The use of composite materials in practical applications can be further enhanced by joining them effectively. In the current research, composites of Al 5083 reinforced with 10% B 4 C were prepared using the stir casting technique and were joined by friction stir welding. The process parameters, i.e. tool revolving speed, welding feed, and vertical plunge force were considered and taken in three levels to analyse their influence on mechanical properties, such as ultimate tensile strength and

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... o hardness. To make a joint, two tools with a square tool pin profile were machined, one coated with titanium nitride (TiN) and the other with diamond like carbon (DLC).Experiments were planned as per Box -Behenken's design which suggested 15 experiments to analyse the output response. A mathematical model was developed for each output response for both the tools and the reliability of the model was confirmed by conducting the ANOVA test. The effect of varying each parameter on output parameters was studied and compared for both tools. Multi objective optimization was done by the firefly algorithm using the MATLAB 2018a software. For the TiN coated tool, maximum tensile strength of 133.92 MPa and Vickers micro hardness value of 102.54 were obtained with the following process parameters: 1540 rpm, 20 mm/min, 6 KN. As far as the DLC tool is concerned, the maximum values obtained are 129.67 MPa and 102.47 with the following parameters: 1360 rpm, 55 mm/min, and 8 KN.