Machining process usually induces Severe Plastic Deformation (SPD) in the chip and machined surface, which will further lead to rapid increase of dislocation density and alteration of grain size in micro-scale. This paper presents a novel FE model to simulate the dislocation density and grain size evolution in the machined surface and subsurface generated from the orthogonal cutting process of Al6061-T6. A dislocation density model of microstructure evolution is implemented in the FE model as a user-defined subroutine written in FORTRAN. The model can predict the microstructure characteristic in a machined surface. The predicted chip thicknesses, cutting forces, distributions of dislocation density and grain size are verified by the experimental tests of the chip, forces, microstructure and micro-hardness. The predicted results show that the dislocation density decreases along the depths of machined surface; whereas the grain size shows an opposite tendency. Dislocation density in machined surface decreases and grain size increases when cutting speed increases. Higher cutting speeds are associated with thinner deformation layers. Dislocation density in a machined surface decreases initially and then increases with feed rates. Dislocation density increases significantly when cutting tool has a larger negative rake angle. The bigger negative rake angles further lead to the thicker deformation layers in machined surface.

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