Abstract
<title>Abstract</title> <p>Die forging inevitably induces metal flow toward both the die cavity and flash, leading to the formation of a flow boundary between these two regions. However, the influence of such a flow boundary on the final microstructure and properties of forgings remains unclear. To address this gap, this study investigates the effects of flow boundaries on the microstructure and mechanical properties of disk-shaped 7075 aluminum alloy casing forgings via a combination of finite element (FE) simulations and experimental characterizations. Results show that two distinct flow boundaries form at different locations during disk forging, and their formation mechanisms and evolutionary characteristics were systematically clarified. Electron Backscatter Diffraction (EBSD) analysis revealed significant microstructural inhomogeneities at different locations of the forging: regions adjacent to flow boundaries (Locations 2 and 3) exhibit coarse grain structures with an average grain size of 54.02 µm and 32.70 µm, and low recrystallization fractions of 22.7% and 31.9%, which are only half of those in non-boundary regions (48.8%–51.9%). Tensile tests demonstrated that the yield strength of flow boundary regions in the radial direction is 362 MPa–371 MPa, which is 40 MPa–50 MPa lower than that of non-boundary regions (400 MPa–413 MPa). Although flow boundaries have a significant impact on grain morphology and texture development, they exert only a minor effect on phase distribution and texture intensity. These quantitative findings offer critical theoretical support for optimizing the forging processes of high-performance aluminum alloy components and improving the uniformity of forging properties.</p>