Effect of Surface Roughness Profiles on Powdering Resistance Performance of Galvannealed Coatings

摘要

The surface morphology and phase structure of galvannealed steel sheet (GA) coatings prepared at different galvarmealing parameters were analyzed by X-ray diffraction and SEM, and powdering amount of GA coating was investigated by the double-Olsen powdering tester. The results show that when the Al contents below 0.16 wt%, the R_a of Galvannealed coating surface was measured namely below 1.0μm, and powdering amount of GA coating was below 30 mg/m~2, it is within a reasonable value required by automotive makers. After that with the Al contents increased in zinc liquid the amount of powdering increased, This means that the powdering resistance performance of GA coating not only depended on the iron content in the coating, but depended on the roughness profiles of the surface coating. When the galvanizing coating with 0.22 wt% Al content galvannealing at 500°C, with the inhibition effect of Fe_2Al_5Zn_x inhibit layer, the thickness of δ_(1k)-phase was different in the GA coating, which deteriorated the powdering resistance performance of GA coating.