The influence of cold and detonation thermal spraying processes on the microstructure and properties of Al-based composite coatings on Mg alloy

Al-based metal matrix composite (Al-MMC) coatings were produced on AZ91 magnesium alloy substrates utilizing two distinct coating techniques, i.e. cold spraying (CS) and detonation thermal spraying (DS), and the microstructure, hardness, bonding strength and corrosion behaviour were comparatively studied. The results showed that the CS process, which was featured with high kinetic and low thermal input energies, led to the dense structure resulted from the high velocity impact of particles at the solid state. The DS processed coatings showed relatively high porosity owing to the melting and oxidation involved during the deposition. But, due to the high fraction of metallurgical bonding of deposited splats, the DS coating demonstrated superior mechanical properties in terms of hardness and bonding strength when the porosity was reduced at higher volume fraction of the ceramic reinforcement. With increasing the volume fraction of ceramic particles in the source powder, the transitional fracture from the adhesive to cohesive mode was observed for both CS and DS processed composite coatings. In addition, compared to the AZ91 alloy substrate, both CS and DS composite coatings showed improved corrosion resistance.