Grain refinement of Al

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Grain Refinement of High Purity Mg Al Alloy Ingots and Influences
of Minor Amounts of Iron and Manganese on Cast Grain Size*

Grain Refinement of High Purity Mg Al Alloy Ingots and Influences of Minor Amounts of Iron and Manganese on Cast Grain Size*

Grain refining mechanisms of Fe- and Mn-free high-purity Mg–Al alloy ingots and the influence of a small addition of Fe or Mn on their cast structures are investigated. In order to prepare the alloys, distilled pure magnesium ( < 99 . 99%) and commercial high-purity aluminum (99.99%) were melted, and given amounts of Fe and Mn were added to the molten alloys. The grain size of the high-purity alloy is refined naturally without the use of a grain refiner or superheat treatment, and the addition of small amounts of Fe and Mn to the alloy coarsens the grains. In the composition range of Fe or Mn where magnesium does not crystallize from the melt as the primary crystal, both grain-coarsening and the effect of superheat treatment are remarkable. EPMA and AES analyses reveal a dispersion of fine particles composed of Mg, O, Al, and C elements in the high-purity alloy. Some combination of these elements seems to be an effective nucleation substance for magnesium crystal, and the nucleation substance is similar to those whose presence has been confirmed in AZ91E alloy to which a proper amount of carbide was added. In coarse-grained alloys, Fe and Mn elements coexist with the above-mentioned nucleation substances, and this disturbs the grain refinement.
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Effect of Grain Refinement on Electrochemical Behavior of Al– Zn–Mg–Cu Alloys

Effect of Grain Refinement on Electrochemical Behavior of Al– Zn–Mg–Cu Alloys

Similar with strength property, corrosion resistance of alloys also can be related with grain size. The link between grain size and corrosion resistance has been reviewed and studied by N. Birbilis and his coworkers [9, 12, 13] who found that there is a tendency for corrosion rate to decrease as grain size decreases for high purity aluminium, and they further proposed that the Hall-Petch relation might exist between grain size and corrosion resistance. In the present work, the results reconfirmed their proposal. From SCC and electrochemical corrosion results, it can be concluded that the corrosion resistance of Al–6.2Zn–2.3Mg–2.3Cu alloys is inversely proportional to grain size. This is due to different low angle grain boundary (LAGB) densities of the studied alloys. Precious work revealed that in this three Al alloys, AlZnMgCu–Zr–Cr–Yb alloy has the highest proportion of LAGB [25, 27]. Since the energy of the LAGB is much lower than that of the HAGB and similar with grain interior energy, the concentration of η precipitates (anodic phase) at the LAGB is lower and the η phases are more discontinuously distributed [39, 40]. Grain boundaries with discrete η precipitates are noble to anodic dissolution and would cut off the corrosion channels for intergranular corrosion and SCC. Therefore, corrosion resistant of Al–6.2Zn–2.3Mg–2.3Cu alloys is improved by grain refinement which is caused by the addition of Zr or complex addition of Zr, Cr and Yb.
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Low Temperature Superplasticity and Its Deformation Mechanism in Grain Refinement of Al Mg Alloy by Multi Axial Alternative Forging

Low Temperature Superplasticity and Its Deformation Mechanism in Grain Refinement of Al Mg Alloy by Multi Axial Alternative Forging

Kobayashi et al. reported 22) that when Al-Mg alloy was compressed at 473 K and the total rolling reduction ratio was 90%, the recrystallization temperature decreased to about 553 K, a reduction of 20 to 30 K, as the amount of alloy to be compressed increased. This is because with a higher working ratio and at a lower working temperature, a greater number of dislocations occurred as a result of working, and in turn a greater driving force of recrystallization was created. There is still a difference of about 80 K between the recrystallization temperature mentioned above and the test temperature of 473 K. Thus, it is not logical to conclude that the entire specimen is recrystallized, although the possibility of recrystallization in localized areas cannot be denied. Our results showed that the material had dislocations in the grains, and equiaxial grains were locally observed, even though the specimen was furnace-cooled after fracture. At the same time, as shown in Fig. 6(c), grain boundaries inside elongated grains, including dislocations, began to be formed. On the other hand, as shown in Fig. 7, equiaxial subgrains and subgrains began to be formed locally, with a grain size of 0.9 mm (as identified by the arrows in the figure). The formation of such fine grains as shown by the arrows in Fig. 6(b) is deduced to occur by means of the following process: equiaxial subgrains have a relatively higher density of dislocations than other crystal grains; fine subgrains were formed locally during tensile deformation, and were in turn affected by the rearrangement and disappearance of disloca- tions caused by recovery during furnace-cooling; and such recovery increased the grain boundary misorientations in the entire specimen and locally formed high-angle grain boun- daries, that is, recrystallized grains. We were, however,
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Effect of Pass Strain on Grain Refinement in 7475 Al Alloy during Hot Multidirectional Forging

