JP2010025560A - Corrosion resistance evaluating method of metal material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly evaluate the corrosion resistance of aluminum or an aluminum alloy to which rust-proof treatment is applied in a short time. <P>SOLUTION: A corrosion resistance evaluating method of a metal material has the step (A) being a salt adhering step of adhering chloride ions to a test piece as a salt component within a range of 0.1-10,000 mg/m<SP>2</SP>, the step (B) for repeating one cycle composed of a dry state and a wet state a plurality of times being the step of repeating the dry state and the wet state for providing the dry state for holding definite temperature and humidity within a temperature range of 20-60°C and a relative humidity range of 30-70% over a holding time of 1 sec-24 hr and a wet state for holding a temperature of 0-40°C and a relative humidity of 80-98% over a holding time of 1 sec-24 hr as one cycle and repeating this cycle a plurality of times and repeats the step (A) and the step (B) once or a plurality of times. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for evaluating the corrosion resistance of aluminum and aluminum-based alloys used in an atmospheric corrosive environment, and a method for evaluating a rust prevention treatment applied to these metal materials.

  Aluminum and aluminum alloys are subjected to rust prevention treatment such as anodizing treatment, chemical conversion treatment, plating, etc. as necessary, and are used in electronic equipment, home appliances (refrigerators, air conditioners, washing machines, etc.), communication equipment, transportation equipment (automobiles, Used for trains). In recent years, rust prevention treatment that does not use hexavalent chromium has been developed and put into practical use because hexavalent chromium contained in the coating of the rust prevention treatment material is suspected of adversely affecting human health. New rust-proof materials that do not use hexavalent chromium have a short track record of use and no long-term corrosion resistance data.

  As an evaluation method for evaluating the corrosion resistance of the new rust prevention treatment in the atmospheric corrosive environment and selecting the optimum treatment, the salt spray test (JIS Z2371) and the long-term atmospheric exposure test have been conventionally known. Test methods are used.

  The salt spray test can evaluate corrosion resistance in a short period of time, but it is a test in an environment with a large amount of attached salt and high humidity, and it does not reproduce the actual corrosive environment, and the evaluation result is corrosion resistance in the actual environment. And may be different.

  In the atmospheric exposure test, the environment is the actual environment itself, and knowledge about atmospheric corrosion in the actual environment can be obtained. However, the atmospheric exposure test requires a longer test period than the life of the equipment. Therefore, in order to design the equipment, an evaluation method capable of predicting the lifetime in a short period is necessary.

  Japanese Patent Application Laid-Open No. 2004-77260 (Patent Document 1) discloses that after adhesion of salt, the temperature is 40 to 60 ° C., the relative humidity is 40% or less, the drying state is 2 to 12 hours, the temperature is 20 to 60 ° C., and the relative humidity is 80 to 80%. A test method that repeats the wet state of 96% and holding time of 2 to 12 hours has been proposed. This method has a high correlation with the actual environment and can evaluate the corrosion resistance in a relatively short period of time.

JP 2004-77260 A

  In aluminum and aluminum alloys, an oxide film with good corrosion resistance is formed on the surface, which affects the corrosion resistance of aluminum and aluminum alloys. The ease with which this oxide film is formed varies in a temperature range of at least 30 ° C to 60 ° C. Therefore, regarding aluminum and aluminum alloys, setting the temperature of the corrosion resistance evaluation method to a temperature far from the actual environment results in a corrosion form different from that of the actual environment, and there is a risk of misjudging the corrosion resistance.

  In Patent Document 1, this method is directed to a surface-treated steel sheet, and the test temperature is set to 60 ° C. or less at which zinc performs sacrificial corrosion protection against iron. Therefore, this method does not evaluate the corrosion resistance of aluminum or aluminum alloy.

  Therefore, the evaluation of the superiority or inferiority of the corrosion resistance of the rust prevention treatment and the estimation of the lifetime in the usage environment must be performed by a method correlated with the actual environment.

