Studies on 7075 Aluminium Alloy MMCs with Milled Carbon Fibers as Reinforcements

Carbon in various forms (such as fibers, fabrics, sheet, nano tubes, particles and flakes etc.) have found use as reinforcements in metal matrix composites (MMCs) based on aluminium alloys. However, the literature available on AA7075 alloy based composites as well as on the use of milled carbon fibers as reinforcements is rather limited. This was the stimulus for the present work on carbon fiber reinforced AA7075 alloy composites. MMCs with varying volume content of milled carbon fibers were fabricated through Vacuum hot pressing, and were characterized for mechanical, thermal and electrical properties. Micro-structural aspects of these MMCs were studied using Optical microscopy, Scanning electron microscopy, transmission electron microscopy and X-ray diffraction. This was followed by a systematic assessment of the mechanical properties (viz., hardness and compression strength), and thermal and electrical conductivities. The influence of T7 heat treatment on the properties was also investigated. The composites thus produced exhibit uniform distribution of carbon fiber. No evidence has been found of the presence of aluminium carbide (Al4C3) in any of the specimens. While the mechanical properties and electrical conductivity decreases as the amount of carbon fiber increases, thermal conductivity registers an appreciable increase in the In-plane direction. This appears to be the specific advantage of these carbon fibers reinforced MMCs, and is likely to open newer uses for this class of light weight materials.