Hypereutectic Aluminium-Silicon Alloys
Some Al-Si alloys have characteristics such as good wear resistance,low coefficient of thermal expansion, combined with a highstrength to mass ratio. Due to such properties, these alloys have been used in several applications from the automotive to aerospaceand power industries. The outstanding wear resistance is due tothe high volumetric fraction of the silicon phase and intermetallics.
Applications of the Al-Si alloys in the automotive industry, includeengine blocks and parts of engines, particularly, cylinder liners. The main advantages for the use of these alloys are weight reduction, low fuel consumption and less emission of pollutants.
The use of engine blocks made of hypereutectic aluminium alloys has been considered by many world manufacturers.
Hypereutectic alloys can be produced by ingot metallurgy1 or by rapid solidification processes.The use of casting for the production of these alloys is limited by the range of possible chemical compositions. That can be attributed to the formation of eutectics and coarse primary silicon phase, due to the low cooling rates associated to the ingot metallurgy.
The distribution of coarse silicon particles in the alloy leads to low ductility and limited workability of the hypereutectic Al-Si alloys. Many of the problems associated with ingot metallurgy can be overcome by the rapid solidification techniques. The main advantage of the use of the rapid solidification process is the significant modification of size, morphology and distribution of the primary silicon phase in the matrix, comparatively to the conventional process. The refinement of the primary silicon particles is either achieved by rapid solidification hypereutectic Al-Si alloys or co-depositing fine Si particles.