A color metallographic interference film coating solution for pure aluminum and aluminum alloy and a testing method thereof

Abstract

The application discloses a kind of pure aluminum and aluminum alloy color metallographic interference film coating liquid and its testing method, coating liquid includes 2%~5% sodium fluoroborate, 0.03%~0.15% nitric acid, 10%~20% anhydrous ethanol, the rest is distilled water;Its testing method includes the steps of mechanical grinding, electrolytic polishing, anodic coating, metallographic observation.The coating liquid provided by the application has the advantages of less acid, low cost and safe operation, and the testing method has the advantages of bright color, high display contrast and obvious grain differentiation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallographic structure detection and analysis, and more particularly to a pure aluminum and aluminum alloy color metallographic interference film coating solution and a testing method thereof. BACKGROUND

[0002] Metallographic microstructure refers to the composition of the same chemical properties, crystal structure and physical properties in metals and alloys, mainly including solid solution, metal compound and pure substance. Metallographic observation is the most common, most intuitive and most economical method for studying the internal organizational structure of metal materials, predicting and analyzing metal properties, and analyzing metal failure and damage.

[0003] The color metallographic technology of aluminum and aluminum alloy belongs to interference film metallography. Interference film metallography is a method of forming an interference film with different thicknesses on the surface of a polished metal sample through physical etching or electrochemical methods to increase the contrast between components through thin film interference. The principle is to use the reflected light on the surface of the thin film and the reflected light on the lower surface (sample surface) to produce interference phenomena, so that the color is generated. The composition, structure and properties of each phase in the alloy or the different grain orientations result in different interference film thicknesses, different interference wavelengths, and different colors. Compared with the black and white metallographic structure of aluminum alloy prepared by the traditional Keller reagent (2.5 mL HNO3+2.5 mL HCl+1.0 mL HF+95 mL H2O), especially for pure aluminum and Al-Mg alloy which is not easy to corrode, color metallographic observation is helpful for distinguishing phase boundaries or grain boundaries.

[0004] Color metallographic observation first mechanically pre-polishes the metal sample, electrolytically polishes and anodically coats the film, and finally observes the organizational morphology on a polarized microscope with a compensator. At present, the anodic coating solution disclosed in the prior art, such as: "a method for displaying the color metallographic structure of pure aluminum" disclosed in Chinese patent 201410223760.9, "a preparation method of 6061 aluminum alloy metallographic sample" disclosed in Chinese patent 201911308913.9, and "a new type of aluminum alloy anodic coating solution and a testing method thereof" disclosed in Chinese patent 202110889884.0, contains a large amount of fluoroboric acid, sulfuric acid, phosphoric acid or hydrofluoric acid, which has strong corrosivity, and the safety of the experiment cannot be guaranteed. Moreover, the prior art solutions are often only suitable for one or two specific components of aluminum alloy. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a pure aluminum and aluminum alloy color metallographic interference film coating solution and a testing method thereof to solve the problem of small application range of the existing color metallographic interference film coating solution.

[0006] To solve the above technical problems, the technical solutions adopted by the present application are as follows.

[0007] A pure aluminum and aluminum alloy color metallographic interference film coating solution comprises 2-5% sodium fluoroborate, 0.03-0.15% nitric acid, 10-20% anhydrous ethanol, and the rest is distilled water.

[0008] The application further discloses a testing method of the pure aluminum and aluminum alloy color metallographic interference film coating solution.

[0009] S1, mechanical grinding: the sample is pre-ground by using water sandpaper with 240 mesh, 400 mesh, 800 mesh and 1200 mesh in sequence, and the sample is ground only along one direction on each mesh sandpaper; when the scratches are uniformly distributed in the same direction, the next mesh sandpaper is replaced and ground along the 90° direction of the previous direction; and the grinding is sequentially performed until the 1200 mesh sandpaper is used.

[0010] S2, electrolytic polishing: an electrolytic polishing solution with a high-chloric acid and ethanol volume ratio of 1:10 is prepared in an electrolytic tank, the electrolytic tank is placed in a water bath containing an ice-water mixture for electrolytic temperature control; the sample ground in the step S1 is placed in the electrolytic polishing solution, and is electrolytically polished under a voltage of 10-20 V and a current of 0.1-0.2 A / cm2 for 10-15 seconds; and then the sample is cleaned by using ultrasonic cleaning with water and alcohol to obtain a mirror surface effect.

