MAGNESIUM ALLOY

Microstructure of an Magnesium Alloy Coated With Aluminum through the "Cold Spray" Process

Microstructure of an Magnesium Alloy Coated With Aluminum through the "Cold Spray" Process

Cold spray processing is a high-rate deposition process (at velocity 50 - 1000 m/s) in which small particles in solid state are mixed with heated gas and accelerated to supersonic velocities through a nozzle. The particles impact the target surface with sufficient kinetic energy to cause plastic deformation and consolidation with the substrate material to bond together, rapidly building up a layer of deposited material. This process uses high velocity rather than high temperature to produce coatings. The combination of high temperature and velocity will causing deformation of the particle droplets. Upon impact, the droplet will undergo rapid solidification forming a spalt due to continuous impact process. This will lead to thickness build up and forming of lamellar structure. Bonding of the coating to the substrate and cohesion between consecutive splats is influenced by residual stresses within the coating, melting and localized alloying at the contact surfaces between particles and substrates, diffusion of elemental species across spalt boundaries, atomic-level attractive forces and mechanical interlocking between the coating and the substrate. (Klinkov, 2005)

Microstructure of the aluminium coating, interface and substrate was available in Fig. 1, in which it is clear that that the coating particles are tightly bonded to the substrate and have very low percentages of porosity. This may indicates good quality of adhesion, and confirmed by more detailed micrograph in Fig. 2.

The SEM micrograph (Fig. 2) shows the presence of dark layer with thickness of ~1µm along the interface. Referring to EDX analysis at position 4 (see Table 1), the interface shows high oxygen content of 32.1 wt. %. Hence, it indicates formation of Al2O3 due to the reaction of Al particle ...