Microstructure, hardness, and wear properties of AA6061/WC nanocomposite fabricated by friction stir processing

Abstract

Friction stir processing (FSP) is a solid-state microstructural modification technique that has recently become an effective tool to refine microstructures and improve the mechanical properties of metals. In the current study, optimization of FSP parameters, including tool rotational speed, transverse feed, number of passes, and tungsten carbide (WC) nanoparticle volume fractions on mechanical and wear properties of the fabricated AA6061/WC nanocomposite was studied. Optical microscopy and scanning electron microscopy are used for microstructural observations. The process parameters are optimized using the Taguchi technique for single responses towards microhardness and weight loss and the Desirability approach for both responses. The percentage contribution of process parameters is estimated using analysis of variance. The microstructure observation shows that the proper selection of FSP parameters leads to a homogeneous dispersion of the WC particles throughout the matrix, thereby producing a defect-free AA6061/WC nanocomposite without voids. Also, the severe plastic deformation and heat generation during FSP cause the breaking of coarse particles, WC particles, and porous holes and create an ultrafine grain-sized structure via dynamic recrystallization. The results indicated that the microhardness value of the processed composite was found to be 144 VHN, which is 39.81% higher than that of the base metal. Also, the weight loss of all samples decreased as compared to the base metal. Also, it can be observed that the number of passes is the most significant factor for microhardness, with a 40.1% contribution, and for minimum weight loss, the volume fraction is the most significant factor, with a 56.94% contribution. The optimum process parameter combination was found to be 1800 rpm rotation speed, 120 mm/min of transverse feed, 6% volume fraction, and 3 passes that resulted in obtaining optimum values for micro hardness and weight loss. The surface composite developed in this research is considered a suitable material for applications demanding lightweight and enhanced surface properties, including automotive, aerospace, marine, defense, and transportation industries.