Engineers from ASB Industries, the University of Akron, and the University of Nevada have collaborated to develop double-layer coatings on magnesium. Current cold-sprayed (with nitrogen as propellant gas) commercially pure aluminum coatings on magnesium alloys lack acceptable hardness and wear resistance, and are highly susceptible to localized corrosion in chloride-containing solutions.
Hence, a commercially pure α-Ti layer with high passivation propensity (with about 1293.05mV vs. SCE trans-passive potential), hardness, and low wear rate was applied on a CP-aluminum-coated magnesium alloy. The titanium layer deeply penetrated into the aluminum layer with heavy deformation. This was accompanied by noticeable densification of the softer aluminum underlayer by hard titanium particles with high kinetic energy (hammering effect).
The titanium layer raised micro-hardness (HV0.025) from 56.43 (CP-Al coated Mg alloy) to 263.03 for Ti/Al coated Mg alloy. The surface with higher hardness (i.e., Ti/Al coating) provides a lower wear rate, followed by magnesium bulk and aluminum-coated surfaces, respectively.
The researchers note that further studies (long-term corrosion tests) are needed to elucidate the effectiveness and corrosion protection performance of cold-sprayed double-layer coatings on magnesium alloys.
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