Preparation and characterization of Al-SiCp nanocomposites developed by stir casting

Abstract

Al-6061 alloy is mostly used for automobile parts because of its good corrosion behavior and high stiffness. However, it has poor wear resistance which limits its wide applications. Metal matrix composite (MMC) in which hard ceramic particles such as SiC is dispersed leads to an improvement in wear resistance and stiffness but in the expense of its ductility. Major problem of making the MMC is the uniform distribution of the ceramic particles. In the present study, an attempt has been made to distribute SiC particles uniformly within the matrix by stirring casting and further modified by friction stir processing (FSP) and achieving enhanced property. FSP is a novel technique and can be useful to distribute SiC particles along with the refinement of matrix grains. Thus, mechanical properties could be improved by 2 ways: due to ceramic reinforcement and grain size refinement. In this work, Al 6061 alloy matrix composites (AMCs) reinforced with 2 wt. % SiC particles of (microsize 20-160 μm) and (nanosize 30-80 nm) was prepared using casting via stir casting technique. The FSP was conducted at a speed of 720rpm using a tool of cylindrical pin in two condition first in normal air cooling with traverse speed of 20 mm/min and second in forced air cooling with fan and traverse speed 30 mm/min to lower its processing temperature to the minimum possible value. The microstructure and mechanical properties (hardness, tensile strength, and wear resistance) were compared for the both micro and nanocomposites, with and without FSP. The characterization was carried out using X-ray diffraction (XRD), optical and scanning electron microscopy. After FSP of the composite, it was observed that mechanical properties was improved due to homogeneous distribution of SiC particles and grain refinement of the alloy matrix. Significant improvement in the ductility was also measured after FSP as compared to that of the cast composite. Nano reinforces ceramic gives better property than micro-reinforced after FSP but at the same time nano reinforce composite gives very inferior property before FSP due to the high amount of porosity and inhomogeneity present in the material due to the large surface area to weight ratio of nano particle, which was verified by Archimedes principal. The influence of porosity had been observed in wear rate also wear rate of nanocomposite is found to be more than that of micro reinforcement, but after FSP the significant removal of defects, porosity and homogeneous distribution the strength, ductility and hardness had been recovered. Which shows the effectiveness of the FSP in nanocomposite.