Achieving%20low%20temperature%20superplasticity%20in%20AZ31%20Mg%20alloy%20through%20severe%20plastic%20deformation%20%20%20%20%20*H.%20K.%20Lin1%20(???)%20%20J.%20C.%20Huang1%20(???)%20%20T.%20G.%20Langdon2

1
Achieving low temperature superplasticity in AZ31
Mg alloy through severe plastic deformation
H. K. Lin1 (???) J. C. Huang1 (???) 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 lt10-10gt//ED (extrusion direction) of the
extruded specimen changed to the texture
lt27-5-6gt//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
lt10-10gt//ED and lt2 7-5-6gt//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.