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The viscosity of the slurry was maintained at 27 sec measured using zahn flow cup number 5.
Figure 2: Dried patterns Mould was prepared by filling unbounded silica sand with grain fineness number of 40-60 (AFS).
Using finer sand grain size developed smaller void in between the sand grain causing less molten metal penetration compared to coarser grain thus developed a smoother surface finish.
Figure 6: (a) Fine grain size producing less metal penetration height (b) Metal penetration height produced by coarser grain.
Increasing pressure during solidification, suppressed the growth of the grain structure thus producing comparatively small grain structures.

Figure 5: Size distribution of niobium carbides within steel A annealed at 800°C for 30 minutes characterised a) within grains with HRTEM, b) with CTEM, and with HAADF and EFTEM c) within grain and d) within grain boundary.
A further difficulty arises from the fact that precipitation kinetics are expected to be different within the grains and at the grain boundaries.
Precipitation inside the grains was distinguished from precipitation at grain boundaries.
The two populations were then combined following the proportion given by Tamura's equation [18]: the ratio between the grain boundary area and the grain volume is equal to (4/�π) divided by the diameter of the grain, expressed in µm.
The present EFTEM evaluation is then consistent with these results, although a larger number of observations are still required in order to obtain more representative statistic.

The elongated deformation microstructure is not found in the area A, many very small grains are observed insteadly.
There is elongated martensite laths in BF image, instead of a large number of small equiaxed grains in the size of 100~200nm, and the dislocation density among grains is very low.
The formation of these equiaxed grains can be explained by a mechanism of rotational dynamic recrystallization.
The deformation time during HSM is very short, hence it is unlikely that these equiaxed grains are formed by migration of grain boundary.
(2)The white band within primary deformation zone consists of small equiaxed grains which formed due to dynamic recrystallization during adiabatic shear.

Sn is the effective element for precipitating thermally stable Mg2Sn finely and uniformly at the grain boundary and Sr is the effective element for refining microstructure.
With the addition of Sr (Fig. 2(c)) or Sn (Fig. 2(d)), microstructural changes can be clearly observed: (1) morphology of the Mg2Si particles is modified and refined from coarse Chinese script shape to polygonal shape; (2) the fine and uniform Mg2Sn particles are precipitated at grain boundary; (3) the average grain size of α-Mg matrix also refined (36 to 31µm on average).
Obviously, the improvement in tensile strength could be mainly ascribed to three aspects : (1) strengthening by grain-refinement ; (2) the morphology modification of Mg2Si from coarse Chinese script to fine polygonal shape; (3) strengthening by fine Mg2Sn which is uniformly and continuously distributed around grain boundary as shown in Fig. 6.
This improvement is attributed to the following four aspects; (1) the suppression of formation of thermally unstable β phase [5] ; (2) morphology modification of Mg2Si from coarse Chinese script to refined polygonal shape; (3) distribution of larger number of refined polygonal shape Mg2Si and plate-like Mg2Sn particles with thermal stability distributed in the grain boundary and pinning the grain boundary sliding during creep (4) grain boundary sliding can not be easily operated and cracks can not be easily nucleated along the interface between refined polygonal shape Mg2Si particles or plate-like Mg2Sn particles and Mg matrix.
(ii) It was also shown that the plate-like Mg2Sn phase particles finely and uniformly around the grain boundary in the AS52-Sn-Sr alloy system.

Al could weaken the tendency of heterogeneous deformation and modified the annealing texture by refining hot-rolling grain size.
There have been a limited number of works concerning in the control of annealing texture in DP steels [3-4] however, texture evolution and improvement are still not completely understood.
Martensite islands distributes on ferrite matrix, and the volume fraction of the martensite is about 2% and mean grain size of ferrite is 11μm.
With the increment of temperature, the average grain size of ferrite increases and tenders to be uniform gradually.
Al can result in the grain refinement in the hot band(Fig.2a) by the solute drag effect and AlN precipitation[6].

Observed grains are even several centimeters large and equivalent to the primary austenitic grains (AG) formed during primary solidification of steel.
The grains can be several millimeters large and are equivalent to origin austenitic grains.
They occur in large numbers.
Its creation is connected with very coarse grain.
Their shape and size depends on shape and size of grains.

The existence of nano-Al2O3 will initiate grain nucleation so they will refine the grain.
Although adding Al2O3 can increase grain boundary of composite because of grain refinement mechanism but at critical point impact from porosity on composite more significant than the grain refinement mechanism, the result is will lower the strength of material[12].
Grain size become smaller with increasing particle content.
The smaller grain size means the hardness increase.
JCPDF Number Al : 4 – 0787 JCPDF Number Mg2Si : 65 - 2988 Figure 5 XRD intensity graph of aluminium composites reinforced by 0.5% volume fraction of Nano-Al2O3.

It is seen that an average grain size is ~140 μm; grains are subdivided into bands outlined by LAGBs with an average thickness of ~4 μm.
Bands outlined by extended HAGBs appeared within grain interiors (Fig.4a).
In addition, chains of grains with an average size of ~100 nm and an equiaxed shape (Fig.4c) and micron scale grains elongated along the last shear direction (Fig.4a) are observed.
It seems that the formation of grained structure could not significantly affect YS due to the low volume fraction of deformation-induced grains.
It is obvious that the AA2014 alloy has to be subjected to several ECAP pressings to achieve sufficient ductility despite the fact that the number of ECAP passes does not affect YS as in the other alloys [2-5].

On the other hand, Mg-Zn binary alloy had high strength but too coarse crystal grain, which seriously restricted its application.
It was noted that the main alloy phases in the alloy were Zn-rich phases distributed along grain boundaries or interdendritic area.
The contents of Zn and Zr in the designed alloys and their serial numbers were listed in table 1.
Fine grains with granular eutectic along grain boundaries could be obtained when the Zn content was fixed at 6% and Zr content was increased from 0.3% to 0.9%.
Thereby, it would have profound mean to maximize Zr content in the matrix and minimize Zr-containing phases inside the grain.

The first considered factors are grain size and shape factor.
The microstructure revealed consistent anisotropy, with elongated grains along L direction, and consistent presence of clustered secondary phase particles, at grain boundaries.
A phase mixture model, that considers grain boundary region and grain interior, was assumed in order to highlight the effect of elongated grain aspect ratio on mechanical properties [7].
Not only the grain shape but also detrimental effect of secondary particles at grain boundary that impart reduced mechanical properties at grain boundary region has to be considered.
B – Secondary electron image, with grain boundaries decorated by particles.