New Grain Formation in a Coarse-Grained 7475 Al Alloy during Severe Hot Forging

2004 ◽  
Vol 467-470 ◽  
pp. 421-428 ◽  
Author(s):  
Oleg Sitdikov ◽  
Tetsuo Sakai ◽  
Alexandre Goloborodko ◽  
Hiromi Miura ◽  
Rustam Kaibyshev
Keyword(s):  
Grain Refinement ◽  
Hot Forging ◽  
Grain Boundary Sliding ◽  
Grain Structure ◽  
Coarse Grained ◽  
Al Alloy ◽  
Continuous Dynamic Recrystallization ◽  
Multidirectional Forging ◽  
Fine Grain ◽  
Continuous Dynamic

Strain-induced grain refinement in a coarse-grained 7475Al alloy was studied by means of multidirectional forging (MDF) carried out at T = 490oC under a strain rate of 3 x 10-4 s-1. Integrated flow curves exhibit significant work softening just after yielding, followed by steady-state-like behavior at high strains. The evolution of new fine grain structure during deformation can be assisted by grain-boundary sliding, resulting in frequent formation of high strain gradients and subsequently microshear bands in grain interiors. Microshear bands developed in various directions are intersected with each other, subdividing original grains into misoriented small domains. The number and the misorientation angle of microshear bands progressively increase during deformation, finally followed by their transformation into high-angle boundaries. It is concluded that grain refinement under hot MDF conditions occurs by a series of deformation-induced continuous reactions; that is essentially similar to continuous dynamic recrystallization.

Effect of Multidirectional Forging and Subsequent Annealing to the Microstructure of Al-Mg-Mn Type Alloy

2020 ◽  
Vol 306 ◽  
pp. 23-32
Author(s):  
Anton D. Kotov ◽  
Mikhail Kishchik ◽  
Anastasia V. Mikhaylovskaya
Keyword(s):  
Room Temperature ◽  
Elevated Temperatures ◽  
Shear Bands ◽  
Grain Structure ◽  
Coarse Grained ◽  
Recrystallization Annealing ◽  
Type Alloy ◽  
Rich Phase ◽  
Multidirectional Forging ◽  
Fine Grain

The grain refinement is important to improve both service properties at room temperature and superplasticity at elevated temperatures. This study focuses on the effect of multidirectional forging in isothermal conditions on the microstructure of Al-Mg-Mn-type alloy. The evolution of dislocation and grain structure, and precipitates of Mn-rich phase during multidirectional forging in a temperature range of 200 to 500 °C was studied. Multidirectional forging at temperatures of 200 and 300 °C leads to the formation of shear bands in the deformed grains. The multidirectional forging at 400 and 500 °C leads to the formation of a bimodal grain structure with fine- and coarse-grained areas. Subsequent recrystallization annealing at 500 °C increases the grain size and decreases the fine grains fraction in the samples pre-deformed at 400-500°C, and, on the contrary, annealing leads to formation homogeneous and fine grain structure with size up to 6.5 μm in samples pre-deformed at 200 and 300 °C.

Grain Refinement of 6061 Al Alloy by the Modified Strain-Induced Melt- Activated(SIMA) Process for Semi-Solid Processing

2007 ◽  
Vol 119 ◽  
pp. 311-314 ◽  
Author(s):  
Young Buem Song ◽  
Chun Pyo Hong
Keyword(s):  
Grain Refinement ◽  
Grain Structure ◽  
Al Alloy ◽  
Fine Grained ◽  
Fine Grain ◽  
Fine Grained Structure ◽  
Size Uniformity ◽  
Sima Process ◽  
Semi Solid ◽  
6061 Al Alloy

The dynamic process of fine grain evolution of 6061 aluminum alloy during modified strain-induced, melt-activated (SIMA) process was studied. The modified SIMA process employed casting, two stage homogenization, warm multi-forging, and recrystallization and partial melting (RAP). Multi-forging was carried out at a strain rate of 9x10-3 s-1 to accumulate high strains, with decreasing temperature from 250 to 200 °C. The alloy multi-forged with the accumulated strain of about 12 and RAP at 640 °C for 10 min exhibited the uniform equiaxed recrystallized grain structure. Accordingly, it was evident that multi-forging was very effective on grain refinement and grain size uniformity. The present modified SIMA process was discussed as an alternative thermo-mechanical processing for preparing the alloys with fine grained structure for semi solid processing.

