| Isothermal hot torsion tests were performed on 6061 Al alloy followed by a constitutive analysis of the alloy and three metal matrix composites previously tested (10%Al2O3/6061, 15%SiC/6061, and 20%Al 2O3/6061). The flow stresses decrease with increasing deformation temperature and the rate at which this occurs increases with percent reinforcement. Flow stress as a function of strain rate and temperature was suitably represented by the hyperbolic sine and Arrhenius equations for the alloy and metal matrix composites. Extrusion, modeling was performed for the four materials using the constitutive equations above and the finite element software DEFORM which is a registered trademark of Scientific Forming Technologies Corporation. Simulations were run for various extrusion conditions and the output was placed in table format to facilitate interpolation. The simulation results were validated with comparison to real life extrusions and modeling of other researchers. The results showed that an increase in billet temperature, a reduction in ram speed, or a reduction in extrusion ratio, had the effect of reducing the ram load. According to the modeling results, maximum strain rate and maximum extrudate velocity increased with increasing ram speed or extrusion ratio and were not influenced by the percent reinforcement or initial billet temperature. The rate of decrease of nun load as a function of time (distance) increased with increasing percent reinforcement as a result of deformation heating. |
