Modified lanthanum conversion coatings were obtained by immersing hot-dip galvanized (HDG) steelsheets that underwent silicate pretreatment in a lanthanum nitrate solution. The results ofpotentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurementsrevealed that silicate pretreatment improved the protective property of the lanthanum conversioncoatings, and this conclusion was then corroborated by neutral salt spray (NSS) tests. The morphologyand chemical compositions of coatings were examined by scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS), scanning tunnelling microscopy (STM) and Auger electronspectroscopy (AES). The results showed that many silicate particles were dispersed evenly onto thesurface of HDG after silicate pretreatment; as a result, the growth of the lanthanum conversioncoatings tended to be homogeneous, so that more uniform and compact coatings can be obtained.
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