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In particular the α grain size could be over-estimated.
It can be also noticed that by increasing the temperature, the number of α grains decreases for the same surface analyzed and so a grain growth occurs.
It appears that the β fraction around 60%, can induce modifications of the nature and number of interfaces/boundaries (α/α and/or β/α and/or β/β) and so to probably interfere with the grain boundary sliding mechanism as well as with the accommodation mechanisms.
However none assumption can be made on the evolution of the β texture because the number of grains analyzed is insufficient and so the statistics is not good enough.
In particular the high hardening could be due to the grain growth but also to the decrease of the “α/thin-β/α” interfaces number.

If that is the case, defragmentation of grains can occur (see Figure 1, (d) - (e)) to form fine recrystallized grains.
Description Parameter Strain ϕ Grain diameter d Grain diameter d0 Recrystallized grain diameter drex Grain boundary energy γgb Recrystallized grain fraction X Driving force (stored energy) PD Retarding force (Zener Drag) PZ, PZ,sub Number of nucleii N Change in number of nucleii ∆N Experimental Procedure Light Metals Technologies Ranshofen (LKR) owns a semi-industrial extrusion press (type Müller Engineering NEHP 1500.01), used to perform the experiments.
Fig. 2: Histogram of dispersoid number density per volume for the homogenized sample.
grains.
One of the input parameters for the grain growth model was therefore the average grain size of the cast billet.

The first type is the grains whose c axes parallel to the tensile direction of sheet (grains with this orientation are called P grains here for short).
The c axis of grains of this type tends to parallel to the normal direction of sheet (grains this orientation are called N grains here for short).
N grains have a small proportion.
P grain tends to show tensile twinning and N grain tends to compressive twinning
Acknowledgements The authors express their sincere thanks to the support of the Natural Science Foundation of China with the Grant Number: 50775211 and the cooperation with Prof W.

Al-Ti-C grain refiner is a kind of grain refinement material that has excellent application prospect and is studied emphasisly[1-8].
After the columnar grain converges in the central area of refinement experiment mould, the grain growth terminates.
After the addition of Al5Ti0.25C grain refiner, columnar grain zone disappears completely (Figure 3(b)) and the columnar grain entirely transforms into equiaxed grain whose mean grain size is 180μm.
Thus it can be seen that Al-Ti-C grain refiner prepared under ultrasonic coupling has excellent capability in grain refinement.
Acknowledgements Authors thanks for the supports of The national natural science foundation of China（Fund number: 51174061）.

In the water-quenched samples, equi-axed fine-grained microstructure with grain size under 2.1μm was attained and maintained throughout the hot rolling process.
Therefore, in the present study, control conditions in hot rolling such as cooling way from homogenization temperature, cooling way after a rolling pass, total number of passes, etc. have been investigated in a Zn-Al alloy to obtain fine-grained microstructures by rolling processes.
Degree of grain refinement was evaluated with average grain size, L＝1.75d [6], where d is the linear intercept length and averaged in two directions for the three sections.
A minimum grain size of 1.7 μm was observed at 6 passes in the 7mm thick sheet.
Fig.2 SEM micrographs in L-LT section of the samples hot-rolled under condition (1) from 20mm to different thickness (with different number of passes).

It shows that grain coarsening would occur after annealing as the grain size increases from 600 µm to 859 µm.
Fig. 5 The mean grain size values versus the number of ECAP passes for commercially pure aluminum [10].
Fig. 6 shows the variations of the Vickers hardness with the number of ECAP passes performed on pure aluminum at room temperature [11].
By performing TE the grains of about 150 µm was developed.
Although post-rolling resulted in elongated grains, it lessened the mean grain size to 80 µm. 2.

The variation of the strength with the pass number was explained by the texture and grain size.
Fig. 3 shows the variations of the average grain size, yield stress(YS), tensile strength(UTS), uniform elongation and total elongation as a function of pass number in ECAP process.
In Fig. 3, the grain size decreases continuously as the pass number increases.
The grain size after 8 passes is 3.6µm.
The yield stresses of 6 and 8 passed materials are also lower than that of 1 passed material. 0 1 2 3 4 5 6 7 8 9 0 10 20 30 40 50 60 0 50 100 150 200 250 300 Grain Size (µm), Elongation (%) Pass Number Grain Size Uniform elongation Total elongation Yield Stress Ultimate Stress Stress (MPa) Fig. 3 Grain size and mechanical properties of the ECAPed AZ31 Mg Alloy as a function of pass number in ECAP process.

The grain size hardly changed during drying.
However, although the number of pores decreased when annealed at 240 o C, the size of pores increased when annealed at 170 or 240 o C.
As indicated in Figs. 4(b) and 4(c), whilst the number density of pores dropped, the pores became significantly large.
Normal grain growth was identified when annealed at 170 or 200 oC.
On the contrary, when annealed at 240 oC, abnormal grain growth with sufficiently large grain size was observed to occur, although macropores still resided therein.

By addition of colloidal silica in copper electrolytic bath and Au pre-coating on substrate, the grains of deposits became fined and uniform and the number of grains were increased.
When plating over-voltage is low, the size of grains is large and the number of nuclei is a little.
As silica was dispersed, however, grains were refined, the grain size of copper significantly decreased and the number of grains and the thickness of Au pre-coating increased.
As Au pre-coating increased the number of nucleation sites, the nucleation became faster than that of the grain growth, which is considered to the role of prohibiting grains growth by refining and increasing the number of grains.
Fig. 4 X-ray diffraction patterns of electrodeposited copper obtained with different amounts of colloidal silica added and/or with different amounts of Au pre-coating thickness Summary The grains of copper electrodeposited film refined, uniformly grow and increased the number of grains by Silica dispersion and Au pre-coating.

An ultrafine-grained (UFG) material with the submicrocrystalline (SMC) grain size between 0.1 and 1mm can be obtained by using a severe plastic deformation (SPD) technique.
The average grain size in Fig. 1(a) is determined to be 0.2 mm.
In addition, considerable numbers of equiaxed grains consisting of high angle boundary and subgrain formation consisting of low angle boundary with misorientation less than 15゜ in the martensite variant can be noted in Fig. 2(b).
Figure 4 shows (a) EBSD-grain boundary (GB) map and (b) distribution of area fraction of grain size in hot rolled sample.
The average grain size of a phase from Fig. 4(b) is determined to be 0.3 mm.