Squeeze infiltration processing of lightweight smart aluminum graphite functionally graded composite for enhanced wear resistance

Aluminum - Graphite functionally graded metal matrix composites (A356-Gr FGMMC) with 20-60 volume percentage (vol%) of natural graphite (Gr) as reinforcement are developed by liquid metal squeeze infiltration technique. The density of A356-Gr FGMMC with 60 % Gr is reduced by 27 % (1.968 g/cm3) in particle rich region from the value of the base A356 alloy (2.68 g/cm3) making the FGMMC lighter. In comparison to monolithic A356 alloy, the coefficient of thermal expansion (CTE) of composites decreases with an increase in the volume fraction of Gr reinforcement. The CTE value is significantly reduced from 22.24 x 10-6/degrees C for A356 alloy to 9.62 x 10-6/degrees C for the composite with 60 % Gr. With the addition of Gr from 20 % to 60 %, the microhardness is found to be decreased from 74 HV to 46 HV and the compressive strength decreased from 364 MPa for the unreinforced matrix to 42 MPa for A356-Gr FGMMC with 60 % of Gr addition. Wear studies carried out on A356-Gr FGMMC using pin-on-disc tribometer shows excellent wear resistance with the addition of Gr particles compared to matrix alloy. The wear rate reduces with increasing Gr vol%, reaching a minimum at 60 % Gr. The scanning electron microscopy (SEM) analysis of worn surfaces indicate the formation of self-lubricating tribolayer which limits the interaction between matrix metal and the counter surface leading to the development of a smart composite with functionally graded properties in the particle rich region.