Effect of hybrid nano particle reinforcements on fractographic, mechanical and wear behavior of Al6061 alloy composites manufactured by ultrasonic assisted stir casting technique

Composites are the most promising materials of recent interest because they can fulfill the increasing demands of contemporary technology and surpass the constraints of traditional monolithic materials in achieving good combinations of strength, toughness, and density, among other properties. Ecologically friendly nano- composites present novel economic and technological opportunities for the aerospace, automotive, electronics, and biotechnology industries [1-4]. Hard ceramic particles are introduced into the matrix of MMCs to improve their mechanical characteristics and wear resistance. Discontinuous reinforcement is used to strengthen aluminum MMCs, improving their mechanical and physical properties. Metal matrix composites outperform pure alloys in terms of specific strength, modulus, damping capacity, and wear resistance [5-7]. Therefore, ongoing attempts are made to create novel composites and improve those that already exist in order to obtain the needed qualities for specific applications.
Reason being, its great strength, low weight, and resistance to corrosion, Al6061 is most popular alloy used in a various applications, including defense, automotive, and marine. Aluminum alloys are soft and offer less resistance to wear, which limits their usefulness. When hard ceramic reinforcement particles are added to aluminium and its alloys, they make a matrix composite that is strengthened in places and has almost uniform properties [8]. Zirconia has many unique qualities that make it stand out from other ceramics. It has good mechanical strength because it is very tough, great resistance to crack spreading, good thermal resistance, and low thermal conductivity at high temperatures [9]. International interest in
the production of hybrid metal matrix composites (HMMCs) is rising. The combined qualities of its reinforcements are present in HMMCs, which also have better mechanical and tribological qualities. Based on this, it looks like mixing a ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ matrix with a hard nanostructure material like ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ will make a great composite reinforcement and make the composite's mechanical qualities better [10]. Various casting techniques, including squeeze casting, stir casting, spray atomization casting, powder metallurgy, and plasma spraying can be used to create HMMC [11, 12]. One of the common production technique used to fabricate metal matrix composites is stir casting, which is presently used in commercial applications and is considered as a particularly promising approach. Stir casting is a great way to make aluminium alloy metal matrix composites with discontinuous reinforcement because the matrix and reinforcement pieces stick together very well, it's easy to make, and it doesn't cost much [7]. The uneven distribution of the particulate is the main issue with this process due to poor wettability and gravity-regulated segregation. Yong Yang et al. [13] and G.I. Eskin et al. [14] devised a novel technique that integrates the solidification process with ultrasonic cavitation to achieve uniform dispersion and distribution of nanoparticles in aluminium matrix nano composites.
Huda A et al. [15] examined the mechanical and wear characteristics of AA7075 aluminium matrix composites reinforced with ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ nanoparticles by incorporating $0,1,3$$0,1,3$0,1,30,1,3$0,1,3$, and $5\mathrm{\%}$$5\mathrm{\%}$5%5 \%$5\mathrm{\%}$ of ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ nanoparticles, concluding Investigating the tribological properties of nano-sized ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ ceramic particles in automobile lubricants, A D Toth et al.[16] Incorporating ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ nano ceramic powder as a lubricant additive, a tribometer was used to evaluate the tribological performance of the samples and find an ideal concentration of 0.4 weight percent. The mechanical properties of aluminium alloy reinforced with silicon carbide nanoparticles were explored by Pradeep et al. [17] and they found that incorporation of nanoparticle reinforcement improved compressive strength, yield strength, tensile strength, and hardness.
According to the literature review, various studies have been published on aluminium alloy metal matrix composites with nanoparticle reinforcement; nevertheless, there is a paucity of research on hybrid nanoparticle reinforcement. Current study aims to produce an aluminium metal matrix composite utilizing alumina and zirconia as reinforcements to create a novel material and examine the impact of nano-reinforcement on the mechanical and wear properties of the resultant composite. Stir casting is a widely acknowledged and economically viable technique for the mass production of MMCs. Ultrasonic-assisted stir casting is a technique that enhances matrix particle adhesion, regulates matrix structure, and reduces production costs [19-20]. Aluminum-based composites are regarded as viable substitutes for steel or aluminium alloys in numerous contemporary applications. In this epoch, novel formulations and property assessments are requisite. This study examines the influence of nano hybrid reinforcement on the mechanical and wears properties of Al 6061 hybrid metal matrix composites.

