ALUSIL ® -Cylinder Blocks Porsche V6/V8 - KSPG AG

ALUSIL ® Cylinder Blocks
for the AUDI V6, V8 and V10 Gasoline Engines

1. Audi setting standards in lightweight design
With its vehicle model series, Audi is setting new standards
in lightweight design. So it is only logical for the carmaker
again to count on aluminium in developing the cylinder
blocks for its actual gasoline V-engines (Fig. 1). On account
of the reduced wall thickness (cylinder land width of only
5.5 mm (Fig. 2) between cylinder bores), Audi relies on the
hypereutectic aluminium-silicon alloy AlSi17Cu4Mg registered
for KS Aluminium-Technologie under the brand name
of ALUSIL ® . This concept allows the pistons to move directly
V6 cylinder block
V8 cylinder block
(multi-point injection)
Fig. 1: ALUSIL ® cylinder block of the Audi V6, V8 and V10 gasoline engine generation
along the honed cylinder bore surfaces of the aluminium
casting – an ideal condition for compact high-performing
engines.
2. Reasons in favor of ALUSIL ® from the viewpoint
of Audi:
There are many technical reasons which induced the carmaker
Audi to adhere to the proven ALUSIL ® concept:
V8 cylinder block
(fuel stratified injection [FSI])
V10 cylinder block
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4
5.5 mm
Fig. 2: Cylinder head flange surface with a land width of only
5.5 mm
Fig. 3: Material structure of the alloy AlSi17Cu4Mg / ALUSIL ®
with primarily precipitated silicon crystals (dark areas in the
picture)
Fig. 4: Mechanically exposed ALUSIL ® cylinder bore surface
ALUSIL ® makes a minimum weight at a high degree of integration
of engine functions like lubricant, coolant and
engine venting circuits.
ALUSIL ® enables minimum overall cylinder block lengths
to be implemented because the engines can be operated
without inserted cylinder liners. To achieve the shortest
possible engine length at a specified swept volume and
stroke, the cylinder bore diameter should be kept as large
as possible, at minimum land width. In such cases, the
land width of the jointly cast cylinders is determined in
practice by the safe and reliable performance of the cylinder
head gasket, by the cutting pressure applied for machining
and the cylinder distortion in engine operation.
ALUSIL ® boasts excellent tribological characteristics. As
the pistons and piston rings slide along the exposed silicon
crystals, their susceptibility to seizing is minimized
(Fig. 3).
ALUSIL ® displays optimum thermal conductivity; Audi is
thus in a position to achieve a high specific engine performance.
ALUSIL ® does not imply any recycling problems because
the cylinder block does not contain extraneous materials
– such as cast-in cylinder liners made of grey cast iron.
ALUSIL ® allows cylinder blocks to be cast monolithically
without cylinder liners or subsequent coating of the cylinder
bores. This makes it possible to achieve:
components of optimum structural rigidity through
the benefit of a by 12 % higher Young’s modulus of the
ALUSIL ® alloy compared to a hypoeutectic standard
alloy as well as,
process reliability in machining without having to interrupt
the process flow for costly additional working
steps specifically for the cylinder bore surfaces. A decisive
milestone in this area was the mechanical exposure
of the silicon crystals by means of a third honing
step (Fig. 4) as a substitute for the chemical laying
bare (etching) after the two-step honing process which
was a must before. Laying bare the silicon grains by
mechanical means allows perfect on-line production.

The above described assets of the ALUSIL ® alloy are certainly
significant arguments in favor of the use of this material.
But also the low-pressure die casting method (Fig. 5) which
has since then proven to be the best by far is an important
prerequisite for process reliability in making mass-produced
cylinder block castings of ALUSIL ® .
3. Reasons in favor of low-pressure die casting from
the viewpoint of Audi:
Low-pressure die casting, LPDC (Figs. 5 – 6) allows to use
sand cores where necessary, e.g. for water jackets (Fig. 7).
In this way, structurally rigid closed-deck cylinder blocks
can be produced, a prerequisite for high specific engine
outputs.
