Corrosion behaviour of Mg/Al alloys with composite coatings

The corrosion behaviour of aluminium/silicon carbide (Al/SiC) composite coatings deposited by thermal spray on AZ31, AZ80 and AZ91D magnesium-aluminium alloys was investigated by electrochemical and gravimetric measurements in 3.5 wt.% NaCl solution at 22 °C. Corrosion products were examined by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and low-angle X-ray diffraction (XRD). Al/SiC composite coatings in the as-sprayed state revealed high level of porosity with poor bonding at the Al/SiC and coating/substrate interfaces, which facilitated degradation of the magnesium substrates by a mechanism of galvanic corrosion. Cold-pressing post-treatment produced more compact coatings with improved corrosion performance in 3.5 wt.% NaCl compared with as-sprayed coatings.