Proceedings of SerbiaTrib '13

(a)(b)Figure 2. Showing (a) representative SEPhotomicrograph showing the reinforcing particlesdispersed in the Al-Mg-Si matrix; and (b) EDS profile ofthe particle in 2(a) confirming the presence of Al 2 O 3 ,SiO 2 , Fe 2 O 3 , K 2 O, CaO, SiC and Na.(a)3.2 Composite Density and Estimated PercentPorosityThe results of the composite densities andestimated percent porosity are presented in Table 3.It is observed from the results that the estimatedporosity values are not dependent on the weightpercent of the reinforcement phase or the weightratio of RHA to SiC. It is however noted that theestimated porosity levels are less than 4 % whichhas been reported to be the maximum permissiblein cast AMCs [26]. The low porosity levels of thecomposites supports our submission that the twostep stir casting method adopted for producing thecomposites is reliable. As a result of the lowerdensity of RHA (0.31 g/cm 3 ) in comparison to SiC(3.6 g/cm 3 ), it is expected that the density of thecomposites will reduce with increase in the RHAcontent in the composite as observed from Table 3.3.3 Mechanical BehaviourThe variation of tensile strength and yieldstrength of the composites produced is presented inFigure 4. It is observed that there is a generalincrease in tensile strength (Figure 4a) and yieldstrength (Figure 4b) with increase in weight percentof the RHA-SiC hybrid reinforcement. However,for specific weight percents of the hybridcomposites (that is B, C, and D series), it is notedthat the tensile and yield strength decreases withincrease in the weight proportion of RHA in theRHA-SiC reinforcement. For the compositescontaining 5 wt% of the reinforcing phase, it isobserved that 4.9, 8.9, 12.5, and 15.8 % reductionin tensile strength was obtained from thecomposites with weight ratio RHA:SiC of 1:3, 1:1,3:1, and 1:0 (that is containing 25, 50, 75, and 100% RHA) in comparison to the 5 wt% SiC singlereinforced Al matrix composite. For the compositescontaining 7.5 wt% of the reinforcing phase,reductions of 5, 9, 13.4, and 19 % were observedfor the compositions of 1:3, 1:1, 3:1, 1:0 RHA:SiCweight ratios respectively (in comparison with the7.5 wt% SiC single reinforced composite). In thecase of the composites containing 10 wt%reinforcements, reductions of 4, 8.1, 13.2, and 18.3% was observed in comparison to the 10 wt % SiCsingle reinforced Al matrix composite.(b)Figure 3. Showing (a) representative SEPhotomicrograph of some clustered particles dispersed inthe Al-Mg-Si matrix; and (b): EDS profile the particlesidentified in 3(a) confirming the presence of Al 2 O 3 ,SiO 2 , Fe 2 O 3 , SiC, Cao, and Na which are constituentsfrom the RHA-SiC hybrid reinforcement.164 13 th International Conference on Tribology – Serbiatrib’13