LPDC allows controlled, low-turbulence die filling, and
what is even more important, controlled cooling of the die
to ensure component-specific, virtually ideal directional
solidification. The compilation of all casting-relevant data
and the resulting control of the casting process are implemented
today computer-assisted. Especially a purposedesigned
cylinder sleeve cooling system is an indispensable
prerequisite for uniform precipitation of the silicon
crystals in the cylinder area (criteria: distribution, grain
size range (Fig. 8) and number of crystals per cm²), low
porosity and minimizing casting defects like shrinkage
holes, pores, cold fusion, etc. This process control ensures
constant quality of the castings.
LPDC permits unrestricted heat treatment of the casting.
It is already possible to achieve a certain increase in hardness
and strength by applying controlled cooling of the
cylinder blocks from the casting temperature by means
of customary T5 heat treatment. The subsequent artificial
aging not only serves to enhance hardness and strength,
but primarily also to stabilize the volume, i.e. avoid an
irreversible expansion in length and volume (distortion)
referred to as “growth” when the casting is exposed to
the operating temperature of the engine.
To cope with even higher engine stresses, a modified T5
heat treatment solution is available where the hardness and
strength of the components are enhanced through the casting
heat, e.g. locally in the cylinder deck or bearing bulkhead
area by means of chilling with water which leads to precipitation
hardening.
Sleeve yoke with
movable die half
Open die
Stationary
die half
Crucible
with melt
(holding
furnace)
Cylinder sleeves
Casting
Lifting table,
stroke about 2 m
Hydraulic cylinder
sleeve lifters
Hydraulic
lateral slides
Feed tube
Fig. 5: Low-pressure die casting, illustrated principle of a casting
cell with opened die (movable die half in lifted position)
Fig. 6: Design of a low-pressure die for aluminium cylinder
block
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For absolute high-performance engines, Audi applies full
heat treatment (T6) comprising homogenizing, chilling and
artificial aging. This method contributes to a further distinct
improvement in terms of static and dynamic strength. As the
T6 heat treatment without specific artificial ageing only contributes
little to volume stabilisation, but implies the risk of
distortion in engine operation, the artificial ageing process
is stretched in the T7 heat treatment mode, thus increasing
extension.
4. Audi’s V-engine generation
The V-engine generation of Audi – both petrol and diesel
engines – is setting standards with respect to compactness
and overall length. Customers’ requests for more powerful
engines even in smaller vehicle model series implied the
need for shorter overall engine lengths and for reducing the
vehicle front-part weight. As a result the current V-engine
generation has been created.
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Audi is the market leader in lightweight design, specifically
in the premium segment. The lightweight strategy is impressively
implemented in the car body through the Audi space
frame aluminium technology. It was a logical consequence
therefore to rely on a weight-optimizing all-aluminium solution
for the petrol V engines – i.e. ALUSIL ® cylinder blocks.
5. The Audi V6, V8 and V10 gasoline engine concept
The V6 in the large displacement version of 3.2 l, the V8 with
a swept volume of 4.2 l as well as V10 of 5.2 l swept volume
originate from the current Audi-V engine family with a stroke
of 92.8 mm (Fig. 9a and 9b ), a V angle of the cylinder banks
of 90° and a central division of the cylinder block (bedplate
concept). The distance between cylinders is 90 mm, the cylinder
bank offset being 18.5 mm. For the V6 of 3.2 l swept
volume, the V8 of 4.2 l and the V10 of 5.2 l displacement,
the cylinder bore is 84.5 mm. It is 81 mm in the case of the
Fig. 7: View of a water-jacket core box in the core shooter: water-jacket sand cores for Audi V6 cylinder block (left) and V8 cylinder block
(right)

smaller V6 engine with a swept volume of 2.4 l. The cylinders
are cast jointly, at a cylinder land width of 5.5 mm or, respectively,
9 mm for the smaller V6.
The V6 engine in the large swept-volume version is operated
with fuel stratified injection (FSI) and with compressor supercharging
for optimised charge air cycles with TFSI. The smaller
swept-volume version is still designed for multi-point injection
(MPI). The different cylinder bore dimensions do not
require adjustment on the water jacket side, and this allowed
implementing a low-cost concept. The V8 and V10 gasoline
engines are likewise available in two versions. A new engine
version with bi-turbo charging has been added to the series,
which also distinguishes itself in the cylinder block.
