## 3 Results and Discussion
### Wear Behavior  
Figure 14 demonstrates that the wear rate of Al-20%Mg\({}_{2}\)Si composites correspond to different B\({}_{4}\)C additions under the applied loads of 20 and 40 N. As seen, with the addition of 5 wt% B\({}_{4}\)C, the wear resistance increased when the wear rate of Al-20%Mg\({}_{2}\)Si composites decreased from 0.85 mm\({}^{3}\)/km to 0.46 mm\({}^{3}\)/km under 20N applied load. This improvement was the result of the load bearing capacity of the composites by ceramic particles during sliding. This was similar to the results reported by [43] in Mg-TiO\({}_{2}\) magnesium matrix composite, where, the addition of 5 wt% TiO\({}_{2}\) into the Mg matrix improved the wear resistance of the composite. The enhancement in wear resistance could be associated with the increase in hardness, in which the hardness of the Al-20%Mg\({}_{2}\)Si composites with the addition of 5 wt% B\({}_{4}\)C increased to 100 HV (Figure 11). The connection between hardness and wear rate can be explained by Archard's law, which describes an inverse proportionality between hardness and the wear rate of a material [44]. Another reason for the decrease in the wear rate of the composite is due to the partial refinement of primary Mg\({}_{2}\)Si particles, as shown in Figures 3 and 4. It was expected that during the wear test, the wear rate of the hybrid composite with a finer Mg\({}_{2}\)Si size decreases because grain boundary strengthening occurs with smaller particle size, leading to strain hardening [45]. With the addition of 10 wt% B\({}_{4}\)C to the Al-20%Mg\({}_{2}\)Si composites, the wear resistant was supposed to increase; however, as seen in Figure 14, the wear rate increased to 0.73 mm\({}^{3}\)/km, causing the increase in material removal. The high wear rate of Al-20%Mg\({}_{2}\)Si-10%B\({}_{4}\)C hybrid composite was due to the agglomeration of the B\({}_{4}\)C particles in the matrix (Figure 3d), which resulted in the 'three-body' wear during sliding and increment of the composite's wear rate. Additionally, due to the fragile bonding between the matrix and B\({}_{4}\)C in the agglomerated regions, the B\({}_{4}\)C particles were unable to support the applied load efficiently. Therefore, the interface offered a site for crack nucleation and tended to pull out the particles from the wear surface, which led to the formation and propagation of crack in the subsurface wear region [46]. In addition, as mentioned before in Figure 4, increasing the content of B\({}_{4}\)C to 10 wt%, decreased the density of primary Mg\({}_{2}\)Si particles. As a result, the load bearing effect of the hybrid composite reduced and during  
Figure 14: Wear rate of Al-Mg\({}_{2}\)Si composite reinforced with different amount of B\({}_{4}\)C particles under applied loads of 20 and 40 N.  
the wear rate the soft Al matrix was subjected to the asperities of the steel disc which led to an increase in the wear rate. Figure 14 also illustrates the increased wear rate when the applied load is increased from 20N to 40N. This is expected as the number of contact asperities and the separation of surface asperities increased at the higher loads. Increasing the applied load also contributed to the accumulation of wear debris in the space between the pin and disc that led to a more serious abrasive wear, increasing the wear rate. The coefficient of friction (COF) of the Al-20%Mg\({}_{2}\)Si composites added with various content of B\({}_{4}\)C for the applied loads of 20 and 40 N is depicted in Figure 15. As seen, similar to the trend of wear rate, under the applied load of 20N, the COF (\(\upmu\)) of the Al-20%Mg\({}_{2}\)Si composite decreased from 0.46 in the base Al-20%Mg\({}_{2}\)Si composite to 0.43 and 0.39 when the composite was treated with 2.5 and 5 wt% B\({}_{4}\)C respectively. Hence, Al-20%Mg\({}_{2}\)Si-5%B\({}_{4}\)C hybrid composite has the lowest COF compared to other fabricated composites.