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With the addition of Cu, local accumulation of new compounds ε (CuZn4) occur in grain boundary [5, 6].
The surface of the samples after corrosion tests consist of Cl, C and a large number of O, which are resulted from corrosion products on the surface of the samples which should have cleaned thoroughly.
With the corrosion tests proceeding, corrosion originates and develops from grain boundary due to the presence of compound Sb-Al-Zn in grain boundary, as shown in 5C.
The surface of the samples after corrosion tests consist of Cl, C and a large number of O, which are resulted from corrosion products on the surface of the samples which should have cleaned thoroughly.
The tests indicated that the intergranular corrosion of ZnAl27 alloy is related with electrode potential between Zn and Al in grain boundary.

There are a number of requisites that have to be met, some of them related to the casting process (chemical composition, inclusion content, cleanliness), others related to the forming process.
The third aspect is the microstructure evolution, which has to be achieved by destroying the initial cast structure and by controlling the grain evolution all over the hot sequence, ensuring a homogeneous grain size distribution, a proper recrystallization and avoiding excessive grain growth during the intermediate reheatings.
The models are organized following a tree structure, the branching depth being equal to the number of passes and each level is divided into two branches, the recrystallized and the unrecrystallized zones, respectively.
Effects of prior ferritic grain size have been analyzed in order to take in to account an abnormal reheating condition the evolve in abnormal growth of grain on billet boundary.
Differences in the evolution of the ferritic grain are significant.

The amount of grain determined in accordance with GOST 5639-82. weld metal microstructures are shown in Figure 2.
The microstructures of weld joints of samples a) sample number 1b) sample number 2; c) the sample number 3 The structure of the weld metal of ferrite samples was uneven as grains elongated in the direction of heat removal.
There is a noticeable shift from uniform ferrite-pearlite structure to widmanstatten In the samples there is little change on the scale of the grain size grain are shown in Table №6.
The amount of grain welds in accordance with GOST 5639-82 Sample Grain size grain scale 1 №4, №5 2 №4, №5, №6 3 №5, №4 The results of mechanical tests of samples are given in Table 7.
Introduction PD-UVB additive reduces the level of contamination by nonmetallic inclusions, reducing their size and number.

After 15 min, the grains evolved to a much more equiaxed shape but grain boundaries were rest winding.
Prolonging the holding time to 60 min, more and more grain boundaries are lubricated, the number of solid grains decreases while the mean grain size increases.
The mean grain size is about 75µm.
With increasing holding time, the number of intergranular droplets decreases and their mean size increases.
The average grain size does not exceed 70 µm.

For random morphology of "grain like" materials, we define an effective "correlation length (distance)" λ as: ( ) ( )ϕλ=ϕ'λ=+ϕϕ∫ ∞ Varxdh 2 0 h)(x'(x)' , (5) which is in the order of a typical grain size.
It is shown that in addition to its high accuracy, the FPM gives solutions for any mode number.
In grain like materials, λ correspond to an average grain size. λ also defines different regions of analysis that will be described later.
The range where λ is very small (λ<<1), means that the statistical correlation is limited to a small range (small grains).
The FPM gives solutions for any mode number.

One of the methods of increasing the strength of steel is grain refining.
Steel 09Mn2Si in the initial state has a lineage ferritic-pearlitic structure with grain sizes of ~10 μm, which corresponds to the 10th grain size index.
The grain size of WAZ exceeds the size of initial grains, which is due to metal overheating during the welding process.
In the central part of the weld coarse bainite grains with ferrite grains on the boundaries are typical of the structure.
An increased magnetic hardness of the WAZ metal and the weld is conditioned by a greater number of alloying elements in the electrode material as well as by the presence of dispersed bainite in their structure and an increased level of internal stresses in the weld metals and WAZ metals.

Results According to a previous report [7] the microstructure of the starting material consists of recrystallized, almost equiaxed grains with a grain size in the range of 30 - 40 mm displaying annealing twins.
During ECAP a fibrous grain structure develops with the orientation of the stringers with respect to the extrusion direction α changing with the number of passes from 22° over 14° to 10°, in good agreement with the expectation from simple shear α =1/2 arc tan 2/γ, with shear strains γ = 2, 4, and 6, respectively.
a) b) Figure 5: Change of intensity and position of component BE with the number of passes.
The inhomogeneity decreases with the number of passes.
Zhernaov: Ultrafine Grained Materials III (Y.T.

Some dark spots are present within single grains, while larger areas are present around the grain boundaries.
Microsegregation also occurs at the grain boundaries reaching higher levels of concentration compared to those found in interdendritic spaces inside the grains.
The use of inoculants for refining the equiaxed grain structure is often adopted.
Due to the extreme complexity of the physics represented in such models, the calculation domains contain a very large number of elements and nodes, the number of cores used and computing time become also very large.
Beckermann, Rayleigh number criterion for formation of A-Segregates in steel castings and ingots Metallurgical and Materials Transactions A 44.9 (2013) 4266-4281

The average grain size of microstructure is about 38 µm.
Therefore, the size of spheroidal grains is very fine.
It illustrates that plastic deformation of solid grains is small.
However, in the bottom region, the deformation mainly depends on sliding between solid grains (SS) mechanism and plastic deformation of solid grains (PDS) [16].
The microstrucure in the top region of side wall of thixoformed part also consists of spheroidal grains and a large number of liquid phase (Fig.4(d)).

If the concentration of intrinsic defects in oxide is very small, matter transport via oxide grain boundaries may be predominant, in particular if the grains are small.
columnar grains.
Assuming constant driving force for inward transport of oxidant, the following should be taken into account: (i) size of the grains; (ii) the level of alignment of the grain boundaries parallel to the thickening direction in adjacent sub-layers; and (iii) number of grains/sub-layers across the oxide layer.
Fraction of grain boundaries is higher for smaller grains.
For smaller number of grains/sub-layers across the scale and for higher level of alignment of grain boundaries between the sub-layers the grain boundary transport is less perturbed by effects leading to broadening of the tracer distribution profile across the scale.