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The result shows that equiaxed grains are the main microstructure characterristic of welding nugget.
Effect of pin on thermal-machanical affected zone is much smaller than the welding nugget, so microstructure of this area is reply grain.
The Heat- affected zone is just influenced by the welding thermal cycle, so the grain of this area is coarse than that of the parent metal.
The microstructure of Shoulder affected zone is fine-equiaxed grains.
However, If the magnesium alloy is welded by the traditional fusion welding, there are many problems such as the weld metal and near the weld area are prone to overheating and grain growth, greater thermal stress, welding deformation, the great tendency to produce welding cracks and grain burned and easily formed hydrogen hole in the welding process. 

The basic principle of polishing Mechanical polishing is under the conditions of certain pressure and speed, pouring the polishing liquid between workpiece and polishing disk, relying on the fine grinding machine grain to removal the workpiece surface , to meet the requirement of the workpiece surface ultra-precision mirror machining.
Polishing principle as shown in Figure.1, at the begin of machining, the workpiece in the form of grinding removal, abrasive is in the form of sliding and rolling on the surface to removal the material; At the same time, under the action of proper pressure, abrasive will be broken, the number of blunt abrasive increased, the cutting effect gradually weakened, at the same time, the abrasive disk is in the form of friction to removal the workpiece surface, so the surface smoothness increased.
On the basis of this, the polishing additive in the liquid formats film layer on the workpiece surface, with the further increase of workpiece surface roughness, grain size is further reduced and homogenization, abrasive and adhesive film combined, so the polishing film is smoothness, flexibility and uniformity, with the new surface and attached film alternating generation and removal, the surface machining quality is getting better, so as to achieve the lower surface roughness.
This is mainly duing to the different sizes of abrasive grains of the two types of polishing fluid, under certain conditions of other polishing parameters , the smaller abrasive particle size is , the smaller unit area of the force of the individual abrasive grains is , and the removal amount of the surface of the artifacts material also reduce, and the efficiency of processing also reduce ; However, as research the conduct of the polishing , the polishing fluid II may form more and finer abrasive grains, the process involve more abrasive, and it can get a higher quality of surface and lower roughness .
The main reason is that when the artifacts is polishing , the smaller the size of abrasive particles are used , the more and the more finer abrasive grains will be formed during processing , so that the abrasive grains per unit area in contact with the surface of the artifacts is much more ,and the scratches left after polishing is much weaker.

Number of papers and monographs are dedicated to austenitic steels [1-3].
Therefore, actually, the mechanics of fracture is based on the formation of slip bands in grains during LCF.
The changes of grain orientation at high stresses may contribute the processes of deformation and crack formation as well.
Doherty, “Influence of Grain Size and Stacking Fault Energy … FCC Metals”, Metallurgical and Materials Transactions, 30A, pp. 1223-1233, (1999)
Martin, A crystallographic mechanism for fatigue crack propagation through grain boundaries.

When jet penetration capability is poorer, obvious pit zone exists on the bottom, namely, the farther the jet ejects, the more the number of the fringes; When the jet pressure is smaller, a large quantity of striations appear on the surface.
It was found from the face that, when the metal was cut by pre-mixed AWJ, obvious ripples and grains appeared on the side walls.
Furthermore, the direction of ripples and grains is about 60-80°angle with the moving direction of the nozzle.
It can be seen from the figures that, the cutting trough face (1,000 times) gradually becomes smooth as pressure increases, and the surface grains gradually disappear.
As pressure increases, at 38MPa the white and black zones become larger, the grains distribute simply, and the pictures become clearer than the case at 30MPa.

After many comparison, total number of mesh set for 4864000, results as shown in figure 3.
In figure 6a, b, c, d,the branced are α(Al) substrate, distributed not evenly in grain boundary is eutectic Si [6].
Through the graph a,b,c,d, part 2’s grain size is biggest, part 3 and part 4’s grain size is same,but part 1’s grain size is smallest,this is because of the position is short distance from type,have good heat condition and high temperature gradient.Part3 and part 4’s heat condition is worse than part 1 because of its upper set the riser and no direct contact its type wall,while part 2 in the centre,cooling condition is the worst,high temperature and solidificate the last,so its grain coarse.In optical microscopy photograph also can see the forming process of casting defects, such as casting shrinkage porosity (Fig.6e).
Visiblely, wheel hub in different parts’ grain size is differ, it related with the heat condition.
In the organization distribute the fishbone Mg2Si,in the thick type wall and finally solidification appear shrinkage porosity and holes casting defects.From figure 6 eutectic Si can be seen by a relatively coarse needle or flake, indicating that this wheel’s grains modificate inadequately.

