A hypoeutectic aluminum silicon casting alloy having a refined primary silicon
particle size and a modified iron morphology. The alloy includes 10 to 11.5% by
weight silicon, 0.10 to 0.70% by weight magnesium and also contains 0.05 to 0.07%
by weight strontium. On cooling from the solution temperature, the strontium serves
to modify the silicon eutectic structure as well as create an iron phase morphology
change. Such changes facilitate feeding through the aluminum interdendritic matrix.
This, in turn, creates a finished die cast product with extremely low levels of
microporosity defects. The alloy may be used to cast engine blocks for marine outboard
and stern drive motors. Furthermore, when the magnesium levels are adjusted to
approximately 0.10 to 0.20% by weight magnesium, propellers having a highly advantageous
ductility may be obtained.
