A two-step surface treatment, combining anodisation and silanisation, for improved corrosion protection of the Mg alloy WE54

The present work reports an innovative approach for surface functionalisation of magnesium alloys (WE54) containing yttrium and rare-earth (RE) elements. A two-step surface modification consisting on the formation of an anodic film followed by the deposition of a hybrid silane layer obtained by dipping in a bis-[triethoxysilylpropyl]tetrasulfide silane (BTESPT) solution was performed on the WE54 alloy. The anodic films were formed by two different ways: (i) a passive film was formed by anodic polarisation of the alloy at 0.5 V in NaOH solutions of pH 13 for 24 h and (ii) an anodic layer was formed by anodising the substrate for 1 h at a potential of 50 V in the same solution. The corrosion behaviour was evaluated by electrochemical impedance spectroscopy in 0.005 M NaCl solutions for one week. The results show that the two-step treatment improves the corrosion resistance comparatively to the untreated blank substrate. The corrosion resistance of the anodised sample treated with silane is significantly better than the treatment combining passive film and silane. For this system, the overall impedance increases by three orders of magnitude. (C) 2010 Elsevier B.V. All rights reserved.