Microstructure development and thixoextrusion of magnesium alloy prepared by repetitive upsetting-extrusion

Thixoextrusion involves processing alloys with a spheroidal microstructure in the semi-solid state. Before thixoextrusion, repetitive upsetting-extrusion (RUE) is introduced into the strain induced metal activation (SIMA) process to predeform AZ80 magnesium alloy. Microstructure evolution of RUE formed AZ80 magnesium alloy during partial remelting is studied at temperatures for times. Tensile mechanical properties of thixoextruded components are determined and compared with those of AZ80 magnesium alloy thixoextruded from starting material produced by casting. The results show that with increasing number of RUE passes solid grain size decreases and the rate of liquation is improved. Prolonged holding time results in grain coarsening and the improvement of degree of spheroidization. The variation of the solid grains with holding time obeys the Lifshitz, Slyozov and Wagner law. Increasing the heating temperature is favorable for the formation of spheroidal solid grains. The tensile properties for AZ80 magnesium alloy thixoextruded from starting material produced by RUE are better than those of AZ80 magnesium alloy thixoextruded from starting material produced by casting.

► Repetitive upsetting-extrusion (RUE) was introduced into strain induced melt activation.
► With increasing the number of RUE passes, the solid grain size decreased and the degree of spheroidization was improved.
► Prolonged holding time resulted in grain coarsening.
► Proper increase in temperature was favorable for obtaining semi-solid microstructure with small and spheroidal solid grains
► The tensile properties for AZ80 thixoextruded from starting material produced by RUE are better than those of AZ80 thixoextruded from starting material produced by casting.