CN111595770A - A kind of test method of aluminum alloy open circuit potential - Google Patents

Abstract

The invention provides a method for testing the open circuit potential of an aluminum alloy. The method adopts a mixed solution of NaCl and acetic acid as a testing system, uses an electrochemical workstation, and performs testing by an open circuit potential method (OCP). The method has high stability and good repeatability, is suitable for detecting the open circuit potential (natural potential) of aluminum and aluminum alloy ingots, cast-rolled plates, plates, strips, and foils, and is particularly suitable for aluminum alloys with a thickness greater than 0.2 mm.

Description

A kind of test method of aluminum alloy open circuit potential

technical field

The invention belongs to the technical field of metal open-circuit potential testing, in particular to a method for testing the open-circuit potential of aluminum alloys, which is suitable for the detection of the open-circuit potential (natural potential) of aluminum and aluminum alloy ingots, cast-rolled sheets, plates, strips, and foils. It is suitable for aluminum alloys with a thickness greater than 0.2mm, especially for aluminum alloys with a thickness greater than 1.0mm.

Background technique

Spontaneous potential is an important thermodynamic parameter for corroding metal electrodes. It is of great significance in the study of metal corrosion behavior and analysis of corrosion process, and is widely used in anti-corrosion engineering technology. Potentiometric measurement is an important means to evaluate the effect of cathodic protection, and to detect and monitor the corrosion state of protected structures.

At present, the test method of aluminum alloy open circuit potential adopts the potentiometer method in the ASTM-G69-12 test standard, which has certain defects, as follows:

1. The use of potentiometer mentioned in ASTM-G69-12 to add 9±1mL of 30% H ₂ O ₂ to 58.5±0.1g of NaCl per liter of aqueous solution as a test solution to detect the open circuit potential (natural potential) of aluminum alloys should be When the detected sample thickness is less than 0.2mm, the potential fluctuation is greater than 10mv, and the reproducibility is poor.

2. In the method of using a potentiometer to add 9±1mL 30% H ₂ O ₂ to 58.5±0.1g NaCl per liter of aqueous solution as a test solution mentioned in ASTM-G69-12 to detect the open circuit potential (natural potential) of aluminum alloys, in In practice, it is found that when the thickness of the sample to be tested is greater than 0.20mm, especially when the thickness of the sample is greater than 1.0mm, the potential curve at the beginning of the test needs a period of stabilization time, generally 10-15min, and the overall test time is 30min or 60min, which is more efficient. It is not conducive to production applications. It is necessary to improve the method and develop an efficient test method to further shorten the test time and improve the efficiency.

Therefore, it is necessary to develop a test method for the open circuit potential of aluminum alloys that can compensate for the above-mentioned defects.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the inventor has developed a test method for the open circuit potential of aluminum alloys (CN110455881A), but the test method is mainly aimed at aluminum alloy samples with a thickness of less than 0.2 mm, and for the thickness greater than 0.2 mm, especially the thickness greater than 0.2 mm. 1.0mm aluminum alloy sample, the test efficiency is still unsatisfactory, and strong acid is used in this technical solution. In view of this, the inventor has conducted intensive research on the composition of the test solution, using acetic acid instead of hydrochloric acid, to provide a test method for open circuit potential of aluminum alloys with a thickness greater than 0.2 mm, especially a thickness greater than 1.0 mm.

The present invention provides an efficient test method for the open circuit potential of aluminum alloys, which uses an electrochemical workstation to test by open circuit potential (OCP). It also has good stability and repeatability.

Specifically, the method for testing the open circuit potential of the aluminum alloy includes the following steps:

1) Preparation of test samples;

2) Preparation of the test system: prepare a mixed solution of NaCl and acetic acid as the test solution, wherein the concentration of acetic acid is 0.00875mol/L-0.02625mol/L;

3) Potential test: The open-circuit potential test of the sample to be tested is carried out by using the electrochemical workstation using the potential-time open-circuit potential method.

More specifically, the method for testing the open circuit potential of the aluminum alloy includes the following steps:

1) Preparation of test samples;

2) Preparation of the test system: prepare a mixed solution of NaCl and acetic acid as the test solution, and the concentration of acetic acid is 0.00875mol/L-0.02625mol/L;

3) Potential test: The open-circuit potential test of the sample to be tested is carried out by using the electrochemical workstation using the potential-time open-circuit potential method.

