Microstructure and Mechanical Properties of Al/MgAl2O4 In Situ Composites Synthesized by Ultrasonic Cavitation

Al–4Mg/MgAl2O4 composites were successfully synthesized by the in situ reaction of Al–4Mg alloy melt and H3BO3 precursor in the presence of ultrasonic cavitation field. Ultrasonic-assisted synthesis facilitated generation of ~ 350-nm-sized MgAl2O4 particles. Enhanced reaction along with dispersion of MgAl2O4 was perceived due to the synergetic effect of ultrasonic cavitation. The presence of MgAl2O4 particles resulted in 3–4 times reduction in matrix alloy grain size, and the grain refinement was further enhanced by ultrasonic treatment. Compared to unreinforced alloy, ultrasonicated Al/MgAl2O4 composite exhibited an improvement in ultimate tensile strength by ~ 30 MPa with ~ 85% of ductility retention. Grain boundary strengthening, Orowan dispersion strengthening, coefficient of thermal expansion mismatch strengthening and load-bearing strengthening were the anticipated mechanism for enhancement in mechanical properties.