FABRICATION AND TRIBOLOGY OF FRICTION STIR PROCESSED Al ALLOY SURFACE COMPOSITES

Abstract

Friction stir processing (FSP) is recently identified as a potential technique in fabrication of surface composites. It needs to be recognized that microstructural characteristics and mechanical behavior of aluminum alloy bulk composites prepared by conventional technique are well reported, whereas systematic study on the effect of FSP parameters on microstructure and tribological performance of surface composites of aluminium alloys is not available. In the present work, surface composites of SiC, TiC, Al2O3, graphite or Sn particles reinforced AA2014, LM24 or AA5083 alloys were fabricated by FSP. The influence of FSP parameters was studied on microstructure, hardness and tensile behavior of surface composites. The tribological performance of the FSPed surface composites against steel ball was studied using a ball-on-disc tribometer in unlubricated sliding conditions. First, the effect of multi-pass on microstructure and mechanical characteristics of AA2014 alloy was studied. Further, critical analysis of the addition of SiC or TiC particles in multi-pass FSPed AA2014 surface was done to study the influence on microstructure and mechanical behavior. In the second set of experiments, processing strategies like multi-pass, change in rotational speed or traverse speed, tool offset and dual tool probe were examined in fabricating defect free SiC/AA5083 surface composites with uniform distribution of reinforcement particles. The microstructure, hardness and tensile behavior were related for the surface composites prepared with each strategy. The influence of the addition of low melting point metal tin in graphite/LM24 alloy surface composite was investigated in third set of experiments. The heat input conditions in FSP were changed by manipulating rotational speed. The synergetic effect of rotational speed, tin addition and sliding load on the friction and wear characteristics of graphite/LM24 alloy surface composites was investigated. In the last set, the tribological performance of FSPed Al2O3/AA5083 surface composites was estimated as function of hardness of the counterbody steel ball and sliding load. Further, the dominant mechanisms of material removal in third and fourth sets of experiments were studied and correlated with FSP parameters, reinforcement or sliding test conditions.