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RESEARCH
Twin-roll casting of light metals and
composite materials for lightweight application
A. Dorner-Reisel, University of Applied Sciences Schmalkalden
Fig. 1: The frame of BMW i3 is a hybrid construction of light metal and fibre reinforced polymer
Twin-roll casting applies the direct conversion
of liquid metal into thin sheet.
Besides the twin-roll caster, additional
process equipment for hot or cold rolling
is not needed. Low capital investment
and metal conversation costs continue
to make it a process of choice for metallic
sheet today. Not only the twin-roll
casting process has the ability to directly
bring out thin light metal strip, but to
reinforce light metal foils or produce
multilayered light metal strips in an efficient
way. In recent years, the roll
casting equipment was improved and a
lot of aluminium as well as magnesium
alloys, which were not pourable by other
casting technologies can be produced
with improved microstructure by modern
twin-roll casting equipment. A significant
advantage of light metal strip produced
by twin-roll casting is the ability to obtain
extremely fine grained microstructure.
Mechanical properties gain from fine
grained microstructure as well as the
formability. Superplasticity is discussed in
this context. New materials for the rolls
and solidification under pressure enhance
the cooling rate and the roll speed leading
to an improved productivity. Because
twin-roll casting provides higher cooling
rats in comparison to die casting, segregations
can be expected to be enhanced.
Therefore, a follow-up homogenisation of
the structure by heat treatment is recommendable.
Wire and fibre reinforced light
metal strips or thin foils were produced
with twin-roll casters in a laboratory
scale. Here further development of the
casting equipment for a large scale production
is ongoing.
Cost effective production of lightweight sheet
and panels is a major demand for moving technical
elements with a multitude of purposes.
Auto-body, chassis, parts of aircrafts and supporting
elements are some examples only.
In transportation, the importance of a low
specific strength increased in recent years essentially.
While fibre reinforced polymers for
flat products like auto-bodies were rare used
for middle class automobiles some years ago,
today the demand for low weight sheet materials
with high specific strength is essentially
stronger. In present times, more expensive materials
like fibre reinforced polymer structures
find their way not only into aircraft and upper
class automobiles, but are used for small and
middle class automobiles also (Fig. 1).
Dorner-Reisel
Twin-roll casting of steel was introduced by
Henry Bessemer already in 1891 [1]. Some
decades ago, this process was applied for light
metal also [2]. Nowadays twin-roll casting is
a markedly cost-effective process for the production
of light metal sheet with excellent mechanical
properties for automotive and other
transportation task [3, 4] due to procedural
advantages like process savings and rapid solidification
[3, 5, 6]. Twin-roll casting applies
the direct conversion of liquid metal into thin
sheet. Besides the twin-roll caster, additional
process equipment for hot or cold rolling is
not needed. Low capital investment and metal
conversation costs continue to make it a process
of choice for metallic sheet today. Not only
is the twin-roll casting process able to directly
bring out thin light metal strip, but to reinforce
light metal foils or produce multilayered light
metal strips in an efficient way [3].
In recent years, the roll casting equipment
was improved and a lot of aluminium as well
as magnesium alloys, which were not pourable
by other casting technologies, can be produced
with improved microstructure by modern
twin-roll casting equipment. At present, thin
light metal sheet of magnesium alloy strip produced
by conventional reforming of casts is
very expensive due to extensive production
cost. Twin-roll casting could be a cost-efficient
alternative, if a large scale production of high
quality sheet can be accomplished. Considering
the recent progresses in twin-roll casting
of un- and reinforced light metal alloys and
multilayered strips, one can expect a considerably
more widespread utilisation of twin-roll
cast sheets in future.
Progress in twin-roll casting equipment
In general, the rolls of the twin-roll caster can
be horizontally or vertically positioned in relation
to the casting direction. Fig. 2 illustrates
a twin-roll caster for horizontal casting direction.
Molten metal is fed onto two, mostly water
cooled rolls, where it solidifies, and is than
rolled. The rolls fill both a heat exchanger and
a rolling function. Using twin-roll casting, the
casting as a primary shaping process s of the
liquid metal is combined with metal forming
and its plastic deformation. Before solidification,
the liquid metal is poured in the space
between the rolls called ‘pool’. It solidifies in
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