Printability of low-cost pre-heat-treated ball milled Al7075 powders using compressed air assisted cold spray additive manufacturing

Abstract

• Cold spray printing using low-cost ball-milled powders was successfully demonstrated. • As-received powders were irregular in shape and size, significantly work-hardened, and consisted of very fine precipitates in its microstructure that affected its printability. • Annealing the powders resulted in significant reduction in hardness and coarsening of precipitates, thereby facilitating cold spray printability. • A deposition efficiency of 59% was realized with pre-treated powders using compressed air as propulsive gas, which is higher than the deposition efficiencies reported in published literature. A successful attempt at the cold spray additive manufacturing (CSAM) of low-cost ball milled Al7075 powders using air as the carrier gas is demonstrated. The irregular shape and hardness of the as-received powders are identified as a primary obstacle to the successful printability which demonstrated 0% deposition efficiency. Thus, different annealing procedures are suggested as an optimization technique to facilitate printing. These annealing procedures are compared and contrasted using differential scanning calorimetry (DSC) and the hardness/printability of the annealed powders are correlated exactly to the enthalpies in the low temperature i.e., <300 °C region. The annealing procedure of 300 °C for 4h (referred to as the C4 powder) is found to be the most optimal based on the combination of hardness, deposition efficiency, porosity and enthalpy values. On printing, the C4 powder also shows the best combination of good quality edge spraying, highest deposition efficiency of 59% and low porosity of 1.80%. Finally, while the microstructure of the C4 powder particles is retained in the microstructure of the printed part, the hardness of the printed part is higher than that of the C4 powder. This is attributed to a combination of deformation strain induced within the interparticle boundaries during the cold spray process and excellent interparticle interlocking.