Corrosion behaviour of Mg-Al alloys with Al-11Si thermal spray coatings

Abstract

The corrosion resistance of AZ31, AZ80 and AZ91D Mg–Al alloys with Al–11Sithermal spray coatings was evaluated by electrochemical and gravimetricmeasurements in 3.5 wt% NaCl solution. The changes in the morphology andcorrosion behaviour of the Al–11Si coatings induced by a cold-pressingpost-treatment under 32 MPa were also examined. The as-sprayed Al–11Sicoatings revealed high degree of porosity and poor corrosion protection, whichresulted in galvanic acceleration of the corrosion of the magnesium substrates.The application of a cold-pressing post-treatment produced more compactAl–11Si coatings with better bonding at the substrate/coating interface andslightly higher corrosion resistance. However, interconnected pores remained inthe cold-pressed coatings due to the low plasticity of the Al–11Si powder andgalvanic corrosion of the substrate was observed after immersion in 3.5 wt%NaCl for 10 days