The Inﬂuence of Ultrasonic Cavitation
on the Formation of Fe-Rich Intermetallics in A383
YANG XUAN, TAO LIU, LAURENTIU NASTAC, LUKE BREWER, ILYA LEVIN,
and VISH ARVIKAR
The eﬀect of ultrasonic treatment (UST) on the formation of Fe-rich intermetallics (including
sludge) in the A383 alloy is investigated for diﬀerent processing temperatures in the present
study. Diﬀerential scanning calorimetry is used to analyze the precipitation temperature of the
sludge phase. The results revealed that the sludge will precipitate at a temperature above that of
the Al matrix and the precipitation temperature decreases with an increasing cooling rate. UST
cavitation applied at diﬀerent temperatures (600 °C to 750 °C) during the solidiﬁcation process
breaks the sludge into small island-like pieces. However, the aggregation trend of the sludge is
not changed. Sludge with small size and uniform distribution is obtained when UST is applied at
600 °C, which is lower than the precipitation temperature of the sludge. At the highest
temperature (850 °C), the application of UST has no eﬀect on the formation of either sludge or
a-Fe intermetallics. At 750 °C, UST promotes the formation of the sludge when applied at
Ó The Minerals, Metals & Materials Society and ASM International 2018
alloys have been widely used in the
automotive industry because of their good castability
and high strength-to-weight ratio.
Iron is a common
impurity and is regarded as the most detrimental
element that lessens the mechanical properties of
Iron does have the positive eﬀect
of preventing die soldering during casting processes.
Depending on the cooling rate and amount of Fe and
Mn, Fe-rich intermetallics may form as pre-dendritic,
pre-eutectic, co-eutectic and post-eutectic phases during
the solidiﬁcation process.
The Fe-rich intermetallics
that precipitate before the formation of the Al dendritic
phase are called pre-dendritic phases. These Fe-rich
intermetallics have polyhedral morphology. According
the 3D morphology of pre-dendritic
Fe-rich intermetallics corresponds to a regular rhombic
dodecahedron. The pre-dendritic Fe-rich intermetallics
can cause severe stress concentration at the matrix/
intermetallics interface because of their faceted
geometry. The Fe-rich intermetallics that precipitate
after the formation of the primary Al dendrites are
called post-dendritic phases, and the most common
phases are the a-Fe (Al
) phases with
and b-Fe (Al
metallics, which have long, needle-like shapes.
post-dendritic Fe-rich phases can block the feeding
channels of the interdendritic network, resulting in the
formation of a large number of porosities and shrinkage
in the cast Al alloy, which in turn will signiﬁcantly
decrease its ductility. The platelet b-Fe phases, which are
hard and brittle and have a relatively low bonding
strength with the matrix Al, are regarded as the most
detrimental of the Fe-rich intermetallics, and they can
act as stress concentrators, which result in the brittleness
of these cast Al alloys.
In this study, we will follow
the literature conventions and use the term ‘‘sludge’’ for
the pre-dendritic Fe-rich intermetallics phase,
the term ‘‘a-Fe’’ and ‘‘b-Fe’’ will be used for the
post-dendritic a-Fe phase and b-Fe phase, respectively.
It is important to control the number and morphol-
ogy of the Fe-rich intermetallics in Al-Si-Cu alloys to
improve their mechanical performance. It has been
indicated that a rapid solidiﬁcation rate or the addition
of Sr will promote the formation of the more compact,
less harmful a-Fe phase rather than b-Fe inter-
Basak et al.
introduced a gravitational
segregation method to eliminate b-Fe intermetallics in
Al-Si alloys. Some other physical segregation
YANG XUAN, TAO LIU, LAURENTIU NASTAC, and LUKE
BREWER are with the Department of Metallurgical and Materials
Engineering, The University of Alabama, Tuscaloosa, AL 35487.
Contact e-mail: email@example.com ILYA LEVIN and VISH
ARVIKAR are with Nemak Alabama, Sylacauga, AL 35150.
Manuscript submitted January 26, 2018.
Article published online June 1, 2018
3346—VOLUME 49A, AUGUST 2018 METALLURGICAL AND MATERIALS TRANSACTIONS A