Alexandre Goloborodko

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

Grain refinement taking place in a coarse-grained 7475 Al alloy was studied in multidirectional compression at 490°C and at a strain rate of 3 × 10−4 s−1. The integrated flow curve displays significant work softening just after yielding and an apparent steady-state plastic flow at high strains. The structural changes are characterized by the development of deformation or microshear bands in coarse-grain interiors, followed by homogeneous evolution of new grains at high strains. The new grains are considered to be developed by a kind of continuous reaction through grain fragmentation that is similar to continuous dynamic recrystallization (cDRX). The mechanism of fine grain production and the factors controlling grain refinement during hot multidirectional deformation are discussed in detail.

Microstructure Development during Equal Channel Angular Extrusion of an Al-3%Cu Alloy

Microstructural evolution during equal channel angular extrusion (ECAE) was investigated in a coarse-grained dilute aluminum alloy, Al-3%Cu, at a temperature of 250oC. Scanning electron microscopy (SEM) with electron back scattering diffraction (EBSD) and optical metallography (OM) was used to reveal the structural changes in the alloy deformed up to a strain of ε=12. The microstructural evolution at initial and moderate stages of deformation is characterized by the formation of low angle boundaries and deformation bands with moderate misorientations in grain interiors. With further deformation the number and the misorientation of the deformation bands increase, finally leading to the subdivision of original grains by these bands and then the development of fine grains with an average size of about 6 μm at ε=12. The evolution of deformation bands in initial grain interiors and their role on new grain formation are discussed in detail.

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

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.

Strain Rate Effect on Fine-Grain Development in 7475 Al Alloy during Hot Multidirectional Forging

