Cold spray blended Al + Mg17Al12 coating for corrosion protection of AZ91D magnesium alloy

Commercially pure aluminum and aluminum blended with 50 vol.% and 75 vol.% of the intermetallic Mg17Al12 compound feedstock powders were successfully deposited onto as cast AZ91D magnesium substrate using a cold spray process that was employed at low working gas pressure and temperature. The microstructure, mechanical performance and corrosion resistance properties of the Al coatings with and without reinforcement particles were investigated and discussed. The results show that under the same deposition conditions, the coating porosity level can be significantly decreased by adding hard particles into the pure aluminum feedstock. Although, only a small fraction (less than 10 vol.%) of the Mg17Al12 particles was retained in the coatings, the hardness, was increased from 47 ± 5 HV0.1 to 58 ± 3 HV0.1, while the bonding strength was 2 to 3 times higher than the pure Al coating. The spherical Mg17Al12 particles play a role similar to that of the hard ceramic reinforcement particles in the metal matrix composite (MMC) coatings. Electrochemical corrosion experiments also demonstrated that the composite coatings have similar electrochemical characteristics to the bulk Al, and they can provide suitable protection for the as cast AZ91D magnesium material.