Dynamic Recrystallization in Al-Li Based Alloy during Equal Channel Angular Extrusion

2012 ◽  
Vol 715-716 ◽  
pp. 286-291
Author(s):  
Sivaswamy Giribaskar ◽  
Gouthama ◽  
Rajesh Prasad
Keyword(s):  
Dynamic Recrystallization ◽  
Equal Channel Angular Extrusion ◽  
Effective Strain ◽  
Dimensional Change ◽  
Second Phase ◽  
Fine Grained ◽  
Microstructure Observation ◽  
Deformable Particles ◽  
Second Phase Particles ◽  
Angular Extrusion

Development of bulk ultra-fine grained (UFG) materials by severe plastic deformation to attain improved mechanical properties is becoming more attractive and extensively studied nowadays. Equal channel angular extrusion (ECAE) is one of technique used effectively for obtaining bulk UFG materials. Novelty of this technique is one can build up significant amount of plastic strain by increasing the number of passes without much dimensional change. In present investigation dynamic recrystallization at deformation zones around the non-shearable second phase particles in Al-Li based alloy processed by ECAE is reported. Transmission electron microscopy technique involving imaging the regions of such deformation zones with different specimen tilt conditions is used. It is shown that the dynamic recrystallisation occurring in the proximities of second phase particles during the deformation at room temperature, leads to very fine grained microstructure. Observation of multiple active nucleation sites around even sub-micrometer sized non-deformable particles in the as-processed material indicates that the system exhibits efficiency >1 based on the concept of particle stimulated nucleation (PSN). Crystallites of ultra-fine/nanocrystalline size ranges are formed in the deformation zones around the non-deformable particles during deformation itself. Effect of short term post deformation annealing to understand the recovery and recrystallization was undertaken. Based on these results effect of optimal post deformation heat treatment conditions on the thermal stability of the microstructures is emphasized. It is suggested that with significant fraction of non-shearable particles it might be possible to get grain size in the nanocrystalline or ultra-fine range with relatively low effective strain levels using ECAE.

Microstructure of Friction Stir Processed Mg-Y-Zn Alloy

2007 ◽  
Vol 558-559 ◽  
pp. 777-780 ◽  
Author(s):  
Taiki Morishige ◽  
Masato Tsujikawa ◽  
Sung Wook Chung ◽  
Sachio Oki ◽  
Kenji Higashi
Keyword(s):  
Equal Channel Angular Extrusion ◽  
Second Phase ◽  
Ingot Metallurgy ◽  
Friction Stir ◽  
Fine Grained ◽  
Probe Diameter ◽  
Fine Grain ◽  
Second Phase Particles ◽  
The Matrix ◽  
Zn Alloy

Friction stir processing (FSP) is the effective method of the grain refinement for light metals. The aim of this study is to acquire the fine grained bulk Mg-Y-Zn alloy by ingot metallurgy route much lower in cost. Such bulk alloy can be formed by the superplastic forging. The microstructure of as-cast Mg-Y-Zn alloy was dendrite. The dendrite arm spacing was 72.5 [(m], and there are the lamellar structures in it. FSP was conducted on allover the plate of Mg-Y-Zn alloy for both surfaces by the rotational tool with FSW machine. The stirring passes were shifted half of the probe diameter every execution. The dendrite structures disappeared after FSP, but the lamellar structure could be observed by TEM. The matrix became recrystallized fine grain, and interdendritic second phase particles were dispersed in the grain boundaries. By using FSP, cast Mg-Y-Zn alloy could have fine-grained. This result compared to this material produced by equal channel angular extrusion (ECAE) or rapid-solidified powder metallurgy (RS P/M). As the result, as-FSPed material has the higher hardness than materials produced by the other processes at the similar grain size.

TEM Studies on the Effect of Nature of Precipitates in Al-Li Alloy on Microstructural Evolution during Severe Plastic Deformation

2008 ◽  
Vol 584-586 ◽  
pp. 411-416 ◽  
Author(s):  
Sivaswamy Giribaskar ◽  
Gouthama ◽  
Rajesh Prasad
Keyword(s):  
Equal Channel Angular Extrusion ◽  
Applied Pressure ◽  
Second Phase ◽  
Fine Grained ◽  
Second Phase Particles ◽  
Formed Precipitate ◽  
Different Temperatures ◽  
Grain Fragmentation ◽  
Dynamic Recrystallisation ◽  
Evolution Of Microstructure

