Application of cast Al-Si alloys in internal combustion engine components

Excellent thermal conductivity and lower density make Al-Si alloys a suitable alternative for cast iron in the fabrication of engine components. The increase in the maximum operation temperature and pressure of engines necessitates improving the thermomechanical fatigue performance of Al-Si alloys. This paper has two major parts focussing on the use of Al-Si based alloys in cylinder heads and engine blocks. In the first part, the structural stress-strain and material property requirements of cylinder heads are discussed. In addition, the physical and mechanical properties of different competing materials used in the manufacture of engine components are reviewed. The physical metallurgy, solidification sequence and thermal conductivity of Al-Si based alloys are reviewed. Also discussed is the effect of microstructural features on thermomechanical fatigue lifetime. This part also includes an overview of the strengthening mechanisms of cast Al-Si alloys, by dispersed phases and heat treatment. Demands to improve fuel, economy and reduce emissions necessitate modifications in the materials and design of engine blocks. Wear resistance and low friction coefficient are the major characteristics required for engine block materials. In the second part, the most promising alternative approaches to manufacturing liner-less Al-Si alloy cylinder blocks are elaborated.