The tendency to use aluminum alloys to replace conventional gray
cast irons (GCI) materials in engine blocks of passenger cars is
gaining more and more importance driven by reduction of engine
weight to achieve expectation for lowering fuel consumption and CO₂
emissions.
Cast-in cylinder liners are commonly applied inside of aluminum
engine blocks with designs of the outer surface usually selected
through analysis of the aluminum casting process (e.g., high
pressure die casting, precision sand cast), geometry complexity,
thermal and mechanical loads.
A good quality of clamping (bonding and shear strength) between
the cast-in cylinder liner and aluminum block might guarantee a
reliable heat transfer and thus low bore distortion. The good
clamping can also contribute to improve the final machining of the
liner after block casting.
The most effective variants of cast-in cylinder liner designs
were selected for the evaluation of clamping performance. The
variants were based on conventional thread turned, threaded with
addition of undercuts profile, and two designs based on as-cast
rough surface with different roughness depth (0.62 and 1.26
mm).
The results showed that the as-cast rough surface with roughness
depth of 1.26 mm reached maximum values for bonding strength (30
MPa) and shear strength (98 MPa) due to better penetration of the
melted aluminum into the rough volume surface. The threaded with
addition of undercuts profile design also meets higher targets in
the bonding (22.7 MPa) and shear strength (37 MPa) when compared to
conventional machined liners. The good clamping performance added
with freedom of outer diameter that enable different shapes in
connection with tighter tolerance, places this design as promising
technology for modern aluminum engine blocks with low inter-bore
distance.