A method for simulating corrosion test of plated steel in extremely cold atmospheric environment

Abstract

The present application belongs to the technical field of corrosion simulation of coating, and discloses a method for simulating corrosion test of plated steel in extremely cold atmospheric environment, comprising the following steps: (a) pretreatment of the sample to be tested: acetone degreasing, alcohol cleaning, and pasting adhesive tape on both ends and one side of the sample; (b) stress loading on the sample to be tested by using a three-point bending device; (c) simulation of corrosion test: depositing corrosion medium NaHSO3 solution on the surface of the sample, and then placing the stress loading device and the sample in a high-low temperature alternating damp-heat test chamber, and performing the test according to "room temperature-constant low temperature-room temperature wetting-room temperature drying", each cycle being 12-24 h, and the total test time being 84 h-840 h. The present application can realize mechanical and chemical effects under stress and multi-environment factor coupling during the process of tensile stress under different loads, and conforms to the corrosion failure characteristics of structural parts in actual service.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of corrosion simulation of plated layer, and particularly relates to a method for simulating corrosion test of plated steel in extremely cold atmospheric environment. BACKGROUND

[0002] With the development of society, the phenomenon of resource shortage is becoming more and more prominent, and the extremely cold region rich in resources has begun to attract people's attention. In view of the complexity of the environment in the extremely cold region, the research and development and promotion of materials suitable for the extremely cold region are crucial to promote the development and construction of the region. Therefore, in recent years, the application research of materials in the extremely cold region has attracted widespread attention. Zn-Al-Mg plated layer is a kind of corrosion-resistant plated layer with superior performance, and has broad application prospects in the fields of highway guardrails, photovoltaic supports, household appliances and buildings. The atmospheric corrosion of Zn-Al-Mg plated layer exposed to different atmospheric conditions has been reported in recent years. However, most of the existing researches are focused on the strong corrosive atmosphere, and the research on extremely cold atmospheric corrosion is less due to the lower corrosion rate. However, in the extremely cold region, corrosion will still occur, and even some studies have found that the atmospheric corrosion in the extremely cold region is even more serious than that in other common regions, which is closely related to the environmental factors of the extremely cold atmosphere, such as pollutants, liquid water molecules, ultraviolet radiation, temperature changes, etc.

[0003] Corrosion problem is one of the common problems in the service process of materials. In natural environment, except for a few noble metals, most metals are thermodynamically unstable and have a spontaneous corrosion tendency. Similarly, materials will inevitably be affected by stress during service, such as residual stress generated during manufacturing and processing processes such as welding, mechanical processing, cold processing, and stress generated during assembly and use processes such as quenching, periodic heating and cooling, thermal expansion, etc. E. M. Gutman et al. through theoretical derivation and experimental verification, considered that the metal material under the action of external stress will accelerate the corrosion of the material, and named this phenomenon as mechanochemistry effect (MCE).

[0004] Many studies have shown that elastic stress can cause corrosion potential negative shift, significantly accelerate the corrosion of the material. Some people think that the applied stress accelerates the formation of the double electric layer of the aluminum alloy / solution interface, and the formation time is shortened with the increase of the stress. The potential fluctuation gradually decreases with the prolongation of the loading time. When the stress is released from the test piece, the potential fluctuation is obviously weakened. Some studies also believe that the applied stress does not affect the corrosion rate of the diffusion process, but can accelerate the corrosion rate of the activation process and the mixed control process. In the research on the electrochemical properties of steel under the action of external stress by linear sweep voltammetry and alternating current impedance method, it is found that with the increase of the external elastic load, the electrochemical impedance of the sample decreases, which accelerates the corrosion of the metal. Therefore, the stress corrosion failure process of the material under the coupling action of multiple environmental factors in the extremely cold atmosphere is inevitable. In order to further understand the corrosion failure mechanism of Zn-Al-Mg coating in actual service, a method for simulating the stress corrosion test of plated steel in the extremely cold atmospheric environment under the coupling condition of multiple factors needs to be constructed. SUMMARY

[0005] The purpose of the present application is to provide a method for simulating the corrosion test of plated steel in the extremely cold atmospheric environment, which has simulation, acceleration and reproducibility.

