Establishment of macro-micro constitutive model and deformation mechanism of semi-solid Al6061

The compression stress-strain curves of semi-solid metals have evident segmentation characteristics composed of three sections: stress increasing section, stress decreasing section, and stress steady section. At the same time, the semi-solid holding time is introduced into the constitutive model as a new independent variable. Therefore, it is unsatisfactory to use the traditional metal constitutive model to fit semi-solid metals. In this paper, a new form of the constitutive model is proposed. The modified Hansel-Spittel formula is used to fit the characteristic stress points, and these are then used as divides to fit the entire stress-strain curve using the function segment method. The fitting error for the first two stages of the stress-strain curves is found to be 7.01%. At the same time, the microstructure morphologies of different liquid fraction samples at different deformation stages are compared. It was proposed that the three-segment characteristics of the semi-solid stress-strain curve correspond to the process of incubation, growth, and connection of voids in the shear-deformation zone. However, this mechanism of action weakens with the increment of the liquid fraction. For semi-solid metals with liquid fraction more than 25%, it is more appropriate to describe the deformation behavior using non-Newtonian liquid flow model.