  An object of the present invention is to appropriately evaluate the corrosion resistance of aluminum or aluminum alloy subjected to rust prevention treatment in a short period of time.

(1) The present invention is characterized by a method for evaluating the corrosion resistance of a metal material by repeating the step consisting of the following step (A) and the following step (B) once or a plurality of times.
(A) A step of adhering a salt content, and a step of adhering chloride ions as a salt content to a test piece in a range of 0.1 to 10000 mg / m ² .
(B) A process of repeating a dry state and a wet state, wherein the temperature is 20 ° C. to 60 ° C., the relative humidity is 30% to 70%, the constant temperature and humidity, and the holding time is 1 second to 24 hours, and the temperature A process in which a wet state of 0 to 40 ° C., relative humidity of 80% to 98% and a holding time of 1 second to 24 hours is defined as one cycle, and this cycle is repeated a plurality of times.
(2) The present invention is characterized in that the metal material in the corrosion resistance evaluation method of (1) is aluminum, an aluminum-based alloy, and a material obtained by subjecting them to rust prevention treatment.
(3) The present invention is characterized by being an apparatus for performing the corrosion resistance evaluation method in (1) to (2).

  ADVANTAGE OF THE INVENTION According to this invention, the corrosion form in the atmospheric corrosive environment of metal materials, especially aluminum and aluminum alloy can be reproduced. Therefore, it is possible to appropriately evaluate the superiority or inferiority of the rust prevention treatment applied to aluminum or aluminum alloy, which is useful for selecting the rust prevention treatment.

  FIG. 1 shows the process of the present invention. The corrosion resistance evaluation method according to the present invention comprises (A) a step of adhering chloride ions, and (B) a step of performing this a plurality of times with one cycle consisting of wetting, drying and transfer thereof.

In the step (A), the method for attaching the salt is not particularly limited, and the salt is attached by a method such as salt water immersion, salt spray, salt water dropping or the like. Artificial sea water or sodium chloride aqueous solution is used for the salt water to be used. The amount of salt attached is in the range of 0.1 to 10,000 mg / m ² , and the amount of salt attached is selected according to the assumed environment. Corrosion can be promoted by increasing the amount of attached salt from the actual environment, but if it is too large, the result may be different from the actual environment. Therefore, it is better to set the amount of adhering salt to two or more levels for testing.

  FIG. 2 is a diagram schematically showing the relationship between the amount of adhering salt and the degree of corrosion of materials X, Y, and Z that are aluminum or an aluminum alloy. In the amount of adhering salt x, y, z, the order of the degree of corrosion is switched. As described above, there is a possibility that the judgment of the corrosion resistance evaluation may be mistaken for the amount of adhered salt far from the actual environment. On the other hand, the corrosion resistance characteristics of the material can be examined by performing the test with the adhering salt content set at two levels.

  In the step (B), the dry state simulates a high temperature dry state during the day, and the wet state simulates a dew condensation state at night. In an actual environment, the relative humidity changes according to the temperature change with the dew point temperature being constant. Therefore, the dew point temperature is constant in the dry state and the wet state. Further, the transition from the dry state to the wet state and the transition from the wet state to the dry state are also performed at a constant dew point temperature.

  The step (B) is performed using a constant temperature and humidity chamber. In the dry state, the temperature range is 20 to 60 ° C., and is set to a constant temperature equivalent to the maximum temperature of the assumed environment. Moreover, since the relative humidity in the drying period of an atmospheric corrosive environment is 30 to 70%, the relative humidity is set to a constant humidity of 30 to 70% in the dry state. Further, in the dry state, the holding time is set to 0.01 s to 2 hours.

  In a wet state, it is set to a constant temperature in the temperature range of 0 to 55 ° C.

