Impact of alkaline and acid treatment on the surface chemistry of a hot-dip galvanized Zn–Al–Mg coating

Abstract The surface chemistry of an exemplary hot-dip galvanized Zn–Al–Mg coating comprising 1.6 wt.% aluminum and 1.1 wt.% magnesium was characterized by means of secondary and transmission electron microscopy as well as synchrotron radiation X-ray photoelectron spectroscopy. Lamellae of the coating prepared via focused ion beam technique were examined through energy dispersive X-ray analysis. Further the effect of alkaline and acid treatment respectively was investigated by employing time of flight secondary ion mass spectroscopy, energy dispersive X-ray analysis and glow discharge optical emission spectroscopy. Throughout this work it is shown that both alkaline (NaOH) and acid (H2SO4) solutions alter the chemical composition when applied to the coating surface. With the native Zn–Al–Mg system yielding a complex microstructure covered by a magnesium and aluminum rich oxide film, highly alkaline surroundings (pH > 13) caused a decrease of aluminum at the uppermost surface. Every deployed acid solution (pH