Development of superplastic-aluminum-alloy piston formed with controlled forging technology

Powder metallurgical aluminum alloys and forging technology have been developed to mass produce high-performance-engine pistons. The Al-Si base powder metallurgical alloys have shown much higher fatigue strength as well, as better wear resistance than a conventional cast piston alloy. The alloys show high strain rate superplasticity at a limited temperature and strain rate range. In order to bring out the alloy's formability, the forging has been programmed using an integrated process that involves the precise control on the die temperatures and the spray conditions of the lubricant. With these procedures, near-net-shaped pistons are efficiently obtained. The newly developed pistons have improved engine performance and are being put into practical use in Yamaha's commercially available engines.