Extruded Mg-6%Al-1%Zn (AZ61) alloy bar was subjected to 4-pass Equal Channel Angular Extrusion (ECAE) processing at 448-573 K. At the processing temperature of 448 K, extremely fine grains with the average grain size of 0.5 mm are formed as a result of dynamic recrystallization originated by fine Mg 17 Al 12 (b) phase particles having 50-100 nm diameter dynamically-precipitated during ECAE processing. The sizes of both a matrix and b phase decrease with decreasing processing temperatures. In tensile test at room temperature under the strain rate of 1!10 K3 s -1 , tensile strength increases with decreasing ECAE processing temperatures due to fine grains, fine precipitates and residual strain hardening. Especially, highest strength of 351 MPa was achieved in the specimen ECAE-processed at 448 K. In addition to such high strength, elongation reaches 33% in that specimen. This specimen exhibits clear strain rate dependencies of both flow stress and elongation even at room temperature. As a result, higher elongation of 67% is obtained under low strain rate of 1!10 K5 s K1. In such specimen, non-basal slip and grain boundary sliding occur in addition to basal slip. Furthermore, there are grains with no dislocations, suggesting the occurrence of dynamic recovery. The contribution of all the deformation mechanisms would cause high ductility in finegrained AZ61 alloy specimen with high strength. q

Extruded Mg-6 mass%Al-1 mass%Zn (AZ61) alloy was grain-refined utilizing Equal Channel Angular Extrusion (ECAE) processing. Initially, the extruded bar of the alloy was ECAE-processed 2-times at 473 K. Subsequently, it was processed 4-times at 448 K. As a result, the grains are refined to less than 1 mm and a large amount of fine Mg 17 Al 12 compound precipitates. Subsequently, the superplastic properties of the ECAE-processed specimens were investigated. Large fracture elongations of over 300% are obtained at 423 K and 448 K, which is below T m =2 (T m : melting point of the alloy), at strain rates above 1 Â 10 À4 s À1 and 1 Â 10 À3 s À1 , respectively. That is, low temperature superplasticity occurs. Furthermore, at a high strain rate of 1 Â 10 À2 s À1 , superplasticity occurs with the elongation of 242% and 398% at relatively low temperatures of 473 K and 523 K, respectively. In the extraordinarily elongated specimens, significant grain boundary sliding is observed with strain rate sensitivity of 0:3$0:4. The activation energy for superplastic deformation is about 91 kJ/mol, which is close to that for grain boundary diffusion of pure magnesium. It is concluded that the superplastic deformation mechanism of the investigated alloy would be grain boundary sliding accommodated by dislocation slip controlled by grain boundary diffusion.

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Recently, magnesium alloys have been considered as a promising alternative for high-strength steel and aluminum in some applications because of its advantages such as low density, high specific strength etc. However, the application of formed magnesium wrought alloys components is restricted due to lack of knowledge for processing magnesium alloys at elevated temperatures. In this study, the deformation behavior of a cylindrical deep drawing of magnesium alloy sheets at elevated temperatures are simulated by using a non-isothermal finite element based on DEFORM 3D commercial software. In order to validate the finite element analysis, deep drawing test of cylindrical cup of AZ31 and AZ52 rolled sheets at given conditions was also performed. The experimental results show a good agreement with the finite element simulation predictions. The optimal forming temperature, thickness distribution of the cup and punch force were determined for the process.

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