Solidification behaviour of AZ91D alloy under intensive forced convection in the RDC process

Fan, Z.; Liu, G.

doi:10.1016/j.actamat.2005.05.033

Cited by 122 publications

(76 citation statements)

References 18 publications

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“…One can found that f s(T) increases rapidly from about 0.2 at T ¼ 590 C (863 K) to about 0.5 to 0.6 when vibration starts at lower temperatures of T ¼ 570 C (843 K) and T ¼ 560 C (833 K). The calculated fraction solids are consistent with delicate measurements conducted in a differential scanning calorimeter with a mathematical heattransfer model 23) and thermodynamic prediction by the CALPHAD approach 24) for the AZ91D alloy. Moreover, good agreement can be found between this theoretical calculation and semisolid casting experiment, in which coarsening is assumed to be negligible from the semisolid state to the compete crystallization.…”

Section: Discussionsupporting

confidence: 59%

Effect of Vibration Timing on the Microstructure and Microtexture Formation of AZ91D Magnesium Alloys during Electromagnetic Vibration

Tamura

Omura

et al. 2009

Mater. Trans.

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For an electric conductor in a static magnet, electromagnetic vibration (EMV) is activated to take place when an alternating current flows through the conductor in the direction perpendicular to that of the magnetic field. Following the principle, in the present study we solidified the AZ91D magnesium alloys at various vibration timing moments and then examined the microtexture and microtexture. It is revealed that the decrease of the starting vibration temperature in the mushy zone results in coarse microstructures with large dendritic fragments and eventually with fully developed dendrites that are well oriented with their basal planes being perpendicular to the direction of magnetic field. It has been demonstrated that melt flow is responsible for structural refinement during EMV processing due to the electrical resistivity difference of the solid and liquid. In mushy zone, when vibration is imposed at a low temperature, the fraction solid of the primary phase prior to vibration has been large, which makes the semisolid slurry rather viscous. The intensity and scale of the melt flow is weakened and thus yielding coarse structures. Meanwhile, as the magnetic field is imposed throughout the entire experimental operation, the magnetization torque takes into effect to orient dendrites. The bridging of dendrites may have been accomplished at low vibration temperature before EMV is activated. In this case, the magnetization torque becomes predominant to align crystals along their preferential crystallographic orientation and thus resulting in highly oriented textures.

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Section: Discussionsupporting

confidence: 59%

Effect of Vibration Timing on the Microstructure and Microtexture Formation of AZ91D Magnesium Alloys during Electromagnetic Vibration

Tamura

Omura

et al. 2009

Mater. Trans.

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“…After the alloys were completely melted, the temperature of the melting furnace was changed to 700 o C for the use of isothermal holding. The pouring temperature for either the TP-1 mould or the MCAST unit [23,24] was always at 700 o C. For the sheared samples, the alloy melts were sheared in the MCAST unit for 60 s, which was set at 700 o C and the screw rotation speed at 500rpm. In view of the fact that magnesium has high affinity with oxygen and the low value of PBR for MgO with a value of 0.73, there should be less protective oxide scale formed on the surface of liquid Al-Mg melts.…”

Section: Methodsmentioning

confidence: 99%

Mechanisms of enhanced heterogeneous nucleation during solidification in binary Al–Mg alloys

Li¹,

Wang²,

Fan³

2012

Acta Materialia

183

120

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This paper investigates the mechanisms involved in the grain refinement of Al-Mg alloys through varying the Mg content and applying intensive melt shearing. It was found that the oxide formed in Al-Mg alloys under normal melting conditions is MgAl 2 O 4 , which displays an equiaxed and faceted morphology with {111} planes exposed as its natural surfaces. Depending on the Mg content, MgAl 2 O 4 particles exist either as oxide films in dilute Al-Mg alloys (Mg<1wt.%) or naturally dispersed discrete particles in more concentrated Al-Mg alloys (Mg>1wt.%). Such MgAl 2 O 4 particles can act as potent sites for nucleation of α-Al grains, which is evidenced by the well-defined cube-on-cube orientation relationship between MgAl 2 O 4 and α-Al. Enhanced heterogeneous nucleation in Al-Mg alloys can be attributed to the high potency of MgAl 2 O 4 particles with a lattice misfit of 1.4% and the increased number density of MgAl 2 O 4 particles due to either natural dispersion by the increased Mg content or forced dispersion through intensive melt shearing. It was also found that intensive melt shearing leads to significant grain refinement of dilute Al-Mg alloys by effective dispersion of the MgAl 2 O 4 particles entrapped in oxide films, but it has marginal effect on the grain refinement of concentrated Al-Mg alloys, where MgAl 2 O 4 particles have been naturally dispersed into individual particles by the increased Mg content.

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“…[28] Physical melt treatment is an alternative option and melt conditioning by intensive shear prior to solidification has been developed for this purpose. [24,29,30] This technique has been applied successfully for both aluminum and magnesium alloys prior to casting by a range of casting methods, [31][32][33] and it has proved to be particularly effective for the solidification processing of magnesium alloys. [24,29,34] Magnesium alloy strip produced by conventional twin-roll casting requires additional processing including homogenization, rolling, and annealing.…”

Section: Introductionmentioning

confidence: 99%

“…[24,29,30] This technique has been applied successfully for both aluminum and magnesium alloys prior to casting by a range of casting methods, [31][32][33] and it has proved to be particularly effective for the solidification processing of magnesium alloys. [24,29,34] Magnesium alloy strip produced by conventional twin-roll casting requires additional processing including homogenization, rolling, and annealing. Because of the thickness of constraints associated with twin-roll casting, the possibility of modifying the as-cast microstructures and formability before final shape forming and application is limited somewhat.…”

Section: Introductionmentioning

confidence: 99%

The Impact of Melt-Conditioned Twin-Roll Casting on the Downstream Processing of an AZ31 Magnesium Alloy

Bayandorian

Huang

Fan

et al. 2011

Metall Mater Trans A

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Melt conditioning by intensive shear was used prior to twin-roll casting of AZ31 magnesium alloy strip to promote heterogeneous nucleation and to provide a refined and uniform microstructure without severe macrosegregation. The cast strip was then processed by homogenization, hot rolling, and annealing, and its downstream processing was compared with a similar cast strip produced without melt conditioning. Melt conditioning produced strip with accelerated kinetics of recrystallization during homogenization and improved performance in hot rolling and improved tensile properties. An average tensile elongation of~28 pct was achieved, which is substantially higher than the~9 pct obtained for the strip produced without melt conditioning which is consistent with reported values (~6 pct to 16 pct). The as-cast, homogenized, and hot-rolled microstructures of the strip were characterized. The kinetics of homogenization and hot-rolling process have been discussed in detail.

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Solidification behaviour of AZ91D alloy under intensive forced convection in the RDC process

Cited by 122 publications

References 18 publications

Effect of Vibration Timing on the Microstructure and Microtexture Formation of AZ91D Magnesium Alloys during Electromagnetic Vibration

Effect of Vibration Timing on the Microstructure and Microtexture Formation of AZ91D Magnesium Alloys during Electromagnetic Vibration

Mechanisms of enhanced heterogeneous nucleation during solidification in binary Al–Mg alloys

The Impact of Melt-Conditioned Twin-Roll Casting on the Downstream Processing of an AZ31 Magnesium Alloy

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