Title: Mechanisms of Fracture and Inhomogeneous Deformation on Transverse Tensile Test of Friction-Stir-Processed AZ31 Mg Alloy Abstract: Three kinds of AZ31 plates with different initial grain orientations
were friction stir processed (FSP). Detailed microstructure and texture
evolutions of the FSP plates were obtained. Fracture behavior and
non-uniform plastic deformation were focused on. It was found that
initial grain orientation had little effect on grain size and texture
evolution in stir zone (SZ), but it greatly affected the texture
transition at thermal-mechanical affected zone (TMAZ)/SZ interface.
Non-uniform plastic deformation was observed in all the three kinds of
FSP plates along the tensile direction. The strength difference of the
FSP plates was largely reduced compared with the initial plates.
Fracture consistently initiated in transition region on advancing side
even for the 90° specimen, in which no sudden texture transition was
present at TMAZ/SZ interface. As revealed in electron backscatter
diffraction (EBSD) maps, SZ-side could be divided into two
micro-regions. One was adjacent to TMAZ/SZ interface, named as the
region of easy to activate extension twinning (EAET region), where the c-axis
was almost parallel with transverse direction (TD). The other was
slightly away from TMAZ/SZ interface, named as the region of easy to
activate basal slip (EABS region), where the c-axis was tilted
about 45° towards TD. The activation of different deformation mechanisms
in SZ-side may cause plastic deformation incompatibility and initiate
fracture. An “embossed” phenomenon appeared in SZ-center during the
transverse tensile tests of all the three kinds of FSP plates, which was
related to the distribution of basal plane and caused by the different
deformation between SZ-center and SZ-side. The activation of basal slip
in EABS region was considered as a major role in the formation of the
“embossed phenomenon”. The findings of this study extend understanding
the mechanism of fracture and inhomogeneous deformation behaviors of FSP
Mg alloys.
Fig. 13 SF maps for extension twinning and basal slip at the
region between TMAZ and SZ-side for the 0° specimen, (a) SF map for
extension twinning, (b) SF map for basal slip and (c) {0 0 0 1} pole
figures at the region between TMAZ and SZ-side.