Improving mechanical properties of wire arc additively manufactured AA2196 Al–Li alloy by controlling solidification defects

Additive manufacturing has advantages of cutting the time from design to making new parts but it suffers from metallurgical defects such as porosity. For example, wired arc additive manufacturing(WAAM) of new alloys such as Al–Li alloys is very challenging due to the fact that the porosity level is so high as to degrade not only fatigue life but also the static mechanical properties. In this study, we found that large chains of porosity could form at the interdendritic liquid during WAAM of an AA2196 Al–Li alloy. After T6 heat treatment, those chains of porosity actually grow bigger than the as-deposit state, with the microporosity size over 50 µm increasing from 2.8% to 5.8% and the maximum size grow up to 107 µm. Using X-ray Computed Tomography (XCT), we have quantified the spatial distribution of microporosity as a function of hot deformation after WAAM. It was found that the chain of microporosity along the direction of deposition could be effectively eliminated by controlling the strain. Combining the 42% hot deformation and T6 heat treatment, the closure of microporosity together with nano-sized T₁ precipitates can be achieved and yield tensile strength (YTS) can be improved by 199%, the ultimate tensile strength (UTS) can be increased by 168%, and the elongation can be extended by 460%, reaching up to 372 MPa, 439 MPa, and 6.9%, respectively. Therefore, the solidification defects during WAAM can be remediated by applying proper hot deformation which is extremely useful for the Al–Li alloys with a long solidification range and high susceptibility to solidification cracking.