4) Data processing: Take the average value of all test values as the open circuit potential value of the aluminum alloy.

The test method mentioned in the ASTM-G69-12 standard is: potentiometer in 58.5±0.1g/L NaCl plus 9±1mL 30% H ₂ O ₂ solution to test the open circuit potential of aluminum alloy, the H ₂ O ₂ used is due to It is weakly acidic, so the surface potential of the aluminum alloy needs a period of time to stabilize the potential curve; and the acetic acid used in the present invention is stronger than hydrogen peroxide, easy to ionize H ⁺ , and can quickly balance the potential of the aluminum alloy sample in the solution. Stable potential-time curve. Compared with CN110455881A, the use of acetic acid instead of strong acid hydrochloric acid can quickly obtain a stable potential, because the pH value of the test solution is about 3.0, and the overall surface of the aluminum alloy is passivated. Although there is pitting corrosion on the surface, However, due to the thick aluminum alloy, the composition of the corrosion site is relatively uniform, and the potential curve does not fluctuate too much. Therefore, it is suitable for samples with a thickness greater than 0.20mm, and the stable potential can be quickly obtained.

Specifically, the preparation of the test sample includes:

Sand the sample with water sandpaper in a flowing water bath;

Wash the polished test samples with acetone and anhydrous ethanol in turn, and dry them naturally;

Retain the detection area: select a certain area of the detection area and the length of the clamping end, and seal other non-detection areas;

Air dry or blow dry in cold air.

More specifically, the preparation of the test sample includes:

Cut aluminum alloy samples of appropriate size;

Use water sandpaper with a model of 320~2000# to sand the sample in the flowing water tank;

Wash the polished test samples with acetone and anhydrous ethanol in turn, and dry them naturally;

Retain the detection area: select a certain area of the detection area and the length of the clamping end, and other non-detection areas are coated and sealed;

Air dry or blow dry in cold air.

Specifically, the area of the detection zone and the test solution maintain the following relationship: every 100mm ² of the test area ensures at least 100mL of the test solution. In order to ensure that the test sample is fully contacted with the test liquid, the accuracy of the test is increased.

According to some embodiments provided by the present invention, the area of the detection area is 10×10 mm ² or 15×15 mm ² , and the length of the clamping end is 10-20 mm.

According to some embodiments provided by the present invention, the test sample is washed again with acetone, absolute ethanol and deionized water before being tested.

According to some embodiments provided by the present invention, the mass fraction of NaCl in the test solution is 2-10%, for example: 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% , 10%, etc.

In some embodiments, the mass fraction of NaCl in the test solution is 4-8%.

According to some embodiments provided by the present invention, in the test solution, the concentration of acetic acid is 0.00875mol/L-0.02625mol/L, for example: 0.00875mol/L, 0.0088mol/L, 0.0090mol/L, 0.0095mol/L , 0.0100mol/L, 0.0105mol/L, 0.0110mol/L, 0.0115mol/L, 0.012mol/L, 0.0125mol/L, 0.0130mol/L, 0.0135mol/L, 0.0140mol/L, 0.0145mol/L , 0.0150mol/L, 0.0155mol/L, 0.0160mol/L, 0.0165mol/L, 0.0170mol/L, 0.0175mol/L, 0.0180mol/L, 0.0185mol/L, 0.0190mol/L, 0.0195mol/L , 0.0200mol/L, 0.0205mol/L, 0.0210mol/L, etc.

In some embodiments, in the test solution, the concentration of acetic acid is 0.014-0.021 mol/L.

According to some embodiments provided by the present invention, the pH of the test solution is 2.0-4.0, for example: 2.0, 2.5, 3.0, 3.5, 4.0, and the like.

Specifically, the preparation of the test solution includes: weighing an appropriate amount of NaCl solid in a 1L beaker, adding 500mL deionized water to dissolve, then transferring it to a 1L volumetric flask to make the volume, and then adding acetic acid to the solution to prepare acetic acid NaCl solution, wherein the concentration of acetic acid is 0.00875mol/L-0.02625mol/L, and the mass fraction of NaCl is 2-10%.

Specifically, AB glue or silica gel can be used for the coating and sealing.

Choose natural drying or cold air drying to avoid drying too fast and cracking of the sealing layer.

Specifically, during the potential test, a three-electrode system was used, one of a saturated calomel electrode, a silver/silver chloride electrode, and a mercury/mercury oxide electrode was selected as the reference electrode, and the platinum electrode was used as the auxiliary electrode to test The sample is the working electrode.