Equal channel angular extrusion (ECAE), involving intense plastic straining under high applied pressure is generally recognized and extensively studied top down approach for producing bulk ultra-fine grained (UFG) metallic materials, and even going down in size to the nanometer range. In this research efforts are made to identify conditional under which grains with size less than 100 nm form after ECAE. Evolution of microstructure of Al-Li based alloy processed by ECAE is analyzed using transmission electron microscopy (TEM). Observations on the effect of precipitates/second phase particles in the sample on the deformation characteristics and their role on the increased degree of grain fragmentation process is highlighted. Samples of Al-Li based alloy are solutionized, quenched and aged at different temperatures to obtain well formed precipitate laths/plates before subjecting to ECAE. During the deformation process these precipitates disintegrate into fragments and get dispersed into the Al matrix. The fragments of a few nanometers size bring about drastic changes in the flow as well as the recovery characteristics of processed samples. Evidence for dynamic recrystallisation taking place during the ECAE processing is presented. It was observed that optimal thermal treatment leads to more effective grain refinement and consequently an ultra-fine grained microstructure could be achieved even after single pass in Al-Li based alloy containing precipitates and second phase particles.

Effect of Second Phase on the Mechanical Properties of Mg-Al-Zn Alloy by Equal Channel Angular Extrusion

2007 ◽  
Vol 546-549 ◽  
pp. 249-252 ◽  
Author(s):  
Wen Jiang Ding ◽  
Li Jin ◽  
Dong Liang Lin ◽  
Xiao Qin Zeng ◽  
Da Li Mao
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Magnesium Alloy ◽  
Equal Channel Angular Extrusion ◽  
Tensile Deformation ◽  
Second Phase ◽  
Second Phase Particles ◽  
Angular Extrusion ◽  
Zn Alloy ◽  
Zn Alloys

The effect of second phase on the mechanical properties of AZ61 and AZ91 Mg-Al-Zn magnesium alloy processed by equal-channel angular extrusion (ECAE) has been investigated. The results revealed that cracks initiated at and propagated through the α-Mg/β-Mg17Al12 interfaces and grain boundaries of Mg-Al-Zn alloys during tensile deformation. For AZ61, the elongation increased with the increase of ECAE pass number and the decrease of grain size. However, the elongation of AZ91 with more second phase particles decreased with the increase of ECAE pass number and the decrease of grain size.

Fine-Grain Processing by Equal Channel Angular Extrusion of Rapidly Quenched Bulk Mg–Y–Zn Alloy

2005 ◽  
Vol 20 (1) ◽  
pp. 93-101 ◽  
Author(s):  
Hiroyuki Watanabe ◽  
Hidetoshi Somekawa ◽  
Kenji Higashi
Keyword(s):  
Grain Boundaries ◽  
Equal Channel Angular Extrusion ◽  
Second Phase ◽  
Ingot Metallurgy ◽  
Grain Processing ◽  
Fine Grain ◽  
Processed Material ◽  
Second Phase Particles ◽  
Angular Extrusion ◽  
Zn Alloy

The fine-grain processing of ingot metallurgy (IM) Mg–Y–Zn alloy, WZ73, was investigated. The alloy was initially produced by casting into a copper mold at a cooling rate of ∼50 K/s. The rapidly quenched bulk material was processed by means of equal channel angular extrusion (ECAE). The ECAE-processed material had equiaxed grains of 5.1 μm in size, and fine second-phase particles of Mg12YZn were dispersed in the grain boundaries. The Vickers hardness of the ECAE-processed material was 78. The dispersion of the second-phase particles, solid solution strengthening, and grain refinement contributed to the material’s hardness. The structure remained virtually unchanged, at least up to 673 K because the Mg12YZn phase served to pin the grain boundaries. The microstructure of IM WZ73 alloy, which is a suitable starting material for ECAE, was also considered.

Effect of Second-Phase Particles on Grain Refinement of Mg-Al-Zn Alloy during ECAE

2007 ◽  
Vol 546-549 ◽  
pp. 315-318
Author(s):  
Li Jin ◽  
Dong Liang Lin ◽  
Xiao Qin Zeng ◽  
Da Li Mao ◽  
Wen Jiang Ding
Keyword(s):  
Electron Microscopy ◽  
Grain Refinement ◽  
Equal Channel Angular Extrusion ◽  
Second Phase ◽  
Transmission Electron ◽  
Initial Stage ◽  
Mg17al12 Phase ◽  
Second Phase Particles ◽  
Zn Alloy ◽  
Zn Alloys

The effect of second-phase particles on the grain refinement of AZ61 and AZ91 Mg-Al-Zn alloys with different volume fractions of β-Mg17Al12 phase particles during equal channel angular extrusion (ECAE) has been investigated. The microstructure were observed by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed that grain refinement was enhanced by second phase particles at initial stage of ECAE. And finer grains with the high angle grain boundaries (HAGBs) and disperse second-phase particles could be obtained in AZ61 and AZ91 after 8 passes of ECAE.

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