Hot Deformation Behavior Of An As-cast Mg-4Li-4Zn-Y Alloy

Hot deformation behavior of the as-cast Mg-4.35%Li-4.09%Zn-1.42%Y-0.08%Al alloy has been studied by hot compression experiment.The stress-strain curves under different temperatures at differernt strain rates were analyzed.The flow stress constitutive equation was established with hyperbolic sine function.The hot processing map was formed to acquire the optimal deformation parameters of alloy.The microstructural development of the alloy during hot compression was observed.The as cast alloy is mainly composed of?-Mg phase,Mg₂₂.₀₇Al_20.90Y_20.27Zn_23.73 phase,Mg_0.97Zn_0.03 phase and W-Mg₃Zn₃Y₂ phase.The alloy has fine strength,toughness and ductility that?_0.2=100.8MPa,?_b=165.7MPa,?=14.5%and HB=64.6.The curves of alloy are typical dynamic recrystallization curves that there is strain hardening with dynamic recrystallization.At the beginning of the deformation,the flow curves raise,after reaching the peak,the curves come down by dynamic recrystallization softening,and reach a steady state.The hot deformation behavior of alloy can be described more accurately by hyperbolic sine function.The hot average deformation activation energy of alloy is higher,as Q=150.50kJ/mol.When the deformation temperature is lower than 400?,the deformation mechanism is mainly controlled by dislocation climbing,When the deformation temperature is higher than 400?,the deformation mechanism is mainly affected by second-phase particles.There is a peak efficiency region in the hot processing map of alloy with 30%³1%energy dissipation efficiency.The phenomenon of shear fracture is observed in flow instable region.The optimal parameters for hot working are T=393⁴50?,??5?=0.0575⁰.195s^-1.The strengthening phase of the compressed alloy are mainly MgZn phase and W-Mg₃Zn₃Y₂ phase.The dynamic recrystallization nucleation was restrained by the dispersive MgZn phase.When deformation temperature was higher than 300?,MgZn phase dissolved in the matrix.When the temperature was above 400?,dynamic recrystallization of?phase took place under all of the deformation conditions.The W phase which was smashed in the compression process promotes the recrystallization nucleation.And it was smashed further at450?to hinder growing up of the recrystallization grains.MgZn phase not only result from Mg_0.97 Zn_0.03 phase,but also had the potential that it might precipitate from the matrix.The percentage of dynamic recrystallization and grain size increased with the increase of deformation temperature and decrease in strain rate.When the strain rate was 0.1s^-1,quantities of precipitates hindered the recrystallization nucleation and the grain growth,so the grain size was refined abnormally.