Semi-solid moulding technology in making automotive turbocharge compressor wheels

Diesel and gasoline engines are the most important sources of energy consuming, emission and global warming. To increase fuel efficiency and reduce emission, air pressure ratio of the engine needs to be further increased. The increase of air pressure is achieved by a compressor wheel in the turbocharger. The compressor wheel needs very complex blade geometry to achieve high pressure ratios. The very latest technique for impeller manufacture is called semi-solid moulding (SSM). This paper will present recent development of SSM including thixo-casting and rheo-casting processes in making aluminium compressor wheels. Experimental results show SSM material has superior microstructure and mechanical properties over cast and is comparable to material machined from solid. Component testing including performance and durability testing proves the SSM compressor wheels emerge as being significantly more durable than cast equivalents and approaching that of machined impellers.