고전압 대전 파우더 분사에 의한 용융 Al-Si 도금강판의 스팽글 미세화 및 내식성 향상

Abstract

Hot-dip aluminizing (HDA), particularly Al-Si coatings, has been widely employed as a pre-treatment process for hot-stamping steels to enhance corrosion and heat resistance through the formation of passivation films and intermetallic compound layers. However, during the solidification of molten coatings, surface dendritic structures known as spangles are generated. Large spangles not only produce surface defects but also contribute to coating delamination. Therefore, electrostatic powder coating process is used to suppression of dendrite growths by spraying metal powders on the surface of molten coatings which provide abundant nucleation sites. In this study, zinc (Zn) powder was selected as the primary additive, and aluminum (Al) powder was co-sprayed to improve adhesion. The incorporation of Zn into molten Al increases viscosity and decreases surface tension, improving alloy flowability. Consequently, the formation of dense coatings is promoted and the driving force for grain boundary migration during recrystallization is reduced, leading to refinement of Al grains and spangle structures. Moreover, because Zn exhibits a more negative electrode potential than Al, it provides sacrificial anodic protection, further enhancing the corrosion resistance of the substrate. Herein, the effects of sprayed powders on the microstructures and corrosion resistance of hot-dip Al-Si coated steel were investigated.