Effects of different heat treatments on anisotropy of cold sprayed 7075 Al deposits

In this work, dense and thick 7075 Al deposits were prepared by cold spray additive manufacturing (CSAM). The effects of different heat treatments (i.e. annealing (A), homogenization annealing (HA), solution treatment + artificial aging (T6), and sintering (S)) on the inherent anisotropy of CSAMed 7075 Al deposits were investigated in detail. The scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), Vicker's micro-hardness tests (performed at the vertical plane (V-plane) and horizontal plane (H-plane)), and tensile tests (performed at various tensile orientations) were employed to characterize the microstructural and mechanical anisotropy before and after heat treatments. The results revealed that secondary phases may preferentially nucleate and grow at the particle-particle interfaces of the feeding powders. After heat treatments, recovery and recrystallization phenomena occurred in the samples but it did not eliminate microstructural anisotropy. The recrystallization process resulted in the formation of non-equiaxed grains thereby leading to microstructural anisotropy. Further, mechanical anisotropy can be alleviated by heat-treatment but it can not be completely eliminated in the samples. In general, the ultimate tensile strength (UTS) of the samples decreased gradually with increasing the tensile angle (tensile direction relative to the H-plane). Due to the precipitation hardening mechanism, the T6 sample showed the highest UTS and microhardness. The elongation of CSAMed Al deposit was greatly improved after sintering treatment.