[0006] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0007] A method for simulating the corrosion test of plated steel in the extremely cold atmospheric environment, comprising the following steps:

[0008] (a) Pretreatment of the test sample: acetone degreasing, alcohol cleaning, and at the same time, in order to avoid edge effect, the sample is pasted with adhesive tape at both ends and one side to avoid being corroded by the external atmospheric environment;

[0009] (b) Stress loading of the test sample by using a three-point bending device;

[0010] (c) Simulation of corrosion test: depositing corrosion medium NaHSO3 solution on the surface of the test sample, then placing the stress loading device and the test sample in a high-low temperature alternating humidity test chamber, and performing the experiment according to "room temperature-constant low temperature-room temperature wetting-constant drying", each cycle is 12-24h, and the total test time is 84h-840h.

[0011] In step (b) of the present application, the maximum deflection of the test sample during stress loading is controlled to be between 0-600mm; the relationship between the maximum bending stress and the maximum deflection is converted according to the simply supported beam, assuming that the test plane and the unidirectional stress, and the relationship between the maximum deflection and the maximum bending normal stress can be obtained by derivation as follows:

[0012]

[0013] wherein E is the elastic modulus of the material, h is the thickness of the beam, l is the span of the beam,б max is the maximum bending normal stress. The maximum deflection W max corresponds to the maximum bending normal stressб max corresponds to the maximum bending normal stressб max is about 0-600Mpa.

[0014] In the corrosion test of step (c), the corrosion medium is deposited on the surface of the sample once every 1-7 cycles.

[0015] The deposition amount of NaHSO3 in step (c) is determined by amplifying the deposition rate of SO2 in the actual environment by 1-10 times, and is 0-5.09*10-2mg·cm -2 ·d -1 .

[0016] The normal temperature stage in step (c) is a preheating process before the start of the cycle test, and the temperature range is 10-30℃; the constant low temperature stage, the humidity range is-30-60℃; the normal temperature wet stage, the temperature is 10-30℃, the humidity is 80-95%RH; the normal temperature drying stage, the temperature is 10-30℃, the humidity is 20-35%RH.

[0017] The beneficial effects of the present application are:

[0018] (1) The present application can simulate the corrosion process of zinc-aluminum-magnesium plated steel for automobiles, photovoltaic power generation and buildings in the Mohe extremely cold atmospheric environment, and study the stress corrosion failure process of zinc-aluminum-magnesium plating under the condition of multi-factor coupling. Compared with the existing indoor accelerated method, the present application increases the authenticity of the indoor simulation test.

[0019] (2) The composition of the corrosion product on the surface of the coating obtained by the method of the present application is consistent with that after exposure in the actual extremely cold atmospheric environment.

[0020] (3) Using the method of the present application, the stress corrosion under the action of temperature and humidity alternation in the extremely cold atmosphere can be studied alone, or the coupling effect of deposited salt and stress corrosion under the same conditions can be studied.

[0021] (4) The method of the present application has the properties of simulation, acceleration and reproducibility, which can be used to study the stress corrosion process of various zinc-aluminum-magnesium plated steels under the condition of multi-factor coupling in the extremely cold atmospheric environment, quickly evaluate and predict its corrosion resistance, and provide a basis for reasonable design and performance improvement. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1It is a schematic diagram of simulation test device, in which: 1-high and low temperature alternating damp heat test box; 2-sample table; 3-stress force frame; 4-sample; 5-bolt.

[0023] Figure 2 It is XRD spectrum of corrosion product after corrosion for 168h in simulated extremely cold atmospheric environment.

[0024] Figure 3 It is XRD spectrum of corrosion product after exposure for 360d in Mohe atmospheric environment.

