problems in the prior art, the present invention provides a method for testing the internal stress of an aluminum alloy sheet, which can accurately evaluate the internal stress of the aluminum alloy sheet. In this method, a rectangular plate is used for the determination of residual stress. When a part of the material parallel to the neutral plane is removed, the original stress equilibrium state will be destroyed, and the specimen will undergo redistribution of internal stress and bending deformation. The present invention has been completed based on the evaluation of the magnitude of the internal stress of the thin plate by measuring the warpage value of the aluminum alloy thin plate.

In order to achieve the above object, the present invention provides the following technical solutions:

A method for testing internal stress of an aluminum alloy sheet, comprising the following steps:

Step 1): prepare a rectangular aluminum alloy test piece, the length direction x of the test piece is parallel to the rolling direction, and one of the surfaces formed by the length direction x and width direction y of the test piece is denoted as the front side, and the side opposite to the front side is designated as the front side. The other side is negative;

Step 2): coating protective glue on the other five surfaces of the test piece except the negative in step 1);

Step 3): configure alkaline corrosion solution;

Step 4): soak the test piece coated with the protective glue in step 2) in the alkaline etching solution of step 3) to carry out chemical corrosion, so that the thickness of the test piece is reduced to half of the original thickness;

Step 5): post-processing the thinned specimen in step 4);

Step 6): Measure the warpage value of the post-processed specimen in Step 5).

According to an embodiment of the present invention, in the step 1), the aspect ratio of the rectangular aluminum alloy specimen is 3:1 to 6:1, such as 3:1, 4:1, 5:1 or 6:1, The length ranges from 90mm to 120mm, such as 90mm, 100mm, 110mm or 120mm, and the thickness ranges from 1.0mm to 4.0mm, such as 1.0mm, 2.0mm, 3.0mm or 4.0mm.

According to an embodiment of the present invention, in the step 1), the rectangular aluminum alloy test piece is a rectangular aluminum alloy test piece obtained by leveling and reducing internal stress through a stretching process after solution heat treatment.

According to an embodiment of the present invention, in the step 1), the rectangular aluminum alloy test piece is preferably a rectangular aluminum alloy test piece that has undergone pretreatment such as cleaning and decontamination.

According to an embodiment of the present invention, in the step 2), the coating method of the protective glue is to use a soft brush to evenly and completely coat the front of the test piece and the four surfaces in the thickness direction z of the test piece, and the natural air-drying time is 24h～48h.

According to an embodiment of the present invention, in the step 2), the thickness of the protective glue is 0.2 mm˜0.3 mm.

According to an embodiment of the present invention, in the step 2), the protective glue is a protective glue known in the art that can prevent the aluminum alloy from being corroded by an alkaline corrosion solution, and is exemplarily selected from HX-150 protective glue.

According to an embodiment of the present invention, in the step 3), the composition ratio of the alkaline corrosion solution is sodium hydroxide: 200-300 g/L, benzotriazole and its derivatives: 5-20 g/L; The alkaline corrosion solution can realize the rapid thinning treatment of the aluminum alloy specimen, so that it can complete the uneven distribution of stress as soon as possible to generate uniform deformation, and further increase the test accuracy of the warpage value.

According to the embodiment of the present invention, in the step 3), preferably, the composition ratio of the alkaline corrosion solution is sodium hydroxide: 200-300g/L (such as 200g/L, 210g/L, 220g/L, 230g/L) /L, 240g/L, 250g/L, 260g/L, 270g/L, 280g/L, 290g/L or 300g/L), benzotriazole and its derivatives: 5～20g/L (such as 5g/L) /L, 6g/L, 7g/L, 8g/L, 9g/L, 10g/L, 11g/L, 12g/L, 13g/L, 14g/L, 15g/L, 16g/L, 17g/L , 18g/L, 19g/L or 20g/L).

According to an embodiment of the present invention, in the step 3), the temperature of the alkaline etching solution is 80-90°C.

According to an embodiment of the present invention, the step 4) specifically includes: vertically immersing the test piece in step 1) in an alkaline corrosion solution, recording the remaining thickness of the sheet every 5 minutes, and when the thickness is close to 1/2 Shorten the time of each measurement to 1-3min until the thickness reaches 1/2, and record the total corrosion time t; according to the corrosion rate, corrode the test piece coated with protective glue in step 2) to a thickness equal to 1/2 of the total thickness of the test piece. 1/2, the corrosion rate of the test piece coated with protective glue in step 2) should be 2t.

According to an embodiment of the present invention, in the step 4), the specimens are placed vertically (perpendicular to the ground) in the solution.

