The effect of machining process thermo-mechanical loading on workpiece average grain size

Abstract

This paper introduces an iterative process-material analysis approach, to predict the evolution of grain size on the surface of a workpiece material, resulting from the mechanical and thermal loading effects during the machining process. The proposed approach endeavors to describe the effects, the resulting changes of the workpiece properties have on the process behaviors. The retroactive mechanism, in the context of how process behaviors are affected by material-microstructural variations, is jointly considered, while both mechanisms of grain refinement, as a result of dynamic recrystallization and grain growth due to thermal energy, are incorporated in the analysis of the final grain size. The dynamic recrystallization process is described by a Zener-Hollomon-based model. Furthermore, the thermal energy dissipation effect is quantified by a thermally activated cross-slip mechanism contributing to the increase of grain size. Subsequently, the outputs of these process mechanics, such as the strain, strain rate, and temperature, are calculated, and the microstructure behavior is predicted in response to the material properties and machining parameters. The experimental validations of the proposed approach are accomplished on two aluminum systems, AA7075 and AA 6061.