scholarly journals A study of hot tearing during solidification of B206 aluminum alloy.

2021 ◽  
Author(s):  
Francesco D’Elia
Keyword(s):  
Grain Refinement ◽  
Solid Fraction ◽  
Grain Morphology ◽  
Hot Tearing ◽  
Interactive Effects ◽  
Ex Situ ◽  
Bulk Liquid ◽  
Al Alloy ◽  
Automotive Suspension

Aluminum-copper (Al-Cu) alloy B206 is a high strength and ductile alloy showing promise for use in automotive suspension components. Incorporation of lightweight B206 alloy in automotive suspension components may significantly reduce overall vehicle weight and increase the vehicle’s fuel efficiency. However, one of the major factors inhibiting the use of B206 is its high susceptibility to hot tearing during casting. Hot tearing is a complex phenomenon attributed to alloy solidification, microstructure and stress/strain development within a casting. Numerous methods (e.g. preheating of mold, grain refinement, elimination of sharp corners in a component) help to reduce the occurrence of hot tears in castings, but the underlying mechanisms responsible for hot tearing remain ambiguous. This research aims to advance the understanding of the mechanisms responsible for hot tearing in B206 Al alloy. In this research, the conditions associated with the formation of hot tears in B206 were investigated via ex situ and in situ methods. Titanium was added in three levels (i.e. unrefined, 0.02 and 0.05 wt%) to investigate the effect of grain refinement on hot tearing. Ex situ neutron diffraction strain mapping was carried out on the three B206 castings to determine casting strain and stress. Further, in situ techniques were used to establish the onset temperature and solid fraction of hot tearing in B206 and to improve the understanding of microstructure development in B206. The results indicate that titanium additions had a significant impact on the hot tearing susceptibility of B206, by effectively reducing grain size and transforming grain morphology from coarse dendrites to fine globular grains. Further, thermal analysis suggested that grain refinement delayed the onset of dendrite coherency in B206 and therefore enhanced the duration of bulk liquid metal feeding for the refined casting conditions. As a result, the interactive effects of such factors resulted in a more uniform distribution of strain, and subsequent higher resistance to hot tearing for the grain refined castings. Finally, in situ analysis determined the onset solid fraction of hot tearing in B206 and provided an understanding of the role of microstructure on hot tearing in B206.

scholarly journals A study of hot tearing during solidification of B206 aluminum alloy.

2021 ◽  
Author(s):  
Francesco D’Elia
Keyword(s):  
Grain Refinement ◽  
Solid Fraction ◽  
Grain Morphology ◽  
Hot Tearing ◽  
Interactive Effects ◽  
Ex Situ ◽  
Bulk Liquid ◽  
Al Alloy ◽  
Automotive Suspension

Aluminum-copper (Al-Cu) alloy B206 is a high strength and ductile alloy showing promise for use in automotive suspension components. Incorporation of lightweight B206 alloy in automotive suspension components may significantly reduce overall vehicle weight and increase the vehicle’s fuel efficiency. However, one of the major factors inhibiting the use of B206 is its high susceptibility to hot tearing during casting. Hot tearing is a complex phenomenon attributed to alloy solidification, microstructure and stress/strain development within a casting. Numerous methods (e.g. preheating of mold, grain refinement, elimination of sharp corners in a component) help to reduce the occurrence of hot tears in castings, but the underlying mechanisms responsible for hot tearing remain ambiguous. This research aims to advance the understanding of the mechanisms responsible for hot tearing in B206 Al alloy. In this research, the conditions associated with the formation of hot tears in B206 were investigated via ex situ and in situ methods. Titanium was added in three levels (i.e. unrefined, 0.02 and 0.05 wt%) to investigate the effect of grain refinement on hot tearing. Ex situ neutron diffraction strain mapping was carried out on the three B206 castings to determine casting strain and stress. Further, in situ techniques were used to establish the onset temperature and solid fraction of hot tearing in B206 and to improve the understanding of microstructure development in B206. The results indicate that titanium additions had a significant impact on the hot tearing susceptibility of B206, by effectively reducing grain size and transforming grain morphology from coarse dendrites to fine globular grains. Further, thermal analysis suggested that grain refinement delayed the onset of dendrite coherency in B206 and therefore enhanced the duration of bulk liquid metal feeding for the refined casting conditions. As a result, the interactive effects of such factors resulted in a more uniform distribution of strain, and subsequent higher resistance to hot tearing for the grain refined castings. Finally, in situ analysis determined the onset solid fraction of hot tearing in B206 and provided an understanding of the role of microstructure on hot tearing in B206.