Preferably, the test temperature is 20-25°C, such as 20°C, 21°C, 22°C, 23°C, 24°C, 25°C.

Preferably, the test is carried out with stirring at a rotational speed of 60-120 r/min (eg 60 r/min, 70 r/min, 80 r/min, 90 r/min, 100 r/min, 110 r/min, 120 r/min, etc. Wait). By stirring, the adhering air bubbles generated on the surface of the test sample can be eliminated, and the test liquid can be kept uniform.

During the test, the detection surface of the sample detection part and the liquid junction of the reference electrode should be completely immersed in the test solution to ensure the accuracy of the test.

The used reference electrode, auxiliary electrode, test tank, rotor, working electrode, etc., need to be cleaned with deionized water.

The data processing method is determined according to the fluctuation of the test potential curve. Generally, the fluctuation is less than 3mv within 3min, which is stable. Preferably, during data processing, the average value of all data is selected as the open circuit potential value of the test sample, for example: the test time is 15min, and the average value of all data obtained in 15min is taken as the test result; the test time is 10min, and the average value of all data obtained in 10min is taken as the test result. Test Results. The electrochemical workstation is not particularly limited, and the electrochemical workstation of Princeton, Chenhua or other manufacturers can be selected.

Preferably, at least two samples are repeatedly measured, the average value of all the measured values of each sample is taken as the open circuit potential value of the sample, and the average value of the last two samples is taken as the open circuit potential value of the sample. If the potential values of the two samples are different If it is greater than 5mv, more test samples should be added, and the average value should be taken.

The test method provided by the present invention is suitable for the detection of the open circuit potential (natural potential) of aluminum and aluminum alloy ingots, cast-rolled sheets, plates, strips, and foils, and is especially suitable for aluminum alloys with a thickness greater than 0.2 mm, especially suitable for Aluminum alloy larger than 1.0mm.

Compared with the prior art, the present invention has the following technical effects:

Compared with the ASTM-G69-12 standard, the test method provided by the present invention can obtain a stable potential-time curve in a short time for aluminum alloy samples with a thickness greater than 0.20 mm, that is, a potential-time curve with very small fluctuation ( less than 3mv), and the original test time is reduced from 30min to less than 10min, and has high reproducibility.

Description of drawings

Figure 1: Potential-time curves obtained from the tests of Example 1 and Comparative Example 1; and

Figure 2: Potential-time graph obtained from the test of Example 2.

Detailed ways

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All patents and publications referred to herein are incorporated by reference in their entirety. The term "comprising" or "including" is an open-ended expression, ie, it includes what is specified in the present invention, but does not exclude other aspects.

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples, but those skilled in the art will understand that the following examples are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. If the specific conditions are not indicated in the examples, the conditions described in the description or the conventional conditions or the conditions suggested by the manufacturer are used. The reagents or instruments used without the manufacturer's indication are conventional products that can be purchased from the market.

Example 1

Test sample: thickness of 1.50mm, annealed state, 3XXX series and 4XXX series double-layer composite aluminum plate, its 3XXX series alloy potential measurement.

Sample preparation: Use a cutter to cut a 12×2mm sample, and use 320#, 600#, 1000# sandpaper to polish the unmarked end of the sample to smooth the surface, then wash the sample with acetone and anhydrous ethanol in turn, and dry it naturally. Seal the non-working surface with silicone, leave the working surface 10×10mm ² and the clamping end about 20mm long, and let it dry naturally. Then, use acetone, anhydrous ethanol, and deionized water to wash it again in order to be tested.

Test solution preparation: Weigh 50.00g of NaCl solid in a 1L beaker, add 500mL of deionized water to dissolve, then use a pipette or pipette to take 1mL of acetic acid into the solution, and then transfer it to a 1L volumetric flask to make up the volume , prepared into the liquid to be tested, wherein the concentration of acetic acid is 0.0175mol/L, and the mass fraction of NaCl is 5%;

Testing instrument: Shanghai Chenhua CHI660E electrochemical workstation; three-electrode system: saturated calomel electrode as reference electrode, sample as working electrode, platinum electrode as auxiliary electrode;

Measurement steps:

(1) Clean each electrode, rotor and a 250mL special test beaker;

(2) Add 200 mL of test solution to the beaker, use the sample as the working electrode, the platinum electrode as the auxiliary electrode, and the saturated calomel electrode as the reference electrode to build a three-electrode measurement system;

