How to detect the failure point of the coating in the salt spray chamber, combined with the salt spray test standard and the actual operation method
I. Parameter setting and preparation before test
Simulation condition setting
Salt spray concentration: 5% NaCl solution is usually used to simulate the Marine environment, and the specific concentration can be adjusted according to the test standards (such as GB/T2423.17, ASTM_B117).
Temperature and humidity: the common setting is 35 ° C ±2 ° C, and the humidity is maintained above 95% to achieve stable salt spray settlement.
Cycle cycle: Designed according to the expected life of the coating, such as a salt spray + drying cycle every 24 hours, the total time can be hundreds of hours.
Sample pretreatment
Clean the surface of the coating to remove oil or impurities and ensure that the test results are not disturbed.
Key areas (such as welds and edges) are marked for subsequent focus observation.
Second, the failure point monitoring method in the test
Visual inspection
Direct observation: Periodically interrupt the test and use a magnifying glass or microscope to observe whether the coating surface has rust spots, bubbles, cracks and other failure characteristics.
Color change: Record discoloration, darkening of the coating, or exposure of the substrate metal, which may signal the beginning of corrosion.
Electrochemical test
The impedance value of the coating was measured by an electrochemical workstation. The decrease of the impedance indicates that the protection performance of the coating is reduced.
The polarization curve was used to analyze the corrosion current density and quantify the coating failure degree.
Video recording
High-definition cameras or scanning electron microscopy (SEM) were used to dynamically record the surface changes of the coating, compare the image differences at different time points, and locate the earliest areas of corrosion.
Third, failure point analysis technology after the test
Corrosion area calculation
Image analysis software (such as ImageJ) is used to calculate the proportion of the corroded area to the total coating area, and if it exceeds a preset threshold (such as 5%), it is deemed to be invalid.
Microstructure detection
Cross-section analysis: Cut the sample to observe whether the interface between the coating and the substrate has peeling, holes and other defects.
Energy spectrum analysis (EDS) : detection of the elemental composition of corrosion products to determine the type of corrosion (such as pitting caused by chloride ion penetration).
Coating adhesion test
The adhesion strength of the corroded area is measured using a grid method or a drawing instrument, and the data of the non-corroded area is compared to evaluate the degree of coating failure.
4. Precautions
Parameter consistency: Ensure the stability of salt spray settling amount, temperature and other parameters to avoid data deviation.
Multiple test verification: Repeat the test on the same batch of samples to improve the accuracy of failure point detection.
Sum up
The core of detecting the failure point of coating salt spray lies in the combination of dynamic monitoring and microscopic analysis. By setting standardized conditions, regularly observing and recording, and quantifying corrosion parameters, the weak area of coating can be accurately located. For key components (such as automotive chassis, electronic components), it is recommended to add non-destructive testing means such as X-ray tomography (CT) to comprehensively evaluate the internal defects of the coating.
Simulation condition setting
Salt spray concentration: 5% NaCl solution is usually used to simulate the Marine environment, and the specific concentration can be adjusted according to the test standards (such as GB/T2423.17, ASTM_B117).
Temperature and humidity: the common setting is 35 ° C ±2 ° C, and the humidity is maintained above 95% to achieve stable salt spray settlement.
Cycle cycle: Designed according to the expected life of the coating, such as a salt spray + drying cycle every 24 hours, the total time can be hundreds of hours.
Sample pretreatment
Clean the surface of the coating to remove oil or impurities and ensure that the test results are not disturbed.
Key areas (such as welds and edges) are marked for subsequent focus observation.
Second, the failure point monitoring method in the test
Visual inspection
Direct observation: Periodically interrupt the test and use a magnifying glass or microscope to observe whether the coating surface has rust spots, bubbles, cracks and other failure characteristics.
Color change: Record discoloration, darkening of the coating, or exposure of the substrate metal, which may signal the beginning of corrosion.
Electrochemical test
The impedance value of the coating was measured by an electrochemical workstation. The decrease of the impedance indicates that the protection performance of the coating is reduced.
The polarization curve was used to analyze the corrosion current density and quantify the coating failure degree.
Video recording
High-definition cameras or scanning electron microscopy (SEM) were used to dynamically record the surface changes of the coating, compare the image differences at different time points, and locate the earliest areas of corrosion.
Third, failure point analysis technology after the test
Corrosion area calculation
Image analysis software (such as ImageJ) is used to calculate the proportion of the corroded area to the total coating area, and if it exceeds a preset threshold (such as 5%), it is deemed to be invalid.
Microstructure detection
Cross-section analysis: Cut the sample to observe whether the interface between the coating and the substrate has peeling, holes and other defects.
Energy spectrum analysis (EDS) : detection of the elemental composition of corrosion products to determine the type of corrosion (such as pitting caused by chloride ion penetration).
Coating adhesion test
The adhesion strength of the corroded area is measured using a grid method or a drawing instrument, and the data of the non-corroded area is compared to evaluate the degree of coating failure.
4. Precautions
Parameter consistency: Ensure the stability of salt spray settling amount, temperature and other parameters to avoid data deviation.
Multiple test verification: Repeat the test on the same batch of samples to improve the accuracy of failure point detection.
Sum up
The core of detecting the failure point of coating salt spray lies in the combination of dynamic monitoring and microscopic analysis. By setting standardized conditions, regularly observing and recording, and quantifying corrosion parameters, the weak area of coating can be accurately located. For key components (such as automotive chassis, electronic components), it is recommended to add non-destructive testing means such as X-ray tomography (CT) to comprehensively evaluate the internal defects of the coating.