Effect of Pass Strain on Grain Refinement in 7475 Al Alloy during Hot Multidirectional Forging

each compression exhibit significant work softening just after yielding, followed by apparent steady state plastic flow at high strains. Structural changes were characterized by grain fragmentation due to frequent development of deformation and/or microshear bands followed by full evolution of new fine grains in the original grains. Increasing " accelerates significantly the kinetics of grain refinement, leading to more clear reduction of flow stresses at moderate to high strains. MDF of " ¼ 0:7 results finally in formation of a finer grained structure with an average size of around 7.5 mm at strains of above 3.5, while, the processing with " ¼ 0:4 develops a slightly coarser grain structure at higher strain of about 6. The effect of MDF on new grain evolution and the mechanisms of grain refinement are discussed in details.
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Grain Refinement of As Cast Pure Al by Cold Rolled Al Ti Alloy Refiner

Grain Refinement of As Cast Pure Al by Cold Rolled Al Ti Alloy Refiner

studies, fragmentation of the intermetallic particles in the refiners can accelerate grain refinement of as-cast pure Al and Al alloys. However, it is still difficult to use ECAP in industrial processes since it cannot deform large samples. Although the influence of extrusion of Al­5 mass%Ti­ 1 mass%B alloy refiner on its grain refining efficiency has been reported by Venkateswarlu et al., 15) it is necessary to heat up the refiner for the extrusion. Considering about industrial process for the deformation of the refiner, cold rolling is expected to be a useful process for improving the effectiveness of re fi ners in industrial applications. But the efficiency of grain refinement of as-cast pure Al by cold- rolled refiners is unclear since the deformation strain induced by cold rolling is much smaller than that induced by ECAP. If the grain refinement ability of the refiners can be significantly enhanced by cold rolling, this technique would be suitable for industrial processes.
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Partial Grain Refinement in Al 3%Cu Alloy during ECAP at Elevated Temperatures

Partial Grain Refinement in Al 3%Cu Alloy during ECAP at Elevated Temperatures

by single spot electron diffraction (SAED) pattern obtained in 6 mm diameter. Further straining to " ¼ 8 provides a formation of roughly equiaxed (sub)grained structure, which can be resulted from gradual breaking-up of the bands described above (Fig. 8(b)). The SAED pattern suggests that most of these boundaries have high misorientation angles. After 12 passes of ECAP, roughly equiaxial (sub)grains surrounded by HABs are formed (Fig. 8(c)). There are rather coarse precipitates of -phase distributed roughly homoge- neously in elongated bands and (sub)grain interiors and also along the boundaries developed in Fig. 8. It is interesting to note here that the particle size in Fig. 8(a) is remarkably smaller than that of coarse precipitates present in the original structure (Fig. 1(b)). This may suggest that the initial coarse Al 2 Cu precipitates are fragmented and/or dissolved and re-
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Grain Refinement and Mechanical Behavior of the Al Alloy, Subjected to the New SPD Technique

Grain Refinement and Mechanical Behavior of the Al Alloy, Subjected to the New SPD Technique

It is well-known, that ECAP processing significantly increases the strength, but reduces ductility. The Al 6061 alloy after ECAP-PC through 1 and 2 passes behaved in accordance with this rule. However, it showed considerable increase in ductility with the small reduction of strength (to 30–40 MPa) after ECAP-PC through 4 passes. Such extra- ordinary combination of high strength and high ductility of UFG Al alloy was also observed recently. 5,15–17) This attractive mechanical behavior can be caused by either formation of UFG structure with high-angle grain boundaries capable to grain boundary sliding, 16) or difficulty in strain
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Grain Refinement of Aluminum Alloy Bar by a Modified RAP Process for Semi Solid Forming

Grain Refinement of Aluminum Alloy Bar by a Modified RAP Process for Semi Solid Forming

