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.

No abstract

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.

No abstract

Abstract

The semisolid tensile properties of two AA6111 direct-chill cast alloys (A and B) have been studied. The Cu, Mn, and Si contents of alloy A are higher than those of alloy B. The microstructures of the alloys were analyzed before tensile testing and after tensile fracture. Isothermal holding was performed in the temperatures of 510, 520, 535, 552, 564 and 580 °C for 1 h to study porosity/void formation in both alloys. Tensile tests were conducted near the solidus temperature in the temperature range of 450-580 °C at a strain rate of 10 -4 s -1 . The strain during tensile testing was measured using the digital image correlation method to obtain reliable stress-strain curves. The results revealed that the tensile strengths of the alloys gradually decreased to zero with increasing temperature to arrive at the zero-stress temperature, whereas the strains at the failure decreased sharply with increasing temperature until zero-ductility temperature (ZDT) was reached. Moreover, the failure strain of alloy B at any given testing temperature was higher than that of alloy A. Non-mechanical and mechanical hot-tearing criteria were used to study the hot-tearing susceptibilities (HTSs) of the alloys. Considering the mechanical criterion, the ZDT and brittle temperature range of alloy A were lower and larger than those of alloy B, respectively, indicating that the HTS index of alloy A was higher than that of alloy B.

No abstract

No abstract