Study on coating corrosion resistance of color coated steel sheet
The corrosion resistance test of color coated steel sheet generally adopts the method of salt spray test. The test contents and evaluation methods such as marking, notch, bending and stamping are added to the sample preparation, mainly to investigate the corrosion resistance problems of bending, stamping deformation, scratch and notch that may exist in the processing of color coated steel sheet. While using salt spray test for experimental research, we also used cyclic corrosion test (CCT) for comparative study of some products.
Test methods for color coated steel sheets
Salt spray test (SST) shall be conducted according to the neutral salt spray resistance test in GB / t13448-2006. 5% NaCl solution was prepared to keep the pH value between 6.5~7.2 and temperature at (35 + 2) C, and continuous spray test was carried out. The test cycle shall be determined according to the specific project. Cyclic corrosion test (CCT) shall be conducted for 30 cycles according to 2H salt spray test - 4H drying (60 ℃) - 2H damp heat (50 ℃, 95% RH).
Preparation of test samples for color coated steel sheets
Select the color coated steel sheet under normal process conditions or the color coated steel sheet prepared by laboratory bar coating. The surface of the steel sheet shall be free of scratches, bubbles, impurities and other defects. The sample shall be prepared in the following ways: flat sample: the sample size is 75MN * 150mm, and the edge of the steel sheet shall be sealed with adhesive tape.
Scribe sample: the sample size is 75mm * 150mm. Seal the edge of the steel sheet with adhesive tape, scribe or cross the sample surface with a special scratch tool, and the scratch must be scratched through the coating.
Notch sample: the sample size is 75mm * 150mm, and the upper and lower edges of the steel sheet shall be closed with adhesive tape or all four sides shall not be closed. When cutting the template, pay attention to make the burr of the template notch downward.
Bending sample: the sample size is 75mm * 150mm. Use bending machine and flattener to bend the surface to be measured of the sample sheet by 180 °.
Stamping sample: the sample size is 150mm * 150mm, and the sample is stamped with a cup punch. The test face can be determined according to the actual use of the sample.
Evaluation method of color coated steel sheet
The evaluation of corrosion resistance of color coated steel sheet mainly includes the evaluation of blister size, blister density, corrosion propagation distance at scratch or notch, etc. The foaming degree (size and density) shall be evaluated according to CB / t1766. The maximum, minimum and average corrosion spread width shall be measured directly with a ruler for the corrosion spread distance at the notch or scratch.
It is the most conventional method to evaluate the coating corrosion resistance of color coated steel sheet after salt spray test. It is mainly used to evaluate the corrosion resistance of steel sheet when the paint film is complete. This method is used to investigate the corrosion resistance of coating on the plane of color coated steel sheet during normal processing. Generally, it is considered that the foaming grade of sheet in salt spray test is related to the performance of coating itself and coating process, but it is found that the foaming grade of color coated steel sheet is also significantly related to the type of substrate. After summarizing and analyzing a large number of data of salt spray test of color coated steel sheet, from the occurrence probability of foaming grade, the hot-dip galvanized substrate with the highest zinc layer thickness has the lowest foaming grade and the highest corrosion resistance after salt spray test.
Tag：Test methods for color coated steel sheets,Preparation of test samples for color coated steel sheets,Evaluation method of color coated steel sheet
