Influence of high -temperature powder pre-oxidation on the deposition efficiency and the mechanical properties of solid-state cold spray additive-manufactured aluminium deposits

Cold spraying (CS), as a solid-state additive manufacturing technique, offers a unique metallurgical process in metal deposition. This work focuses on Al powder properties, particularly particle size and oxide film, which influence deposition efficiency (DE) and the final properties of the Al deposits produced by cold spray additive manufacturing (CSAM). Fine-sized powder exhibits the highest strength among the three powder sizes studied; however, pre-oxidation at 550°C for 10 h increases its oxygen content from 0.09 wt.% to 0.31 wt.% and the oxide film thickness from 8 nm to 31 nm, leading to an approximately 25 MPa reduction in its strength. The softening effect induced by high-temperature pre-oxidation makes the DE of oxidised Al powders higher than that of as-atomised ones when the spray gas temperature during CSAM exceeds 300°C, which is also reflected by the single-particle deposition efficiency increasing from 45% to 75%. However, high-temperature pre-oxidation decreases particle bonding quality and reduces the mechanical and electrical properties of the Al deposits. These effects become more pronounced under increased spray gas temperatures, emphasising the need for finding the right balance between powder pre-oxidation with spray parameters to optimise the deposit performance.