Characterization of Prepared Superhydrophobic Surfaces on AZ31 and AZ91 Alloys Etched with ZnCl2 and SnCl2

Superhydrophobic surfaces were prepared using a two-step method that involved the etching of AZ31 and AZ91 magnesium alloys and then modifying the etched alloys with stearic acid. Magnesium alloys etched with ZnCl2 and SnCl2 exhibited surfaces roughened with micro- and nanoscale hierarchical structures consisting of two chemically distinct regions (Zn/Zn(OH)2 or Sn/SnO2 and Mg(OH)2). An optimum etching time of ten minutes was chosen for both etchants. Superhydrophobic surfaces with the highest contact angle were prepared when stearic acid reacted with the etched alloys at 50 °C for 4 h. Stearic acid was bound as zinc stearate and magnesium stearate on Mg alloys etched with ZnCl2 and SnCl2 solutions, respectively. The superhydrophobic process on AZ31 alloys etched with ZnCl2 and SnCl2 improved the corrosion resistance in phosphate buffered saline (PBS) solution compared to bare AZ31 alloy, with the use of ZnCl2 etchant leading to better results. An improvement in the corrosion resistance of AZ91 alloy was observed when the stearic-acid-modified AZ91 alloy was etched with SnCl2. In contrast, the use of ZnCl2 etchant to pretreat AZ91 alloy resulted in a significant deterioration in corrosion properties compared to bare AZ91 alloy. The microstructure of the Mg alloy had an impact on the etching and modification process. On the basis of the findings, a characterization of the chemistry of etching magnesium alloys and the formation of superhydrophobic surfaces was proposed. Magnesium alloys were prepared with superhydrophobic surfaces, incorporating antibacterial metals, features which may increase their potential for use in medical applications.