Theoretical and Experimental Investigation of the Viscoplastic Deformation of an Al6061 Aluminum Alloy in the Semisolid State

Viscoplastic deformation plays a dominant role in the compression of semisolid Al6061 aluminum alloy, directly affecting its toughness, formability and processing performance. Nevertheless, in the deformation of semisolid-state Al6061 aluminum alloys, the volume fractions of the solid and liquid phases are very important for determining the viscoplastic rheological characteristics, especially for accurately obtaining the critical solid phase volume fraction required for viscoplastic deformation. To describe the semisolid viscoplastic deformation of Al6061, viscoplastic equations for porous media in the semisolid state with isothermal compression deformation were established in this work on the basis of continuum mechanics and mixture theory. The deformation behavior of Al6061 under semisolid compression conditions was investigated with a thermal simulator (THERCMEMASTOR-Z/100), and the relevant constitutive equations were determined. Combined with the results of the penetration experiments, the rheological behavior in the semisolid forming process was subsequently investigated. The critical temperature of viscoplastic deformation for Al6061 is 644.5 °C, and the critical solid fraction for viscoplastic deformation is 56.4 pct. During the semisolid processing of Al6061, the rheological stress increased with increasing strain rate and decreasing deformation temperature. For the viscoplastic deformation process of the Al6061 aluminum alloy, rheological parameters (A and B) directly related to the solid phase volume fraction were also redefined to calculate the equivalent stress parameters. This work is highly important for precisely characterizing the timing of viscoplastic deformation during the alloy solidification process.