According to an embodiment of the present invention, in the step 5), the post-processing includes the steps of removing the protective glue and light-emitting, wherein the deformation of the test piece will be further increased after the protective glue is removed, which is beneficial to obtain more accurate warpage of the test piece value to increase the accuracy of the internal stress test method for aluminum alloy sheets. In addition, because the aluminum alloy will produce black ash after contacting with the alkaline corrosion solution, the dirty surface is not conducive to subsequent testing.

Wherein, the light emitting is, for example, using 500 mL/L nitric acid (w=65%) light emitting solution at room temperature of 25±5° C. to emit light for 30-60 s until the surface of the test piece is bright.

According to an embodiment of the present invention, in the step 6), the method of determining the warpage value is as follows: the test piece is placed on a flat surface with the convex side up, the width direction y of the test piece is parallel to the plane and attached to the plane, and the convexity of the convex surface is measured. The highest distance from the highest point to the plane is the warpage value, for example, please refer to Figure 2.

According to an embodiment of the present invention, in the step 6), the measurement method of the warpage value is specifically: measuring the length L of the test piece along the x direction after bending, and using a vernier caliper to measure the L/2 position of the test piece and the distance L/2 The vertical distance from the horizontal plane at the 1/2 position of the specimen width to the specimen at 1 mm and 2 mm in total, the maximum value of which is taken as the warpage value of the specimen.

According to the embodiment of the present invention, the thickness measurement method of the test piece is specifically: at the position of 1/2 of the width of the test piece, 5 points on the length direction x of the test piece are selected on average, and the thickness of the 5 points is measured with a vernier caliper. The average value is the thickness of the test piece.

According to an embodiment of the present invention, at least three samples of each type of aluminum alloy sheet are taken to perform the above steps, and the average value of the warpage values of the three samples is used as the warpage value of this type of samples for internal stress evaluation.

According to an embodiment of the present invention, the test method includes the following steps:

Step 1: Prepare an internal stress test specimen, which specifically includes: taking a rectangular aluminum alloy sheet without obvious defects as an internal stress test specimen, with an aspect ratio of 3:1 to 6:1, a length range of 90mm to 120mm, and a thickness range of 90mm to 120mm. 1.0mm～4.0mm, to clean the test piece, first rub the front and back sides of the test piece with a clean cloth for 30s to 60s in flowing water with a flow rate of 0.5m/s to remove obvious stains, and then use absorbent cotton dipped in alcohol The ball is wiped clean and subjected to 20 kHz ultrasonic vibration for 5 min to 10 min in a mixed solution of acetone and water with a volume ratio of 1:2. 40m/s;

Step 2: Apply protective glue to the corresponding position on the test piece described in Step 1, which specifically includes: stirring the protective glue with a stirring rod at 120 r/min for 1 min to stir the protective glue evenly, and using a soft brush on the front of the test piece and the thickness of the test piece The four surfaces in the direction z are evenly coated with protective glue with a thickness of 0.2mm ~ 0.3mm and air-dried for 24h ~ 48h until the protective glue is completely combined with the surface of the sheet;

Step 3: configure an alkaline corrosion solution, which specifically includes: the composition ratio of the alkaline corrosion solution is: sodium hydroxide: 200-300 g/L, benzotriazole and its derivatives: 5-20 g/L; solution temperature The temperature is 80-90°C; weigh out the experimental materials on the balance, put them into a beaker, slowly add deionized water and stir to make a uniform solution, and perform heating and heat preservation operations in a constant temperature water bath; the volume of the container used should be greater than 1L, the height should be greater than the length of the test piece to ensure that the test piece can be completely immersed in the solution;

Step 4: vertically immerse the specimen treated in step 2 in an alkaline corrosion solution to corrode to a certain thickness, specifically including: conducting a pre-test to determine the corrosion rate of the specimen, The remaining thickness of the thin plate is recorded every 5 minutes when the specimen is soaked in the alkaline corrosion solution obtained in step 3. When the thickness is close to 1/2, the time for each measurement is shortened to 1-3 minutes until the thickness reaches 1/2, and the total thickness is recorded. Corrosion time t; according to the corrosion rate, corrode the thin plate to a thickness of 1/2 of the total thickness of the test piece, and the corrosion time for the test piece coated with the protective glue obtained in step 2 is 2t;

Step 5: Post-processing the specimen treated in Step 4, which specifically includes: taking out the specimen corroded to 1/2 of the total thickness of the specimen, rinsing it in flowing water with a flow rate of 0.5m/s, and peeling off the protective glue by hand , and then emit light in 500mL/L nitric acid (w=65%) light-emitting solution at room temperature of 25±5℃ for 30-60s until the surface of the test piece is bright, rinse with flowing water with a flow rate of 0.5m/s, and then blow it with a hair dryer. Dry, the wind speed is 20m/s～40m/s;

Step 6: Measure the warpage value of the specimen processed in Step 5, which specifically includes: placing the specimen obtained in Step 5 on a horizontal plane with the convex side up, and the width direction y of the specimen is parallel to the plane and fits with the plane. . The vertical distance from the horizontal plane to the highest point of the convex surface is measured as the warpage value of the test piece.