[0011] S3, anodic coating: a coating solution containing 2-5% sodium fluoroborate, 0.03-0.15% nitric acid, 10-20% anhydrous ethanol and the rest distilled water is prepared; the sample prepared in the step S2 is placed in the coating solution, an anodic coating voltage of 15-30 V, a coating current of 0.12-0.35 A / cm2 and a coating time of 30-90 seconds are set, then the sample is washed with alcohol and dried by using cold air;

[0012] S4, metallographic observation: a polarizing microscope with a lambda compensator is used, a polarizer and an analyzer are inserted into the light path, and the color metallographic structure is observed by focusing.

[0013] In the further optimized technical solution, the water sandpaper in the step S1 is silicon carbide water sandpaper.

[0014] In the further optimized technical solution, the sample in the step S1 is a pure aluminum or aluminum alloy sample with a length, width and height less than 25*25*10 mm.

[0015] In the further optimized technical solution, the cathode material used in the electrolytic process in the step S2 is any one of a stainless steel plate, a nickel plate and a lead plate.

[0016] In the further optimized technical solution, when the coating solution is prepared in the step S3, the anhydrous ethanol is first mixed with the distilled water, then the sodium fluoroborate is added and stirred to dissolve, and finally the nitric acid is added.

[0017] Further optimization technical solutions, the step S3 in the film process used cathode material is any one of stainless steel plate, nickel plate, lead plate.

[0018] Further optimization technical solutions, the step S4 in the film process used cathode material is any one of stainless steel plate, nickel plate, lead plate.

[0019] Due to the adoption of the above technical scheme, the technical progress achieved by the present application is as follows.

[0020] The pure aluminum and aluminum alloy color metallographic interference film coating solution provided by the present application greatly reduces the amount of acid compared to the prior art formula, contains only 0.03% to 0.15% nitric acid, has the advantages of low acid consumption, low cost and safe operation. The coating solution and the test method provided by the present application are suitable for color metallography of pure aluminum and all commercial aluminum alloys, have strong universality, and the color metallography detected has the advantages of bright color, high display contrast and obvious grain differentiation. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The pure aluminum color metallography prepared in Example 1 in the present application;

[0022] Figure 2 The Al-7Si-Mg alloy color metallography prepared in Example 2 in the present application;

[0023] Figure 3 The Al-5Cu-1.5Mg alloy color metallography prepared in Example 3 in the present application;

[0024] Figure 4 The Al-9Zn-2.5Mg-1.8Cu alloy color metallography prepared in Example 4 in the present application. DETAILED DESCRIPTION

[0025] A pure aluminum and aluminum alloy color metallographic interference film coating solution, comprising 2% to 5% sodium fluoroborate, 0.03% to 0.15% nitric acid, 10% to 20% anhydrous ethanol, and the rest is distilled water.

[0026] A test method for a pure aluminum and aluminum alloy color metallographic interference film coating solution, comprising the following steps:

[0027] S1. Mechanical Grinding: Take a pure aluminum or aluminum alloy sample with a length × width × height of less than 25 × 25 × 10 mm. Use 240 grit, 400 grit, 800 grit, and 1200 grit silicon carbide wet sandpaper to pre-grind the sample. Grind the sample in only one direction on each grit of sandpaper. When the scratches are evenly distributed in the same direction, change to the next grit of sandpaper and grind in the direction of the previous pass at a 90° angle. Continue grinding until the 1200 grit sandpaper is used.

[0028] S2. Electrolytic Polishing: Prepare an electrolytic polishing solution with a perchloric acid to ethanol volume ratio of 1:10 in an electrolytic cell, using stainless steel plate, nickel plate, or lead plate as the cathode material. Place the electrolytic cell in a water bath containing an ice-water mixture for temperature control during electrolysis. Place the sample mechanically ground in step S1 into the electrolytic polishing solution and electrolytically polish for 10–20V and 0.1–0.2A / cm² for 10–15 seconds. Then, ultrasonically clean with water and alcohol to obtain a mirror-like surface.