  In addition, the humidity is set to a constant humidity of 80 to 98%. When the relative humidity is 80% or more, sodium chloride, which is one of the main components of sea salt, adsorbs and dissolves moisture to form a water film. Further, in a wet state, the holding time is set to 0.01 s to 2 hours.

  FIG. 3 is a diagram connecting the conditions of a constant dew point temperature. The vertical axis represents temperature, and the horizontal axis represents relative humidity. Wet temperature and relative humidity are the same as the dew point temperature under dry temperature and humidity conditions, and the error is within ± 5 ° C. In FIG. 3, when the dew point temperature of 20 ° C. is selected, for example, the dry state is 35 ° C. and the relative humidity is 40% RH, and the wet state is 22 ° C. and the relative humidity is 95%.

  In the step (B), the cycle of wetting, drying, and their transfer is repeated a predetermined number of times. After the step (B), it is again subjected to the step (A). In the step (A), the salt is removed by washing with water, or the salt is newly attached without removing the salt, and the test is repeated.

  FIG. 4 is a diagram showing a polarization curve of an aluminum alloy in 3.5% artificial seawater. The polarization curve was obtained by scanning the voltage in the positive direction starting from the corrosion potential and measuring the current at that potential. The polarization curves differed by changing the temperature of the artificial seawater in the range of 30 ° C to 60 ° C.

  The polarization curve 11 at 30 ° C. is a polarization curve measured at a liquid temperature of 30 ° C. As the potential was scanned in the positive direction, the current increased rapidly.

  A polarization curve 12 at 40 ° C. is a polarization curve measured at a liquid temperature of 40 ° C. There was a passive region where the current did not increase even when the current was scanned in the positive direction. It was considered that a passive state film was easily formed at 40 ° C. because a passive state region was observed.

  The polarization curve 13 at 60 ° C. is a polarization curve measured at a liquid temperature of 60 ° C. The passive state region at 60 ° C. was larger than that at 40 ° C.

  Thus, it is considered that the presence or absence and degree of the passive state region vary depending on the temperature, and the corrosion resistance changes. Moreover, it is thought that the corrosion form is also different. Therefore, it is preferable to set the test temperature with the maximum temperature as an upper limit.

  FIG. 5 shows the results of measuring the corrosion rate of an aluminum alloy by an electrochemical method. The vertical axis represents the corrosion rate and the horizontal axis represents time. The corrosion rate was large in the wet state and small in the dry state. In addition, a phenomenon was observed in which the corrosion rate increased during the transition from wet to dry. This phenomenon is more conspicuous when the cycle of drying and wetting is short than when the cycle is long, and the effect of promoting the test is large.

  As Example 1, the corrosion resistance of the material A, which is a pure aluminum material, the material B, which is an aluminum die cast alloy, and the material C, which is an aluminum alloy wrought material, was evaluated by the evaluation method of the present invention. The test conditions were determined as follows. In a certain salt damage area, the annual maximum temperature was approximately 35 ° C., so the dry temperature was set to 35 ° C. Furthermore, since the lowest daily relative humidity in this region was approximately 40% RH, the relative humidity for drying was set to 40% RH. Therefore, the dew point temperature of this example is approximately 20 ° C. In this area, the dew condensation phenomenon is observed at night, so the relative humidity when wet is 95% RH. Since the dew point temperature is approximately 20 ° C., the wet temperature was set to 20 ° C.

FIG. 6 shows the temperature and humidity cycle of this example. In the drying / wetting repetition step, the time for the dry state and the wet state was 3 h, the time for transition from dry to wet and the time for transition from wet to dry were 1 h, and the cycle was 8 h. Adhesion of salt was performed by spraying artificial seawater in the form of a mist. Since the amount of attached salt in this region was 1 g / m ² , the amount of attached salt was set to 1 g / m ² . Specifically, artificial seawater having a concentration of 3.5% was attached by 30 g / m ² . Moreover, it carried out also about the conditions which made the amount of adhesion salt into 4 g / m < ² >.