Compared with the prior art, the beneficial effects of the present invention are:

Compared with the destructive testing method, this method will not cause material damage and yield due to mechanical damage, which will affect the measurement effect. Compared with the mechanical damage method, the corrosion method is used to remove the thickness of the test piece, which is easy to control and can be applied to thin plates. Internal stress measurement. The non-destructive testing method has no damage to the test piece, but the cost is high, the equipment required is expensive, and it is difficult to accurately measure the thin plate with complex texture, while this method is easy to operate, requires less experimental equipment, and does not require expensive The large-scale equipment can accurately evaluate the internal stress of aluminum alloy thin materials. In addition, other methods all have complicated calculation processes, and are dedicated to determining the value of the internal stress of the alloy, which cannot be compared intuitively. However, this method evaluates the internal stress by measuring the warpage value of the bending of the sheet, which can accurately reflect the size of the internal stress value of the sheet, and is convenient to intuitively compare the internal stress between the aluminum alloy sheets, so as to evaluate the aluminum alloy. The quality of the sheet.

In addition, the test method of the present invention simulates the deformation of aviation aluminum alloy sheet parts after weight reduction treatment by single-sided milling, the test method of the present invention can be combined with the actual engineering application, and the internal stress level of the tested aluminum alloy sheet It can measure the accuracy of the parts after milling, predict the deformation, and provide a basis for the setting of forming parameters, and at the same time measure the internal stress level of the aluminum alloy sheet to screen materials with small deformation for application.

Description of drawings

Figure 1 is a schematic diagram of the coating position of the protective adhesive.

Figure 2 is a schematic diagram of the warpage value of the specimen after corrosion.

FIG. 3 is a schematic structural diagram of the warpage value of the specimen after corrosion in Example 1. FIG.

Detailed ways

The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following examples are only for illustrating and explaining the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the intended protection scope of the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

Example 1:

(1) Take a rectangular 2024 aluminum alloy sheet as the internal stress test specimen, the aspect ratio is 6:1, the length is 120mm, and the thickness is 1.24mm, and the surface formed by the length direction x and width direction y of the test piece is marked. It is the front side, and the opposite side of the front side is recorded as the back side, and the longitudinal direction x of the test piece is parallel to the rolling direction. To clean the test piece, first rub the front and back sides of the test piece with a clean cloth for 30 s in flowing water of 0.5m/s to remove obvious stains, and then wipe it with a absorbent cotton ball dipped in alcohol and in a volume ratio of 1:1: 2 in a mixed solution of acetone and water for 5 min at 20 kHz ultrasonic vibration, then take out and rinse with alcohol and deionized water in turn, and dry with a hair dryer at a wind speed of 20 m/s.

(2) Stir the HX-150 protective glue with a stirring rod at 120r/min for 1min, and then use a soft brush to evenly and completely coat HX-150 on the front of the test piece described in step (1). 150 protective glue and air-dried naturally for 24h, the thickness of the coated protective glue is 0.2mm, as shown in Figure 1, until the protective glue is completely combined with the surface of the board.

(3) Prepare an alkaline corrosion solution in a beaker, first weigh out 210g of sodium hydroxide, benzotriazole: 10g/L on an electronic balance, place the above-mentioned experimental materials in the beaker and slowly add a small amount of deionized water and Stir to completely dissolve the experimental materials, and then slowly add deionized water to 1L while stirring. The stabilized uniform corrosion solution was placed in a constant temperature water bath for heating and heat preservation to 85°C.

(4) The test piece treated in step (1) is immersed vertically in the solution prepared in step (3) for corrosion. First, a pre-test is performed to determine the corrosion rate of the sample. The test piece treated in step (1) is in step (1). 3) The remaining thickness of the thin plate was recorded every 5 minutes of immersion in the corrosion solution. When the thickness was close to 1/2, the time for each measurement was shortened to 2 minutes, and the remaining 1/2 of the thickness of the specimen was obtained when the specimen was corroded for 18 minutes. Afterwards, the specimen treated in step (2) was etched for 36 minutes at one time (the corrosion thickness was 0.62 mm).

