THE DEVELOPMENT OF ALUMINUM DISK BRAKE CALIPERS USING RHEOCASTING PROCESS

摘要

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.