Table 1 Summary of LTSP in Mg alloys subject to ECAP processing.

1. Achieving low temperature superplasticity in AZ31 Mg alloy through severe plastic deformation＊H. K. Lin1 (林鉉凱) J. C. Huang1 (黃志青) T. G. Langdon2 1Institute of Materials Science and Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan 804, ROC 2Departments of Aerospace & Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453, USA （NSC 92-2917-I-110-003& NSC 91-2216-E-110-006） The relationship between low temperature superplasticity (LTSP) and texture in the AZ31 Mg alloys subject to extrusion and ECAP is examined. The highest LTSP elongation of 461% was attained at 150oC, or at 0.46 Tm. It is found that the texture <10-10>//ED (extrusion direction) of the extruded specimen changed to the texture <27-5-6>//ED after ECAP, affecting the resulting LTSP behavior. Table 1 Summary of LTSP in Mg alloys subject to ECAP processing. Table 2 Grain size and room temperature tensile properties of the billet, extruded and ECAP specimens. Table 3 Schmid factors calculated for extruded and ECAP specimens. • Fig. 1. Grain structure micrographs of the AZ31 alloy after • extrusion at 300oC (OM micrograph) • and (b) ECAP at 200oC (TEM micrograph). Fig. 2. Grain size versus annealing temperature after static annealing of the material. Fig. 3. Typical room temperature stress and strain curves for as-received, extruded, and ECAP specimens. Untested Extruded ECAPed Fig. 4. The fracture morphology of the extruded and ECAP specimens. Fig. 6. Variation of elongation as a function of strain rate at 150 to 250oC for the (a) extruded and (b) ECAP specimens. Fig. 5. Plots of true stress versus at 150oC for samples processed by ECAP for 8 passes at 200oC. Fig. 7. X-ray diffraction patterns for the (a) the transverse cross-sectional plane of the extruded specimen, and (b) the transverse cross-sectional plane of the ECAP specimen. Fig. 9. The schematic illustration of extruded and ECAP specimens. Summary 1. The grain size of ~75 m in the AZ31 billet can be refined to 2.5 m by one-pass extrusion at 300oC, and further to 0.7 m after 8-pass ECAP at 200oC. 2. After extrusion plus ECAP, the AZ31 bars exhibit LTSP of 461% at 150oC, or 0.46 Tm. 3. The extruded and ECAP specimens contain the dominant textures with the characteristic of <10-10>//ED and <2 7-5-6>//ED, respectively. 4. Using the measured textures and the calculated Schmid factors, the ECAP specimens would exhibit lower YS and higher elongation at room and LTSP (150oC) temperatures, where dislocation slip acts as the dominant deformation role. Fig. 8. The X-ray (0002), (10-10) and (10-11) pole figures of the extruded and ECAP specimens.