Heterogeneous Nucleation for AZ91 with In Situ Synthesis Al4C3

2010 ◽  
Vol 97-101 ◽  
pp. 1069-1072
Author(s):  
Xue Quan Luo ◽  
Hong Min Guo ◽  
Xiang Jie Yang
Keyword(s):  
Grain Refinement ◽  
Magnesium Alloys ◽  
Master Alloy ◽  
Heterogeneous Nucleation ◽  
Critical Factor ◽  
In Situ Synthesis ◽  
Experimental Results ◽  
Al Alloy

Heterogeneous nucleation is a critical factor for grain refinement magnesium alloys. The paper reports the Al-9wt.%Mg-10wt.%SiCp master alloy were prepared by adding SiCp into the Al-Mg molten with stirring in 610-595°C, which were introduced into AZ91. Experimental results indicated Al4C3 were in situ synthesis on the surface of SiCp by the reaction between SiCp and Al in 850°C, which could be as nucleant substrate for primary Mg during the solildification of magnesium alloys. This investigation provided a novel idea for grain refinement Mg-Al alloy.

scholarly journals Inclusion removal and grain refinement of magnesium alloy castings

2021 ◽  
Author(s):  
Abdallah Elsayed
Keyword(s):  
Magnesium Alloy ◽  
Neutron Diffraction ◽  
Grain Refinement ◽  
Magnesium Alloys ◽  
Ex Situ ◽  
Inclusion Removal ◽  
Carbon Inoculation ◽  
Aluminum Silicon Carbide ◽  
In Situ Neutron Diffraction

Magnesium alloys show promise to be materials for lightweighting of automotive and aerospace vehicles improving fuel efficiencies and vehicle performance. A majority of magnesium alloy components are produced using casting where susceptibility to forming inclusions and coarse grain sizes could result. Development of effective inclusion removal techniques and better understanding of grain refinement of magnesium alloys could help in improving their mechanical properties to advance them to more structurally demanding applications. This research aimed to develop an environmentally friendly alternative to the grain refinement and inclusion removal capabilities of carbon based hexachloroethane as it releases dioxins, chlorine gas and corrodes foundry equipment. A secondary aim was to pioneer in-situ neutron diffraction to examine the solidification of magnesium alloys. The research involved preparing tensile samples of AZ91E magnesium alloy using permanent mould casting. Inclusion removal was conducted by using filtration and argon gas bubbling. Castings grain refined using hexachloroethane (0.25, 0.50 and 0.75 wt.%) were compared against ex-situ aluminum-silicon carbide and in-situ aluminum-carbon based grain refiners combined with filtration and argon gas bubbling. Further, in-situ neutron diffraction was utilized for phase analysis and fraction solid determination of magnesium-zinc and magnesium-aluminum alloys. There was a significant improvement in yield strength, ultimate tensile strength and elongation with filtration plus argon bubbling, carbon inoculation or both filtration plus argon bubbling and carbon inoculation. The results indicated that the mechanism of the observed ~20% reduction in grain sizes with carbon inoculation (hexachloroethane, ex-situ aluminum-silicon carbide and in-situ aluminum-carbon) was explained through duplex nucleation of Mn-Al and Al-Mg-C-O (likely Al2MgC2) phases. Finally, in-situ neutron diffraction was used to follow the formation of Mg17Al12 eutectic phase in a magnesium-9 wt.% aluminum alloy. For the magnesium-zinc alloys, in-situ neutron diffraction enabled characterization of the effects of zirconium to the fraction solid growth of (1010), (0002) and (1011) α-Mg planes. The societal and environmental impact of this research is significant. There is a clear demonstration of alternatives to the universally used hexachloroethane grain refiner promoting harmful emissions. Improved mechanical properties resulting from new grain refinement and iv inclusion filtration are a major advancement in promoting weight reduction, improved castability and decreased environmental impact for automotive and aerospace industries.

