Wear Analysis of Friction Stir Processed AA7075-SiC-Graphite Hybrid Surface Composites

Abstract

High specific strength and superior corrosion resistance are two key characteristics of the aerospace grade AA7075-T6 alloy. However, the surface behavior of AA7075-T6 is found to be deprived, because of its behavior of being prone to fretting fatigue and adhesive wear under dry sliding conditions. Thus, surface wear behavior improvement with the retention of the microhardness of the alloy is required for increasing its wider application. For this, surface isomorphous precipitates and the soft matrix need to be protected through dispersion of hard thermally stable ceramic SiC with solid-lubricant graphite particles. The dispersion through friction stir processing (FSP) avoids detrimental phase formations by processing the metal alloy below its melting point temperature. Thus, dispersion of SiC-Graphite inside the AA7075-T6 using FSP is the focal point of the study. The low and high wear rate samples have been analyzed using SEM imaging and elemental analysis through XRD and EDS mapping. In this study, reinforcing the SiC-Gr particles greatly improved the wear behavior of the AA7075 alloy. Wear resistance has been controlled by combining soft solid lubricant Gr particles with load-bearing hard SiC nanoparticles. In dry sliding action, the base alloy matrix was severely exposed to wear, but the hard SiC nanoparticles served as load-bearing asperities and improved the wear resistance. Simultaneously, the graphite layers generated the soft solid lubricating tribofilm further to reduce the wear and friction between mating surfaces. The wear mechanisms have changed prominently from adhesion to abrasion and delamination through reinforcing the SiC-Gr reinforcements. The graphite content in a hybrid ratio with SiC hard particles was found to have improved the wear resistance by 78%. The tendency of fatigue was more effectively improved in surface composites as compared to the base alloy.