抄録
Mg–10 mass%Gd–3 mass%Nd–Zr alloy and Mg–10 mass%Dy–3 mass%Nd–Zr alloy have high strength at elevated temperatures and their application to automotive engine parts is expected. In this paper, the corrosion propeties of these alloys in salt solution are discussed. The corrosion properties are evaluated by immersion test in salt solution and electrochemical impedance spectroscopy (EIS). The corroded surface is also characterized by SEM and XPS analysis. From the results of immersion test, it is found that corrosion resistance of as-cast, solution-treated and peak-aged specimens of these alloys are comparable with that AZ91D which has a good corrosion resistance. From the results of EIS, it is clear that stable protective film on the surface of over-aged specimen is formed in salt solution. The surface of the protective film consists of fine needle like compounds. It is suggested that the compounds are MgO, Mg(OH)2 and 3MgCO3·Mg(OH)2·3H2O stabilized by Gd or Dy from the results of XPS. The compounds play the important role as stable protection film on the surface of over-aged specimens of the examined Mg–RE alloys, and results in higher corrosion resistance of the specimens than that of an AZ91D magnesium alloy.