(5) Post-processing the test piece treated in step (4), take out the test piece corroded to 1/2 of the total thickness of the test piece, rinse it in flowing water with a flow rate of 0.5m/s, and peel off the test piece by hand The coated protective glue, then emit light in 500mL/L nitric acid (w=65%) light-emitting solution at room temperature of 25±5℃ for 35s until the surface of the test piece is bright, rinse it with flowing water with a flow rate of 0.5m/s, and then use it. Dry with a hair dryer at a wind speed of 20m/s.

(6) The sample obtained in step (5) is placed on a flat surface with its convex surface upward, and the width direction y of the sample is parallel to and attached to the flat surface. According to the schematic diagram of warpage value in Figure 2, measure the maximum distance from the highest point of the convex surface to the plane, measure the length L of the specimen along the x-direction after bending, and use a vernier caliper to measure the L/2 position of the specimen and 1mm and 2mm from L/2. The vertical distance from the horizontal plane at the 1/2 position of the specimen width to the specimen, the maximum value is taken as the warpage value of the specimen, and the warpage value is 2.85mm, as shown in Figure 3 Show.

Examples 2-3, Comparative Examples 1-4

The other operations are the same as in Example 1, except that the thickness of the aluminum alloy sheet is different (only the thickness is different, the composition is exactly the same), and the composition of the alkaline corrosion solution is different, as shown in Table 1 below:

Table 1 Plate thickness, composition of alkaline etching solution and warpage value of Examples 1-3 and Comparative Examples 1-4

The results of the examples and comparative examples show that the present invention removes 1/2 of the thickness of the aluminum alloy sheet by chemically corroding the aluminum alloy sheet to bend the sheet. size. In summary, the present invention provides a simple internal stress evaluation method, which solves the difficult problem of internal stress evaluation of aluminum alloy sheets, and can accurately compare the quality of aluminum alloy sheets horizontally without complicated calculations. The internal stress evaluation and comparison of thin plates has important reference value.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. The internal stress testing method of the aluminum alloy sheet is characterized by comprising the following steps of:

step 1): preparing a rectangular aluminum alloy test piece, wherein the length direction x of the test piece is parallel to the rolling direction, one surface formed in the length direction x and the width direction y of the test piece is marked as a positive surface, and the other surface opposite to the positive surface is a negative surface;

step 2): coating protective glue on the other five surfaces of the test piece in the step 1) except the negative side;

step 3): preparing an alkaline corrosion solution;

step 4): soaking the test piece coated with the protective adhesive in the step 2) in the alkaline corrosion solution in the step 3) for chemical corrosion, so that the thickness of the test piece is reduced to half of the original thickness;

step 5): carrying out post-treatment on the thinned test piece in the step 4);

step 6): and measuring the warpage value of the test piece after the post-treatment in the step 5).

2. The internal stress test method of the aluminum alloy sheet according to claim 1, wherein in the step 1), the length-width ratio of the rectangular aluminum alloy test piece is 3:1 to 6:1, the length range is 90mm to 120mm, and the thickness range is 1.0mm to 4.0 mm.

3. The method for testing the internal stress of the aluminum alloy sheet as recited in claim 1, wherein in the step 1), the rectangular aluminum alloy test piece is obtained by performing solution heat treatment, and then flattening and reducing the internal stress by using a stretching process.

4. The internal stress test method of the aluminum alloy sheet according to claim 1, wherein in the step 2), the thickness of the protective glue is 0.2mm to 0.3 mm.

5. The internal stress test method of the aluminum alloy sheet according to claim 1, wherein in the step 3), the alkaline etching solution comprises the following components: 200-300 g/L, benzotriazole and derivatives thereof: 5 to 20 g/L.

6. The internal stress testing method of the aluminum alloy sheet according to claim 1, wherein the step 4) specifically comprises the following steps: vertically soaking the test piece obtained in the step 1) in an alkaline corrosion solution, recording the residual thickness of the thin plate every 5min of soaking, shortening the time of each measurement to 1-3 min when the thickness approaches 1/2 until the thickness reaches 1/2, and recording the total corrosion time t; the test piece coated with the protective adhesive in the step 2) is corroded to 1/2 the thickness of the total thickness of the test piece according to the corrosion speed, and the corrosion speed of the test piece coated with the protective adhesive in the step 2) is 2 t.

