Cold spray deposition of solution heat treated, artificially aged and naturally aged Al 7075 powder

The deformation behaviour of particles and substrate in cold spray is dictated by the intrinsic properties of both materials, and their bonding directly affects the resulting properties of the deposited coating. The processing through heat treatment of aluminium alloy powders has only recently been developed for both cold spray and additive manufacturing, hence the necessity to evaluate and further understand the evolution of their properties. In this study, an Al 7075 gas-atomised powder was solution heat treated, quenched and subsequently aged. The powder in its as-quenched, T4 (natural ageing at room temperature for 21 days) and T6 (artificial ageing at 120 C for 24 h) condition was characterised through differential scanning calorimetry and scanning electron microscopy to evaluate the precipitation kinetics. Powders were cold sprayed using heated N-2 at 500 C and 6.0 MPa and the resulting deposits were evaluated using tubular coating tensile and pull-off bond strength tests. The precipitation development in the gas atomised powder was found to be similar to the bulk alloys, with development eta' precipitates during artificial ageing and Guinier-Preston zone formation and development during natural ageing. A relationship between the deposition efficiency of the powders and the coating properties was discovered and explained through an adapted densification mechanism based on powder tamping.