Development of Lightweight Forged Piston Material by Optimizing Size of Needle-type Intermetallic Compound

In order to produce lightweight, high-strength pistons for engines, the manufacturing process has been changed from casting to forging. However, the strength of conventionally forged aluminum alloys tends to be lower in the high-temperature region and the advantages of mass reduction have not been sufficiently achieved. Adding a transition metal to the piston material can enhance thermal stability. The specific gravity of the strengthened materials, however, becomes heavy and the formability is lessened. In order to solve these problems, the authors have developed a new piston material which was designed by dispersing a very fine-scale needle-type intermetallic compound within an Al-Si alloy. Compared to conventionally forged piston materials, this new alloy was 50% stronger at elevated temperatures while maintaining the same specific gravity. The new material has forging capabilities equal to those found in conventional materials, due to the added fine-scale intermetallic compound. As a result, we have achieved the development of a lightweight forged piston, with dramatically enhanced strength in the high-temperature region. Moreover, we can manufacture a lightweight piston without increasing costs while using a high-powered forging machine.