7. The internal stress testing method of the aluminum alloy sheet according to claim 1, wherein in the step 5), the post-treatment comprises the steps of removing the protective glue and the light extraction.

8. The internal stress test method of an aluminum alloy sheet according to claim 1, wherein in the step 6), the warpage value is determined by: the test piece is placed on a plane with the convex surface facing upwards, the width direction y of the test piece is parallel to the plane and is attached to the plane, and the maximum distance from the highest point of the convex surface to the plane is measured, namely the warping value.

9. The internal stress testing method of the aluminum alloy sheet according to claim 8, wherein in the step 6), the warpage value is measured by: and measuring the length L of the bent test piece along the x direction, measuring the vertical distances from the L/2 position of the test piece and the horizontal planes which are 1mm and 2mm away from the L/2 position and are positioned at 5 positions of the test piece width 1/2 to the test piece by using a vernier caliper, and taking the maximum value as the warpage value of the test piece.

10. The internal stress testing method of an aluminum alloy sheet according to claim 1, comprising the steps of:

the method comprises the following steps: preparing an internal stress test piece, which specifically comprises: taking a rectangular aluminum alloy sheet without obvious defects as an internal stress test piece, wherein the length-width ratio is 3: 1-6: 1, the length range is 90-120 mm, the thickness range is 1.0-4.0 mm, cleaning the test piece, firstly lightly rubbing the front and back surfaces of the test piece with clean wiping cloth in flowing water at the flow rate of 0.5m/s for 30-60 s respectively to remove obvious stains, then wiping the test piece with a degreasing cotton ball dipped with alcohol, carrying out 20kHz ultrasonic oscillation in a mixed solution of acetone and water at the volume ratio of 1:2 for 5-10 min, then taking out, sequentially washing the test piece with alcohol and deionized water, and blowing the test piece by using a blowing cylinder, wherein the air speed is 20-40 m/s;

step two: coating a protective adhesive at a corresponding position on the test piece in the first step, specifically comprising: stirring the protective glue by a stirring rod at 120r/min for 1min, uniformly stirring the protective glue, uniformly coating the protective glue with the thickness of 0.2-0.3 mm on the front surface of the test piece and four surfaces of the test piece in the thickness direction z by using a soft brush, and naturally air-drying the protective glue for 24-48 h until the protective glue is completely combined with the surface of the plate;

step three: preparing an alkaline etching solution, which specifically comprises the following steps: the alkaline corrosion solution comprises the following components in percentage by weight: sodium hydroxide: 200-300 g/L, benzotriazole and derivatives thereof: 5-20 g/L; the temperature of the solution is 80-90 ℃; weighing the experimental materials on a balance, putting the materials into a beaker, slowly adding deionized water and stirring the materials to prepare a uniform solution, and heating and preserving heat in a constant-temperature water bath box; the volume of the adopted container is more than 1L, and the height is more than the length of the test piece, so that the test piece can be completely soaked in the solution;

step four: vertically soaking the test piece treated in the step two in an alkaline corrosion solution to be corroded to a certain thickness, and specifically comprising the following steps: performing a pre-test to determine the corrosion speed of the test piece, soaking the test piece which is not coated with the protective adhesive and is obtained in the step one in the alkaline corrosion solution obtained in the step three for 5min to record the residual thickness of the thin plate, shortening the time of each measurement to 1-3 min when the thickness approaches 1/2 until the thickness reaches 1/2, and recording the total corrosion time t; corroding the thin plate to 1/2 with the thickness being the total thickness of the test piece according to the corrosion speed, wherein the corrosion time of the test piece coated with the protective adhesive obtained in the step two is 2 t;

step five: and D, carrying out post-treatment on the test piece treated in the step four, and specifically comprising the following steps of: taking out 1/2 test pieces corroded to the total thickness of the test pieces, washing the test pieces in flowing water with the flow rate of 0.5m/s, removing protective glue by hands, then, brightening the test pieces by 500mL/L nitric acid (w is 65%) in brightening solution at the room temperature of 25 +/-5 ℃ for 30-60 s until the surfaces of the test pieces are bright, washing the test pieces by the flowing water with the flow rate of 0.5m/s, and then, drying the test pieces by a blowing cylinder at the wind speed of 20 m/s-40 m/s;

step six: measuring the warpage value of the test piece processed in the fifth step, and specifically comprising the following steps: and D, placing the sample obtained in the fifth step on a horizontal plane with the convex surface upward, enabling the width direction y of the sample to be parallel to the plane and attached to the plane, and measuring the vertical distance from the horizontal plane to the highest point of the convex surface to be the warping value of the test piece.

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