Influence of surface condition of hot-dip galvanized steel sheet on film performance

Hot-dip galvanized steel sheets are widely used in industries such as automobiles, construction, machinery, electronics, and electrical appliances. Among them, the hot-dip galvanized steel sheets used in the household appliance electronics industry are mainly zinc-free galvanized steel sheets. In the past, in the research and production of galvanized steel sheets, most of them only focused on the material properties of chromium-free anti-fingerprint passivators, ignoring the factors affecting the passivation quality of galvanized steel sheets, the uniformity of zinc layer, and the surface roughness of steel sheets. "The influence of the surface condition of hot-dip galvanized steel sheet on the performance of the paint film" introduces the author's research on the factors affecting the performance of the coated steel sheet, and analyzes the reasons.

Performance Testing

(1) Surface roughness of the galvanized steel sheet: The surface roughness of the galvanized steel sheet was tested with a SE-3000 roughness meter.

(2) Morphological observation of galvanized steel sheet: use QUANTA400 scanning electron microscope to observe the microscopic morphology of the specific area of ​​the steel sheet, and use the attached OXFORD energy dispersive spectrometer (EDS) to conduct qualitative and quantitative analysis of the material composition in the specific area.

(3) Component analysis of galvanized steel sheet (EPMA): JXA-8800R electron probe microanalyzer was used to observe specific areas of galvanized steel sheet and conduct elemental analysis.

(4) Salt spray resistance of passivated galvanized steel sheet: the sample size is 60 mm×100 mm, and the neutral salt spray test is carried out according to JISZ2371: 5% NaCl aqueous solution is used, pH=6.5 ~ 7.2, and the temperature in the box is (35 ± 2) °C, the test piece is placed at an angle of 30° to the vertical direction.

(5) Surface resistance of passivated galvanized steel sheet: refer to the JISK7194 standard, and use a Loresta-GPMCP-T610 resistance measuring instrument to test the surface resistance of the test piece.

(6) Thickness of sprayed coating: Measure the coating thickness of the coated test piece with LAT-A intelligent Thickness Gauge.

(7) Adhesion performance of passivated galvanized steel coating film: evaluation by scratch test

in conclusion

(1) The surface roughness of the galvanized steel sheet has a great influence on the performance of the chromium-free passivation film. In order to take into account both corrosion resistance and electrical conductivity, the surface roughness of galvanized steel sheets should be controlled within an appropriate range.

(2) The uniformity of the zinc layer of galvanized steel sheet directly affects the uniformity of the chromium-free passivation film, which in turn affects the adhesion of the coating. The better the uniformity of the galvanized layer, the stronger the adhesion of the coating.

(3) The zinc slag on the surface of the galvanized steel sheet reduces the coverage of the fingerprint-resistant passivation film. The corrosion of the fingerprint-resistant galvanized steel sheet mostly starts from the zinc slag, and such defects should be minimized.