The effect of process parameters on metallurgical properties of friction stir welded aluminium alloy 6063-O was analysed in the present study. Samples were friction stir welded under tool rotational speed of 600, 800 and 1200 rpm and traversing speed of 0.6, 0.9 and 1.2 mm sec-1, with an axial load of 8000 kg constant for all trials and the process parameters were optimized by using Taguchi orthogonal array. Optical microstructure analysis were carried out to define the metallurgical properties at various zones of friction stir welded samples (Unaffected Base Material, Heat Affected Zone, Thermo Mechanically Affected Zone and Weld Nugget Zone) and scanning electron microscopy analysis (SEM) was carried out to determine the material flow path at the heat affected zone (HAZ) and weld nugget zone (WN) of friction stir welded samples. In present work two sets of experiments were carried out on AA 6063-O one with silicon carbide powder and without silicon carbide powder. Tool used for the FSW process is high carbon steel D3 (Heat treated 58-60 HRC), the SiC powders were inserted along the breadth of the plates by making a drill of 1 mm to a depth of 15 mm. Micro hardness survey was done across the weld regions using vickers hardness test. Correlation of micro hardness tests and metallurgical properties of the friction stir weldments were studied by optical microscope analysis, scanning electron microscopy analysis and the samples were chosen for (SEM) using grey relational analysis (GRA). It was observed that the sample 9 with SiC powders, welded with a traverse speed of 1.2 mm sec-1, tool speed of 1200 rpm and axial load of 8000 Kg showed the best behavior.