Comparative study of microstructural evolution and mechanical properties in friction stir processed, reinforced friction stir processed, and heat-treated reinforced friction stir processed Al composites

The development of friction stir welding (FSW) created the basic foundation for friction stir processing (FSP). This process entails refining the local microstructure and achieving the localised plastic deformation due to the stirring effect of the tool, which may involve adding additional filler material as required. The rotating tool involved in the process has a shoulder and pin responsible for heat generation for plastic deformation and localised mixing. The rotating tool is inserted and traversed on the desired surface, tailoring the material properties. The tool’s exposure to the surface causes localised plastic deformation and thermal gradient, and microstructural changes occur locally. The present investigation uses Friction Stir Processing (FSP) to fabricate an aluminium metal matrix composite. Recently, the use of aluminium alloy has been replaced by composites because of their increased mechanical and physical properties (specific properties). The experiment leads to manufacturing an aluminium metal matrix composite using aluminium oxide, boron carbide and commercially pure copper dust. Later, the effect of heat treatment on the respective metal matrix composite is studied. A comparative study among three different types of FSP techniques viz. FSP, Reinforced FSP, and Heat-treated Reinforced FSP have been performed. The tool revolution speed (RPM) and tool traverse speed of 400 RPM and 10 mm/min had been implemented, respectively. The T4 Heat-Treatment cycle was used during the current investigation. This investigative study was performed to analyse the changes in grain sizes and hardness values at the stir zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and on the base materials (BM) of the samples. The reinforced FSP metal matrix composite (MMC) showed an 81.26% increase in the micro-hardness value (HV) compared to the base metal. Further on analysing the microstructures, the reinforced FSP composite showed a 65.20% reduction in grain size. Moreover, the Heat-Treated sample showed an increase in the micro-hardness value by 99.8%.