[0025] Figure 4 It is cross-section morphology of coating after simulation test stress and SO2 corrosion: wherein (a) maximum deflection is 0; (b) maximum deflection is 2mm; (c) maximum deflection is 4mm; (d) maximum deflection is 6mm.

[0026] Figure 5 It is cross-section morphology of corrosion sample under maximum stress. DETAILED DESCRIPTION

[0027] The application establishes a method for simulating stress corrosion test of plated steel under multi-factor coupling conditions in extremely cold atmospheric environment. The test device used in the method is shown in Figure 1 . The test device is a combination of conventional high and low temperature alternating damp heat test box 1 and stress force frame 3, sample 4 is placed on sample table 2, and different stress loads are realized by using bolt 5.

[0028] The stress force frame can realize different stress loads, and the relationship between maximum bending stress and deflection is converted according to simply supported beam. Assuming that the test plane and unidirectional stress are realized, the relationship between maximum deflection and maximum bending normal stress can be obtained by derivation as follows:

[0029]

[0030] Wherein E is the elastic modulus of material, h is the thickness of beam, l is the span of beam, and max Maximum bending normal stress. Maximum deflection W max Corresponds to maximum bending normal stress max Corresponding maximum bending normal stress max In turn is about 0-600Mpa.

[0031] Zn-2.0Al-1.5Mg plated steel is used as sample to be tested in each embodiment and comparative example, the mass of coating is 275g·m -2 , and the chemical composition of coating is shown in table 1.

[0032] The sample size for the atmospheric exposure test was 150 mm x 70 mm x 0.85 mm. The sample was pretreated before the test: the sample was numbered, the oil was removed with acetone, and the sample was cleaned with alcohol. In order to avoid edge effects, the sample was pasted with adhesive tape around the four sides to avoid corrosion in the external atmospheric environment.

[0033] The sample size for the indoor simulation test was 100 mm x 20 mm x 0.85 mm. The sample was pretreated before the test: the sample was numbered, the oil was removed with acetone, and the sample was cleaned with alcohol. In order to avoid edge effects, the sample was pasted with adhesive tape around the two ends and one side to avoid corrosion in the external atmospheric environment.

[0034] Table 1 Chemical composition of Zn-Al-Mg coating

[0035]

[0036] The atmospheric exposure test was carried out in Mohe City, northern Heilongjiang Province, according to ISO-4542, and the environmental parameters are shown in Table 2.

[0037] Table 2 Environmental parameters of Mohe atmosphere

[0038]

[0039] The indoor simulation test process: the sample was stress-loaded using a three-point bending device, and the maximum deflection of the sample was controlled between 0 and 600 mm. After loading, the corrosion solution was pre-deposited, and the corrosion medium used was a NaHSO3 solution with a concentration of 0-5.09 x 10 -2 mg·cm -2 ·d -1 After the deposition of the corrosion medium, the loaded sample was placed in a high-low temperature alternating humidity test chamber, according to the "room temperature-constant low temperature-room temperature wet-constant temperature dry" cycle, each cycle was 12-24 h, and the total test time was 84 h-840 h. During the test, the sample surface was deposited with the corrosion medium once every 1-7 cycles. The room temperature was the preheating process before the start of the cycle test, with a temperature range of 10-30°C; the constant low temperature stage had a humidity range of -30 to -60°C; the room temperature wet stage had a temperature of 10-30°C and a humidity of 80-95% RH; and the room temperature dry stage had a temperature of 10-30°C and a humidity of 20-35% RH.

[0040] Example 1

[0041] A microsyringe was used to deposit the corrosion medium NaHSO3 solution on the surface of the sample. The test was performed according to the alternating test of "warm-up at room temperature to 20°C - constant low temperature -60°C, 4h - room temperature humidification (T 20°C, 95% RH), 1h - room temperature drying (T 20°C, 20% RH), 2h", and the process of 20°C dropping to -60°C was set to 2.5h, and the process of -60°C rising to 20°C was set to 2.5h. The salt was deposited on the surface of the sample once every 7 cycle periods, so as to ensure that the deposition amount of NaHSO3 during the cycle test was 5.09 x 10 -2 mg·cm -2 ·d -1 . The test time was 168h.

