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Abstract : The present works describes the mechanical properties of Al 7075 metal matrix composites reinforced with Si3N4. Si3N4 particles of size 325 mesh were taken as the reinforcement material to prepare the metal matrix composites by using stir casting technique. The percentage of reinforcement varied from 0 to 12% wt in steps of 3%. Mechanical characterization such as tensile strength hardness test, density tests were conducted as per ASTM standards. Experiment results reveal that there is an improvement in Ultimate tensile strength and hardness properties with the increase in the weight percentage of reinforcement. Optical microscopy technique was used to examine microstructures of the sample specimens and the microstructure revealed uniform distribution, of particles and presence of reinforcements in the matrix phase. A fractured surface on the tensile test specimen was investigated to determine the fracture mechanism by using scanning electron microscope. Experimental studies invoke that the 12%wt of Si3N4 increases the tensile strength by 7% and hardness values by 8% compared with that of as cast Al7075. Results also evident that there was a decrease in ductility and percentage of elongation with the increase in the percentage reinforcement. © TJPRC Pvt. Ltd./p