6. Description of the cylinder block top
As mentioned above, the Audi cylinder blocks (Fig. 10) are
made of the hypereutectic alloy AlSi17Cu4Mg. The low-pressure
die casting method is applied, with controlled cooling
from the casting temperature. Cooling takes place at ambient
air or its partly assisted by an air blower. This is followed by
Number of grains in the area measured
25.0
20.0
15.0
10.0
5.0
0
10 20 30 40 50 60 70 80
Grain size [µm]
Fig. 8: Representative grain distribution of the primarily precipitated silicon crystals
artificial aging for volume stabilizing (T5 heat treatment), a
process which only implies a slight decrease in hardness. The
associated bedplates – not included in the scope of supply
of KS Aluminium-Technologie – are high-pressure die castings
made from the hypoeutectic alloy AlSi9Cu3 with castin
bearing bulkheads of nodular cast iron. The bedplates of
the V8 and V10 engines are made from alloy AlSi12Cu1(Fe).
The cylinder blocks of the V8 FSI, of the V10 FSI as well as
the V10 bi-turbo were subjected to structural optimisation
to account for increased performance output. Externally, this
is visible at the cross members in the V space between the
cylinder banks. Further modifications relate to the oil filter
flange area.
The water jackets of the cylinder banks produced by using
sand cores as well as the water supply channels are integrated
on the left and right sides in the cylinder blocks. In the
case of the V6, in addition the part of the water pump housing
on the discharge-nozzle side is arranged at the front,
above the V space but connected with it. Water supply to the
jackets of the two cylinder banks is accomplished by means
of a manifold, flange-mounted in the V space.
Area measured
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Whereas in the standard FSI engines the cooling water flows
around the cylinders from the front to the rear, in the case of
the V10 bi-turbo a cross-flow principle has been implemented.
Thanks to forced flow, the cooling effect is enhanced in
both the cylinder block and the cylinder head.
The oil circuit ducts are partly pre-cast, partly drilled. The
two deep-hole bores centrally arranged in the V, for the main
oil and injection nozzle channels for piston cooling, which
virtually cover the whole block length, are machined at KS
Aluminium-Technologie. The non-pressurized oil drain backs
and cylinder block vent ducts are pre-cast for the V8 and V10
cylinder blocks. They are arranged externally on the side
walls, in parallel with the cylinders. These channels are connected
with the bedplate through bores in order to exclude
the risk of casting fins being left.
Subsequently, after removing the sand cores, the cylinder
blocks are submitted to first cut machining (Fig. 11).
Adjustment in the crankcase area is achieved by alignment
in the first clamping step, starting from cast locating points
at the interface to the bedplate. To this effect, the three locating
points on the gearbox side are machined and two index
bores (fitting bores) are set.
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Fig. 9a : The Audi V6 gasoline engine
Further machining steps in the first and second clamping operations
are the drilling of the oil ducts, pre-drilling of the
cylinders, pre-milling of the main bearing area and cubing of
the external faces. In this last step, all “important” surfaces
are re-milled in order to remove casting fins, for instance, in
order to enable a process-reliable leak test to be carried out
subsequently.
To ensure proper casting quality, the cylinder blocks are
submitted to comprehensive x-ray, hardness and ultrasonic
tests. The latter serves to check the bearing bulkheads for
porosity. The oil and water systems are checked for leaks by
means of a differential pressure test, followed by a 100% visual
inspection before the cylinder blocks are dispatched to
Audi on purpose-designed loading devices.
At AUDI HUNGARIA MOTOR Kft. (AHM), the cylinder blocks
are integrated into the machining line on the locating points
and aligned on gearbox flange level by means of the fitting
bores provided in the gearbox flange. Next, the cylinder
block is machined as an individual part, with most of the
machining work being done in these working steps. Subsequently,
the finished bedplate is “matched” with the cylinder
block, i.e. pinned and bolted. From this moment, the cylinder

lock and the bedplate constitute one unit and move jointly
through the assembly line. An important machining step is
the mechanical exposure of the silicon crystals in a third
honing step with “soft” honing stones which means honing
with cutting material embedded in a non-rigid matrix.
