A composite coating using mixed powders of pure Al and α-Al2O3 as feedstock was deposited on AZ91D alloy substrate by cold spraying. The content of α-Al2O3 in mixed powders was 50wt%. Electrochemical experiments were carried out using 3.5wt.% NaCl solution as electrolyte. Because of dense structure, the composite coating could separate substrate from electrolyte thoroughly for long time immersion. The corrosion behavior of the composite coating was evaluated by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. It is found that the composite coating presented much better corrosion resistance than bare AZ91D alloy, even than bulk 1050 aluminum by electrochemical studies in 3.5wt.% NaCl solution.

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TiAl3-Al composite coating on γ-TiAl alloy was prepared by cold spray and subsequent heat-treatment. The Oxidation test, which was carried out at 950 °C in air, indicated that the bare alloy exhibited poor oxidation resistance, significant weight loss was observed after oxidation for 70 h. The oxides formed were the mixture of TiO2 /Al2O3. For the specimen with the TiAl3–Al coating, great improvement in oxidation resistance was observed. Approximate parabolic oxidation kinetics was observed for the oxidation period. The microstructure analysis showed a dense TiAl2 interlayer and a reticular Cr rich phase formed between the composite coating and the substrate. The oxides in the oxidized coating were mainly alumina, with only trace of titanium dioxide and titanium nitrides after oxidation up to 1000 h. A certain amount of TiAl3 phase in the coating remained unoxidized and unconsumed. The EPMA analyses of the coated samples showed that no trend of oxygen or nitride diffusion into the substrate and no oxide formed beneath the TiAl2 interlayer.

Aluminum-titanium powder mixtures were deposited on γ-TiAl alloy substrates by cold spraying then heat treated for 5 h at 600, 650, and 700 °C. SEM and XRD examination showed that the treatment caused Al to diffuse into the substrate where it reacted with Ti, resulting in changes in microstructure. The diffusion of Al left pores in the fringes of the TiAl3 phase, increasing the porosity of the coatings. A surplus of Al remained in the coatings after heat treatment at 600-650 °C, but at 700 °C, all Al was consumed, contributing to the formation of a continuous TiAl3 layer.