Microstructural and mechanical properties of in-situ ZrB2/Al7068 nanocomposites synthesized by ultrasonic-assisted stir casting technique

The focus of this study is the investigation of the microstructural and mechanical properties of in-situ (0-9wt%) ZrB2/Al7068 nanocomposites synthesized by ultrasonic-assisted stir casting technique. The optimized reaction time of 30 minutes resulted in ZrB2 with a mean size of 46 nm. The combined mixing by mechanical stirring for 25 minutes and ultrasonic vibration for 5 minutes indicated an even distribution at the lower ZrB2 fraction (<= 2wt%), whereas interdendritic became prominent with a higher ZrB2 fraction. The addition of ZrB2 increased the tensile strength upto 2wt% nanocomposite (328 MPa), followed by gradual decrement with further addition of ZrB2. Interestingly, a continuous increment in total elongation is observed with increasing ZrB2 in the matrix. Grain refinement is observed in all the nanocomposites compared to the base alloy, but the least grain size (87 mu m) obtained for the 2wt% ZrB2 nanocomposite. The lower weight fraction of ZrB2 (1wt% and 2wt%) indicated a uniform distribution of reinforcement particles in the matrix, and higher ZrB2 addition indicated particle agglomeration.