Corrosion processes of Mg-Y-Nd-Zr alloys in Na2SO4 electrolyte

The corrosion behavior of Mg-Y-Nd-Zr (WE43 commercial alloy) was investigated in Na2SO4 electrolyte using potentiodynamic polarization curves, X-Ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiles, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectrometry (EDS) analyzes. SEM and EDS data show that Nd-rich precipitates are mainly located at the grains boundaries. Zr/Y-rich zones are distributed inside the most of the grains. XPS study indicates a depletion of Mg on surface that could be attributed to Mg dissolution and an enrichment of the addition element oxides. XPS and ToF-SIMS analyzes demonstrate that the corrosion films are made up of a magnesium hydroxide (Mg(OH)(2)) outer layer and an inner layer containing magnesium oxide (MgO), yttrium oxide (Y2O3) and hydroxide (Y(OH)(3)), mixed with a small amount of MgH2, zirconium oxide (ZrO2) and neodymium oxide (Nd2O3). The Y2O3 and Y(OH)(3) signals increase slightly in the inner layer towards the corrosion film/alloy interface. Unlike these compounds, ZrO2 and Nd2O3 compound signals are constant inside the inner layer. It is concluded that: (i) neodymium, zirconium and yttrium play a key role in the slightly improved corrosion resistance of the alloy and (ii) the cathodic reaction is slower on WE43 than on pure Mg and AZ91. (C) 2013 Elsevier Ltd. All rights reserved.