Insightful investigation for the strengthening mechanisms of Al-Cu alloy prepared by wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) has high potential in fabricating large-scale structural components, offering advantages such as high forming efficiency, mold-free production, and superior energy utilization. Al-Cu alloys undergo rapid solidification and thermal cycling during WAAM, leading to anisotropy in their mechanical properties, which can compromise the performance of the alloys. To address this issue, this study proposes a homogenization treatment strategy. Employing electron microscopy, mechanical testing machines and other testing methods, a systematic analysis of the microstructure and mechanical properties of as-deposited Al-Cu alloys before and after homogenization is conducted. The investigation reveals that the as-deposited WAAM Al-Cu alloys exhibits a heterogeneous structure of fine equiaxed grains and coarse columnar grains, which significantly differentiates the mechanical properties along the scanning direction and the deposition direction. Notably, the elongation along the deposition direction falls below 8%, unsatisfactory for practical applications. An optimized homogenization treatment of 510 degrees C for 24 h is established. After homogenization, the coarse columnar grains transform into equiaxed grains, while the fine equiaxed grains grow, enhancing microstructural uniformity. Additionally, the homogenization treatment mitigates geometrically necessary dislocations and reduces solute segregation at grain boundaries. Consequently, the anisotropy in mechanical properties of WAAM Al-Cu alloys is eliminated after homogenization, and the elongation is elevated to over 10.2%. Moreover, we also found that homogenization facilitates the dissolution of coarse theta ' phases and promotes the precipitation of theta '' phases during artificial aging, resulting in higher strength and ductility in T6 treated Al-Cu alloy.