The third honing run, i.e. finish honing, is accomplished using
elastic honing stones – made of corundum or SiC grains
in a porous plastic bond – whose cutting grains rebounce on
contact with the hard silicon grains so that they remove more
of the aluminium matrix than of the silicon grains. Compared
to a conventionally honed grey casting bore surface, this
three-step honing operation results in a relatively smooth
bore surface (Fig. 4) which has a favourable effect on oil consumption
(hydrocarbon emissions), friction losses and wear
of the contact partners (piston and piston rings).
ALUSIL ® features sufficiently high strength so that even for
the high-strength bolt joints like those of main bearing cap
and cylinder head the nut thread can be cut directly into
the cast material. When “overtightening” the bolt, it will invariably
tear off before the nut threads are shorn. The high
compressive strength of ALUSIL ® has an extremely positive
effect on the bolted joints. It exceeds the tensile strength by
Fig. 9b : The Audi V8 gasoline engine
Fig. 10: Aluminium cylinder block concept, consisting of
monolithic cylinder block top and bedplate with cast-in
bearing bulkheads made of spheroidal casting
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nearly 100 %, depending on the heat treatment condition. As
a result, commercial bolt heads hardly lead to an appreciable
setting of the aluminium even if the bolt was tightened up to
the tensile yield point.
7. Description of the casting die and development/adjustment
of the casting process
The synergy effect envisioned by Audi when changing from
the V6 to the V10 cylinder blocks was fully achieved in terms
of casting tool design, conceptual design of the machining
equipment and test devices and, in particular, the development
and adjustment of the casting process. Thanks to sustainable
exploitation of all possibilities of virtual product and
Fig. 11: Solidification simulation with the example of the V6 cylinder block
Top: Residual solidification zone (risk of blowholes) in the gearbox flange area without active cooling measures
Bottom: Optimized condition; avoidance of blowholes (no residual solidification zones) through selective active cooling measures
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Critical residual solidification zone
process development based on a consistent CAD, CAE, CAM
line (Figs. 11, 12), the targeted effective optimisation of the
cylinder blocks was accomplished.
8. Summary, conclusion and outlook
For its state-of-the-art high-performance gasoline engines of
V design, Audi stakes on the combination of ALUSIL ® lowpressure
die casting and mechanical silicon grain exposure.
In the present situation, this combination offers optimum
conditions for the engine functions, production and process
reliability as well as quality. Hence there are quite a number
of factors speaking in favor of ALUSIL ® to be rated as one of
the best materials available today for high-performance gas-

oline V engines when weighing the many convincing positive
properties up against occasionally adduced less favourable
characteristics like low ductility and the somewhat higher
machining costs. What is a decisive aspect is the potential it
implies for further strength improvements through full hardening
heat treatment (T6) the entire component or local, socalled
modified T5 heat treatment.
KS Aluminium-Technologie has pursued for decades the continuous
optimisation of the ALUSIL ® concept. This includes
the relevant further development of the low-pressure die
casting process which has been fully integrated. Manufacturers
favouring the respective technologies, be it the conventional
or the future-oriented one, appreciate the qualitative
advantages of this casting process. Of late, the low-pressure
1a
1b
2a
2b
Fig. 12: Die filling simulation of the gearbox flange with the example of the V8 cylinder block
Top (pictures 1a -3a): turbulent filling (surging melt due to abrupt cross-sectional change)
Bottom (pictures 1b -3b): stabilized filling by adjusting the geometry and optimum filling parameters
die casting process has been gaining further in importance
because it offers the possibility to fully exploit the strength
potential of the material by artificial ageing in connection
with the development of passenger car engines which are
subjected to ever higher stresses. By casting in sand cores,
further functions can be integrated into the component and
additional lightweight construction potential is generated.
3a
3b
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KS Aluminium-Technologie GmbH · Hafenstraße 25 · 74172 Neckarsulm · GERMANY
Tel. +49 7132 33-1 · Fax +49 7132 33-4357 · www.kspg.com
Subject to alterations. Printed in Germany. A|IX|k
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