Environmental friendly anodizing of AZ91D magnesium alloy in alkaline borate–benzoate electrolyte

A kind of environmental friendly anodizing routine for AZ91D magnesium alloy, based on an alkaline borate–sodium benzoate electrolyte (NaBz) was studied. The effect of NaBz on the properties of the anodized film was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), respectively. The results showed that the anodizing process, surface morphology, thickness, phase structure and corrosion resistance of the anodized film were strongly dependent on the concentration of NaBz. In the presence of adequate NaBz, a thick, compact and smoothing anodized film with excellent corrosion resistance was produced. Moreover, the forming mechanism of the anodized film in the presence of NaBz additive was also approached, which was a suppression of arc discharge process by the adsorption of Bz− on the surface of magnesium alloy substrate.

► Environmental friendly PEO technology for AZ91 magnesium alloy is developed.
► NaBz is used as new additive and it is low-cost and environmental friendly.
► The effect of NaBz additive on the properties of the anodized film was studied.
► Anodized film with excellent corrosion resistance is obtained.
► The forming mechanism of anodized film in the presence of NaBz is approached.