[0029] S3. Anode Coating: Prepare a coating solution containing 2%–5% sodium fluoroborate, 0.03%–0.15% nitric acid, 10%–20% anhydrous ethanol, and the remainder being distilled water. First, mix the ethanol and distilled water, then add the sodium fluoroborate and stir to dissolve it, and finally add the nitric acid. Place the sample prepared in step S2 into the coating solution, using any one of stainless steel plate, nickel plate, or lead plate as the cathode material. Set the anode coating voltage to 15–30V, the coating current to 0.12–0.35A / cm², and the coating time to 30–90 seconds. Then rinse the sample with alcohol and dry it with cold air.

[0030] S4. Metallographic observation: Using a polarizing microscope with a λ compensation filter, insert the polarizer and analyzer into the optical path and observe the colored metallographic structure by focusing. If the light source of the metallographic microscope is warm light, insert a blue filter into the optical path of the microscope before observation.

[0031] The following will combine Figures 1 to 4 The present invention will be further described in detail with reference to specific embodiments.

[0032] Example 1:

[0033] A coating solution for colored metallographic interference films of pure aluminum and aluminum alloys comprises 4% sodium fluoroborate, 0.05% nitric acid, 10% anhydrous ethanol, and the remainder being distilled water.

[0034] The test method for the coating solution of pure aluminum and aluminum alloy colored metallographic interference film includes the following steps:

[0035] S1, mechanical grinding: an industrial pure aluminum (A00) is wire cut into a 15x15x10mm cuboid sample, and the sample is mechanically roughened by using 240 mesh, 400 mesh, 800 mesh and 1200 mesh water sandpaper in turn. Considering that pure aluminum is soft, the grinding machine speed is selected below 200r / min, and after polishing, the surface is washed with clean water and dried with alcohol.

[0036] S2, electrolytic polishing: prepare an electrolytic polishing solution with a volume ratio of perchloric acid to ethanol of 1:10, pour it into an electrolytic tank, use stainless steel as the cathode and the sample as the anode, connect the circuit, electrolyze at a voltage of 15V and a current density of 0.2A / cm 2 for 15 seconds, ultrasonically clean the surface in alcohol to remove the surface acid solution, and dry to obtain a mirror-like bright surface.

[0037] S3, anodic film: mix 10% anhydrous ethanol, 85.95% distilled water, then add 4% sodium fluoroborate, stir to dissolve, then add 0.05% nitric acid and mix evenly to prepare an interference film coating solution. Pour the solution into an electrolytic tank, use stainless steel as the cathode and the sample as the anode, connect the circuit, anodize at a voltage of 20V and a current density of 0.2A / cm 2 for 60 seconds, and after the film is formed, spray alcohol on the surface of the sample and dry.

[0038] S4, metallographic observation: the sample treated as described above can be clearly observed under a polarized light microscope with a lambda compensator, and the color metallographic structure of the pure aluminum can be clearly observed, as shown in Figure 1 .

[0039] Example 2:

[0040] A color metallographic interference film coating solution for pure aluminum and aluminum alloy, comprising 3% sodium fluoroborate, 0.1% nitric acid, 15% anhydrous ethanol, and the rest being distilled water.

[0041] The test method of the pure aluminum and aluminum alloy color metallographic interference film coating solution comprises the following steps:

[0042] S1, mechanical grinding: an Al-Mg-Si alloy is wire cut into a 15x15x10mm cuboid sample, and the composition is Al-7Si-Mg (mass fraction), and the alloy material is as-cast. First, the sample is mechanically roughened by using 240 mesh, 400 mesh, 800 mesh and 1200 mesh water sandpaper in turn. The grinding machine speed is selected to be 300-400r / min, and after polishing, the surface is washed with clean water and dried with alcohol.

[0043] S2, electrolytic polishing: prepare electrolytic polishing solution with the volume ratio of perchloric acid and ethanol being 1:10, pour into the electrolytic tank, use stainless steel as cathode, sample as anode, connect the circuit, electrolyze for 15 seconds under the voltage of 20V and the current density of 0.2A / cm 2 , remove the surface acid solution by ultrasonic cleaning in alcohol, and get the surface like mirror bright and clean after blowing dry.

[0044] S3, anodic film: mix 15% anhydrous ethanol and 81.9% distilled water, then add 3% sodium fluoroborate, 0.1% nitric acid, and mix uniformly to prepare the interference film coating solution. Pour the solution into the electrolytic tank, use stainless steel as cathode, sample as anode, connect the circuit, anodic film for 70 seconds under the voltage of 25V and the current density of 0.2A / cm 2 , spray alcohol on the surface of the sample after the anodic film is completed and blow dry.