  As the test piece, an aluminum and aluminum alloy plate having a shape of 70 × 70 mm was used, and one side was used as an evaluation surface.

  The wet and dry repeating process was paused twice a week to perform the salt adhesion process. In the salt adhesion process, the test piece was washed with pure water, the salt was again adhered, and the drying and wetting cycle was restarted. This was continued for 42 days.

  As a result of performing the test, corrosion consisting of a white corrosion product was generated on the test piece. Material A had a dulled metallic luster on the surface. In addition, corrosion consisting of white corrosion products having a size of about 2 to 5 mm was observed in some places. In material B, high density and minute corrosion consisting of a white corrosion product was observed. In material C, the corrosion form was similar to that in material A. These agreed with the results in the real environment.

  The ratio of the area where corrosion occurred to the test piece evaluation surface was measured. Moreover, after removing the white corrosion product by the method of JIS Z2371, the pitting corrosion depth was calculated | required using the optical microscope. As a result, the corrosion of the material B proceeded most, and the corrosion proceeded in the order of the material C and the material A. This superiority or inferiority relationship of the corrosion resistance was consistent with the result of the actual environment. Therefore, according to the present invention, the corrosion resistance of aluminum and aluminum alloys in an atmospheric corrosion environment can be properly evaluated in a short period of time. In the conventional accelerated test method, the corrosion form and the superiority or inferiority of the corrosion resistance between materials differed from the results in the actual environment.

  In order to increase the acceleration rate, the cycle of repeated wet and dry was shortened. FIG. 7 shows the temperature and humidity cycle of this example. The temperature and humidity conditions were the same as in Example 1, the drying and wetting time was 1 h, the transition time from drying to wetting and the transition time from wetting to drying were 1 h, and the cycle was 4 h. Thus, even when the acceleration rate was increased, the corrosion resistance of the aluminum and the aluminum alloy in the atmospheric corrosion environment could be appropriately evaluated as in Example 1.

  As Example 3, according to the evaluation method of the present invention, the material a, which is an aluminum die-cast alloy, the material b obtained by anodizing the material a, the material c obtained by metal plating the material a, and the chemical conversion treatment were performed on the material a. The material d was evaluated for corrosion resistance. The test conditions were determined as follows. In a certain salt damage area, since the maximum annual temperature was 35 ° C, the set temperature of the dry state was set to 35 ° C. Furthermore, since the minimum daily relative humidity in this region was approximately 55% RH, the relative humidity for drying was set to 55% RH. Therefore, the dew point temperature of this example is 20 ° C. In this region, since dew condensation is observed at night, the relative humidity in a wet state was set to 95% RH. Since the dew point temperature in this example was 20 ° C., the wet temperature was set to 26 ° C. In this region, while the nighttime condensation time continues, the time during which the daytime relative humidity is 55% is temporary. FIG. 8 shows the temperature and humidity cycle of this example. In this example, the wet time was 1.8 h, and the dry time was 0.2 h. The transition time from dry to wet and the transition time from wet to dry was 1 h, and the period was 4 h. The wet and dry repeating process and the salt adhesion process were performed in the same procedure as in Example 1, and the test was continued for 42 days.

  According to the test, a high density and minute corrosion made of a white corrosion product was observed in the material a. No significant corrosion was observed with material b. In the material c, corrosion consisting of white corrosion products having a size of about 2 to 5 mm was observed in some places. In material d, although not as high as material a, high density and minute corrosion of white corrosion products was observed. These agreed with the results in the real environment. In the conventional accelerated test method, the corrosion form and the superiority or inferiority of the corrosion resistance between materials differed from the results in the actual environment.

  The amount of corrosion was determined by the same method as in Example 1. As a result, the corrosion of the material a was the most advanced, and then the corrosion proceeded in the order of the material d, the material c, and the material b. This superiority or inferiority relationship of the corrosion resistance was consistent with the result of the actual environment. Therefore, according to the present invention, the corrosion resistance of aluminum and aluminum alloys in an atmospheric corrosion environment can be properly evaluated in a short period of time.

