In this study, the novel composites were fabricated by the introduction of Mg-0.3Sr-0.3Ca alloy as the matrix and addition of different amounts of graphene nanoplatelets (0.1, 0.2, and 0.4 wt.%) as reinforcement using a stir casting technique followed by homogenization and extrusion in order to improve the mechanical properties of the base alloy. Optimum weight percent of adding graphene nanoplatelets was 0.2 wt.%. The addition of 0.2 wt.% graphene nanoplatelets in the extruded Mg–Sr–Ca alloy led to the grain refinement (∼36%), the decrease of anisotropy (∼14%) and the lowest twin formation. Moreover, the tensile and compressive yield strengths and tensile and compressive fracture strains of extruded Mg-0.3Sr-0.3Ca/0.2GNP composite were enhanced by 22.8%, 66.7%, 43.1% and 28%, respectively. The load transfer was significant strengthening mechanism. The uniform dispersion of graphene nanoplatelets followed by the increase of non-basal slip and grain refinement improved tensile fracture strain. In addition to maintained factors, the increase of compressive fracture strain in the extruded Mg-0.3Sr-0.3Ca/0.2GNP composite was affected by local stresses caused by twins which resulted non-basal slip and conserved basal slip due to presence of twins. Simultaneously, enhancement of the strengthening and elongation efficiencies in both tensile and compressive tests was achieved in Mg-0.3Ca-0.3Sr/0.2GNP. The biocorrosion behavior of extruded Mg-0.3Sr-0.3Ca/0.2GNP composite was promoted by 11% compared with Mg-0.3Sr-0.3Ca alloy. Comparative plots indicated that the fabricated materials can be introduced as a new class of composites for the purpose of structural as well as biomedical applications.

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