Optimization and effect of B4C/Al2O3 with graphite particulates on tribological properties of Al7075 surface hybrid nanocomposite

Abstract

Aluminium alloy surface hybrid nanocomposite, reinforced with boron carbide (B4C), aluminium oxide (Al2O3), and Graphite (Gr) at different combination mixtures by weight ratio have been fabricated on Al7075-T6 aluminium plate by employing friction stir processing (FSP). The mixtures of definite proportions were packed in an array of blind holes 2.5 mm in diameter and 3 mm deep which are 6 mm apart from each other. FSP was done with processing factors of 750 rpm revolving speed, 20 mm min−1 feed, and tool angle of 3°. The prepared hybrid composites were sectioned for microstructure, macrostructure, wear, and hardness evaluation. In the metal matrix surface composite, the scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM) depict the homogeneity in the distribution of reinforcement elements, microstructure, and wear behaviour. Under dry sliding conditions, the nanocomposite’s wear behaviour was investigated by adopting a central composite design (CCD) at 3 levels in response surface methodology (RSM) for optimization. The wear characteristics are analyzed using pin on disc apparatus. The wear property of the nanocomposites with distinct reinforcement ratios was evaluated. Higher hardness values (maximum of 191 Hv) were found in hybrid nanocomposite samples than in the plain FSPed samples (149Hv) without reinforcement. It is evident, that the wear loss depends on the relative weight ratio of B4C and Al2O3 with a constant amount of graphite and the minimum wear loss of 2.9421 mm3 is obtained from composite with 30 B4C + 60 Al2O3+10 Gr reinforcement ratio than the wear loss of 8.2292 mm3 obtained from plain FSPed composite. The optimal combination of parameters, Al2O3 60%, load 20 N, and velocity 1 m s−1 was identified from RSM. The hybrid nanocomposite having a reinforcement mixture of 30 B4C + 60 Al2O3 + 10 Gr exhibits a significant wear resistance than other combination ratios. This is endorsed by the enhancement in binding strength of the matrix and the pinning effect of hard reinforcements, which act against the applied shear force.