Corrosion protection of different environmentally friendly coatings on powder metallurgy magnesium

Pure magnesium was processed by a powder metallurgy (PM) route to generate microstructural features that provide higher mechanical properties than those of cast pure magnesium and commercial AZ31 alloy. Nevertheless, corrosion resistance of PM Mg needs to be improved if this material is to be used for structural applications in a corrosive medium. In the present work, the corrosion protection effectiveness of three simple, economical and environmentally friendly coatings has been evaluated over immersion time in a chloride-containing solution. A silane coating, an anticorrosive paint formulated with ion-exchangeable pigments (IEPs) and a chemical conversion treatment to form a MgF2 layer have been studied. Silane film and anticorrosive paint enhance the corrosion behaviour of PM Mg during the first hours of immersion, but their protection effectiveness completely disappears after 2 days. For longer immersion times, the fluoride conversion coating may be considered the only viable and effective barrier to protect PM magnesium from degradation. (C) 2010 Elsevier B.V. All rights reserved.