Investigations on microstructure and tensile properties of hybrid WAAM deposition and cold/hot rolling for 2219 aluminum alloy

The inferior mechanical properties of additive-manufactured aluminum components compared to wrought material restrict their application in the aerospace industry. Hybrid additive manufacturing and hot/cold rolling were applied. Hot rolling was achieved using flame heating, and larger deformation can be achieved with a small rolling force compared to cold rolling. Both the cold and hot rolling increase the hardness, and the hardened depth in hot rolling is 50% larger than the cold rolled sample. The maximum hardness is located at the position beneath the rolled surface, indicating the heterogeneous hardness distribution induced by the rolling process. The equiaxed grains and dendrites change to a banded structure under the rolling process, and it changes to fine equiaxed grains induced by the recrystallization process during the subsequent layer deposition. The inter-layer rolling and heat treatment obviously increase the strengths and reduce the ductility. However, there is no difference in strength between the as-deposited and the inter-layer rolled samples, while the rolled samples show higher isotropic elongation. The rolling process significantly increases the elongation by 35.3% and 53.7% in horizontal and vertical directions after heat treatment due to the porosity closure and elimination. The reason for the improvement of strengths and ductility with the rolling process is discussed.