Aluminum lithium alloy composites reinforced with Cu-coated SiC particles

Aluminum lithium alloys are good candidates for aerospace applications because of their light weight and relatively high strength. The addition of ceramic reinforcement can improve the specific strength, modulus and elevated temperature performance of these alloys. However, the processing and fabrication of aluminum lithium alloys composites is hampered by problems such as agglomeration, uneven distribution and poor interfacial relationships between the matrix and the reinforcement. Previous work in this composite system has shown that mechanical alloying can alleviate the distribution problems of the ceramics. As a result mechanical properties such as Young's modulus improved by 10-15%. The present work attempts to address the interfacial relationship between the matrix and reinforcement. Cu-coated SiC particles are introduced as reinforcement and the composite is processed by conventional milling followed by hot pressing and hot extrusion. The influence exerted by extrusion ratios and extrusion temperature are studied. Post-extrusion processing by hot isostatic pressing (HIP) was also performed. Results showed that the increase in Young's modulus of the composites reinforced with the Cu-coated SIC is more significant than mechanically alloyed Al-Li/SiC composites. A maximum Young's modulus of 92 GPa was obtained for a 10 wt.% SiC reinforced Al-Li after hot extrusion and HIP. This indicates that interfacial strengthening has a more profound impact on the overall properties than uniform distribution of the ceramic reinforcements.