(3) The temperature of the system to be tested is maintained at 23°C, and the stirring speed is 100r/min;

(4) under the above-mentioned measuring conditions, select open-circuit potential method with Shanghai Chenhua CHI660E electrochemical workstation to carry out electrochemical open-circuit potential test on the sample to be tested, and the test time is 30min;

(5) Repeat the measurement of at least two samples, take the average value of all the values of each measured data as the open circuit potential value of the sample, and the average value of the last two samples as the open circuit potential value of the sample, if the potential value of the two samples is different If it is greater than 5mv, more test samples should be added, and the average value should be taken. The test results are shown in Table 1.

The potential-time curves obtained by the three samples are shown in Figure 1, a is the first sample, b is the second sample, and c is the third sample.

Comparative Example 1 was tested with ASTM-G69-12 standard

Test sample: thickness of 1.50mm, annealed state, 3XXX series and 4XXX series double-layer composite aluminum plate, its 3XXX series alloy potential measurement.

Sample preparation: Use a cutter to cut a 12×2mm sample, and use 320#, 600#, 1000# sandpaper to polish the unmarked end of the sample to smooth the surface, then wash the sample with acetone and anhydrous ethanol in turn, and dry it naturally. Seal the non-working surface with silicone, leave the working surface 10×10mm ² and the clamping end about 20mm long, and let it dry naturally. Then, use acetone, anhydrous ethanol, and deionized water to wash it again in order to be tested.

Test solution preparation: Weigh 58.5g of NaCl solid in a 1L beaker and add 500mL of deionized water to dissolve, then move it to a 1L volumetric flask to make up the volume, and then add 10mL of H ₂ O ₂ to the solution to prepare a test solution;

Test instrument: potentiometer; three-electrode system: saturated calomel electrode as reference electrode, sample as working electrode, platinum electrode as auxiliary electrode;

Measurement steps:

(1) Clean each electrode, rotor and a 250mL special test beaker;

(2) Add 200 mL of test solution to the beaker, use the sample as the working electrode, the platinum electrode as the auxiliary electrode, and the saturated calomel electrode as the reference electrode to build a three-electrode measurement system;

(3) The temperature of the system to be tested is maintained at 23°C, and the stirring speed is 100r/min;

(4) under the above-mentioned measuring conditions, carry out electrochemical test on the sample to be tested with HE-104A type potentiometer, and the test time is 30min;

(5) According to the test results, the same batch of samples was repeatedly tested for three samples, and the potential average value was processed according to the ASTM-G69-12 standard. The test results are shown in Table 1.

The potential-time curves obtained by the three samples are shown in Figure 1, where d is the first sample, e is the second sample, and f is the third sample.

Table 1

From the test comparison of Fig. 1 and Table 1, it can be seen that the a, b, and c potential curves obtained by the technical testing method of the present invention can quickly reach stability, and the e, d, and f potential curves obtained in the ASTM-G69-12 method are at the beginning stage. The fluctuation is large, and it takes a period of time to obtain a stable potential. The test method of the invention can quickly obtain the potential-time stability curve, the test time can be shortened, and the potential value is equivalent to the value obtained by the ASTM-G69-12 standard.

Example 2

Test sample: thickness of 0.27mm, annealed state, four-layer composite aluminum plate of 1XXX series, 3XXX series and 4XXX series, and the potential measurement of 1050 aluminum alloy in the middle layer.

Sample preparation: Use a cutter to cut a 12×2mm sample, and use 320#, 600#, 1000# sandpaper to polish the unmarked end of the sample to smooth the surface, then wash the sample with acetone and anhydrous ethanol in turn, and dry it naturally. Seal the non-working surface with silicone, leave the working surface 10×10mm ² and the clamping end about 20mm long, and let it dry naturally. Then, use acetone, anhydrous ethanol, and deionized water to wash it again in order to be tested.

