## 1 Introduction  
Compared with traditional metal materials, particle-reinforced metal matrix composites (PRAMCs) have more prominent advantages in specific strength, specific stiffness, hardness, high temperature strength, and fatigue strength [1; 2; 3; 4]. In addition, the performance of metal matrix composites can be adjusted according to the performance requirements of products, which is impossible for traditional metal materials [5; 6; 7]. At present, low-volume-fraction SiCp/6061 Al composites have gradually replaced traditional materials and are widely used in the aerospace, automotive, and satellite communications industries [8; 9; 10]. It is of great theoretical significance and engineering value to study the fracture failure behavior of SiCp/6061 Al composites with a low volume fraction. The strength, stiffness, strengthening mechanism, deformation, and fracture behavior of particle-reinforced metal matrix composites are of great significance to meet the harsh service requirements. The finite element method (FEM) based on the RVE model has become a powerful and effective tool to study the deformation and fracture behavior of PRAMCs and to reveal the deformation mechanism and microscopic fracture characteristics [11]. Most research on PRAMCs by finite element simulations has used a simple structural model, in which the particles in the model are treated as spheres, ellipsoids, or regular polyhedrons [12; 13; 14]. However, in practice, the geometry of most PRAMC reinforcement particles is complex, mainly presenting as irregular polyhedrons. [PERSON] et al. [15] pointed out that the simplified particle shape cannot present the angular characteristics of the particles. They proposed a method for establishing a finite element model based on the 2D microstructure observed by a scanning electron microscope (SEM). In this paper, the real microstructure of SiCp/6061 Al composites is integrated into the RVE model, which can further improve the prediction accuracy of the model. At present, the constitutive model of the matrix material in the RVE model is mostly obtained directly from the PRAMC matrix raw material [16; 17; 18; 19; 20], ignoring the influence of the addition of particles on the microstructure and mechanical properties of the matrix (such as the increase in the dislocation density, the decrease in the grain size, etc. ), resulting in the deviation of the prediction results of the RVE model. In order to characterize the mechanical properties of the PRAMC matrix more accurately, the nanoindentation technology was introduced to characterize the mechanical properties of the PRAMC matrix. The indenter of the nanoindentation instrument is in the order of nanometers. When the load is applied to the matrix region of the particle-reinforced composite sample, the influence of the reinforcing particles can be eliminated, so as to accurately characterize the elastoplastic mechanical behavior of the matrix material. [PERSON] et al. [21] tested the mechanical properties of Ti-Al3 Ti core-shell particle-reinforced A356 composites Ti-Al2 Ti/A356 by the nanoindentation technique and carried out an FEM simulation based on the microstructure. [PERSON] et al. used the nanoindentation technique to determine the elastic-plastic properties of the matrix and demonstrated the effect of the particles on the nanoindentation response [22]. [PERSON] et al. [23]. proposed forward and reverse analysis algorithms for nanoindentation technology and obtained the elastoplastic constitutive model of the tested material. In this paper, the elastoplastic properties of the matrix region of SiCp/6061 Al composites were characterized by the method proposed by [PERSON]. In this paper, the elastic-plastic mechanical properties of SiCp/6061 Al composites prepared by powder metallurgy were evaluated by nanoindentation experiments.