An innovative thermal simulation study of microstructure improvement by delay forging during solidification

Abstract

The solid fraction at the beginning of the forging process is an important factor affecting the performance of the casting-forging integrated forming, which is an innovative and efficient process. The solid fraction depends on the delayed forging time during the casting-forging integrated forming. This paper investigates the effect of delayed forging time on the microstructure of aluminum alloy forged during solidification using an innovative physical simulation method. In this work, a solidification-forging device compatible with the Gleeble system has been developed. Then, experiments were conducted at various delayed forging time. Temperature and force data were collected using the Gleeble system for analysis. Microstructural evolution was investigated using methods including Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Backscattered Diffraction (EBSD), and Three Dimensional Computed Tomography (3D-CT). The results demonstrate that with the extension of the delayed forging time, the grain size of the alloy decreases gradually, and the coarse dendrite structure changes to the rose-shaped grains, and the local misorientation in the grain increases. Moreover, the effect of forging under different forging time on the casting defects of the alloy is studied. When the forging delay is extended to 8 s, the forging promotes the porosity caused by the liquid phase convection. However, with further extension of forging delay, the reduction of the liquid phase and the fracture of dendrites lead to the complexity of liquid phase channels, resulting in the increase of porosity. Additionally, forging near solidification can close shrinkage porosity.