  As Example 4, the corrosion resistance of the material A, which is a pure aluminum material, the material B, which is an aluminum die cast alloy, and the material C, which is an aluminum alloy wrought material, was evaluated by the evaluation method of the present invention. The test conditions were determined as follows. The usage environment of an electric device using an aluminum alloy was repeatedly dried and wet every 24 hours, and the maximum temperature was 60 ° C. Therefore, the dry temperature was set to 60 ° C. Furthermore, since the lowest daily relative humidity in this region was approximately 35% RH, the relative humidity for drying was set to 35% RH. Therefore, the dew point temperature of this example is 40 ° C. In this environment, a dew condensation phenomenon is observed at night, so the relative humidity at the time of humidity was set to 95% RH. The temperature range is significantly different from Example 1. FIG. 9 shows the temperature and humidity cycle of this example. In this example, the wet time was 3 hours and the dry time was 3 hours. The transition time from dry to wet and the transition time from wet to dry was 1 h, and the period was 8 h. The wet and dry repeating process and the salt adhesion process were performed in the same procedure as in Example 1, and the test was continued for 42 days.

  As a result of performing the test, corrosion consisting of a white corrosion product was generated on the test piece. In the material A, minute corrosion having a size of less than 1 mm was observed at high density. The boundary between the healthy part and the discolored part was clear. In material B, high density and minute corrosion consisting of a white corrosion product was observed. In material C, corrosion consisting of white corrosion products having a size of about 2 to 5 mm was observed in some places. The superiority or inferiority relationship between these corrosion forms and corrosion resistance was consistent with the results in the actual environment. In addition, since the temperature range of Example 4 differs greatly from Example 1, the superiority or inferiority relationship of the corrosion form and the corrosion resistance between the materials of Example 1 was different.

  The present invention relates to a technique for evaluating corrosion resistance in an atmospheric corrosive environment.

The figure which shows the process of this invention. The figure showing the relationship between the amount of adhering salt and the degree of corrosion in the corrosion promotion test method. The figure which shows dew point temperature. The figure which shows the polarization curve of the aluminum alloy in artificial seawater. The figure which shows the example which measured the corrosion rate of the aluminum alloy. The figure which shows an example of the temperature-humidity cycle of this invention (the 1). The figure which shows an example of the temperature-humidity cycle of this invention (the 2). The figure which shows an example of the temperature-humidity cycle of this invention (the 3). The figure which shows an example of the temperature-humidity cycle of this invention (the 3).

Explanation of symbols

11 Polarization curve at 30 ° C. 12 Polarization curve at 40 ° C. 13 Polarization curve at 60 ° C.

Claims (3)

A step of attaching a salt to a metal material, a step of holding the metal material to which the salt is attached in a dry state, a step of holding the metal material held in the dry state in a wet state, and the dry state And the step of holding in the wet state a plurality of times, the corrosion resistance evaluation method for evaluating the corrosion resistance from the metal material that has undergone the step,
The step of attaching the salt content is a step of attaching 0.1 to 10,000 mg / m ² of chloride ions to the metal material, and the step of maintaining the dry state is a temperature of 20 ° C. to 60 ° C. and a relative humidity of 30%. -70% and holding time of 1 second to 24 hours. The step of holding in the wet state is performed under the conditions of temperature 0 ° C to 55 ° C, relative humidity 80% to 98%, holding time 1 second to 24 hours. A corrosion resistance evaluation method characterized by being. The corrosion resistance evaluation method according to claim 1,
The method for evaluating corrosion resistance, wherein the metal material is aluminum or an aluminum-based alloy.   The corrosion resistance evaluation method according to claim 1 or 2, wherein the metal material has a rust-proofing layer on a surface thereof.

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