COMPARATIVE-EVALUATION OF EXTRUSION AND HOT ISOSTATIC PRESSING AS FABRICATION TECHNIQUES FOR AL-SIC COMPOSITES

Aluminium matrix composites can be manufactured by using the powder metallurgy techniques of either extrusion or hot isostatic pressing (HIP). An evaluation of the existing literature revealed that the properties of extruded Al-SiC composites have been studied in detail by many researchers, but only a few investigations describing properties of HIP composites were published recently. However, the results indicate that compared with extruded material better mechanical properties can be achieved by the HIP technique: for Al 6061 + 30 wt.% SiC an improvement of 25% in strength accompanied by a 7% increase in Young's modulus were obtained, but the increase in strength occurred at the expense of ductility. A relationship between material properties and density, which could be used as a tool to predict mechanical properties, has been reported. Another important factor which has a considerable influence on the mechanical properties, independent of the fabrication method, is the consolidation temperature. A suitably chosen temperature is necessary for a good bond between matrix and reinforcement. In the present study, the microstructure and hardness of extruded or HIP Al 6061 reinforced with SiC particles of different sizes and volume fractions were investigated. The microstructural features due to the consolidation method were evaluated.