The aim of this study is to investigate the mechanical effect of graphene nanoparticles and boron carbide microparticles together on Al-17Si alloy. For this purpose, graphene nanoparticles were firstly attached to boron carbide surfaces by semi-powder method. The Al-17Si alloy was then infiltrated into these particles. Systematic characterization of produced composites, microstructure investigations, strengthening mechanisms were investigated respectively. The composites were systematically characterized by XRD, DSC, SEM and TEM. Their mechanical strength was determined experimentally by compression test. In addition, the contribution of these reinforcements to strength by using some models has been calculated theoretically and the results have been associated with the microstructure. According to these results, the yield strength of pure matrix was increased from 185 MPa to 547 MPa by increasing 195% with the reinforcement of 0.5 vol% GNPs thorn B4C at most. This result is also the case where the theoretical and experimental are the most compatible. In this case, it is thought that load transfer mechanism and dislocations make the most positive contribution while porosity makes the most negative effect. (C) 2019 Elsevier B.V. All rights reserved.