Microstructural characterization, hardness and impact behavior of AA7075/steel slag surface composites fabricated through multipass friction stir process

Abstract

Aluminium-based Surface Composites (SCs) fabricated through Friction Stir Process (FSP) with excellent hardness and impact strength are predominantly suited for piston skirt applications. This paves the way for the exploration of multipass effects in steel slag-reinforced AA7075 SCs for analysis of microstructure, hardness and impact strength. Microstructural examination reveals the homogenous distribution of steel slag particulates on the matrix and on increasing the number of FSP passes, the grain size is reduced. Furthermore, a clear interface is obtained between the reinforcements and base AA7075 matrix identified through the macrostructure. X-Ray Diffraction technique (XRD) and Elemental mapping with Energy Dispersive Spectroscopy (EDS) confirm the existence and dispersion of reinforcing constituents available in the composite layer. The superior microhardness along with prodigious impact strength are accomplished in the third pass. The obtained hardness results are attributed to the reduced grain size with decreased oxide content. The enhanced tendency of the reinforcements to blockade the crack initiation and its propagation results in high-impact strength. In addition, the fractography of impact testing specimens is evaluated through SEM and reveals that the ductile mechanism is a dominant failure mode.