(ΙΙΗΦΩ ΡΙ ςΩΥ∆ΛΘ Υ∆ΩΗ ΡΘ θΥ∆ΛΘ ΥΗΙΛΘΗΠΗΘΩ Ζ∆ς ςΩΞΓΛΗΓ ΛΘ ΠΞΟΩΛΓΛΥΗΦΩΛΡΘ∆Ο ΙΡΥθΛΘθ (0∋)) ΡΙ ∆ ΦΡ∆ΥςΗ-θΥ∆ΛΘΗΓ 7475 ∃Ο ∆ΟΟΡ∴ ∆Ω 490 Ρ & ΞΘΓΗΥ ςΩΥ∆ΛΘ Υ∆ΩΗς ΡΙ 3 υ 10 ς ∆ΘΓ 3 υ 10 ς. ∃Ω ∆ ςΩΥ∆ΛΘ Υ∆ΩΗ ΡΙ 3 υ 10 ς, ΩΚΗ ςΩΥΗςς ± ςΩΥ∆ΛΘ (ς -Η) ΕΗΚ∆ΨΛΡΥ ςΚΡΖς ςΛθΘΛΙΛΦ∆ΘΩ ΖΡΥΝ ςΡΙΩΗΘΛΘθ ΜΞςΩ ∆ΙΩΗΥ ∴ΛΗΟΓΛΘθ ∆ΘΓ ∆ ςΩΗ∆Γ∴-ςΩ∆ΩΗ ΙΟΡΖ ∆Ω ΚΛθΚΗΥ ςΩΥ∆ΛΘς. 7ΚΗ ςΩΥΞΦΩΞΥ∆Ο ΦΚ∆ΘθΗς ∆ΥΗ ΦΚ∆Υ∆ΦΩΗΥΛ]ΗΓ Ε∴ ΓΗΨΗΟΡΣΠΗΘΩ ΡΙ ΓΗΙΡΥΠ∆ΩΛΡΘ Ε∆ΘΓς ∆Ω Η∆ΥΟ∴ ςΩ∆θΗς ΡΙ ΓΗΙΡΥΠ∆ΩΛΡΘ, ΙΡΟΟΡΖΗΓ Ε∴ ΙΡΥΠ∆ΩΛΡΘ ΡΙ ∆ ΙΛΘΗ-θΥ∆ΛΘ ςΩΥΞΦΩΞΥΗ ΛΘ ΚΛθΚ ςΩΥ∆ΛΘ ΛΘ ΩΚΗ ΖΚΡΟΗ Π∆ΩΗΥΛ∆Ο. 7ΚΗ ΨΡΟΞΠΗ ΙΥ∆ΦΩΛΡΘ ΡΙ ΘΗΖ θΥ∆ΛΘς ΛΘΦΥΗ∆ςΗς ΖΛΩΚ ςΩΥ∆ΛΘ ∆ΘΓ ∆ΣΣΥΡ∆ΦΚΗς ∆ Ψ∆ΟΞΗ ΡΙ ∆ΕΡΞΩ 0.85 ΡΨΗΥ ∆ ςΩΥ∆ΛΘ ΡΙ 3. ∃Ω ∆ ΚΛθΚΗΥ ςΩΥ∆ΛΘ Υ∆ΩΗ ΡΙ 3 υ 10 ς, ΛΘ ΦΡΘΩΥ∆ςΩ, ∆ ςΩΗ∆Γ∴-ςΩ∆ΩΗ ΙΟΡΖ ΙΡΟΟΡΖΛΘθ ςΠ∆ΟΟ ΙΟΡΖ ςΡΙΩΗΘΛΘθ ∆ΣΣΗ∆Υς ∆Ω ∆ ΥΗΟ∆ΩΛΨΗΟ∴ ΟΡΖ ςΩΥ∆ΛΘ. 1ΗΖ θΥ∆ΛΘς ∆ΥΗ ΙΡΥΠΗΓ ΓΞΥΛΘθ ςΩΗ∆Γ∴ ςΩ∆ΩΗ ΙΟΡΖ ∆ΟΡΘθ ΡΥΛθΛΘ∆Ο θΥ∆ΛΘ ΕΡΞΘΓ∆ΥΛΗς ∆ΘΓ ΩΚΗ ΨΡΟΞΠΗ ΙΥ∆ΦΩΛΡΘ ΥΗ∆ΦΚΗς ΕΗΟΡΖ 0.2 ΗΨΗΘ ∆Ω ∆ ςΩΥ∆ΛΘ ΡΙ 6.3. 7ΚΗ ΡΦΦΞΥΥΗΘΦΗ ΦΡΘΓΛΩΛΡΘς ∆ΘΓ ΩΚΗ ΠΗΦΚ∆ΘΛςΠς ΡΙ θΥ∆ΛΘ ΥΗΙΛΘΗΠΗΘΩ ∆ΥΗ ΓΛςΦΞςςΗΓ ΛΘ ΓΗΩ∆ΛΟ. Introduction 0ΗΩ∆ΟΟΛΦ Π∆ΩΗΥΛ∆Ος ΖΛΩΚ ΙΛΘΗ-θΥ∆ΛΘΗΓ ΠΛΦΥΡςΩΥΞΦΩΞΥΗς Κ∆ΨΗ Π∆Θ∴ ∆ΓΨ∆ΘΩ∆θΗς ΡΙ ΩΚΗ ΦΚΗΠΛΦ∆Ο, ΣΚ∴ςΛΦ∆Ο ∆ΘΓ ΠΗΦΚ∆ΘΛΦ∆Ο ΣΥΡΣΗΥΩΛΗς >1≅. ∃Ω ΣΥΗςΗΘΩ ΩΛΠΗ, ςΗΨΗΥ∆Ο ΠΗΩΚΡΓς ∆Ψ∆ΛΟ∆ΕΟΗ ΙΡΥ ΣΥΡΓΞΦΛΘθ ΡΙ ΕΞΟΝ Π∆ΩΗΥΛ∆Ος ΦΡΠΣΡςΗΓ ΡΙ ∆ ΙΛΘΗ-θΥ∆ΛΘΗΓ ςΩΥΞΦΩΞΥΗ ∆ΥΗ Ε∆ςΗΓ ΠΡςΩΟ∴ ΡΘ ςΗΨΗΥΗΟ∴ Ο∆ΥθΗ ΣΟ∆ςΩΛΦ ΓΗΙΡΥΠ∆ΩΛΡΘ >1,2≅. 2ΘΗ ΡΙ ΩΚΗΠ Λς ΠΞΟΩΛΓΛΥΗΦΩΛΡΘ∆Ο ΙΡΥθΛΘθ (0∋)), ΖΚΛΦΚ Λς ΩΚΗ Η∆ςΛΗςΩ ΠΗΩΚΡΓ ΖΛΩΚΡΞΩ ∆Θ∴ ςΣΗΦΛΙΛΦ ΓΗΨΛΦΗ ∆ΘΓ Κ∆ς ∆ θΥΗ∆Ω ΣΡΩΗΘΩΛ∆ΟΛΩ∴ ΙΡΥ ΣΥΡΓΞΦΛΘθ ΡΙ ΥΗΟ∆ΩΛΨΗΟ∴ Ο∆ΥθΗ ΖΡΥΝΣΛΗΦΗ ΩΚ∆Ω Φ∆Θ ΕΗ ΞςΗΓ ΛΘ Π∆ςς ΣΥΡΓΞΦΩΛΡΘ. 7ΚΗ ΣΥΛΘΦΛΣΟΗ ΡΙ 0∋) Λς ΦΡΠΣΥΗςςΛΡΘ ΣΥΡΦΗςς ΥΗΣΗ∆ΩΗΓ ΖΛΩΚ ΦΚ∆ΘθΗ ΛΘ ΩΚΗ ΓΛΥΗΦΩΛΡΘ ΡΙ ΩΚΗ ∆ΣΣΟΛΗΓ ςΩΥ∆ΛΘ (i.e. x ο y ο z ο x ...) ∆Ω Η∆ΦΚ ςΩΗΣ. 6ΛΘΦΗ ∆ ΖΡΥΝΣΛΗΦΗ ΓΡΗς ΘΡΩ ΦΚ∆ΘθΗ ΛΩς ςΚ∆ΣΗ ΞΘΓΗΥ 0∋) ΦΡΘΓΛΩΛΡΘς, Ο∆ΥθΗ ΣΟ∆ςΩΛΦ ςΩΥ∆ΛΘ Φ∆Θ ΕΗ ΛΘΩΥΡΓΞΦΗΓ ΛΘΩΡ Π∆ΩΗΥΛ∆Ο ΓΞΥΛΘθ ΥΗΣΗ∆ΩΗΓ ΦΡΠΣΥΗςςΛΡΘ ∆Ω ∆ΠΕΛΗΘΩ ΩΡ ΗΟΗΨ∆ΩΗΓ ΩΗΠΣΗΥ∆ΩΞΥΗς. ,Ω Κ∆ς ΕΗΗΘ ςΚΡΖΘ ΥΗΦΗΘΩΟ∴ >3-7≅ ΩΚ∆Ω ςΞΦΚ ςΩΥ∆ΛΘ ∆ΦΦΞΠΞΟ∆ΩΛΡΘ ∆ΦΦΡΠΣ∆ΘΛΗΓ ΖΛΩΚ Ψ∆ΥΛΡΞς ςΩΥ∆ΛΘ Σ∆ΩΚς Λς ΨΗΥ∴ ΛΠΣΡΥΩ∆ΘΩ ΙΡΥ ΓΗΨΗΟΡΣΠΗΘΩ ΡΙ ΗΤΞΛ∆[Λ∆Ο ΙΛΘΗ θΥ∆ΛΘς, i.e. θΥ∆ΛΘ ΥΗΙΛΘΗΠΗΘΩ. ∃Ω ΩΚΗ ς∆ΠΗ ΩΛΠΗ, θΥ∆ΛΘ ΥΗΙΛΘΗΠΗΘΩ ΓΞΥΛΘθ 0∋) Φ∆Θ ΕΗ ΦΡΘΩΥΡΟΟΗΓ ΘΡΩ ΡΘΟ∴ Ε∴ ΩΡΩ∆Ο ςΩΥ∆ΛΘ ∆ΦΦΞΠΞΟ∆ΩΗΓ ∆ΘΓ ςΩΥ∆ΛΘ ΣΗΥ Η∆ΦΚ Σ∆ςς, ΕΞΩ ∆ΟςΡ ςΩΥ∆ΛΘ Υ∆ΩΗ ∆ΘΓ ΩΗΠΣΗΥ∆ΩΞΥΗ. 7ΚΗΥΗ ∆ΥΗ, ΚΡΖΗΨΗΥ, ∆ ΙΗΖ Η[ΣΗΥΛΠΗΘΩ∆Ο Γ∆Ω∆ ΡΘ ΩΚΗ Ο∆ΩΩΗΥ∂ς ΗΙΙΗΦΩ ΞΘΓΗΥ 0∋) ΦΡΘΓΛΩΛΡΘς. 7ΚΗ Π∆ΛΘ ∆ΛΠ ΡΙ ΩΚΗ ΣΥΗςΗΘΩ ΖΡΥΝ Ζ∆ς ΩΡ ςΩΞΓ∴ ΗΙΙΗΦΩ ΡΙ ∆ΣΣΟΛΗΓ ςΩΥ∆ΛΘ Υ∆ΩΗ ΡΘ ΙΛΘΗ-θΥ∆ΛΘΗΓ ςΩΥΞΦΩΞΥΗ ΙΡΥΠ∆ΩΛΡΘ ΛΘ ∆ ΦΡ∆ΥςΗ-θΥ∆ΛΘΗΓ 7475 ∃Ο ∆ΟΟΡ∴ ΓΞΥΛΘθ ΚΡΩ 0∋). 7ΚΗ ΠΗΦΚ∆ΘΛςΠς ΡΙ ΚΡΩ ΓΗΙΡΥΠ∆ΩΛΡΘ, ΠΛΦΥΡςΩΥΞΦΩΞΥ∆Ο ΓΗΨΗΟΡΣΠΗΘΩ ΓΞΥΛΘθ 0∋) ∆ΘΓ ΩΚΗΛΥ ΛΘΩΗΥΥΗΟ∆ΩΛΡΘςΚΛΣ ∆ΥΗ ΓΛςΦΞςςΗΓ. Materials Science Forum Online: 2006-01-15 ISSN: 1662-9752, Vols. 503-504, pp 505-510 doi:10.4028/www.scientific.net/MSF.503-504.505

Microstructural Changes in As-Cast 7475 Al Alloy during Warm Sever Forging

Microstructural changes taking place in an as-cast coarse-grained 7475 Al alloy was studied by using multidirectional forging (MDF) at a temperature of 250oC and at a strain rate of 3 × 10-4 s-1. The samples were deformed by MDF with a strain of 0.7 per pass up to cumulative strain (Σε) of 8.4. In the earlier stages of deformation, microstructural changes are mainly characterized by development of dislocation subboundaries with low-to-moderate misorientation angles. The misorientation angle initially increases with straining and reaches a plateau of around 3.7o in the strain range from 0.7 to 2.1, where new grain formation scarcely takes place in the original grain interiors. With further straining, grain fragmentation starts to occur accompanying with deformation bands developed at various directions, followed by rapid evolution of a new fine grain structure at large strain. The average grain size is around 1 μm at large strains and the average misorientation angle approaches a value of about 25o at Σε = 8.4.

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

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.