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Twin roll casting and melt conditioned twin-roll casting of magnesium alloys
Recently, BCAST at Brunel University has developed a MCAST (melt conditioning by advanced shear technology) process for conditioning liquid metal at temperature either above or bellow the alloy liquidus using a high shear twin-screw mechanism. The MCAST process has now been combined with the twin roll casting (TRC) process to form an innovative technology, namely, the melt conditioned twin roll casting (MC-TRC) process for casting Al-alloy and Mg-alloy strips. During the MC-TRC process, liquid alloy with a specified temperature is continuously fed into the MCAST machine. By intensive shearing under the high shear rate and high intensity of turbulence, the liquid is transformed into conditioned melt with uniform temperature and composition throughout the whole volume. The conditioned melt is then fed continuously into the twin-roll caster for strip production. The experimental results show that the AZ91D MC-TRC strips with different thicknesses have fine and uniform microstructure. The strip consists of equiaxed grains with a mean size of 60-70Ī¼m. The strip displays extremely uniform grain size and composition throughout the whole cross-section. Investigation also shows that both TRC and MC-TRC processes with reduced deformation are effective to reduce the formation of defects, particularly the formation of the central line segregations
Neutrino emission from a GRB afterglow shock during an inner supernova shock breakout
The observations of a nearby low-luminosity gamma-ray burst (GRB) 060218
associated with supernova SN 2006aj may imply an interesting astronomical
picture where a supernova shock breakout locates behind a relativistic GRB jet.
Based on this picture, we study neutrino emission for early afterglows of GRB
060218-like GRBs, where neutrinos are expected to be produced from photopion
interactions in a GRB blast wave that propagates into a dense wind.
Relativistic protons for the interactions are accelerated by an external shock,
while target photons are basically provided by the incoming thermal emission
from the shock breakout and its inverse-Compton scattered component. Because of
a high estimated event rate of low-luminosity GRBs, we would have more
opportunities to detect afterglow neutrinos from a single nearby GRB event of
this type by IceCube. Such a possible detection could provide evidence for the
picture described above.Comment: 6 pages, 2 figures, accepted for publication in MNRA
Effect of iron on the microstructure and mechanical property of Al-Mg-Si-Mn and Al-Mg-Si diecast alloys
This article is made available through the Brunel Open Access Publishing Fund. Copyright @ 2012 Elsevier B.V.This article has been made available through the Brunel Open Access Publishing Fund.AlāMgāSi based alloys can provide super ductility to satisfy the demands of thin wall castings in the application of automotive structure. In this work, the effect of iron on the microstructure and mechanical properties of the AlāMgāSi diecast alloys with different Mn concentrations is investigated. The CALPHAD (acronym of Calculation of Phase Diagrams) modelling with the thermodynamic properties of the multi-component AlāMgāSiāMnāFe and AlāMgāSiāFe systems is carried out to understand the role of alloying on the formation of different primary Fe-rich intermetallic compounds. The results showed that the Fe-rich intermetallic phases precipitate in two solidification stages in the high pressure die casting process: one is in the shot sleeve and the other is in the die cavity, resulting in the different morphologies and sizes. In the AlāMgāSiāMn alloys, the Fe-rich intermetallic phase formed in the shot sleeve exhibited coarse compact morphology and those formed in the die cavity were fine compact particles. Although with different morphologies, the compact intermetallics were identified as the same Ī±-AlFeMnSi phase with typical composition of Al24(Fe,Mn)6Si2. With increased Fe content, Ī²-AlFe was found in the microstructure with a long needle-shaped morphology, which was identified as Al13(Fe,Mn)4Si0.25. In the AlāMgāSi alloy, the identified Fe-rich intermetallics included the compact Ī±-AlFeSi phase with typical composition of Al8Fe2Si and the needle-shaped Ī²-AlFe phase with typical composition of Al13Fe4. Generally, the existence of iron in the alloy slightly increases the yield strength, but significantly reduces the elongation. The ultimate tensile strength maintains at similar levels when Fe contents is less than 0.5 wt%, but decreases significantly with the further increased Fe concentration in the alloys. CALPHAD modelling shows that the addition of Mn enlarges the Fe tolerance for the formation of Ī±-AlFeMnSi intermetallics and suppresses the formation of Ī²-AlFe phase in the AlāMgāSi alloys, and thus improves their mechanical properties.EPSRC and JL
Effect of iron on the microstructure and mechanical property of Al-Mg-Si-Mn and Al-Mg-Si diecast alloys
This article is made available through the Brunel Open Access Publishing Fund. Copyright @ 2012 Elsevier B.V.This article has been made available through the Brunel Open Access Publishing Fund.AlāMgāSi based alloys can provide super ductility to satisfy the demands of thin wall castings in the application of automotive structure. In this work, the effect of iron on the microstructure and mechanical properties of the AlāMgāSi diecast alloys with different Mn concentrations is investigated. The CALPHAD (acronym of Calculation of Phase Diagrams) modelling with the thermodynamic properties of the multi-component AlāMgāSiāMnāFe and AlāMgāSiāFe systems is carried out to understand the role of alloying on the formation of different primary Fe-rich intermetallic compounds. The results showed that the Fe-rich intermetallic phases precipitate in two solidification stages in the high pressure die casting process: one is in the shot sleeve and the other is in the die cavity, resulting in the