[0045] S4, metallographic observation: the sample treated above can be clearly observed under the polarized microscope with compensation flake, and the color metallographic structure of the Al-7Si-Mg alloy in casting state can be clearly observed, as shown in Figure 2 .

[0046] Example 3

[0047] A pure aluminum and aluminum alloy color metallographic interference film coating solution, comprising 5% sodium fluoroborate, 0.05% nitric acid, 20% anhydrous ethanol, and the rest is distilled water.

[0048] The test method of the pure aluminum and aluminum alloy color metallographic interference film coating solution, comprising the following steps:

[0049] S1, mechanical grinding: the Al-Cu-Mg alloy is processed into a 15x15x10mm cuboid sample by wire cutting, and the composition is Al-5Cu-1.5Mg(mass fraction), and the alloy is uniformly treated at 505℃ for 2h. First, the sample is mechanically roughened by using 240 mesh, 400 mesh, 800 mesh and 1200 mesh water sandpaper in sequence. The grinding machine speed is selected to be 300-500r / min, the sample is washed with water after grinding, and the surface is sprayed with alcohol and dried.

[0050] S2, electrolytic polishing: prepare electrolytic polishing solution with the volume ratio of perchloric acid and ethanol being 1:10, pour into the electrolytic tank, use stainless steel as cathode, sample as anode, connect the circuit, electrolyze for 15 seconds under the voltage of 20V and the current density of 0.15A / cm 2 , remove the surface acid solution by ultrasonic cleaning in alcohol, and get the surface like mirror bright and clean after blowing dry.

[0051] S3, anodic film: 20% of anhydrous ethanol, 74.95% of distilled water are mixed, then 5% of sodium fluoroborate is added, after stirring and dissolving, 0.05% of nitric acid is added and uniformly mixed to configure an interference film coating solution. The solution is poured into an electrolytic cell, with stainless steel as the cathode and the sample as the anode, and the circuit is connected, and an anodic film is formed under the condition of 20V voltage and 0.25A / cm 2 current density for 70 seconds, and after the film forming is completed, alcohol is sprayed on the surface of the sample and dried.

[0052] S4, metallographic observation: the sample treated by the above method can be clearly observed under a polarized microscope with a compensator, and the color metallographic structure of the Al-5Cu-1.5Mg homogenization treatment can be clearly observed, as shown in Figure 3 , the color metallographic structure is clear.

[0053] Example 4:

[0054] A pure aluminum and aluminum alloy color metallographic interference film coating solution, comprising 3% of sodium fluoroborate, 0.05% of nitric acid, 20% of anhydrous ethanol, and the rest of distilled water.

[0055] The test method of the pure aluminum and aluminum alloy color metallographic interference film coating solution, comprising the following steps:

[0056] S1, mechanical grinding: the Al-Zn-Mg-Cu alloy is processed into a 15x15x10mm cuboid sample by wire cutting, and the composition is Al-9Cu-2.5Mg-1.8Cu(mass fraction), and the alloy material is in a cast state. First, the sample is mechanically rough ground by using 240 mesh, 400 mesh, 800 mesh and 1200 mesh water sandpaper in sequence. The grinding machine speed is selected to be 300-500r / min, and after grinding, the sample is washed with water and the surface is dried by spraying alcohol.

[0057] S2, electrolytic polishing: the electrolytic polishing solution is prepared by mixing perchloric acid and ethanol in a volume ratio of 1:10, poured into an electrolytic cell, with stainless steel as the cathode and the sample as the anode, and the circuit is connected, and electrolytic polishing is performed under the condition of 20V voltage and 0.15A / cm 2 current density for 15 seconds, and the surface is cleaned by ultrasonic cleaning in alcohol to remove the surface acid solution, and then dried to obtain a mirror-like bright and clean surface.

[0058] S3, anodic film: 20% of anhydrous ethanol, 74.95% of distilled water are mixed, then 5% of sodium fluoroborate is added, after stirring and dissolving, 0.05% of nitric acid is added and uniformly mixed to configure an interference film coating solution. The solution is poured into an electrolytic cell, with stainless steel as the cathode and the sample as the anode, and the circuit is connected, and an anodic film is formed under the condition of 20V voltage and 0.25A / cm 2 current density for 70 seconds, and after the film forming is completed, alcohol is sprayed on the surface of the sample and dried.

[0059] S4, metallographic observation: the sample after the above treatment can be clearly seen in the polarizing microscope with a compensator Al-9Cu-2.5Mg-1.8Cu alloy casting color metallographic structure, as shown in Figure 4 Color metallographic structure clear.

[0060] In summary, the pure aluminum and aluminum alloy color metallographic interference film coating solution provided by the present application greatly reduces the amount of acid, only 0.03% to 0.15% nitric acid is needed; therefore, the coating solution provided by the present application has the advantages of low acid consumption, low cost and safe operation. The test method of the present application can be used for pure aluminum and all commercial aluminum alloys, and the obtained sample can be observed by polarizing microscope to obtain clear, bright color, and obvious grain differentiation color metallographic structure, greatly improving the problem that the traditional method is only suitable for one or two specific component aluminum alloys.

Claims

1. A color metallographic interference film coating solution for pure aluminum and aluminum alloys, characterized in that The components are: 2-5% sodium fluoroborate, 0.03-0.15% nitric acid, 10-20% anhydrous ethanol, and the rest is distilled water.

2. A test method for a color metallographic interference film coating solution for pure aluminum and aluminum alloys, characterized in that, The method comprises the following steps: S1, mechanical grinding: sequentially use 240 mesh, 400 mesh, 800 mesh, 1200 mesh water sandpaper to pre-grind the sample, the sample is only polished in one direction on each mesh sandpaper, when the scratches are evenly distributed in the same direction, change the next mesh sandpaper and polish in the 90° direction of the previous direction, sequentially polish until the 1200 mesh sandpaper is finished; S2, electrolytic polishing: an electrolytic polishing solution with a volume ratio of perchloric acid to ethanol of 1:10 is prepared in an electrolytic cell, the electrolytic cell is placed in a water bath containing an ice-water mixture for temperature control; the sample mechanically polished in step S1 is placed in the electrolytic polishing solution, and electrolytic polishing is performed at a voltage of 10-20 V, a current of 0.1-0.2 A / cm 2 , and for 10-15 seconds, and then the sample is cleaned with water and alcohol by ultrasonic cleaning to obtain a mirror surface. S3, anodic film: the sample prepared in step S2 is placed into a film coating solution, an anodic film voltage of 15-30 V, a film coating current of 0.12-0.35 A / cm 2 , a film coating time of 30-90 seconds, then the sample is washed with alcohol and dried with cold air; the film coating solution has the following components: 2%-5% sodium fluoroborate, 0.03%-0.15% nitric acid, 10%-20% anhydrous ethanol, and the rest is distilled water; S4, metallographic observation: use a polarized microscope with a lambda compensator, insert the polarizer and analyzer into the light path, and observe the color metallographic structure by focusing. 3.The testing method of the color metallographic interference film coating solution for pure aluminum and aluminum alloy according to claim 2, characterized in that: The water sandpaper in the step S1 is silicon carbide water sandpaper. 4.The testing method of the color metallographic interference film coating solution for pure aluminum and aluminum alloy according to claim 2, characterized in that: The sample in the step S1 is a pure aluminum or aluminum alloy sample with a length, width and height less than 25*25*10 mm. 5.The testing method of the color metallographic interference film coating solution for pure aluminum and aluminum alloy according to claim 2, characterized in that: The cathode material used in the electrolysis process in the step S2 is any one of a stainless steel plate, a nickel plate and a lead plate.

6. The testing method of the color metallographic interference film coating solution for pure aluminum and aluminum alloy according to claim 2, characterized in that: In the step S3, when preparing the coating solution, first mix ethanol and distilled water, then add sodium fluoroborate and stir to dissolve, and finally add nitric acid. 7.The testing method of a pure aluminum and aluminum alloy color metallographic interference film coating solution according to claim 2, characterized in that: The cathode material used in the coating process in the step S3 is any one of a stainless steel plate, a nickel plate and a lead plate. 8.The testing method of a pure aluminum and aluminum alloy color metallographic interference film coating solution according to claim 2, characterized in that: The lambda compensator in the step S4 needs to be placed after the polarizer, and if the light source of the metallographic microscope used is warm light, a blue filter is inserted into the light path of the microscope before observation.

Images