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Up to now, the similar (Al-Al) and dissimilar (Mg-Al) welding via the high efficiency USW has been reported by a number of researchers [8-10].
The grain structure of BM had slightly been deformed and elongated along the rolling direction (RD) and its grain size distributed roughly from 12 μm to 26 μm, with some larger grain sizes such as 32 μm and 40 μm as well.
The grain sizes were mainly distributed between 3 μm and 6 μm, as shown in Fig. 1(d).
Furthermore, the grain shape of the bulk metal away from the welding line was gradually changed from the deformed grain structure to somewhat equiaxed grain structure, as seen in the Fig. 1(c).
The “necklace”-like grain structure and the slightly larger equiaxed grain size were also seen in the welding line, as indicated by arrows in Fig. 1(e).

The grain size was estimated to be 1.5µm from scanning electron microscopy micrographs.
The environment temperature, the crystallographic texture, the grain size and the thickness of film should affect the flow stress development [3].
Results and Discussion Griffin [4] and Bravman [5] recently showed that the strength of polycrystalline thin films depends on both their grain sizes and their thicknesses.
A number of cracks may propagate when the stress reaches this critical value.
From Fig. 2 the grain size of the film is estimated to be 1.5µm.

The cell wall consisted of fine equiaxial crystal grains after solution treatment.
Superplasticity occurs at over 1/2 TM and with fine equiaxial crystal grains (less than approximately 10 micrometres).
Zn-22Al alloy has high strain rate sensitivity due to grain sliding at over 513 K.
Using TiH2 may occur preventing grain sliding of the deformation mechanism.
This work was supported in part by JSPS KAKENHI Grant Number 25420759.

The longer the reaction time, the more complete the grain, the more uniform the morphology.
Adjuvants have an important effect on the growth of SnO2 grains, which can promote the growth of SnO2 grains with preferential orientation, that is to promote the growth of SnO2 grains in a certain direction and inhibit the growth of tin oxide grains in other directions.
And ammonia and urea due to the reaction is not enough to get the grain size is small, so the reunion and uneven appearance is shown.
It can be seen from Fig.3 that when the molar ratio of salt to alkali is 1: 4, the grain size obtained is larger and more uniform.
From the whole, the concentration of SnCl4 0.05mol/L, NaOH as auxiliaries, salt and alkali molar ratio of 1: 4,200 °C insulation 4 days of the environment, the characteristic peaks have been quite obvious, a large number of crystal phase has been formed, and crystal phase is very complete.

It is well known that, due to the elevated temperature that occurs during the welding process, followed by rapid cooling, defects such as cracking, porosity, lack of fusion, and an increased number of brittle phases affect the welding quality.
Bhadeshia studied the phase transformation during RSW in interstitial free steels and observed that the central area of the nugget comprises equiaxed grains followed by columnar grains that penetrate into the steel in the heat affected zone [4].
Khodabakhshi et al., using RSW, joined ultra-fine grained low carbon steel sheets produced by constrained groove pressing [8].
Acknowledgment This work was supported by a grant of the Romanian Ministry of Research and Innovation, CCCDI-UEFISCDI, project number PN-III-P2-2.1-PTE-2021-0237-Wellformed-Frames, within PNCDI III.
Effect of Acicular Ferrite on Mechanical Properties of Ultra-Fine Grain Ferrite Steel.

Microstructural evaluation of the alloy plates revealed that due to FS welding, fine and fragmented dynamically recrystallized grains have been formed in the weld nugget.
Introduction In the former undivided Soviet Union, additions of the transition element Scandium (Sc) have been used for a number of years as an alternative grain refiner to Ti/TiB2, particularly in the context of welding.
Some of the claims have recently been confirmed in the west and finer grain sizes have been reported in Sc-refined castings.
Grain refinement due to the addition of scandium has been previously shown to arise from the precipitation of primary Al3Sc particles in the melt, which act as potent nucleation sites for aluminum grains [1].
The reduction in the size of the particles and increase in number density of the particles would have also responsible for enhancement of tensile properties of the welded joint.

1 THERMAL BEHAVIOR CHARACTERIZATION OF COLLOIDAL PARTICLES OF NICKEL HYDROXIDE AND ITS CONNECTION WITH THE GRAIN-SIZE EFFECT J.M.
The computed results are illustrated (Fig.2) for the major diffraction planes with both error margin and average value of the grain-sizes. 5 Figure 2: Grain size as a function of the major diffraction planes for Ni(OH)2 (A) and for NiO (B).
The other planes corroborate the grain size in respect of their own positions.
Their transformations into NiO nanoclusters have been shown to occur at different temperature as a function of their grain-size.
WINDSOR "Observation of a metastability limit in liquid gallium", Physical Review Letters, 1975, Vol.35, Number 24, pp. 1652-1655

Microstructures of samples (a) TER (b) WR (c) Raw For TER process, when the pass reduction was 30%, it is obvious that recrystallization occurred at both grain boundaries and intersections of the twins, as shown in Fig. 1(a).
The new recrystallized grains formed a “necklace structure” along the serrated grain boundaries, and some recrystallization nuclei formed inside the twins and grew along the twin boundaries into strip-like grains.
For WR process, numerous deformation twins inside the grains could be observed but there were no recrystallized grains in the microstructure of the sample, as shown in Fig. 1(b).
Compared the microstructure of the samples under TER process with WR process, it is not difficult to find that TER process could obtain more uniform and fine equiaxed grains.
With the aid of electropulsing, the movement of dislocations and vacancies became easier so the number of piling-up dislocations decreased and the number of mobile dislocations increased [5].

It was shown in Fig1c that a majority of sulfide distributed in the grain boundary when the overheat increase to 36℃.
Since the decreasing of the sulfide number, the fraction of intragranular ferrite decreased significantly compared with the samples with lower overheat.
The sulfide showed typical rod-shaped and clustering in the grain boundaries (Fig1f).
So it was difficult to develop new nuclei, thus inhibiting the construction of equiaxed grain zone.
The growth of columnar grain zone decreases the temperature gradient of slab, thus promoting the steady-state eutectic solidification to construct a large number of rod-shaped MnS.Meanwhile, the increase of the liquid core length of continuous casting slabs was propitious to the segregation of S, leading to the agglomeration of sulfide.

When the grain size increases, the grain boundaries density decreases; consequently, the carrier diffusion by the grain boundaries is also reduced.
The optical band gap increases because the crystallinity of the film increases and also due to the increase in grain size.
CZT1, CZT2 and CZT3 showed pebble-like crystal grains with mean diameter about 50 nm, 200 nm, 250 nm, respectively.
CZT3 had staggered and strip-shaped structure with the average grain size of more than 500 nm.
According to (a), (b) and (c), it can be seen that as the substrate temperature increased, the grain size grew.