Cold Spraying a Novel Al7075 Powder: Achieving High Deposition Efficiency using Nitrogen

High strength aluminum alloys, specifically the 7000 series, constitute the majority of the structural weight of many common commercial aircrafts. The most common alloy, aluminum 7075, gains its strength through precipitates that form during heat treatment. These precipitates make it more susceptible to pitting corrosion, in comparison to pure aluminum, leading to a desire for restoration and repair of these corroded areas instead of scrapping entire components. However, typical repair processes, such as welding and thermal spray, pose an issue for these alloys as the precipitates may coarsen or dissolve into solution if held at high temperatures for extended periods of time.

Cold spray offers a possible solution to this problem, as substrate temperatures are much lower than other processes. Unfortunately, the inherent properties of conventional gas or plasma atomized powders results in a lower than desired deposition efficiency when using nitrogen as a process gas. This low DE often pushes the use of helium, an expensive gas recovered from limited natural gas reserves.

A new direct, low energy, solid state powder production process, termed cold mechanically derived powder production, has been developed to produce non-spherical feedstock. The unique morphology and ductility of this powder is promising for cold spray deposition. In this study it is demonstrated that cold mechanically derived aluminum 7075 feedstock powder results in substantially higher deposition efficiencies when compared to conventional atomized powders under the same conditions, using only nitrogen. This work also demonstrates that the use of this powder significantly reduced the spray time and cost, while maintaining similar mechanical properties (porosity, hardness, adhesion) as the gas atomized powders while leaving the heat treatment of the underlying substrate unaffected.