From the above analysis, the higher the ARR, the finer the recrystallized grain, which further induces the decline of av- erage grain size. The main cause for the precipitous reduction in average grain size may be that the RF process makes the deformation energy to be rapidly accumulated and abundant- ly stored in the RF-deformed 6063 Al alloy bar when the ARR increases from 30% to 50%. Hence the average grain sizes of both the peripheral and central parts are rapidly re- duced. When the ARR increases from 50% to 70%, it seems that the accumulating rate of deformation energy gradually falls, which weakens the effect of recrystallization on the evo- lution of grains. Therefore, the reduction tendency becomes gentle. The main cause for the unobvious change may be that the deformation degree of starting material reaches a peak value at 70% ARR and is hard to be further improved, possi- bly because that the vacancies, lattice defects, and disloca- tions are neutralized as the ARR reaches above 70%. There- fore, the deformation process of RF from 70% to 85% ARR plays a weak role in the reduction of the average grain size.
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Effect of Iron and/or Carbon on the Grain Refinement of Mg 3Al Alloy

Effect of Iron and/or Carbon on the Grain Refinement of Mg 3Al Alloy

decreased by the addition of Al-1.5C master alloy from 270 mm to 50 mm for the commercial AZ63 alloy. They also suggested that Fe plays an important role in the formation of the nucleating particle rather than an inhibiting element. Grain refinement by carbon addition is mainly due to the heterogeneous nucleation on the Al-, C-, O-, Fe- and Mn-rich particles. It is very difficult to understand clearly why contradictory conclusion was made for the same phenomen- on. It should be noted that the ultra-high purity raw materials with very low contents of Fe and Mn (<10 ppm) were used by Tamura and Peng et al., 4,8) while the commercial raw
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Grain Refinement and Ductility Improvement by Hot Extrusion Using a Heteromorphic Die with Small Holes

Grain Refinement and Ductility Improvement by Hot Extrusion Using a Heteromorphic Die with Small Holes

which the alloy can be extruded by the extrusion apparatus used in this study. As schematically shown in Fig. 2, the strain–giving die has six small round holes of 5 mm in di- ameter (Fig. 2 (a)), while the shape–giving die has one big rectangular hole of 9 mm ×  15 mm (Fig. 2 (b)), and both the dies are 10 mm in thickness. A ring–shaped spacer of 45 mm in diameter, 24 mm in internal diameter and 10 mm in height (Fig. 2 (c)) was put between these two dies to prevent them from contacting each other. The setup of the dies and the spacer, which is called in this study the heteromorphic die, is illustrated in Fig. 2(d). An Al–Cu alloy disk used as a dum- my was put in the space between the two dies, as indicated in the Fig. 2 (d). It was expected that the Al–Cu alloy billet would be deformed into six thin round rods with the strain– giving die and extruded toward the space between the two dies, and then the six thin round rods would push up the dum- my sample and they all would pass together through the shape–giving die to become a plate. The extrusion ratio calcu- lated from the cross sections of samples before and after ex- trusion was approximately 13, and the true strain calculated from natural logarithm of the extrusion ratio was approxi- mately 2.6. On the other hand, the nominal strain calculated from the ratio of the reduction of cross sectional area to the initial cross sectional area was approximately 92%. The total cross sectional area of the small round holes of the strain–giv- ing die was nearly same as the cross sectional area of the rectangular hole of the shape–giving die. Therefore, it was assumed that little additional strain was introduced by the shape–giving die. Extrusion with the shape–giving die with- out the strain–giving die was also conducted for comparison. Extrusion load was 440 kN, and ram speed was 0.25 mm min −1
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A Study On Effect Of Ultrafine Grain Refinement On Mechanical Properties Of Non-Heat Treatable Alloys

A Study On Effect Of Ultrafine Grain Refinement On Mechanical Properties Of Non-Heat Treatable Alloys

Han et al [7]. They investigated deformation behavior within the deformation zone of a work-piece during equal channel angular pressing (ECAP) using the finite element method. The effects of die geometry on the variations of normal and shear deformations were studied with a deformation rate tensor. The zero dilatation line, at which the normal components of the deformation rate tensor are zero, in the die coincided with the line of intersection of the two die channels irrespective of die geometry such as curvature angle (ψ) and oblique angle (ϕ ), while the maximum shear line, at which the shear components of the deformation rate tensor have maximum value, is dependent on the die geometry.
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Grain Refinement and Hall-Petch Strengthening of Magnesium Alloy Via Alloying and Hot Extrusion