Strain-Induced Grain Refinement in Magnesium Alloy AZ31 during Hot Forging

2006 ◽  
Vol 503-504 ◽  
pp. 521-526 ◽  
Author(s):  
Xu Yue Yang ◽  
Jie Xing ◽  
Hiromi Miura ◽  
Taku Sakai
Keyword(s):  
Magnesium Alloy ◽  
Grain Refinement ◽  
Structural Changes ◽  
Hot Forging ◽  
Kink Bands ◽  
Alloy Az31 ◽  
Continuous Dynamic Recrystallization ◽  
Magnesium Alloy Az31 ◽  
Average Grain Size ◽  
Continuous Dynamic

Strain-induced grain refinement in a magnesium alloy AZ31 was studied in multi-directional forging (MDF) at a temperature range from 423K to 623K and at a strain rate of 3x10-3s-1. MDF with a pass strain of 0.8 was carried out to high cumulative strains of around 5 with changing of the loading direction during decreasing temperature from pass to pass. The structural changes can be characterized by the evolution of many mutually crossing kink bands at low strains followed by increase in their number and misorientation, finally resulting in a fully developed fine-grains at high strains. MDF with decreasing temperature can accelerate the evolution of much finer grains and the improvement of plastic workability. An average grain size of 0.3 μm is formed at an accumulative strain of 4.8 and at 423K. It is concluded that grain refinement under MDF conditions occurs by a series of deformation-induced continuous reactions; that is essentially similar to continuous dynamic recrystallization (cDRX).

Grain refinement in coarse-grained 7475 Al alloy during severe hot forging

2005 ◽  
Vol 85 (11) ◽  
pp. 1159-1175 ◽  
Author(s):  
O. Sitdikov ◽  
T. Sakai * ◽  
A. Goloborodko ◽  
H. Miura ◽  
R. Kaibyshev
Keyword(s):  
Grain Refinement ◽  
Hot Forging ◽  
Coarse Grained ◽  
Al Alloy

Fine-Grained Structure Formation in 7475 Al Alloy during Hot Multidirectional Forging

2006 ◽  
Vol 512 ◽  
pp. 79-84
Author(s):  
Alexandre Goloborodko ◽  
Oleg Sitdikov ◽  
Hiromi Miura ◽  
Taku Sakai
Keyword(s):  
Steady State ◽  
Strain Rate ◽  
Grain Refinement ◽  
High Strain ◽  
Volume Fraction ◽  
Coarse Grained ◽  
Al Alloy ◽  
Steady State Flow ◽  
Multidirectional Forging ◽  
State Flow

Effect of strain rate on grain refinement was studied in multidirectional forging (MDF) of a coarse-grained 7475 Al alloy at 490oC under strain rates of 3 × 10-4 s-1 and 3 × 10-2 s-1. At a strain rate of 3 × 10-4 s-1, the stress – strain ( σ - ε) behavior shows significant work softening just after yielding and a steady-state flow at higher strains. The structural changes are characterized by development of deformation bands at early stages of deformation, followed by formation of a fine grain structure in high strain in the whole material. The volume fraction of new grains increases with strain and approaches a value of about 0.85 over a strain of 3. At a higher strain rate of 3 × 10-2 s-1, in contrast, a steady-state flow following small flow softening appears at a relatively low strain. New grains are formed during steady state flow along original grain boundaries and the volume fraction reaches below 0.2 even in high strain. The occurrence conditions and the mechanisms of grain refinement are discussed in detail.

The Effect of Strain on the Development of Ultra-Fine Grain Structure in 7055 Aluminium Alloy Processed by Equal Channel Angular Extrusion

2008 ◽  
Vol 584-586 ◽  
pp. 691-696 ◽  
Author(s):  
Ilya Nikulin ◽  
Yoshinobu Motohashi ◽  
Rustam Kaibyshev
Keyword(s):  
Grain Boundaries ◽  
Equal Channel Angular Extrusion ◽  
Grain Structure ◽  
High Angle ◽  
Continuous Dynamic Recrystallization ◽  
Fine Grain ◽  
Average Grain Size ◽  
Angular Extrusion ◽  
Continuous Dynamic ◽  
7055 Aluminum Alloy

Grain refinement taking place in a commercial 7055 aluminum alloy under equal channel angular extrusion at a temperature of 250°C, was examined. The material was deformed up to a total strain, ε, of ~12. At ε≈1, the development of subgrain bands was found. Upon further straining the average misorientation of deformation-induced boundaries increases; low-angle grain boundaries (LAGBs) gradually convert into true high-angle grain boundaries (≥15°) (HAGBs). At ε≈4, a structure consisting of boundaries with low and high angle misorientations was observed. At ε≈12, a structure with an average grain size of ∼0.7 µm was formed. This size is roughly similar to that for subgrains developed at preceding strains. It was shown that the formation of submicrocrystalline grains occurs through continuous dynamic recrystallization both along initial boundaries and within interiors of original grains as well.

Microstructural Evolution in a Commercial Al-Mg-Sc Alloy during ECAP at 300°C

2007 ◽  
Vol 558-559 ◽  
pp. 569-574 ◽  
Author(s):  
Oleg Sitdikov ◽  
Taku Sakai ◽  
Elena Avtokratova ◽  
Rustam Kaibyshev ◽  
Kaneaki Tsuzaki ◽  
...  
Keyword(s):  
Microstructural Evolution ◽  
Driving Force ◽  
Static Recrystallization ◽  
Grain Structure ◽  
Coarse Grained ◽  
Microstructural Development ◽  
Continuous Dynamic Recrystallization ◽  
Grain Sizes ◽  
Angular Pressing ◽  
Continuous Dynamic

