Effect of surface texture of galvannealed steel sheet on image clarity after painting

Surface profiles at each producing step of galvannealed steel sheet and at each painting step were measured by stylus profilometer. Galvannealed steel sheet had fine unevenness with short wavelength components (lambda < 100mum) originated in the Fe-Zn alloying reactions, unevenness with relatively long wavelength components (lambda > 100mum) responded to the substrate cold rolled steel sheet. By skin-pass rolling, the amplitudes of almost all wavelength components were reduced. Unevenness of overall wavelength was reduced by painting. Fine unevenness with short wavelength (lambda < 100mum) disappeared completely. Unevenness with relatively long wavelength (lambda > 100mum) slightly remained. Good correlation between the NSIC-value, the index of image clarity, measured after middle coating and the amplitude of wavelength component from 100 to 2000mum of galvannealed surfaces was indicated.