Grain Refinement and Hall-Petch Strengthening of Magnesium Alloy Via Alloying and Hot Extrusion

In this study, the effects of the addition of Al, Zn and Mn along with the application of the hot extrusion process on the microstructural refinement and enhancement of the mechanical properties of magnesium alloy have been examined. The following conclusions can be drawn from this study: (1) Based on Mg-2Al alloy, it was found that the addition of 0.5 wt% Zn to form Mg-2Al-0.5Zn alloy or 0.5 wt% Mn to form Mg-2Al-0.5Mn alloy is the effective way for the grain refinement of α-Mg in the as-cast state. For instance, the average grain size of the as-cast Mg-2Al-0.5Mn alloy was determined to be 1/16.5 that of the as-cast Mg. Moreover, further remarkable refinement of the grain size can be achieved by the extrusion process in such a way that the average grain size of the extruded Mg-2Al- 0.5Mn alloy was determined to be 1/10 that of its as- cast counterpart.
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The Role of Recrystallization in Spontaneous Grain Refinement of Rapidly Solidified Ni₃Ge

The Role of Recrystallization in Spontaneous Grain Refinement of Rapidly Solidified Ni₃Ge

< 280 lm in diameter. Interestingly, this is close to the droplet size (300 to 212 lm) at which Haque et al. [26] first observed the formation of dendrites in their samples, an occurrence they associated with the transi- tion to disordered growth. For droplets in the 53 to 75 lm diameter range undercoolings approaching 400 K (400 °C) are estimated, which would exceed the maximum undercooling achieved by Nash and Nash. [35] The drop-tube powders were then subject to XRD analysis to ensure they remained single phase, following which they were mounted and polished to a 1 lm finish for microstructural analysis. For EBSD analysis polish- ing using 0.1 lm colloidal silica suspension was employed. For metallographic analysis, performed using a Carl Zeiss EVO MA15 scanning electron microscope (SEM), the samples were etched in a mixture of equal parts HF, HCl, and HNO 3 . An Oxford Instrument
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Grain Refinement of Tough Pitch Copper by Electromagnetic Vibrations during Solidification

Grain Refinement of Tough Pitch Copper by Electromagnetic Vibrations during Solidification

Electromagnetic vibrations, which are generated by simultaneous imposition of a static magnetic field and an alternating electric field, were applied to the refinement of crystal grains of tough pitch copper. The electromagnetic vibrations of the frequency range from 100 Hz to 10 kHz were imposed during solidification of the copper rod. Within this frequency range, the vibration frequency of about 100 Hz was found to be the most effective in refining the copper crystal grains and the average grain size was refined up to 200 mm, which otherwise was around 600 mm in a nonvibrated specimen. It was concluded that by the electromagnetic vibration process tough pitch copper could also be refined as well as Al-Si alloys and AZ91D alloys. [doi:10.2320/matertrans.47.1793]
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Development of Severe Torsion Straining Process for Rapid Continuous Grain Refinement

Development of Severe Torsion Straining Process for Rapid Continuous Grain Refinement

This study presents a rapid continuous process for grain refinement in metallic materials through severe plastic deformation (SPD). The principle is described and the process is applied to an Al-5056 alloy and an S45C carbon steel. The new process, designated in this study the severe torsion straining process (STSP), consists of producing a local heated zone in a rod and introducing torsion strain into the zone by rotating one end with the other. The process is continuous because the straining is achieved while the rod is moved so that the heated zone is shifted along the rod. The STSP does not require the use of any die and can be applicable to pipes or wires. Fine-grained structures produced with the STSP are confirmed using optical microscopy and transmission electron microscopy. Tensile properties are measured and compared with the unstrained fully annealed samples. The feasibility of the STSP is discussed with respect to the rotation speed and moving speed.
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Grain Refinement in a Mg AZ91 Alloy via Large Strain Hot Rolling

Grain Refinement in a Mg AZ91 Alloy via Large Strain Hot Rolling

The double-peak texture developed during large strain hot rolling (Fig. 5) is a deformation texture typical of rolled Mg alloys. 23) However, its origin is still not clear. Several explanations have been put forward over the years. Bakarian 24) proposed a {101 11} twinning mechanism. Coul- ing 25) as well as Wonsiewicz and Backofen 26) suggested that {101 11} twinning followed by {101 12} twinning takes place during rolling of Mg alloys, although they did not relate this directly to the rolling texture. Agnew et al. 27) recently simulated the texture evolution during plane strain deforma- tion of randomly oriented pure Mg, Mg-Li, and Mg-Y polycrystals using a viscoplastic self-consistent formulation. They found a good correlation between simulated and double-peak experimental textures when an increasing
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Evaluation of Grain Refinement and Mechanical Property on Friction Stir Welded Inconel 600

