Solid-state additive manufacturing of dissimilar 7075–2024 aluminum alloys by additive friction stir deposition: Interfacial bonding and process optimization

Abstract

Additive Friction Stir Deposition (AFSD), an emerging solid-state additive manufacturing technique, has shown great promise in processing single aluminum alloys. However, its applicability to dissimilar aluminum alloys remains unclear. In this study, the feasibility of additive friction stir deposition for fabricating dissimilar 7075–2024 aluminum alloy structures was investigated for the first time. The effects of tool rotational speed (800–1400 rpm) on interfacial bonding, microstructural evolution, and mechanical properties were systematically studied. All deposited samples exhibited defect-free macrostructures within the studied range. Increasing the rotational speed resulted in grain refinement in the mid-layer regions of both 7075 and 2024, reaching minimum average grain sizes of 1.14 µm and 1.40 µm, respectively. The fraction of high-angle grain boundaries (HAGBs) increased significantly, reaching 86.1 % and 67.0 %, along with recrystallization fractions of 91.04 % and 84.39 % in 7075 and 2024 layers, respectively. At 1100 rpm, a uniform distribution of strengthening precipitates was observed, with the hardness reaching 75 % of the base materials and the highest tensile strength (181.9 MPa) and elongation (6.3 %) obtained. Further increases in rotational speed led to partial dissolution of precipitates due to excessive heat input, reducing hardness. While additive friction stir deposition was proven effective for fabricating dissimilar aluminum alloys, the tensile properties in the build direction (BD) were noticeably inferior to those in the longitudinal direction (LD). This study demonstrates that large-area joining of dissimilar aluminum alloys can be achieved via the AFSD process, providing a novel approach for the bonding of dissimilar alloys and laying a theoretical foundation for the AFSD fabrication of such materials.