Abstract
The heat treatment of a number of gas-atomised aluminium alloys prior to cold spraying recently showed that the resultant microstructural modification was accompanied by an improvement in deposition; however, the relationship between the microstructural homogenisation occurring after recrystallisation and the increase in deposition efficiency and particle–particle bonding had not been investigated. In this study, Al 6061 gas-atomised feedstock powder, before and after solution heat treatment, was cold sprayed and these materials were characterised using electron backscatter diffraction and transmission electron microscopy. The solution heat-treated Al 6061 powder showed large stress-free grains as opposed to the as-atomised feedstock powder which exhibited smaller grains with the presence of dislocations. The coating produced from as-received powder exhibited a homogeneous distribution of misorientation and lattice defects throughout the particles, whereas the coating produced from solution heat-treated powder showed a strain concentration in the interfacial zones. This was attributed to the partial dissolution and the clustering of solute atoms, allowing the aluminium matrix to deform around the newly formed precipitates.
Highlights
Cold gas dynamic spray is a well-established materials processing technique that is based on the kinetic energy of incident particles to deposit coatings
SEM and EBSD techniques were used to investigate the microstructural evolution occurring during deposition
A more intimate bonding was observed between the particles in the coating deposited using the solution heat-treated powder, whereas gaps and inter-particles voids were characterised in the coating sprayed using the feedstock powder
Summary
Cold gas dynamic spray is a well-established materials processing technique that is based on the kinetic energy of incident particles to deposit coatings. Due to the nature of the gas atomisation process and being closely related to the high cooling rates (10-4 to 10-8 K s-1 [6]) reached by the melt during solidification, the powders typically exhibit a cellular/dendritic microstructure [7, 8]. The presence of an inconsistent intermetallic network can affect the formability of the powder and has been shown to affect any post-deposition ageing heat treatment [14]. To solve this issue, the heat treatment of the powder prior to spraying was recently considered and performed on several gasatomised aluminium alloys, such as Al–Zn–Mg, Al– Mg–Si and Al–Cu alloys [15,16,17]. The homogenisation of the microstructure examined was accompanied by an increase in deposition efficiency and a stronger bonding between particles as well as with the substrate [15, 16]
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