Test solution preparation: Weigh 50.00g of NaCl solid in a 1L beaker, add 500mL of deionized water to dissolve, then use a pipette or pipette to take 1mL of acetic acid into the solution, and then transfer it to a 1L volumetric flask to make up the volume , prepared into the liquid to be tested, wherein the concentration of acetic acid is 0.0175mol/L, and the mass fraction of NaCl is 5%;

Testing instrument: Shanghai Chenhua CHI660E electrochemical workstation; three-electrode system: saturated calomel electrode as reference electrode, sample as working electrode, platinum electrode as auxiliary electrode;

Measurement steps:

(1) Clean each electrode, rotor and a 250mL special test beaker;

(2) Add 200 mL of test solution to the beaker, use the sample as the working electrode, the platinum electrode as the auxiliary electrode, and the saturated calomel electrode as the reference electrode to build a three-electrode measurement system;

(3) The temperature of the system to be tested is maintained at 23°C, and the stirring speed is 100r/min;

(4) under the above-mentioned measuring conditions, select the open-circuit potential method with Shanghai Chenhua CHI660E electrochemical workstation to carry out the electrochemical open-circuit potential test of the sample to be tested, and the test time is 10min;

(5) Repeat the measurement of at least two samples, take the average value of all the values of each measured data as the open circuit potential value of the sample, and the average value of the last two samples as the open circuit potential value of the sample, if the potential value of the two samples is different If it is greater than 5mv, more test samples should be added, and the average value should be taken. The test results are shown in Table 2.

The potential-time curves obtained from the two sample tests are shown in Figure 2, where g is the first sample and h is the second sample.

Table 2

It can be seen from Figure 2 and Table 2 that the test results obtained at different test times have a small difference, the test results of 10min and 5min are similar, the error is small, the reproducibility is good, and very small fluctuations (less than 0.5) can be obtained in a shorter time. mv) potential-time curve, which can shorten the test time from 30min to 5min.

In the description of this specification, reference to the terms "some embodiments," "other embodiments," "examples," "examples," and the like, refers to specific features, structures, materials, or Features are included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

Although the embodiments and examples of the present invention have been shown and described above, it should be understood that the above-mentioned embodiments and examples are exemplary and should not be construed as limiting the present invention. Variations, modifications, substitutions and alterations may be made to the above-described embodiments and examples within the scope of .

Claims (10)

1. The method for testing the open-circuit potential of the aluminum alloy is characterized by comprising the following steps of:

1) preparing a test sample;

2) preparation of test system: preparing a mixed solution of NaCl and acetic acid as a test solution, wherein the concentration of the acetic acid is 0.00875mol/L-0.02625 mol/L;

3) and (3) potential testing: and (3) carrying out open-circuit potential test on the sample to be tested by using an electrochemical workstation and adopting a potential-time open-circuit potential method.

2. The method for testing the open circuit potential of an aluminum alloy according to claim 1, wherein the mass fraction of NaCl in the test solution is 2 to 10%.

3. The method for testing the open circuit potential of the aluminum alloy according to claim 2, wherein the mass fraction of NaCl in the test solution is 4 to 8%.

4. The method for testing open circuit potential of aluminum alloy according to claim 1, wherein the concentration of acetic acid in the test solution is 0.014-0.021 mol/L.

5. The method for testing the open circuit potential of an aluminum alloy according to claim 1, wherein the pH of the test solution is 2.0 to 4.0.

6. The method for testing open circuit potential of an aluminum alloy according to any one of claims 1 to 5, wherein the preparation of the test sample comprises:

polishing the sample in a flowing water tank by using waterproof abrasive paper;

cleaning the polished test sample by using acetone and absolute ethyl alcohol in sequence, and naturally airing;

reserving a detection area: selecting a certain detection area and a certain clamping end length, and sealing other non-detection areas;

naturally drying or drying by cold air.

7. The method for testing open circuit potential of aluminum alloy according to claim 6, wherein the area of the detection area and the test solution are in the following relationship: per 100mm²The test area of (2) ensures at least 100mL of test solution.

8. The method for testing the open circuit potential of the aluminum alloy according to any one of claims 1 to 5, wherein a three-electrode system is adopted during the potential test, one of a saturated calomel electrode, a silver/silver chloride electrode and a mercury/mercury oxide electrode is selected as a reference electrode, a platinum electrode is used as an auxiliary electrode, and a test sample is used as a working electrode.

9. The method for testing the open circuit potential of the aluminum alloy according to any one of claims 1 to 5, wherein the potential is tested at a temperature of 20 to 25 ℃ under stirring, and the rotation speed of the stirrer is 60 to 120 r/min.

10. The method for testing open circuit potential of an aluminum alloy according to any one of claims 1 to 5, further comprising 4) data processing: and taking the average value of all the test values as the open circuit potential value of the aluminum alloy.

Images