Microstructure and Mechanical Properties of Fe-Rich Thixotropic Deep-Cavity Al-1.2Si-1.1Fe-0.8Zn Cylindrical Components with Inconsistent Wall Thickness

In this study, the thixotropic behavior of an Fe-rich Al-1.2Si-1.1Fe-0.8Zn aluminum alloy was thoroughly investigated. Firstly, ideal semi-solid billets were prepared through thermal deformation-induced isothermal spheroidization (TDIIS). The application of severe plastic deformation (SPD) via hot upsetting provided a strong driving force for recrystallization. As a result, the fibrous elongated grains gradually transformed into equiaxed grains following the TDIIS process. Overall, the grain size decreased with increasing deformation. However, as the temperature rose, the grain size initially decreased and then increased. The optimal conditions for the hot upsetting process were determined to be a temperature of 400 °C and a deformation of 50%. Under these conditions, the average grain size was 71.1 μm, and the shape factor was approximately 0.8, showcasing the excellent thixotropic properties of the semi-solid billets. Furthermore, the microstructure and mechanical properties of the thixotropic Al-1.2Si-1.1Fe-0.8Zn components were examined. These components, which were deep-cavity cylinders, exhibited an inconsistent wall thickness. Due to variations in the extrusion pressure, the grain morphology transitioned from dendritic at the upper part of cylinder wall to equiaxed at the bottom. This transition caused the elongation of the cylinder wall, resulting in it being lower than the cylinder bottom. During the thixoforming process, the equiaxed grains underwent deformation, and new recrystallized grains were formed. The multiscale synergy between the deformed grains, recrystallized grains and subgrains enabled the Fe-rich Al-1.2Si-1.1Fe-0.8Zn aluminum alloy to achieve well-balanced mechanical properties.