Corrosion behavior of AZ91D magnesium alloy in sodium sulfate solution

Abstract

The corrosion behavior of as-cast AZ91D magnesium alloy in 0.1M sodium sulfate solution at the corrosion potential (Ecorr) was investigated by using electrochemical impedance spectroscopy (EIS), environmental scanning electron microscopy (ESEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that the corrosion of AZ91D started at both the primary α-Mg and the eutectic α-Mg. The surface first was covered by a film (MgO, Mg(OH)2) which became thicker with time. Due to the dissolution of the eutectic α-Mg, the concentration of aluminum increased, MgAl2(SO4)4 · 2H2O precipitated at the primary α-Mg and progressively spread to the eutectic α-Mg areas. The surface film changed from two-layer to three-layer structure with the increase of immersion time.