Study of Recovery and Recrystallisation in a Folded Al Alloy

2013 ◽  
Vol 753 ◽  
pp. 7-10 ◽  
Author(s):  
Harvinder Singh Ubhi ◽  
Ian Brough ◽  
Kim Larsen
Keyword(s):  
Grain Growth ◽  
Ferritic Steel ◽  
Sheet Thickness ◽  
Nucleation And Growth ◽  
Ex Situ ◽  
Al Alloy ◽  
In Situ Heating ◽  
Nickel 200 ◽  
Crystallographic Orientations

Changes in the microstructure and crystallographic orientations during in-situ heating of folded Al 0.1%Mg have been followed by SEM and EBSD. The folding process results in both strain and texture gradients across the folded region which in turn can influence the recovery and recrystallisation processes as well as crystallographic texture. This work is an extension of ex-situ heating experiments on folded nickel 200, titanium and ferritic steel [1,2]. The present findings illustrates that during isothermal in-situ heating at 295oC nucleation and growth starts close to the surface where the deformation is highest, new grains form and grow in a region about quarter depth of the sheet thickness. After this grain growth occurs resulting in large grains that meet up at the centre line. These results are consistent with those found in ex-situ heated Ni200 alloy [2], where fine grains were found in the compressed and tensile regions with large grains in the middle of the sheet.

scholarly journals Inclusion removal and grain refinement of magnesium alloy castings

2021 ◽  
Author(s):  
Abdallah Elsayed
Keyword(s):  
Magnesium Alloy ◽  
Neutron Diffraction ◽  
Grain Refinement ◽  
Magnesium Alloys ◽  
Ex Situ ◽  
Inclusion Removal ◽  
Carbon Inoculation ◽  
Aluminum Silicon Carbide ◽  
In Situ Neutron Diffraction

Magnesium alloys show promise to be materials for lightweighting of automotive and aerospace vehicles improving fuel efficiencies and vehicle performance. A majority of magnesium alloy components are produced using casting where susceptibility to forming inclusions and coarse grain sizes could result. Development of effective inclusion removal techniques and better understanding of grain refinement of magnesium alloys could help in improving their mechanical properties to advance them to more structurally demanding applications. This research aimed to develop an environmentally friendly alternative to the grain refinement and inclusion removal capabilities of carbon based hexachloroethane as it releases dioxins, chlorine gas and corrodes foundry equipment. A secondary aim was to pioneer in-situ neutron diffraction to examine the solidification of magnesium alloys. The research involved preparing tensile samples of AZ91E magnesium alloy using permanent mould casting. Inclusion removal was conducted by using filtration and argon gas bubbling. Castings grain refined using hexachloroethane (0.25, 0.50 and 0.75 wt.%) were compared against ex-situ aluminum-silicon carbide and in-situ aluminum-carbon based grain refiners combined with filtration and argon gas bubbling. Further, in-situ neutron diffraction was utilized for phase analysis and fraction solid determination of magnesium-zinc and magnesium-aluminum alloys. There was a significant improvement in yield strength, ultimate tensile strength and elongation with filtration plus argon bubbling, carbon inoculation or both filtration plus argon bubbling and carbon inoculation. The results indicated that the mechanism of the observed ~20% reduction in grain sizes with carbon inoculation (hexachloroethane, ex-situ aluminum-silicon carbide and in-situ aluminum-carbon) was explained through duplex nucleation of Mn-Al and Al-Mg-C-O (likely Al2MgC2) phases. Finally, in-situ neutron diffraction was used to follow the formation of Mg17Al12 eutectic phase in a magnesium-9 wt.% aluminum alloy. For the magnesium-zinc alloys, in-situ neutron diffraction enabled characterization of the effects of zirconium to the fraction solid growth of (1010), (0002) and (1011) α-Mg planes. The societal and environmental impact of this research is significant. There is a clear demonstration of alternatives to the universally used hexachloroethane grain refiner promoting harmful emissions. Improved mechanical properties resulting from new grain refinement and iv inclusion filtration are a major advancement in promoting weight reduction, improved castability and decreased environmental impact for automotive and aerospace industries.

