Processing and Response of Aluminum-Lithium Alloy Composites Reinforced with Copper-Coated Silicon Carbide Particulates

Lithium-containing aluminum alloys have shown promise for demanding aerospace applications because of their light weight, high strength, and good damage tolerance characteristics. Additions of ceramicreinforcements to an aluminum-lithium alloy can significantly enhance specific strength, andspecific modulus while concurrently offering acceptable performance at elevated temperatures. Theprocessing and fabrication of aluminum-lithium alloy-based composites are hampered by particulate agglomerationor clustering and the existence of poor interfacial relationships between the reinforcingphase and the matrix. The problem of distribution of the reinforcing phase in the metal matrix can be alleviatedby mechanical alloying. This article presents the results of a study aimed at addressing and improvingthe interfacial relationship between the host matrix and the reinforcing phase. Copper-coatedsilicon carbide particulates are introduced as the particulate reinforcing phase, and the resultant compositemixture is processed by conventional milling followed by hot pressing and hot extrusion. The influenceof extrusion ratio and extrusion temperature on microstructure and mechanical properties wasestablished. Post extrusion processing by hot isostatic pressing was also examined. Results reveal the increasein elastic modulus of the aluminum-lithium alloy matrix reinforced with copper-coated SiC to besignificantly more than the mechanically alloyed Al-Li/SiC counterpart. This suggests the possible contributionsof interfacial strengthening on mechanical response in direct comparison with a uniform distributionof the reinforcing ceramic particulates.