different morphologies and sizes. In the AlāMgāSiāMn alloys, the Fe-rich intermetallic phase formed in the shot sleeve exhibited coarse compact morphology and those formed in the die cavity were fine compact particles. Although with different morphologies, the compact intermetallics were identified as the same Ī±-AlFeMnSi phase with typical composition of Al24(Fe,Mn)6Si2. With increased Fe content, Ī²-AlFe was found in the microstructure with a long needle-shaped morphology, which was identified as Al13(Fe,Mn)4Si0.25. In the AlāMgāSi alloy, the identified Fe-rich intermetallics included the compact Ī±-AlFeSi phase with typical composition of Al8Fe2Si and the needle-shaped Ī²-AlFe phase with typical composition of Al13Fe4. Generally, the existence of iron in the alloy slightly increases the yield strength, but significantly reduces the elongation. The ultimate tensile strength maintains at similar levels when Fe contents is less than 0.5 wt%, but decreases significantly with the further increased Fe concentration in the alloys. CALPHAD modelling shows that the addition of Mn enlarges the Fe tolerance for the formation of Ī±-AlFeMnSi intermetallics and suppresses the formation of Ī²-AlFe phase in the AlāMgāSi alloys, and thus improves their mechanical properties.EPSRC and JL
High energy neutrino early afterglows from gamma-ray bursts revisited
The high energy neutrino emission from gamma-ray bursts (GRBs) has been
expected in various scenarios. In this paper, we study the neutrino emission
from early afterglows of GRBs, especially under the reverse-forward shock model
and late prompt emission model. In the former model, the early afterglow
emission occurs due to dissipation made by an external shock with the
circumburst medium (CBM). In the latter model, internal dissipation such as
internal shocks produces the shallow decay emission in early afterglows. We
also discuss implications of recent Swift observations for neutrino signals in
detail. Future neutrino detectors such as IceCube may detect neutrino signals
from early afterglows, especially under the late prompt emission model, while
the detection would be difficult under the reverse-forward shock model.
Contribution to the neutrino background from the early afterglow emission may
be at most comparable to that from the prompt emission unless the outflow
making the early afterglow emission loads more nonthermal protons, and it may
be important in the very high energies. Neutrino-detections are inviting
because they could provide us with not only information on baryon acceleration
but also one of the clues to the model of early afterglows. Finally, we compare
various predictions for the neutrino background from GRBs, which are testable
by future neutrino-observations.Comment: 18 pages, 12 figures, accepted for publication in PR
Effects of lattice mismatch on interfacial structures of liquid and solidified Al in contact with hetero-phase substrates: MD simulations
Published under licence in IOP Conference Series: Material Science and Engineering by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.In this study, the effects of the misfit on in-plane structures of liquid Al and interfacial structure of solidified Al in contact with the heterophase substrates have been investigated, using molecular dynamics (MD) simulations. The MD simulations were conducted for Al/fcc (111) substrates with varied misfits. The order parameter and atomic arrangement indicated that the in-plane ordering of the liquid at the interface decreases significantly with an increase of the misfit, i.e., solid-like for small misfit and liquid-like for large misfit. Further, our MD simulation results revealed that a perfect orientation relationship forms at the interface between the substrate and the solidified Al for a misfit of less than -3% and the boundary is coherent. With an increase in the misfit, Shockley partial and extended dislocations form at the interface, and the boundary becomes a semi-coherent or low-angle twist boundary.EPSR
Influence of intensive melt shearing on the microstructure and mechanical properties of an Al-Mg alloy with high added impurity content
The official published version can be accessed from the link below - Copyright @ The Minerals, Metals & Materials Society and ASM International 2011We have investigated the influence of melt conditioning by intensive shearing on the mechanical behavior and microstructure of Al-Mg-Mn-Fe-Cu-Si alloy sheet produced from a small book mold ingot with high added impurity content. The melt conditioned ingot has fine grains throughout its cross section, whereas a conventionally cast ingot, without melt shearing, has coarser grains and shows a wider variation of grain size. Both needle-shaped and coarse Chinese script iron bearing intermetallic particles are found in the microstructure at the center of the conventionally processed ingot, but for the melt conditioned ingot, only fine Chinese script intermetallic particles are observed. In addition to the iron bearing intermetallics, Mg2Si particles are also observed. The ingots were rolled to thin sheet and solution heat treated (SHT). During rolling, the iron-based intermetallics and Mg2Si particles are broken and aligned along the rolling direction. Yield strength (YS), ultimate tensile strength (UTS), and elongation of the intensively melt sheared and processed sheet are all improved compared to the conventionally cast and processed sheet. Fractographic analysis of the tensile fracture surfaces shows that the clustered and coarse iron bearing intermetallic particles are responsible for the observed reduction in mechanical properties of the conventionally cast sheet. We have shown that by refining the initial microstructure of the ingot by intensive shear melt conditioning, it is possible to achieve improved mechanical properties at the final sheet gage of an AlMgMn alloy with a high content of impurities.This study is under the Technology
Strategy Board funded REALCAR projec
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