Research On The Making Of Semi-Solid Billet Of AZ91D Magnesium Alloy By Direct Extrusion-ECAP

Mg-Al-Zn is the most widely used casting magnesium alloy. Presently, there have no perfect method for preparing semi-solid billet of magnesium alloy which is practical for industry. Equal-Channel Angular Pressing (ECAP) is a plastic formation technology for the preparation of magnesium alloy semi-solid billet. However, magnesium alloy semi-solid billet produced by ECAP are very small, and sharp equivalent effective strain can be obtained only through repeated squeezing. A brand-new method for preparing semi-solid billet was put forward in this paper: Direct extrusion-ECAP. With this method, large diameter bars can be extruded, as a result, batch production become possible; meanwhile, equivalent effective strain would become greater after direct extrusion without multiple ECAP. While simplifying the producing technology, a new method for AZ91D magnesium alloy semi-solid billet preparation was offered.Magnesium alloy AZ91D was employed as object investigated in the paper. The possibility of preparing AZ91D semi-solid billet with Direct extrusion-ECAP was analyzed; Under the circumstance of squeezing deformation, rules that semi-solid isothermal structure was affected under different equivalent effective strain, different temperature and different time of isothermal treatment were also studied in the paper, in order to disclosure suitable processing parameter for AZ91D alloy deformation, offer foundation for the industrialization of preparing magnesium alloy semi-solid billets with SIMA. The experiment shows that Direct extrusion-ECAP is a feasible method for magnesium alloy billet preparation. The microstructures crystal grain of AZ91D Magnesium alloy prepared with Direct extrusion-ECAP were rather fine. Microstructures of Magnesium alloy prepared with extrusion ratio 9.77 and 17.36 are equiax crystal. The greater the equivalent effective strain of Direct extrusion-ECAP, the better microstructures of semi-solid billets prepared with it becomes; as the soaking time prolong, the microstructures of semi-solid billets prepared with Direct extrusion-ECAP will grow. As the temperature of isothermal treatment rise, the average size of solid phase grains will initially increase then decrease, and the form factor approaches to 1 gradually. Microstructures of AZ91D Magnesium alloy billet prepared with extrusion ratio 17.36, isothermal treatment 550℃, soaking time 15min are prominently better than others.