Surface structure characterization and corrosion mechanism study of three types hot-dip galvanized spangles

The microstructure differences of shiny-spangle, feather-spangle and dull-spangle were analyzed by means of LSCM, SEM, XRD, XPS and EBSD. There are parallel secondary and tertiary dendrites on the feather-spangle surface, and the AlSb are densely distributed in the interdendrite. Large number of AlSb are densely distributed on the dull-spangle surface. Feather-spangle surface has a large number of high-angle-grain boundaries (dendrite boundaries), while dull-spangle surface has a large number of low-angle-grain boundaries (AlSb boundaries). Conduct immersion and electrochemical tests on different spangles to obtain the corrosion process. The corrosion products of the coatings are mainly Zn5(OH)8Cl2H2O and ZnO. The orientation and grain boundary differences are the main reasons for different corrosion resistance. Due to the large amount of AlSb concentrated on dull-spangle, the initial corrosion resistance of dull-spangle is the lowest. When the coating surface is consumed, the feather-spangle corrosion rate accelerates.