Microstructure and Mechanical Properties of Hypo- and Hypereutectic Cast Mg/Mg₂Si Composites

In this paper, the microstructure and mechanical properties of two magnesium matrix composites-a hypoeutectic with 1.9 wt% Mg₂Si phase and a hypereutectic with 19 wt% Mg₂Si compound-were analyzed. The investigated materials were prepared using the gravity casting method. Microstructure analyses of the fabricated composites were carried out by XRD and light microscopy. The tensile and compression strength as well as yield strength of the composites were examined in both uniaxial tensile and compression tests. The microstructure of the hypoeutectic composite was in agreement with the phase diagram and composed of primary Mg dendrites and an Mg-Mg₂Si eutectic mixture. For the hypereutectic composite, besides the primary Mg₂Si phase and eutectic mixture, additional magnesium dendrites surrounding the Mg₂Si compound were observed due to nonequilibrium solidification conditions. The composites exhibited a rise in the examined mechanical properties with an increase in the Mg₂Si weight fraction and also a higher tensile and compression strength in comparison to the pure magnesium matrix (cast in the same conditions). Additionally, analyses of fracture surfaces of the composites carried out using scanning electron microscopy (SEM + EDX) are presented.