Influence of heat treatment on the microstructure, mechanical and tribological performances of particle reinforced aluminum matrix surface composite fabricated through friction stir processing

In this investigation, TiC reinforcements were incorporated into Al-Zn-Mg-Cu alloy by integrating reverse engineering and geometry reconstruction technique with a surface composite being developed through the recursive method of friction stir processing (FSP). The fabricated composite was further subjected to T6 and RRA heat treatments and its microstructural changes, mechanical and tribological properties examined. Microstructural studies revealed the formation of well refined equiaxed grain structure with a reduced average grain size of 2.40 mu m for the FSPed composite and 2.90 and 3.03 mu m for T6 and RRA heat treated composites, indicating that grain growth and recrystallization were inhibited effectively by the presence of uniformly dispersed TiC particles during FSP and heat treatments. Improved distribution of hardness with an average of 208.64 HV was observed for the FSPed composite. After T6 and RRA treatments, average hardness was enhanced to 244.29 and 230.26 HV due to the additional strengthening caused by the precipitates. Tribological investigations revealed better wear resistance for the heat treated composites compared to the as-FSPed composite. The presence of a hardened surface with TiC rich tribo-layer and finely distributed precipitates stifled the extent of plastic deformation and improved wear resistance.