[0042] After the simulation test, XRD analysis was performed on the corrosion products on the surface of the sample, and the results are shown in Figure 2 , and the main composition of the corrosion products was Zn4SO4(OH)6·4H2O.

[0043] Comparative Example 1

[0044] The atmospheric exposure test was performed according to ISO-4542 in Mohe City in the north of Heilongjiang Province, and the exposure time was 360d.

[0045] XRD analysis was performed on the corrosion products on the surface of the sample, and the results are shown in Figure 3 , and the main composition of the corrosion products was Zn4(SO4)(OH)6·4H2O.

[0046] The composition of the corrosion products of the outdoor exposure sample was consistent with that of the sample of the simulation accelerated corrosion test, which indicated that the accelerated corrosion test method in the simulation of the extremely cold atmospheric environment was reliable, and laid a foundation for the design of the stress corrosion test method.

[0047] Example 2

[0048] A microsyringe was used to deposit the corrosion medium NaHSO3 solution on the surface of the sample. The test was performed according to the alternating test of "warm-up at room temperature to 20°C - constant low temperature -60°C, 4h - room temperature humidification (T 20°C, 95% RH), 1h - room temperature drying (T 20°C, 20% RH), 2h", and the process of 20°C dropping to -60°C was set to 2.5h, and the process of -60°C rising to 20°C was set to 2.5h. The salt was deposited on the surface of the sample once every 7 cycle periods, so as to ensure that the deposition amount of NaHSO3 during the cycle test was 5.09 x 10 -2 mg·cm -2 ·d -1 . The test time was 840h.

[0049] After the simulated corrosion test, cross-section morphology analysis was performed on the corroded samples, and the results are shown in Figure 4 . Compared with the stress loading, the Zn-Al-Mg coating surface with a maximum deflection of 0 mm only had a small amount of corrosion products generated, as shown in Figure 4 (a). The stress-loaded coating surface could observe obvious corrosion products; the corrosion products on the surface of the sample with a maximum deflection of 2 mm were needle-shaped, and the corrosion products were relatively loose, but no cracks were observed to extend longitudinally, as shown in Figure 4 (b). The cross-section morphologies of the samples with maximum deflections of 4 mm and 6 mm found that the cracks extended longitudinally to the coating, and the crack of 6 mm was wider than that of 4 mm, as shown in Figure 4 (c) and (d), respectively. At the same time, corrosion products were generated along the cracks, and the corrosion products were more dense, and the cracks were filled with corrosion products.

[0050] Example 3

[0051] The samples were stress-loaded with maximum deflections of 0 mm, 2 mm, 4 mm and 6 mm, respectively. The test was performed according to the alternating test of “room temperature preheating to 20°C-constant low temperature-60°C, 4h-constant temperature wetting (T 20°C, 95% RH), 1h-constant temperature drying (T 20°C, 20% RH), 2h”, and the process of 20°C to-60°C was set to 2.5h, and the process of-60°C to 20°C was set to 2.5h. The test time was 840h.

[0052] After the simulated corrosion test, cross-section morphology analysis was performed on the corroded samples, and the results are shown in Figure 5 . The coating surface had no obvious corrosion, and the cracks did not extend longitudinally to the coating. Under the action of no corrosion medium, stress did not cause the cracks on the surface to extend to the deep part of the coating in the cold environment, and the cross-section morphologies of other stress conditions were similar. From the cross-section graph, it was found that stress had no effect on the inside of the coating.

[0053] Example 4

[0054] The corrosion medium NaHSO3 solution was deposited on the surface of the sample by using a microliter syringe. The test was performed according to the alternating test of “room temperature preheating to 30°C-constant low temperature-45°C, 8h-constant temperature wetting (T 30°C, 90% RH), 1h-constant temperature drying (T 30°C, 35% RH), 4h”, and the process of 30°C to-45°C was set to 5h, and the process of-45°C to 30°C was set to 5h. The salt was deposited on the surface of the sample once every 1 cycle, and the deposition amount of NaHSO3 during the cycle test was 5.09×10 -2 mg·cm -2 ·d -1 . The test time was 168h.

