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.

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This paper aims to study the manufacturing of the AlSi10Mg alloy with direct energy deposition (DED) process. Following fabrication, the macro-and microstructural evolution of the as-processed specimens was initially investigated using optical microscopy and scanning electron microscopy. Columnar dendritic structure was the dominant solidification feature of the deposit; nevertheless, detailed microstructural analysis revealed cellular morphology near the substrate and equiaxed dendrites at the top end of the deposit. Moreover, the microstructural morphology in the melt pool boundary of the deposit differed from the one in the core of the layers. The remaining porosity of the deposit was evaluated by Archimedes' principle and by image analysis of the polished surface. Crystallographic texture in the deposit was also assessed using electron backscatter diffraction and x-ray diffraction analysis. The dendrites were unidirectionally oriented at an angle of *80°to the substrate. EPMA line scans were performed to evaluate the compositional variation and elemental segregation in different locations. Eventually, microhardness (HV) tests were conducted in order to study the hardness gradient in the as-DED-processed specimen along the deposition direction. The presented results, which exhibited a deposit with an almost defect free structure, indicate that the DED process can suitable for the deposition of Al-Si-based alloys with a highly consolidated structure.

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