The heterogeneous band microstructure and mechanical performance in a wire + arc additively manufactured 2219 Al alloy

Abstract

In this study, a 2219 Al alloy with a heterogeneous band structure characterized by an alternating distribution of equiaxed and columnar α-Al grains was obtained by wire + arc additive manufacturing. The volume fractions of the equiaxed and columnar grains were varied by adjusting the cooling mode of the substrate. The volume fraction of the columnar grains in a water-cooled (WC) deposit was approximately 16% higher than that in an air-cooled (AC) deposit. Moreover, the WC deposit exhibited smaller primary arm dendrite spacing and lower porosity than those of the AC deposit. The results of in-situ tensile testing revealed that the columnar grains could coordinate and distribute strain more effectively than the equiaxed grains. The ex-situ electron back scatter diffraction data showed that the observed deformations of the columnar and equiaxed grains during tensile testing were non-uniform and non-synchronization. Furthermore, numerous dislocations in the columnar grains of the deposit coordinated the deformation process. According to tensile testing data, the ultimate strength, yield strength, and elongation of the WC deposit were 247.7 ± 17.7 MPa, 110.1 ± 6.3 MPa and 11.9 ± 0.7%, which were higher than those of the AC deposit by 10.76%, 15.78%, and 26.78%, respectively. Therefore, the heterogeneous band structure of the equiaxed and columnar grains ensured good synergy between strength and ductility.