Abstract: In the present research the possibility of studying the solidification of aluminum alloys
by using the quenching technique is analyzed. Since the quenching technique does not provide
reliable information (i.e. due to an overestimation of solid fraction) when measuring the solid
fraction over 2D images from samples quenched at high temperature, the overestimation problem is
investigated by analyzing 3D reconstructed microstructures from quenched samples. The 3D
reconstructed microstructure may provide better understanding about the cause of overestimation of
solid fraction when quenching at high temperatures. Consequently, the reconstruction of the
microstructure that has existed before quenching may be possible after identifying and removing
the solid phase that develops during quenching. In the present research, binary aluminum alloys are
solidified and quenched at different temperatures, and then 3D reconstructed images are analyzed.
The possibility of reconstructing the microstructure that develops during solidification before
quenching is discussed.
Abstract: The influence of different cooling regimes on the surface microstructure of strip cast
AA1XXX alloys was investigated. The cooling rate was varied over a wide range using a bench
scale simulation apparatus. It was found that the type and morphology of the intermetallics varied
over a wide range both at the cast surface and in the near surface regions. These observations were
compared to the compounds formed in the bulk of the slab.
It was found that, a surface layer containing a high concentration of alloying elements, an inverse
segregation layer, forms under some conditions and can result in a high density of intermetallics.
By varying casting conditions, the mechanism of formation for these structures was studied. The
surface microstructure of the slabs was characterized as a function of the different local cooling
Abstract: Intermetallic phases formed during directional Bridgman solidification of a 6xxx series
Al alloy in the growth velocity range 5-120 mm/min have been characterised using conventional
and high-resolution transmission electron microscopy. Cubic αc-AlFeSi and β-AlFeSi were always
present in the alloy, but Al13Fe4 was only observed at 5mm/min and monoclinic αT-AlFeSi at 80
mm/min. Cubic αc-AlFeSi was observed to have a variety of morphologies resulting from flexibility
in its growth mechanisms. β-AlFeSi with twins and faults showed strongly anisotropic growth by
steps, resulting in its platelet morphology. Occasionally blocky β-AlFeSi particles were observed
particularly at 30-60 mm/min, suggesting that other mechanisms could influence their morphology.
Two types of composite particles, β-AlFeSi/Al13Fe4 and β-AlFeSi/cubic αc-AlFeSi, were observed
in this alloy, and likely formed by two quasi-peritectic reactions.
Abstract: The potential use of an Al-9Si-1Cu alloy (W328 alloy) as a replacement for W319
alloy in engine blocks was investigated.. The ambient mechanical properties (tensile,
hardness and fatigue) of sand and permanent mould cast test bars along with bars machined
from a sand cast automotive component were studied. The tensile properties were evaluated
in as-cast and T6 heat-treated conditions. The effects of Fe and Mn on properties were also
investigated. The castings in W328 alloy exhibit lower porosity than W319 alloy, which is
attributed to the smaller solidification range and feeding distance and larger volume fraction
of the eutectic phase. Higher iron levels increased the level of intermetallics and reduced
properties. The addition of Mn did not offset the effect of higher iron levels. The W328 alloy
offers some advantages over the 319 alloy and is a potential candidate for production of
automotive components such as engine blocks and cylinder heads.
Abstract: Cast plates of A356 aluminum alloy with different thickness were fabricated by
rheocasting and squeeze casting. Tear tests were performed on the as-cast and heat-treated products
(T5 and T6), and effects of solidified structure and heat treatment on unit crack propagation energy
(UEp) were examined. Increased cooling rate (corresponding to a decrease in plate thickness)
resulted in refined solidified structure and enlarged UEp values for as-cast samples. For both rheocast
and squeeze-cast samples, both spheroidized eutectic Si particles and age-hardened α-Al matrix by
T6 treatment were effective for increasing UEp. UEp of the squeeze-cast sample was higher than that
of the rheocast sample. Observation of crack growth path and fracture surface revealed that the tear
toughness of the present cast alloy was controlled by distribution of eutectic solidified region in the
cast structure, which provided a preferential crack growth path. The discontinuous distribution for the
squeeze-cast sample is considered to be beneficial for increasing crack growth resistance rather than
the continuous arrangement of the network-like eutectic region for the rheocast sample. Relatively
small UEp was obtained for the T6 treated rheocast sample collected from the 6 mm thickness plate.
This is attributable to the volume fraction of the eutectic solidified region in the sample being larger
than others under the present experimental conditions.
Abstract: The effect of size refinement of primary silicon and modification of eutectic silicon,
separately and simultaneously, on microstructure of hypereutectic Al-20wt%Si has been
investigated under different casting conditions. Results showed that number per unit volume of
primary silicon particles was doubled by inoculation with 0.02% phosphorus in the alloy with
0.0015% phosphorus already in it, whereas 70% of a small ingot (40×35 mm) became modified
eutectic, and the formation of primary silicon was suppressed, on adding 0.1% strontium.
Simultaneous addition of phosphorus and strontium still refined the primary silicon but did not
modify the eutectic. Addition of strontium alone caused roughening of the primary silicon,
exemplified by increased undercooling registered on the cooling curve. Also crystallographic
relationships between polyhedral primary silicon particles have been investigated by Electron Back
Scattered Diffraction (EBSD).
Abstract: Solidification behaviour of 357 Al-alloy under intensive forced convection in the rheo-die-casting
(RDC) process, was investigated experimentally to understand the effects of the intensity of forced
convection and shearing time on the nucleation and growth behaviour. It was found that under
intensive forced convection, heterogeneous nucleation occurred continuously throughout the entire
volume of the solidifying melt. All the nuclei could survive due to the uniform temperature and
composition fields created by the forced convection. This has been named as ‘effective and
continuous nucleation’. It is also found that the nuclei grow spherically with an extremely fast
growth rate. This makes the primary solidification essentially a slow coarsening process, in which
Ostwald ripening takes place by dissolution of the smaller particles. In addition, it was found that
intensive forced convection suppresses partially the formation of the primary phase, promote
nucleation of the primary particles, and hinders the particle growth.
Abstract: A quantitative understanding of the effect of fluid flow on the microstructure of cast
alloys is still lacking. The application of time dependent magnetic fields during solidification offers
the possibility to create defined flow conditions in solidification processing. The effect of rotating
magnetic fields (RMF) on the microstructure formation in cast Al-alloys (Al-7wt.%Si, Al-7wt.%Si-
0.6wt.Mg) is studied experimentally and numerically. The forced fluid flow conditions result in
pronounced macrosegregation effects and affect microstructural parameters. With increasing fluid
flow the primary dendrite spacing decreases whereas the secondary dendrite arm spacing increases.
The experimental analysis is supported by a rigorous application of numerical modeling with the
software package CrysVUn.
Abstract: By imposing a high frequency magnetic field, the surface quality and macro/micro
structure of the direct chill cast billets are improved. The casting speed can also be improved by
simultaneous applying mold and electromagnetic coil, especially for the alloys with a wide freezing
range such as Al-Cu-Mg alloy. The extent of macrosegregation in the Al-Cu-Mg alloy is reduced by
application of the magnetic field. Moreover, the inverse segregation layer usually observed in the
direct chill cast billet is eliminated by the effect of the electromagnetic field. The microstructure of
the hot-rolled and heat treated billets cast under the high frequency field also show better