Effects of Process Parameters on Cold Spray Deposition of Al-6061 Alloy

The effects of several cold spray process parameters on deposition efficiency and bonding quality of Al-6061 powder on the same material were investigated. Single particles were deposited at different particle impact velocities, nozzle-orientations, and nozzle travel speeds. Thick multilayer deposits were prepared to evaluate the effects of substrate surface finish and nozzle-orientation on deposition efficiency and bonding strength. Microstructural evaluation was performed on both deposited single particles and multilayer thick deposits by using optical microscopy, SEM, and TEM. It was confirmed that bonding occurs in peripheral regions of the splats, while only partial bonding develops at the polar region even at high impact velocities. Further, there is a critical spray angle below which no deposition takes place. This critical spray angle depends on nozzle travel speed and the duration of spray. A new method for substrate surface preparation was proposed by spraying at angles below the critical spray angle with the same powder prior to coating. Using low angle spraying as a surface preparation strategy provides a bonding strength of 54 MPa as compared to 22 MPa obtained for grit blasted substrates. Spray angle also affects deposition efficiency, porosity, and microstructure. Reducing the spray angle from 90 degrees to 30 degrees results in decreasing the deposition efficiency from 48 to 16%, increasing the porosity from 0.84 to 1.36%, and changing the microstructure from tightly bonded microstructure into columnar microstructure with porosity developed at inter-columnar regions.

Automated summary

The effects of cold spray process parameters on the deposition efficiency and bonding quality of Al-6061 powder were investigated. The study revealed that nozzle orientation, particle impact velocity, and nozzle travel speed affect the deposition and bonding. Microstructural evaluation showed that bonding occurs in peripheral regions of the splats. A critical spray angle was also identified, below which no deposition takes place. A new method for substrate surface preparation was proposed using low angle spraying. The spray angle was found to influence deposition efficiency, porosity, and microstructure.