Research On Hot Deformation Behavior And Hot Extrusion Technology Of B₄C/AA6061 Composites

In this paper,B₄C/AA6061 composites were prepared by liquid stirring casting method.The flow stress behavior of B₄C/AA6061 composites has been researched by compression test using Gleeble-3800 thermal simulator,in the temperature ranging from360?⁵10?and strain rate ranging from 0.001s^-1 to 1s^-1.Typical true stress-true strain curves showed that the peak stress levels decreased with the rising of temperature but increased with the rising of strain rates.These curves in present work also reveal that the B₄C/AA6061 composite is a positive strain rate sensitive material.The relationship between the peak stress and the strain rate in different stress regions is fitted by the method of linear regression.The coefficient is above 0.97 and linear relationship between the ln[sinh????]and lnZ is good,which indicates that the hyperbolic sine function of the flow stress is reliable in the whole stress range.The hot deformation activation energy is calculated as 151.634kJmol^-1 and the constitutive equation in the form of hyperbolic sine function of B₄C/AA6061 composites is obtained.The effects of Z values on dynamic softening and associated microstructural evolution during hot deformation were investigated by electron back scattered diffraction technique?EBSD?.It was found that with the decrease of Z values,local strain induced by deformation was released and the grain size of aluminum matrix increased gradually,which indicated that the main softening mechanism of B₄C/AA6061 composites was dynamic recrystallization?DRX?,and the lower the Z value was,the easier the DRX occurred.Compared with the difference of DRX behavior between the alloys without particles and the B₄C/AA6061 composites,we easily found that presence of particles promotes DRX by particle stimulate nucleation.Based on The dynamic material modeling?DMM?,the processing map of B₄C/AA6061 composites is drawn.The flow stability domains are mainly concentrated in two regions:low temperature?from 360?to 400??with strain rate from 0.001s^-11 to0.1s^-1 and high strain rate(from 0.3s^-1 to 1s^-1)under deformation temperature from 365?to 480?.The optimum processing area of B₄C/AA6061 composites is:strain rate from0.04s^-1 to 0.08s^-1 under deformation temperature from 470?to 490?.According to the optimum processing area given by the processing map,the hot extrusion test was designed with different extrusion ratio under deformation temperature from 480?to 520?.The results showed that the density of the as-cast samples was about 92.57%,and the average density after hot extrusion reached 98.26%.As the extrusion ratio increases,the density increases.the tensile strength of the original as-cast sample is about 152.8MPa and the elongation is about 6.77%.After hot extrusion,without T6 heat treatment,the tensile strength of the reached 209.8MPa,the elongation reached 12.0%.The average tensile strength of the extrusion samples after T6 heat treatment reached 344.6MPa,the elongation reached 10.66%.Obviously,T6 heat treatment has great effects on mechanical properties of B₄C/AA6061 composites.Hot extrusion can improve the tensile strength greatly but not at the cost of elongation.