Microstructural Characterization of Aluminum 6061 Splats Cold Spray Deposited on Aluminum 6061-T6 Substrate

The microstructural evolution at the interface of Al6061 splats cold sprayed on Al6061 substrate at a supercritical impact velocity was investigated by SEM and S/TEM. Metallurgical bonding was observed in the peripheral (equatorial) region of the splat where a localized outward material flow promoted by continuous dynamic recrystallization (CDRX) occurred to displace the oxide from the interface. No recrystallization or metallurgical bonding was observed at the polar interface where oxide remained in fragments. CDRX produced elongated grains less than 100 nm thick at the equatorial interface which transformed to slightly coarsened (100 to 200 nm) ultrafine grains in the splat side of the interface. Rapid precipitation on the boundaries of recrystallized grains and in the unrecrystallized regions of the splat–substrate interface was discussed in relation to the sequence of structural evolution at the splat–substrate interface during the impact and subsequent cooling. Further work is needed to more fully understand the kinetics of dynamic recovery/recrystallization and precipitation in the presence of excess vacancies that can have impact on the dislocation mobility, mass transport, and thermodynamic stability.