Ion-polished microstructures of the 5056 feedstock powder in (a) & (b) as received, and (c) & (d) degassed conditions.
Researcher – Reza Rokni
The effects of powder preprocessing (degassing at 400C for 6 hours) on microstructure and mechanical properties of 5056 aluminum deposits produced by high-pressure cold spray were investigated. To investigate directionality of the mechanical properties, microtensile coupons were excised from different directions of the deposit, i.e., longitudinal, short transverse, long transverse, and diagonal then tested. The results were compared to properties of wrought 5056 and the coating deposited with as-received 5056 Al powder and correlated with the observed microstructures. Preprocessing softened the particles and eliminated the pores within them, resulting in more extensive and uniform deformation upon impact with the substrate and with underlying deposited material. Microstructural characterization and finite element simulation indicated that upon particle impact, the peripheral regions experienced more extensive deformation and higher temperatures than the central contact zone. This led to more recrystallization and stronger bonding at peripheral regions relative to the contact zone area, and yielded superior properties in the longitudinal direction compared with the short transverse direction. Fractography revealed crack propagation takes place along the particle/particle interfaces in the transverse directions (caused by insufficient bonding and recrystallization), whereas through the deposited particles fracture is dominant in the longitudinal direction.