Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed.The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation.Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA.Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape.The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.
Numerical simulation and experiment of thixoforming angle frame of AZ61 magnesium alloy were investigated.The results show that with the increase in punch displacement,cylinder billet firstly fills into die cavity of angle frame from feed inlet and plastic deformation occurs in touching region between billet and die cavity.After central thin wall of angle frame is created,semi-solid billet fills toward two edges.Lastly,complete plastic deformation occurs in billet,leading to complete filling of semis-olid billet.Effective strain,effective stress and billet temperature decrease with the increase in punch displacement.Effective stress decreases with the increase in billet temperature,die temperature and punch velocity.The optimal conditions decided by numerical simulation are as follows:die temperature of 450 ℃,billet temperature of 560 ℃ and punch velocity of 30 mm/s.Angle frame components with high mechanical properties such as yield strength of 225 MPa,tensile strength of 309 MPa and elongation of 21.8% and fine microstructure could be thixoformed successfully according to process parameters decided by numerical simulation.
Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion(ECAE)in semi-solid isothermal treatment was investigated.The results show that with increasing semi-solid isothermal treatment temperature,the α phase solid grain size of processed Mg-Al-Zn alloy by ECAE increases firstly due to coarsening of α phase solid grains,then decreases due to melting of α phase solid grains.With the increase of extrusion passes during ECAE,the α phase solid grain size in the following semi-solid isothermal treatment decreases.The α phase solid grain size of processed Mg-Al-Zn alloy by ECAE under route BC is the smallest,while the α phase solid grain size of processed material by ECAE under route A is the largest.The primary mechanism of spheroid formation depends on the melting of recrystallizing boundaries and diffusion of solute atoms in the semi-solid state.
