Corrosion resistance of thermally sprayed Al and Al/SiC coatings on Mg

Abstract

Thermally sprayed Al and Al/SiC composite coatings have been deposited on pure magnesium and their corrosion behaviour in 3.5 wt.% NaCl solution has been studied. Al/SiC composite coatings were fabricated with 9 vol.% reinforcement percentage and with porosities around 3.5%, while the porosity of the as-sprayed pure Al coatings was in the range 2.4 vol.% to 4.4 vol.% and depended more on the spraying distance and numbers of layers deposited. A mechanical compaction was applied to the coatings at room temperature and coatings that were nearly free from pores were fabricated for the Al and Al/SiC coatings. In the electrochemical tests, all the coatings showed higher corrosion potentials (about of 200 mV) than uncoated substrates while current densities were nearly two orders of magnitude lower for the Al/SiC composite coatings and three orders of magnitude lower for the pure aluminium coatings. This protective effect was even better in the compacted coatings, currents densities were between five or six orders of magnitude lower than that of uncoated magnesium.