The poor formability of magnesium at room temperature is inherently related to its crystal anisotropy and hexagonal close packed structure, which limit the number of active slip systems and primarily involve only the basal planes [1].
As shown in Fig. 1c,d, due to the strong preferred crystallographic orientation of grains (texture), a metal cannot deform along the thickness direction during rolling.
At the same time, the porosity (and other solidification defects) will exert a contribution when comparing globular morphology with wrought grain structure, known to be fully dense.
It is generally accepted that the globule origin is traced to the alloy grain in the solid state.
However, there is no evident correlation in terms of their sizes, since after recrystallization grain size continues to grow during heating to partial melting.

Praxair Al-1110HP Al2O3 powder was used as reference material having grain size in the micron range.
The partially sintered large powder particles - when sintered at 1200˚C - are α-alumina grains having a crystal size in the 200 nm range.
These grains are covered by Ni-nanoparticles having a size of about 20-50 nm.
On the other hand coatings prepared by using parameters I and II appeared more porous and contained a larger number of interlamellar cracks.
The total length of cracks decreases with increasing Ni-content although the penetration depth of the indent increases as shown in Figure 5(b), where the Vickers hardness numbers of the coatings are given as a function of nickel content.

To evaluate the surface roughness as well as the grain size of the films, an area of 1µm x 1µm was scanned in tapping mode.
The average surface roughness and grain size were being listed in Table 2.
As the Co concentration increased, the grain sizes are found to be decreased but roughness data are not consecutively decrease.
The plot of crystallite size from XRD analysis and grain size from AFM analysis against Co concentration percentage were summerized in Fig. 5.
Table 2 Average surface roughness and grain size of PANI-Ag-Co nanocomposite thin films Samples Surface roughness (nm) Grain size (nm) (a) PANI-Ag0.8-Co0.2 1.327 ± 0.297 69.0 ± 12.4 (b) PANI-Ag0.6-Co0.4 1.187 ± 1.510 36.8 ± 21.2 (c) PANI-Ag0.4-Co0.6 1.827 ± 0.954 20.5 ± 11.1 (d) PANI-Ag0.2-Co0.8 1.508 ± 1.395 19.6 ± 11.8 Fig. 5 Plot of crystallite size and grain size of PANI-Ag-Co nanocomposite thin films against the concentration percentage of Co.

On the basis of the measurement made by using the images demonstrated in the paper published by Djurdjevic et al. [6] it was concluded that the degree of modification is mainly characterized by the roundness and area of Si grains (Fig. 1).
In case of a partially modified (56 ppm) structure, the shape factor is (R)=2.6 ±0.5, the average area of Si grains is (A)= 5.4 ± 1.1 µm2 .
The maximal revolution number of the metallic melt cannot exceed the synchronous revolution number of the rotating magnetic field.
The measurement results of the area of Si grains show that the area of Si grains was almost identical (Fig. 5) in the samples having a velocity of v=0.01 mm/s (Nonstirred: A=21.0±1.3µm2; Stirred: A=19.7±1.6µm2) and v=0.2 mm/s (Nonstirred: A=4.0±1µm2 ; Stirred: A=3.4±0.5 µm2), irrespective of the fact of stirring.
A significant difference (almost three-times more) could be observed at the samples having a velocity of v=0.05 mm/s as the average area of Si grains was A=5.9±1.1µm2 in the non-stirred case and it was A=16.9±1.4µm2 in the stirred case.

After a large number of studies have shown that the fractal characteristics of the cross section has a certain degree of universality [5-6].
After that, the experiment was continued until the next pre-set number of cycles.
At this point, the fractal dimension increases rapidly with the increasing number of cycles, which is approximately linear.
The free surface effect means the constraint of material surface grains by the surrounding grains is weaker than the internal part.
This effect makes the material surface grains still have plastic strain concentration at a lower stress level and therefore the short cracks formed at material surface have a higher growth rate.