Microstructural evolution taking place during equal channel angular pressing (ECAP) was studied in a commercial coarse-grained Al-6%Mg-0.4%Mn-0.3%Sc alloy at a temperature of 300oC (~0.6Tm). Samples were pressed using route A to a total strain of 12 and quenched in water after each ECAP pass. ECAP at moderate-to-high strains leads to the formation of a bimodal grain structure with grain sizes of around 1 and 8 μm and volume fractions of 0.3 and 0.6, respectively. The development of new-grained regions has been shown to result from a concurrent operation of continuous dynamic recrystallization that occurs during deformation and static recrystallization that occurs during each ECAP cycle by the exposure of the as-deformed material in the die kept at 300oC for around 1.5 minutes. The microstructural development during warm-to-hot ECAP is discussed in terms of the enhanced driving force for recrystallization, resulting from the evolution of high-density dislocation substructures due to the localization of plastic flow and inhibition of recovery in the present alloy.

scholarly journals Microstructural evolution during high-temperature tensile creep at 1,500°C of a MoSiBTiC alloy

2020 ◽  
Vol 39 (1) ◽  
pp. 136-145 ◽  
Author(s):  
Sojiro Uemura ◽  
Shiho Yamamoto Kamata ◽  
Kyosuke Yoshimi ◽  
Sadahiro Tsurekawa
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Grain Boundary Sliding ◽  
Primary Creep ◽  
Tensile Creep ◽  
Tertiary Creep ◽  
Continuous Dynamic Recrystallization ◽  
Continuous Dynamic ◽  
Creep Regime

AbstractMicrostructural evolution in the TiC-reinforced Mo–Si–B-based alloy during tensile creep deformation at 1,500°C and 137 MPa was investigated via scanning electron microscope-backscattered electron diffraction (SEM-EBSD) observations. The creep curve of this alloy displayed no clear steady state but was dominated by the tertiary creep regime. The grain size of the Moss phase increased in the primary creep regime. However, the grain size of the Moss phase was found to remarkably decrease to <10 µm with increasing creep strain in the tertiary creep regime. The EBSD observations revealed that the refinement of the Moss phase occurred by continuous dynamic recrystallization including the transformation of low-angle grain boundaries to high-angle grain boundaries. Accordingly, the deformation of this alloy is most likely to be governed by the grain boundary sliding and the rearrangement of Moss grains such as superplasticity in the tertiary creep regime. In addition, the refinement of the Moss grains surrounding large plate-like T2 grains caused the rotation of their surfaces parallel to the loading axis and consequently the cavitation preferentially occurred at the interphases between the end of the rotated T2 grains and the Moss grains.

scholarly journals Microstructural Evolutions of 2N Grade Pure Al and 4N Grade High-Purity Al during Friction Stir Welding

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3606
Author(s):  
Tomoya Nagira ◽  
Xiaochao Liu ◽  
Kohasaku Ushioda ◽  
Hidetoshi Fujii
Keyword(s):  
Friction Stir Welding ◽  
Dynamic Recrystallization ◽  
Grain Refinement ◽  
High Purity ◽  
Cube Texture ◽  
Grain Structure ◽  
Welding Temperature ◽  
Friction Stir ◽  
Continuous Dynamic Recrystallization ◽  
Dislocation Annihilation

The grain refinement mechanisms along the material flow path in pure and high-purity Al were examined, using the marker insert and tool stop action methods, during the rapid cooling friction stir welding using liquid CO2. In pure Al subjected to a low welding temperature of 0.56Tm (Tm: melting point), the resultant microstructure consisted of a mixture of equiaxed and elongated grains, including the subgrains. Discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX), and geometric dynamic recrystallization are the potential mechanisms of grain refinement. Increasing the welding temperature and Al purity encouraged dynamic recovery, including dislocation annihilation and rearrangement into subgrains, leading to the acceleration of CDRX and inhibition of DDRX. Both C- and B/-type shear textures were developed in microstructures consisting of equiaxed and elongated grains. In addition, DDRX via high-angle boundary bulging resulted in the development of the 45° rotated cube texture. The B/ shear texture was strengthened for the fine microstructure, where equiaxed recrystallized grains were fully developed through CDRX. In these cases, the texture is closely related to grain structure development.

Microstructural Changes of Welded Zn-AI Alloy

1994 ◽  
Vol 367 ◽  
Author(s):  
Yao Hua Zhu
Keyword(s):  
Phase Transformation ◽  
Early Stage ◽  
Dendritic Structure ◽  
Metastable Phases ◽  
Grain Structure ◽  
Al Alloy ◽  
Cast State ◽  
Microstructural Changes ◽  
Fine Grain ◽  
Ageing Processes

AbstractExtruded eutectoid Zn-Al alloy was welded by a melt of the same eutectoid alloy. Two different microstructures were observed in the joint part and the bulk of the welded alloy. Typical dendritic structure of as cast Zn-Al alloy was observed in the joint part of the welded alloy. The bulk ofthe welded Zn-Al alloy appeared as fine grain structure. Two different metastable phases η'T decomposed from η's of chilled as cast state and η'E of extruded state were found to be unstable during early stage of ageing. A four phase transformation occurred after the decompositions of these two metastable phases of η'T. Microstructures of both joint part and bulk of the welded alloy were investigated parallely during ageing processes.

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