[0055] After the simulation test, the corrosion products on the surface of the sample were analyzed by XRD, and the results were the same as in Example 1, and the main composition of the corrosion products was Zn4SO4(OH)6·4H2O.

[0056] Example 5

[0057] The corrosion medium NaHSO3 solution was deposited on the surface of the sample by using a microliter syringe. The test was carried out according to the alternating test of "room temperature preheating to 10℃-constant low temperature-30℃, 4h-constant temperature and humidity (T 10℃, 80%RH), 1h-constant temperature and dryness (T 10℃, 20%RH), 2h", and the process of reducing from 10℃ to-30℃ was set to 2.5h, and the process of increasing from-30℃ to 10℃ was set to 2.5h. The salt was deposited on the surface of the sample once every 4 cycle periods, so that the deposition amount of NaHSO3 during the cycle test was 5.09×10 -2 mg·cm -2 ·d -1 . The test time was 168h.

[0058] After the simulation test, the corrosion products on the surface of the sample were analyzed by XRD, and the results were the same as in Example 1, and the main composition of the corrosion products was Zn4SO4(OH)6·4H2O.

[0059] In summary, the stress corrosion process of the simulation plated steel in the multi-factor coupling condition in the extremely cold atmospheric environment by using the method of the application has simulation, acceleration and repeatability. The technical scheme of the application not only embodies the characteristics of the extremely cold atmospheric corrosion "low temperature, dry / wet" cycle alternation, but also considers the stress corrosion process in practical application, and can well simulate the stress corrosion failure process of the zinc-aluminum-magnesium plated steel in the extremely cold atmospheric environment for automobiles, photovoltaic power generation and buildings.

[0060] By using the technical scheme of the application, the stress corrosion under the action of temperature and humidity alternation in the extremely cold atmosphere can be studied alone, the coupling effect of deposited salt and stress corrosion under the same condition can be studied, the corrosion resistance of zinc-aluminum-magnesium plating can be quickly evaluated and predicted, and a basis for reasonable design of composition and improvement of performance is provided.

Claims

1. A method of simulating corrosion test of plated steel in an extremely cold atmospheric environment, characterized by, The method comprises the following steps: (a) Pretreatment of the sample to be tested: acetone oil removal, alcohol cleaning, sample two ends and one side pasting adhesive tape; (b) Stress loading on the sample by using three-point bending device; (c) Simulation of corrosion test: depositing corrosion medium NaHSO3 solution on the surface of the sample, then placing the stress loading device and the sample in a dry-wet alternating test box, and performing the test according to "room temperature-constant low temperature-room temperature wetting-room temperature drying", each cycle being 12-24 h, and the total test time being 84 h-840 h; The room temperature stage in step (c) is a preheating process before the start of the cycle test, the temperature range being 10-30 DEG C; the constant low temperature stage, the humidity range being -30--60 DEG C; the room temperature wetting stage, the temperature being 10-30 DEG C, and the humidity being 80-95% RH; and the room temperature drying stage, the temperature being 10-30 DEG C, and the humidity being 20-35% RH.

2. The method for simulating the corrosion test of plated steel in extremely cold atmospheric environment according to claim 1, characterized in that: In step (b), the maximum deflection of the sample is controlled to be between 0-600 mm during stress loading.

3. The method for simulating the corrosion test of plated steel in extremely cold atmospheric environment according to claim 1, characterized in that: In step (c), the corrosion medium is deposited on the surface of the sample once every 1-7 cycles during the corrosion test.

4. The method for simulating the corrosion test of plated steel in extremely cold atmospheric environment according to claim 1, characterized in that: The deposition amount of NaHSO3 is determined by amplifying 1-10 times of the deposition rate of SO2 in the actual environment, and is 0-5.09×10 -2 mg·cm -2 ·d -1 .

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