Proceedings of SerbiaTrib '13

comparison with the synthetic reinforcements suchas silicon carbide (SiC) and alumina (Al 2 O 3 ) [16].The properties achieved with the sole utilization ofthese cheaper source reinforcements have beenreported to be lower than that of the syntheticreinforced but with promise for use in semistructuraland thermal management applications[17]. The use of hybrid reinforcements utilizingSiC/Al 2 O 3 and agro waste ashes as a means ofimproving the properties of AMCs has attractedinterest recently with very encouraging resultsobtained [18-19].The present work is aimed at investigating theinfluence of the weight ratios of rice husk ash andsilicon carbide on the mechanical behaviourAluminium matrix hybrid composites having variedweight percent of both reinforcements. Themotivation for this work is to establish optimumRHA/SiC weight ratios required to achieveoptimized performance of low cost AMCs developedwith the use of rice husk. Literatures on the use ofsynthetic/agrowaste hybrid reinforcements forAMCs development are still very limited and there iscurrently none that the authors are aware of thatdiscusses the use of RHA and SiC as hybridcomposites in Al-Mg-Si alloy matrix.2. MATERIALS AND METHOD2.1 MaterialsAl-Mg-Si alloy billets with chemicalcomposition determined using spark spectrometricanalysis (Table 1) was selected as Aluminiummatrix for this investigation.Table 1. Elemental composition of Al-Mg-Si alloy.Elementwt%Si 0.4002Fe 0.2201Cu 0.008Mn 0.0109Mg 0.3961Cr 0.0302Zn 0.0202Ti 0.0125Ni 0.0101Sn 0.0021Pb 0.0011Ca 0.0015Cd 0.0003Na 0.0009V 0.0027Al 98.88For the hybrid reinforcing phases, siliconcarbide (SiC) and rice husk ash (RHA) wereselected. The silicon carbide procured was of highchemical purity with average particle size of 28µmwhile rice husks utilized for the processing of ricehusk ash was obtained from Igbemo-Ekiti, EkitiState (a rice producing community in south westernNigeria). Magnesium for improving wettabilitybetween the Al-Mg-Si alloy and the reinforcementswas also procured.2.2 Preparation of Rice Husk AshThe procedure adopted is in accordance withAlaneme et al [16]. It involves the use of a simplemetallic drum with perforations as burner for therice husk. Dry rice husks placed inside the drumwas ignited with the use of charcoal. The husk wasallowed to burn completely and the ashes removed24 hours later. The ash was then heat-treated at atemperature of 650 o C for 180 minutes to reduce itscarbonaceous and volatile constituents. Sieving ofthe bamboo leaf ash was then performed using asieve shaker to obtain ashes with mesh size under50µm. The chemical composition of the rice huskash from this process is presented in Table 2.Table 2. Chemical Composition of the Rice Husk AshCompound/Element (constituent) weight PercentSilica (SiO 2 ) 91.59Carbon, C 4.8Calcium oxide CaO 1.58Magnesium oxide, MgO 0.53Potassium oxide, K 2 O 0.39Haematite, Fe 2 O 3 0.21Sodium, NatraceTitanium oxide, TiO 2 0.202.3 Composites ProductionTwo step stir casting process was utilized toproduce the composites [20]. The process startedwith the determination of the quantities of rice huskash (RHA) and silicon carbide (SiC) required toproduce 5, 7.5, and 10 wt% reinforcementconsisting of RHA and SiC in weight ratios 0:1,1:3, 1:1, 3:1, and 1:0 respectively (which amountsto 0, 25, 50, 75, and 100% RHA in thereinforcement phase). The rice husk ash and siliconcarbide particles were initially preheated separatelyat a temperature of 250 o C to eliminate dampnessand improve wettability with the molten Al-Mg-Sialloy. The Al-Mg-Si alloy billets were charged intoa gas-fired crucible furnace (fitted with atemperature probe), and heated to a temperature of750 o C ± 30 o C (above the liquidus temperature ofthe alloy) to ensure the alloy melts completely. Theliquid alloy was then cooled in the furnace to asemi solid state at a temperature of about 600 o C.The preheated rice husk ash and SiC particles alongwith 0.1 wt% magnesium were then charged into13 th International Conference on Tribology – Serbiatrib’13 161