Effect Of Trace SiC_p On Hot Deformation And Working Behavior Of Mg-5Zn Alloy

Magnesium alloys with hexagonal close-packed(HCP)structure have poor forming plasticity at ambient temperatures.So magnesium alloys are generally deformed at high temperatures.Dynamic recrystallization(DRX)usually occurs in magnesium alloys during the hot deformation processing.The addition of micron SiC_p can form particle deformation zone(PDZ)to promote the nucleation of DRX and refine the grain size of magnesium alloys.However,the high volume fraction of SiC_p can reduce the ductility of Mg alloy.Therefore,based on the idea that micron SiC_p can promote DRX nucleation of Mg-5Zn alloy,the DRX behavior of Mg-5Zn alloy is regulated by micron SiC_p in order to refine the grain size and improve the plastic forming ability.The Gleeble hot simulation was carried out on the trace micron SiC_p/Mg-5Zn material.Based on the stress-strain curve,the constitutive equation and hot processing map were constructed.The influence of trace micro SiC_p on the dynamic recrystallization,high temperature deformation behavior and hot working behavior of Mg-5Zn alloy were investigated.The results show that the addition of trace SiC_pcan effectively refine the as-cast grain size of Mg-5Zn alloy,and the as-cast grain size increases with the increase of PDZ size.Additionally,the flow stress of Mg-5Zn alloy decreases with the increase of temperature and the decrease of strain rate.The addition of trace SiC_p can reduce the peak stress at high strain rate due to the fine grain size.However,with the increase of PDZ size,the peak stress is increased due to the large original grain size.The influence of trace SiC_p on the DRX thermodynamics and kinetics of Mg-5Zn alloy was investigated,the results show that the addition of trace SiC_p reduces the DRX critical strain of Mg-5Zn alloy,and with the increase of the size of PDZ,the DRX critical strain of Mg-5Zn alloy increases.In addition,the addition of trace SiC_p accelerates the DRX kinetics of Mg-5Zn alloy,while the DRX kinetics of Mg-5Zn alloy decreases with the increase of PDZ.The deformation structure of Mg-5Zn alloy after high temperature compression shows that the deformation of Mg-5Zn alloy at low temperature and high speed(543 K and 1 s^-1)is difficult to produce twins to coordinate the deformation.The addition of trace SiC_p causes the dislocation to gather around SiC_p,which provides the conditions for the nucleation of twins.With the increase of strain,the PDZ region around SiC_p has a high dislocation density,which can promote the TDRX at the{10(?)1}compression twin and the{10(?)1}-{10(?)2}twins.In addition,the DRX mechanisms of SiC_p/Mg-5Zn are particle stimulated nucleation(PSN),continuous dynamic recrystallization(CDRX)and twinning dynamic recrystallization(TDRX)due to the introduction of micro amount of SiCp at low deformation temperature.When the temperature rises to 693 K,DDRX and PSN are the dominant DRX mechanisms.The n and Q values of Mg-5Zn alloy and SiC_p/Mg-5Zn materials were calculated by constitutive analysis.The Q value(160.3 k J/mol)of Mg-5Zn alloy was larger than the lattice self-diffusion activation energy(135 k J/mol)of pure magnesium.This is because the addition of Zn reduces the stacking fault energy of Mg-5Zn alloy,which makes it change from dislocation cross slip to high temperature climbing transfer slip during plastic deformation.In addition,the n value of Mg-5Zn alloy is 6,so the deformation mechanism of Mg-5Zn alloy is the dislocation roll-over slip mechanism controlled by lattice diffusion.With the addition of trace SiC_p,the Q value of Mg-5Zn alloy decreases.This is due to the high dislocation density of the PDZ during the deformation due to the introduction of SiC_p,which activated the pipeline diffusion(92 k J/mol).In addition,with the increase of PDZ size,the dislocation density increased,which promoted the pipeline diffusion,and the Q value decreased.Therefore,the deformation mechanism of Mg-5Zn alloy is changed into a dislocation climbing mechanism controlled by lattice diffusion and pipe diffusion.Hot processing maps of Mg-5Zn alloy and SiC_p/Mg-5Zn materials under different strains were constructed by dynamic material model(DDM).It is found that the addition of trace SiC_preduces the high temperature instability zone of Mg-5Zn alloy,improves the surface quality of Mg-5Zn alloy,and increases the plastic deformation property of Mg-5Zn alloy.Compared with the reported instable zone of magnesium alloy and composites,the instable zone of trace SiC_p/Mg-5Zn material is the smallest.The introduction of micro SiC_p can avoid the stress concentration in the PDZ overlapping region caused by the high volume fraction of particles,which leads to the instability of the material fracture.In addition,compared with nanoparticles,SiC_pcan promote the occurrence of DRX through the PSN mechanism to dynamically soften,so as to avoid instability due to excessive deformation resistance at high strain rates.