Issue 71

K. Annapoorna et alii, Frattura ed Integrità Strutturale, 71 (2025) 285-301; DOI: 10.3221/IGF-ESIS.71.21

Figure 5: SEM image of ZrO 2 .

Figure 6: EDS Spectrum of ZrO 2 .

Fabrication Procedure: The proposed hybrid nano composite is produced using Al6061 Alloy having chemical composition as shown in Tab. 1. Nano alumina (n Al 2 O 3 ) and nano zirconia (n-Zro 2 ) having average particle size of 50-90nm were used as reinforcement. The fabrication of the composite material Al6061/Al 2 O 3 /ZrO 2 of variable weight percentage (0.5, 0.75, 1 and 1.25 wt% Al 2 O 3 and 0.5, 0.75, 1 and 1.25 wt% ZrO 2 ) was carried out by using ultrasonic assisted stir casting technique. Fig. 7 shows stir casting experimental setup (make: Swamequip) used in fabricating hybrid MMC. It consists of electrical induction furnace, Crucible, stirring set up, Thermocouples, Weighing scale, Digital timer and an ultrasonic vibrator.

Figure 7: Stir Casting Machine.

Figure 8: Stirring of Molten Metal.

Al6061 ingots were placed inside the induction furnace and melted until it reached the desired molten state at the temperature 750 degree Celsius; once this temperature was attained, solid hexachloroethane was incorporated in the melt for effective degassing. Preheated nano ZrO 2 (0.50, 0.75, 1.00 and 1.25 wt%) and nano Al 2 O 3 (0.50, 0.75, 1.00 & 1.25 wt%) particles at 250°C were introduced in the vortex of the liquefied alloy. The reinforcement was preheated to eliminate any moisture and ensure uniform dispersion during stirring. Stirring was done by mechanical means at speed 500 RPM for a stirring time 10 minutes to form a vortex and disperse the nanoparticles in the melt. The combining of nanoparticles is challenging with traditional mechanical rotary impellers due to the high surface area-to-volume ratio of the nanoparticles and the tendency for clustering prior to integration into molten liquid, attributable to the inadequate wetting properties of ultrafine particles with dense liquids. To mitigate this limitation, an ultrasonic-assisted stirring approach is employed to promote the dispersion of ceramic nanoparticles by disrupting agglomerations and submicron clusters, hence improving wettability. This process occurs at a liquidus temperature over 750 °C, which improves the fluidity of the molten liquid and boosts the wettability of nanoparticles to the matrix, as well as the flow ability of the molten metal, with increasing temperature [21]. Following 10 minutes of mechanical stirring, an ultrasonic vibrator (Probe) was employed to disperse the ceramic nanoparticles inside the metal pool for uniform mixing. The probe is positioned at three-quarters of the liquid's depth and permitted to vibrate. These vibrations generate high-energy waves, resulting in numerous cavitation bubbles within the molten pool. The cavitation bubbles exhibit elevated temperature and pressure, which detonate within microseconds due to pressure differentials, fragmenting clusters and uniformly dispersing the agitated nanoparticles throughout the liquid metal. The molten material was thereafter put into the preheated (400°C)

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