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The microstructure was effectively refined and the mean grain size was decreased from 800 μm to 3–15 μm.
The number of extrusion passes was defined as the number of the specimen passed through the die.
Results and Discussion The mean grain size of the as-received Mg-3Y alloy was estimated to be around 800 μm.
New recrystallized fine grains with new misorientations could easily form at prior grain boundaries during CEC.
Compared with the conventional extrusion, the maximum texture intensity Mg alloys diclined with the increasing number of passes [6,8].

First, the finite element model of the SRM grain is established by using MSC.PATRAN.
The finite element model of the SRM grain According to symmetry of the loading and configuration, as shown in Figure 2, one-twelfth of an axisymmetric start of the motor grain is considered for the analysis.
Fig. 2 The radial and longitudinal section of SRM grain Fig.3 The regional 3-D finite element model of SRM grain and the debonded cracks in stress-release boot (b) Rear of the grain (a) Fore of the grain The SRM grain is a composite structure consisting of variety materials.
As shown in Fig. 5, 11 numbers of crack nodes are used over the crack foreside line.
Fig. 8 shows that one rear debonded crack with width 40mm and depth 16.5mm. 11 numbers of crack nodes are used over the crack foreside line, and crack 1, crack 2 and crack 3 correspond to the depth of 16.5mm, 27.0mm and 36.5mm to simulate the rear debonded crack growth.

A significant grain refinement was observed by using the solute Ta together with stochiometric grain refiner (Al-2.2Ti-1B).
The grain size in Alloy 1 is about 700 µm.
The measured grain size in Alloy 2 is about 223 µm, while the measured grain size in Alloy 3 was approximately 140 µm.
The grain size can be refined to be less than 140 µm, which is much smaller than the grain size that can be achieved using Al-5Ti-1B grain refiner. 2.
StJohn, An analysis of the relationship between grain size, solute content, and the potency and number density of nucleant particles, Metall.

The dynamic recrystallization coefficient can be defined as the capacity to decrease the dislocation density via the growth of fresh grains; this coefficient equals the difference between the number of subgrains with sufficient energy for grain nucleation Nnucl (from whom grain growth occurs) and the number of growing grains Ngrowth, divided by Ngrowth [5].
Grain growth is a thermally activated process, thus Ngrowth follows an Arrhenius form, where the energy barrier for grain growth QDRX is composed by the difference between the energy induced by the boundaries motion when grains are growing (Edisp) and the strain energy to drive grain growth once high-angle grain boundaries form (EHAGB).
(3) The onset for dynamic recrystallization occurs when high-angle grain boundaries (HAGBs) form via the accumulation of dislocations leading to grain nucleation [6].
In analogy to a previous analysis for cell formation [3], dynamic recrystallization can be considered to start when the stored energy at the boundaries (Esub) equals to (i) the necessary energy to nucleate dislocation-free grains (Egrain); (ii) the displacement energy for boundary-dislocations to onset grain growth Edisp and (iii) the equivalent slip energy of dislocations migrating from the grain interior to the boundaries (Eint) [5].
The model results show good agreement in the dynamic recrystallization onset range, number of oscillations before undergoing steady state and the steady state stress for strain rates below 2.7 × 10−1 s−1.

Cu-0.3Cr alloy: The microstructure of Cu0.3%Cr in the starting condition consisted of equiaxed grains with grain size 8-10 µm.
Fig. 3 (a) shows the GBCD as a function of the number of passes.
The components BE /BE got strengthened with number of passes.
The grain size was quite uniform with a fine distribution of equiaxed grains.
Texture weakened after ECAE in the α- phase with number of passes.

A small number of crystal plasticity simulations and tensile tests are carried out with the aim of demonstrating that control of twinning can improve the uniform elongation of magnesium based alloys.
A number of authors have recently drawn attention to this fact in their analysis of Mg-3Al-1Zn subjected to Equal Channel Angular Pressing [2,3].
Fraction of Grains Undergoing Twinning - Sachs Analysis The fraction of grains undergoing twinning, XT, is determined, in part, by the texture.
Assuming that only one deformation mode is active in each grain, the grains expected to twin can be estimated by combining a Schmid factor (SF) analysis with the fact that twinning only works in one direction.
That is, more grains should undergo twinning under uniaxial compression, compared with tension, for a random aggregate.

Equal channel angular pressing (ECAP) is useful method to obtain the ultra-fine grained and the high hardened metal.
The as-deformed metals retained high dislocation densities, a large number of low angle sub-grain boundaries, and showed being in non-equilibrium configurations [7].
The grain of as-heat treated Al exhibited an equi-axial, uniform, and coarse structure.
The grains were elongated, having an angle of 15 - 30 degrees to the ECAPed out direction.
Rotated Goss component, {110}<110>, increases with the number of passes ECAP, decreases with annealing.

Journal Title and Volume Number (to be inserted by the publisher) Fig 2.
Each lattice site is assigned a number, Si, which corresponds to the orientation of the subgrain in which it is embedded.
The number of distinct subgrain orientations is dependent on the measuring step size and area.
A grain boundary energy Ji is attached to the grain boundary sites and zero energy for sites in the grain interior, according to ( )∑δ−⋅= nn j SS i I i ji1JE
(3) Journal Title and Volume Number (to be inserted by the publisher) where ijδ is the Kronecker delta, the sum is taken over nearest neighboring(nn) sites and Ji is a positive grain boundary energy.

Another mechanism of new grains formation is continuous dynamic recrystallization.
Improvement of mechanical properties through grain refinement has contributed to the rapidly expanding field of materials engineering, in which ultrafine-grained materials with the grain size less than 0.5-1 mm are produced using severe plastic deformation (SPD).
Unlike cubic metals with their large number of slip systems (e.g., twelve for fcc metals), hexagonal metals have far fewer deformation modes with which arbitrary imposed strains can be accommodated within polycrystalline aggregates.
The limited number of slip systems in hcp metals may result in the formation of unstable walls of edge dislocations rather than stable dislocation boundaries [6] such as high-angle deformation-induced boundaries.
The microstructure of the rod was homogeneous with a mean grain size of 35 mm.

In addition to the macroscopic grain subdivision, microscopic grain subdivision also occurred within the matrix to form an ultrafine grained structure in the single crystal specimen after high strains.
Introduction It is well known that severe plastic deformation (SPD) of bulky metallic materials can produce ultrafine grained (UFG) microstructures having submicrometer grain size.
It is an effective way to use a single crystal having no initial grain boundary as the starting material for SPD, in order to get a deeper understanding of grain subdivision.
Additionally, several numbers of deformation bands inclined at about 20 degrees to the rolling direction (RD) were also observed within the deformed matrix and the bands subdivided the crystal.
Many fine "grains" surrounded by high-angle boundaries can be seen.