###### Abstract
They claimed that in Al-B\({}_{4}\)C composite, T6 treatment was a dominant factor on the hardness improvement in comparison with hardness increasing due to the addition of B\({}_{4}\)C hard particles. In addition, heat treatment process results in higher strength and wear properties of heat-treated metal matrix composites in comparison with an untreated state. [PERSON] et al. [11] investigated the effect of a novel ultrasonic assisted stir casting on mechanical properties of AA6061-B\({}_{4}\)C composites. Based on their findings, individual B\({}_{4}\)C distribution and the refinement of microstructure was achieved at 4 wt% B\({}_{4}\)C. The improved specific ultimate and compressive strengths at 4 wt% B\({}_{4}\)C were observed as 36.32% and 43.92%, whereas specific Vicker's and Brinell hardness as 53.41% and 50.89% respectively. A hybrid composite contains two or more reinforcement materials; in which each of the reinforcements deliver superior properties in the composite. As a result, unique mechanical, physical, and tribological properties exist in the hybrid composites, which are not attainable in other materials. Stir casting is implemented to produce the ex-situ (hybrid) aluminium MMCs due to their simplicity and lower cost compared to other fabrication processes [12]. [PERSON] et al. [13] reported that with the addition of 10 wt% SiC particles to Al-20%Mg\({}_{2}\)Si composite, the morphology of primary Mg\({}_{2}\)Si was altered to polygonal and its size decreased to 30 \(\upmu\)m. Similarly, [PERSON] et al. [14] reported that when the Al-15%Mg\({}_{2}\)Si composite was added with 6 wt% YSZ, the mean size of primary Mg\({}_{2}\)Si reduced to 72.4 \(\upmu\)m with subsequent improvement in tensile properties of the composite. [PERSON] et al. [15] examined the effect of SiC and B\({}_{4}\)C particulates-reinforced composite on Al6061 matrix. It was observed that hybrid metal matrix composites (HMMCs) showed a high level of hardness as compared to alloy because silicon carbide and boron carbide particles were uniformly embedded in the Al6061 matrix. [PERSON] et al. [16] studied the heat treatment and wear properties of Al\({}_{2}\)O\({}_{3}\) and TiC particulates in reinforced Al6063 hybrid composites. The hardness of the composites was improved after heat treatment due to the presence of reinforcements in the composite, which accelerated the aging kinetics and caused an increase in dislocation density at the surrounding area of the reinforcement particles. [PERSON] et al. [17] studied the effects of reinforcement with SiC and E-glass fibers on the wear properties of Al6061 hybrid composites. Due to the presence of both hard reinforcements and coherent precipitates in the matrix, increased hardness was observed during aging treatment. [PERSON] et al. [18] studied the effect of stir casting processing method to prepare Al6061-SiC-Al\({}_{2}\)O\({}_{3}\) hybrid composites. It was observed that by adding reinforcement particles to the alloy matrix, micro-hardness increases with increased reinforcement due to solid solution hardening of the matrix. [PERSON] et al. [19] evaluated the tensile behavior and microstructure of Al\({}_{2}\)O\({}_{3}\)/SiCp-reinforced AMMCs fabricated by the stir casting technique. Strength of the hybrid composite was higher than the unreinforced alloy. The significant enhancement in tensile strength of the composites was attributed to the grain and particle size, reinforcement shape, and uniform particle distribution in the alloy matrix. [PERSON] et al. [20] focused on the tribological behavior of novel hybrid composite materials by varying SiC reinforcements and a fixed percentage of B\({}_{4}\)C particles. It was observed that the increase in hardness of the composite was mainly owed to the existence of harder SiC and B\({}_{4}\)C particles in the matrix alloy, which act as obstacles to the dislocation motion. [PERSON] et al. [21] examined the metallography and bulk hardness of artificially aged Al6061-B\({}_{4}\)C-SiC stir cast hybrid composites.