Microstructural evolution of 7075 Al gas atomized powder and high-pressure cold sprayed deposition

• Powder/deposition microstructure relationship study via different techniques
• High dislocation density, recovery and recrystallization in the deposition
• Various microstructural features in different areas of the deposition
• The main and possible recrystallization mechanisms of the observed UFG structures
• Various spatial distributions of precipitates in grains with different sizes

This study investigates the microstructure evolution of as-atomized 7075 aluminum powder during high pressure cold spray deposition. The as-received powder and the deposition were characterized via scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The as-received powder was composed of two different particle types, differentiated by their grain boundary structure and solute element distribution. Significant solute element segregation was observed at grain boundaries for both particle types. The powder also contained nanoscale subgrain and dislocation structures. High pressure cold spray resulted in the formation of a high quality deposition with limited porosity and inter-particle voids. The deposition was characterized by two distinct regions: particle/particle boundaries and particle interiors. Particle/particle boundaries showed a high degree of deformation resulting in the formation of an ultra-fine grain structure and a low density of low angle grain boundaries. The formation of the ultra-fine grain structure is attributed to dynamic recrystallization and recovery processes. Particle interiors were characterized by larger grains containing a high density of low angle grain boundaries and dislocation structure. Large grains in the deposition contained precipitates distributed both within the grain interior and at grain boundaries. Precipitates in small grains were distributed primarily at grain boundaries. The effect of these precipitates on the microstructure evolution was also discussed.