A Study of Cube Grain Nucleation in a Commercial Al Alloy during In Situ and Discontinuous (Ex Situ) Annealing Experiments

2014 ◽  
Vol 794-796 ◽  
pp. 1245-1250 ◽  
Author(s):  
Olga Sukhopar ◽  
Günter Gottstein
Keyword(s):  
Growth Rate ◽  
Incubation Time ◽  
Annealing Temperature ◽  
Ex Situ ◽  
Al Alloy ◽  
Growth Environment ◽  
Transition Zones ◽  
Different Temperatures ◽  
Annealing Experiments

In the current study the nucleation of Cube grains during recrystallization in a commercial Al-Fe-Si alloy was investigated by in-situ and ex-situ annealing experiments at different temperatures. Both methods confirm that the Cube grains can be nucleated during RX both at large deformed Cube bands and other locations. During annealing only about one third of the Cube nuclei from these other locations developed into Cube oriented recrystallized grains owing to an unfavorable growth environment. Such nuclei needed also a longer incubation time due to their small size compared to nuclei formed at large Cube bands which can form nuclei very fast owing to the well-developed substructure and transition zones promoting nucleation. The growth rate of all Cube nuclei was found to be strongly influenced by their environment. This effect became more pronounced with decreasing annealing temperature due to an increasing amount of recovery.

The Effect of Grain Refinement and Cooling Rate on the Hot Tearing of Wrought Aluminium Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 1675-1680 ◽  
Author(s):  
Mark Easton ◽  
John F. Grandfield ◽  
David H. StJohn ◽  
Barbara Rinderer
Keyword(s):  
Grain Size ◽  
Cooling Rate ◽  
Grain Refinement ◽  
Aluminium Alloys ◽  
Grain Morphology ◽  
Hot Tearing ◽  
Grain Refiner ◽  
Cooling Rates ◽  
High Cooling Rates ◽  
Hot Tearing Susceptibility

Using modifications to the Rappaz-Drezet-Gremaud hot tearing model, and using empirical equations developed for grain size and dendrite arm spacing (DAS) on the addition of grain refiner for a range of cooling rates, the effect of grain refinement and cooling rate on hot tearing susceptibility has been analysed. It was found that grain refinement decreased the grain size and made the grain morphology more globular. Therefore refining the grain size of an equiaxed dendritic grain decreased the hot tearing susceptibility. However, when the alloy was grain refined such that globular grain morphologies where obtained, further grain refinement increased the hot tearing susceptibility. Increasing the cooling decreased the grain size and made the grain morphology more dendritic and therefore increased the likelihood of hot tearing. The effect was particularly strong for equiaxed dendritic grain morphologies; hence grain refinement is increasingly important at high cooling rates to obtain more globular grain morphologies to reduce the hot tearing susceptibility.

