###### Abstract  
In the current study, the effect of different B\({}_{4}\)C additions (0, 2.5, 5, and 10 wt%) on the microstructural, solidification behavior, mechanical, and tribological properties of Al-20%Mg\({}_{2}\)Si composite were studied by means of scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Vickers hardness, tensile, and dry sliding wear tests. The cooling curve thermal analysis (CCTA) approach was utilized to monitor the influence of B\({}_{4}\)C particles on the solidification behavior of Al-20%Mg\({}_{2}\)Si composite. The results revealed that the addition of B\({}_{4}\)C particles up to 10 wt% reduced the nucleation temperature (T\({}_{\rm N}\)) and growth temperature (T\({}_{\rm G}\)) of the primary Mg\({}_{2}\)Si phase. Moreover, the proper amount of B\({}_{4}\)C added to Al-20%Mg\({}_{2}\)Si composite has a significant effect on the microstructural alteration, mechanical, and tribological properties of the composite. The mean size of primary Mg\({}_{2}\)Si in Al-Mg\({}_{2}\)Si composite was 47 \(\upmu\)m, in which with the addition of 5 wt% B\({}_{4}\)C, the particle size decreased to 33 \(\upmu\)m. The highest UTS (217 MPa) and El% (7%) was achieved in Al-20%Mg\({}_{2}\)Si-5%B\({}_{4}\)C hybrid composite. The cast Al-20%Mg\({}_{2}\)Si composite revealed the brittle mode of fracture with some cleavage characterization, in which with the addition of 5%B\({}_{4}\)C, the fracture mode altered to a more ductile fracture. The wear results revealed that the Al-20%Mg\({}_{2}\)Si-5%B\({}_{4}\)C hybrid composite has the highest wear resistance with the lowest wear rate (0.46 mm\({}^{3}\)/Km) and friction coefficient (\(\upmu\) = 0.52) under 20 N applied load compared to other fabricated composites with mild abrasion as the governed wear mechanism. Al hybrid composites; Mg\({}_{2}\)Si; B\({}_{4}\)C; microstructure; thermal analysis; mechanical properties; wear behavior +
Footnote †: journal: Applied Sciences  
physical and mechanical properties of the Mg\({}_{2}\)Si phase, Al-Mg\({}_{2}\)Si or Mg-Mg\({}_{2}\)Si composites are desirable candidate materials for aerospace, automobile, and other applications [2]. Nevertheless, owing to low temperature brittleness, machinability, and insufficient wear resistance, the application of Al-Mg\({}_{2}\)Si composite is limited. Among the various ceramic particles, boron carbide (B\({}_{4}\)C) particles are one of the most promising reinforcement particles as it exhibits unique physical and mechanical properties such as light-weight arm plates for its ballistic properties, wear-resistant components because of its tribological properties, and as abrasive grit. In addition, boron carbide can also be used as a neutron absorber in nuclear reactors due to the nuclear characteristics associated with its high boron content [3; 4]. It has bulk modulus of about 214.8-247 MPa [5; 6], low thermal conductivity of 30-42 mK, low density (2.52 g cm\({}^{-3}\)), high hardness 2900-3580 kg/mm\({}^{2}\) and low CTE of 3.2\(\cdot\)10\({}^{-6}\)\({}^{\circ}\)C\({}^{-1}\)[7; 8]. Good chemical stability and bonding characteristics with Al alloys are other reported features of B\({}_{4}\)C particles [3]. Hence, the B\({}_{4}\)C particles are often used to reinforce Al alloys to fabricate MMCs. [PERSON] et al. [9] identified the influence of B\({}_{4}\)C on the mechanical and tribological behavior of Al 7075 composites. They found increasing hardness of composites compared with the base alloy because of the presence of the increased ceramic phase. The wear resistance of the composites increased with increasing content of B\({}_{4}\)C particles, and the wear rate was significantly less for the composite material compared to the matrix alloy. In another study, [PERSON] et al. [10] studied the influence of heat treatment on tensile properties and wear behavior of A356-10%B\({}_{4}\)C composite.