Corrosion Study of Superhydrophobic Magnesium Alloy AZ31 Surfaces Prepared by Wet Chemical Etching Process

Superhydrophobic surfaces were fabricated on magnesium alloy (AZ31) substrates by chemical etching using H2SO4 and H2O2 solutions, successively. The generated surface layer was characterized using grazing incidence X-ray diffraction, X-ray photoelectron spectroscopy and micro-Raman spectroscopy, and magnesium hydroxide was found to be the chief component. Field emission scanning electron microscopy displayed flower-like microstructure with two types of nanostructures, viz., nanoneedles in dense cluster form and nanosheets in the form of a network. As a result, the etched specimens were very rough and porous. Due to entrapped air in the pores, the droplets were present in Cassie state and so the contact angle measurements demonstrated high static water contact angles (about 154 degrees). The superhydrophobic property was lost after a few minutes immersion in water, due to a transition to the Wenzel state. A decrease in corrosion resistance of the superhydrophobic samples as compared to the polished substrate was also observed through potentiodynamic polarization measurements.