Evaluation of Grain Refinement and Mechanical Property on Friction Stir Welded Inconel 600

Ni base alloy is a material which has low stacking fault energy in F.C.C. metals. It is easy to occur the dynamic recrystallization at the condition which has high stored energy and enough heat input, compared to the materials with a high stacking fault energy, such as Al alloys. 8) Since the FSW was introduced in 1991, the dynamic recrystallization aspect of materials with a high stacking fault energy has been reported at many researches, 9–11) however, that of the materials with a low stacking fault energy in F.C.C. metals has not been reported mainly due to the difficulty of FSW on Ni alloy. Therefore, the present study was carried out to investigate the dynamic recrystallization aspect and the microstructural changes according to increasing the welding speed by EBSD technique and to evaluate relationship between the grain refinement and the mechanical property.
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Effects of Manganese and/or Carbon on the Grain Refinement of Mg 3Al Alloy

Effects of Manganese and/or Carbon on the Grain Refinement of Mg 3Al Alloy

By SEM observation, many Al-Mn-rich intermetallic particles were found in the samples of Mg-3Al alloy modified by Mn. Judged by SEM observations, the higher was the content of Mn, the larger was the number of the Al-Mn-rich particles. Figure 3(a) shows the morphologies of the Al-Mn- rich particles in the sample of the Mg-3Al alloy modified by 0.2 mass%Mn. On the basis of the EDS analyses for about 30 particles, it was found that there existed two types of Al-Mn- rich intermetallic compounds with the average molar ratio between Al and Mn of about 1 : 1 and 3 : 2 in the samples modified by Mn. The result indicates that the Al-Mn intermetallic compounds were AlMn and Al 3 Mn 2 phases
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Effect of Silicon on Grain Refinement of Aluminum Produced by Electrolysis

Effect of Silicon on Grain Refinement of Aluminum Produced by Electrolysis

Silicon is not only the most frequent impurity in commercial pure aluminum, but also the most common alloying element. 1) Al-Si alloys find wide application in the marine, electrical, automobile and aircraft industries because of high fluidity, low shrinkage in casting, high corrosion resistance, good weld-ability, easy brazing and low coeffi- cient of thermal expansion. 2) The master alloys containing titanium contents are usually used as the refiners in Al-Si alloys to ensure the mechanical properties, to improve feeding and surface finish, to reduce hot tearing, and to distribute porosities evenly. 2–4) It is believed that the -Al morphology and the phase structure will change with increase in silicon content, and the grain refinement would show different responses to different silicon contents. 1,2) Using the growth-restriction, Mats Johnsson et al. studied the influence of silicon content ranging up to 9 mass% on the grain size and crystal morphology of the alloys with various titanium contents from 0.01 to 0.05 mass%. 1,5,6) But they did not take the structure evolvement into account. Taking the structure evolvement into account, Xiangfa Liu et al. analyzed the influence of silicon content ranging up to 20 mass% on macro-grains of the unrefined Al-Si alloys. 7,8)
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Mechanism selection for spontaneous grain refinement in undercooled metallic melts

Mechanism selection for spontaneous grain refinement in undercooled metallic melts

Such an extended transition in growth orientation had not previously been reported as a function of undercooling. Abrupt, growth velocity/undercooling-mediated switches in preferred growth orientation have been reported in transparent metal analogue systems [18, 19], in strongly faceting Ge-Fe [1] and in Cu-Sn [20]; and an extended ‘Dendrite Orientation Transition’ (DOT) has been experimentally and computationally observed by Dantzig et al. [21] as a function of increasing Zn content in Al. Here, <100>-oriented growth is observed for low Zn content and <110>-oriented growth is observed for high Zn content. At intermediate Zn concentrations, the close competition between the differently-directed anisotropies is observed to give rise to textured, seaweed-like structures. It is subsequently suggested that the weak anisotropy of the solid-liquid interfacial energy of Al is altered by the addition of Zn, which has a relatively high interfacial energy anisotropy. This reinforced the findings of Haxhimali et al. [22], who had previously reported that changes in the composition-dependant interfacial
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