Effets of surfaces on precipitate morphology in irradiated thin foils

1978 ◽  
Vol 36 (1) ◽  
pp. 654-655
Author(s):  
D.I. Potter ◽  
A. Taylor
Keyword(s):  
Ion Irradiation ◽  
Dark Field Image ◽  
Thin Foil ◽  
Dark Field ◽  
Al Alloy ◽  
Bright Field Image ◽  
Dislocation Loops ◽  
Precipitate Morphology ◽  
Thin Foils

Thermal aging of Ni-12.8 at. % A1 and Ni-12.7 at. % Si produces spatially homogeneous dispersions of cuboidal γ'-Ni3Al or Ni3Si precipitate particles arrayed in the Ni solid solution. We have used 3.5-MeV 58Ni+ ion irradiation to examine the effect of irradiation during precipitation on precipitate morphology and distribution. The nearness of free surfaces produced unusual morphologies in foils thinned prior to irradiation. These thin-foil effects will be important during in-situ investigations of precipitation in the HVEM. The thin foil results can be interpreted in terms of observations from bulk irradiations which are described first.Figure 1a is a dark field image of the γ' precipitate 5000 Å beneath the surface(∿1200 Å short of peak damage) of the Ni-Al alloy irradiated in bulk form. The inhomogeneous spatial distribution of γ' results from the presence of voids and dislocation loops which can be seen in the bright field image of the same area, Fig. 1b.

An in situ and ex situ TEM study of the formation of thin cobalt silicide films by molecular beam epitaxy on the silicon (100) surface

1988 ◽  
Vol 46 ◽  
pp. 884-885
Author(s):  
D. Loretto ◽  
J. M. Gibson ◽  
S. M. Yalisove ◽  
R. T. Tung
Keyword(s):  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
Defect Density ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Ex Situ ◽  
Metal Base ◽  
In Situ Experiments ◽  
Potential Applications

The cobalt disilicide/silicon system has potential applications as a metal-base and as a permeable-base transistor. Although thin, low defect density, films of CoSi2 on Si(111) have been successfully grown, there are reasons to believe that Si(100)/CoSi2 may be better suited to the transmission of electrons at the silicon/silicide interface than Si(111)/CoSi2. A TEM study of the formation of CoSi2 on Si(100) is therefore being conducted. We have previously reported TEM observations on Si(111)/CoSi2 grown both in situ, in an ultra high vacuum (UHV) TEM and ex situ, in a conventional Molecular Beam Epitaxy system.The procedures used for the MBE growth have been described elsewhere. In situ experiments were performed in a JEOL 200CX electron microscope, extensively modified to give a vacuum of better than 10-9 T in the specimen region and the capacity to do in situ sample heating and deposition. Cobalt was deposited onto clean Si(100) samples by thermal evaporation from cobalt-coated Ta filaments.

The use of transmission and analytical electron microscopy in studying reactions and phase transformations in thin film

1993 ◽  
Vol 51 ◽  
pp. 842-843
Author(s):  
K. Barmak
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Phase Transformations ◽  
Analytical Electron Microscopy ◽  
Ex Situ ◽  
Multilayer Thin Films ◽  
Absolute Concentration ◽  
Analytical Electron ◽  
Deposition Step

Generally, processing of thin films involves several annealing steps in addition to the deposition step. During the annealing steps, diffusion, transformations and reactions take place. In this paper, examples of the use of TEM and AEM for ex situ and in situ studies of reactions and phase transformations in thin films will be presented.The ex situ studies were carried out on Nb/Al multilayer thin films annealed to different stages of reaction. Figure 1 shows a multilayer with dNb = 383 and dAl = 117 nm annealed at 750°C for 4 hours. As can be seen in the micrograph, there are four phases, Nb/Nb3-xAl/Nb2-xAl/NbAl3, present in the film at this stage of the reaction. The composition of each of the four regions marked 1-4 was obtained by EDX analysis. The absolute concentration in each region could not be determined due to the lack of thickness and geometry parameters that were required to make the necessary absorption and fluorescence corrections.

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