Understanding the microstructural evolution and fatigue behavior of aluminum 2319 fabricated by wire arc additive manufacturing

Abstract

Aluminum alloys have received substantial interest for the fabrication of complex and large size components for the aerospace industry via additive manufacturing processes. This work explores the fatigue performance of aluminum alloy 2319 fabricated by wire-based Directed Energy Deposition (DED) with Cold Metal Transfer (CMT) process, i.e., wire arc additive manufacturing (WAAM) technology. The as-deposited 2319 wall microstructure was composed by both columnar dendrites and equiaxed grains along the build direction (BD). Also, fine and coarse theta and theta ' precipitates were noticed in the WAAM printed 2319 wall due to repeated thermal cycles while fine precipitates were observed in wrought alloy. The microhardness measurements revealed a gradual decrease from the bottom to the top layers and varied between 65 and 86 HV. Tensile properties (yield strength, ultimate tensile strength, and elongation) measured in the horizontal and vertical directions were 99 +/- 4 MPa, 268 +/- 11 MPa 14.8 +/- 1.5% and 96 +/- 3 MPa, 257 +/- 9 MPa, and 15.6 +/- 2%, respectively. The WAAM 2319 fabricated in this work retained 72% of the strength of their AA2219-T62 wrought counterparts, which can be attributed to the large columnar grains that developed during the additive manufacturing process. The fatigue strength of WAAM 2319 specimen was 67 MPa, corresponding to 65% of the fatigue strength of AA2219-T62. Fracture surface analysis revealed the presence of small and large dimples, secondary micro-cracks, broken intermetallics, and inclusions. This work will provide novel insights and guidance for manufacturing near-net shape aluminum alloys by wire-based DED with improved tensile and fatigue properties.