The effects of heat treatment on 7075 Al cold spray deposits

- Mechanical properties of the deposit can be improved with post-CS HTs.
- Massive precipitation of strengthening phases in low temperature HTs
- Metallurgical bonding occurs at the PPBs in the course of HT.
- High ductility after annealing due to porosity reduction & bonding improvement

High-pressure cold spray was used to deposit 7075 aluminum powder onto 7075-T6 substrates. We investigated the effects of post deposition heat treatments on the microstructure and mechanical properties of the deposits. For this purpose, both low-temperature and high-temperature treatments were carried out on specimens excised from the deposits. Microstructures of the as-deposited and heat treated samples were characterized via different microscopy techniques and mechanical properties were evaluated by microtensile and hardness tests. The results were then correlated with the observed microstructures in different conditions. The strength and ductility of the cold sprayed 7075 deposits increased after both low- and high-temperature treatments, which resulted in precipitation of strengthening phases and increased inter-particle bonding. Because of a change in bonding mechanism, heat treatment at high temperature yielded markedly greater ductility than all other conditions. Diffusion and microstructural sintering at the particle-particle interfaces were proposed to cause the change in bonding mechanism from mechanical interlocking to metallurgical bonding and lead to the ductile characteristics of these samples. The understanding gained from this research should lead to optimization of and pre- and post-processing treatments for cold spray deposits.