Investigations on micro hardness, electrical and thermal conductivity of AA7075 surface hybrid composites produced through friction stir processing

Abstract

High strength, minimum thermal and electrical conductivity are the major requirements of aircraft applications which could be obtained by micro-structural modifications of the composites with particulate reinforcements. The proposed work focus the analysis on the behavior of micro hardness, coefficient of thermal expansion, thermal and electrical conductivity of AA7075 fabricated by friction stir processing with different weight ratios of Al2O3 and SiC. Different surface hybrid composites are formed by varying the weight ratios. It ensures the formation of fine grained structure and decrease in thermal and electrical conductivity values with addition of higher hardness. During the friction stir processing, the working temperature is identified between 99.4 and 316.6 °C for the proposed composites, which shows 15.6% and 49.8% that of the melting point of AA7075 (635 °C). Experimental investigation on thermal conductivity and electrical conductivity has been conducted under different heat input values through varying the applied voltage from 25 to 225 V. The observation shows surface hybrid composites depicts lower conductivity values with Al2O3 and SiC particles due to variation in energy level of electrons and phonons. Among the observations, the specimen S5 reinforced with equal weight ratios of Al2O3 and SiC yields the maximum micro-hardness of about 265 VHN and lower coefficient of thermal expansion of about 13 μm m−1 °C. This is due to the reinforcement behavior and formation of Al4C3 intermetallics. The morphological analysis also supports the requirements of aircraft components.