Abstract
The feature of the aluminum rheocasting process is that the casting is done in
semi-solid state of aluminum alloy. Starting from molten Al-Si alloy, semi-solid slurry with
globular alpha phase is made by controlled cooling rate in the slurry making equipment.
Subsequently, the semi-solid slurry is transferred to the diecasting machine, then casted into
the die cavity. The aluminum rheocasting has high productivity due to short solidification
time, and produces parts with high integrity and precision. Also the castings have high
elongation and high fatigue strength compared to aluminum gravity castings. On the other
hand, there were some technical issues to be cleared for production, such as the stability of
semi-solid slurry. We succeeded in overcoming all those issues by the following key
technologies. 1) Stability control of semi-solid slurry. 2) Temperature and cleanliness
control of molten alloy. 3) Casting simulation for semi-solid metal. 4) Unique die design.
As a result, the aluminum rheocasting disk brake caliper has high ductility. Elongation in
tensile characteristic is 30% higher than the gravity castings due to finer eutectic
microstructure. The part´s weight in as-cast condition is 10% lighter compared to the gravity
casting, due to its near net shape. The disk brake caliper that keeps certain safety factor more
than cast irons and achieved 50% of weight reduction, is adopted for 2003MY car.
Keywords - Brake, Calipers, Aluminum, Rheocasting, Lightweight