In the current work, Al 6061 aluminium alloy functioned as the matrix and was augmented with nano ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ and nano ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$. Supplier Name: Nano Research Lab The raw material was analyzed with Energy Dispersive X-ray Analysis equipment (EDAX) to confirm its chemical makeup. Tab. 1 delineates the constituent composition of the Al6061 alloy, whereas the SEM and EDAX plot reveals peaks corresponding to the base alloy, ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$, and ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$, as illustrated in Fig. (1-6) respectively.

Table 1: Elemental composition of Al6061 alloy.

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Figure 5: SEM image of ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$.

Figure 6: EDS Spectrum of ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$.

The proposed hybrid nano composite is produced using Al6061 Alloy having chemical composition as shown in Tab. 1. Nano alumina ( $\mathrm{n}{\mathrm{Al}}_2{\mathrm{O}}_3$$\mathrm{n}{\mathrm{Al}}_2{\mathrm{O}}_3$nAl_(2)O_(3)\mathrm{n} \mathrm{Al}_{2} \mathrm{O}_{3}$\mathrm{n}{\mathrm{Al}}_2{\mathrm{O}}_3$ ) and nano zirconia ( $\mathrm{n}-{\mathrm{ZrO}}_2$$\mathrm{n}-{\mathrm{ZrO}}_2$n-ZrO_(2)\mathrm{n}-\mathrm{ZrO}_{2}$\mathrm{n}-{\mathrm{ZrO}}_2$ ) having average particle size of $50-90\mathrm{nm}$$50-90\mathrm{nm}$50-90nm50-90 \mathrm{~nm}$50-90\mathrm{nm}$ were used as reinforcement. The fabrication of the composite material $\mathrm{Al}6061/{\mathrm{Al}}_2{\mathrm{O}}_3/{\mathrm{ZrO}}_2$$\mathrm{Al}6061/{\mathrm{Al}}_2{\mathrm{O}}_3/{\mathrm{ZrO}}_2$Al6061//Al_(2)O_(3)//ZrO_(2)\mathrm{Al} 6061 / \mathrm{Al}_{2} \mathrm{O}_{3} / \mathrm{ZrO}_{2}$\mathrm{Al}6061/{\mathrm{Al}}_2{\mathrm{O}}_3/{\mathrm{ZrO}}_2$ of variable weight percentage ( $0.5,0.75,1$$0.5,0.75,1$0.5,0.75,10.5,0.75,1$0.5,0.75,1$ and $1.25{\mathrm{wt}}^0\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1.25{\mathrm{wt}}^0\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1.25wt^(0)%Al_(2)O_(3)1.25 \mathrm{wt}^{0} \% \mathrm{Al}_{2} \mathrm{O}_{3}$1.25{\mathrm{wt}}^0\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$ and $0.5,0.75,1$$0.5,0.75,1$0.5,0.75,10.5,0.75,1$0.5,0.75,1$ and $1.25\mathrm{wt}\mathrm{\%}{\mathrm{ZrO}}_2$$1.25\mathrm{wt}\mathrm{\%}{\mathrm{ZrO}}_2$1.25wt%ZrO_(2)1.25 \mathrm{wt} \% \mathrm{ZrO}_{2}$1.25\mathrm{wt}\mathrm{\%}{\mathrm{ZrO}}_2$ ) 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.

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 ${\mathrm{ZrO}}_2(0.50,0.75,1.00$${\mathrm{ZrO}}_2(0.50,0.75,1.00$ZrO_(2)(0.50,0.75,1.00\mathrm{ZrO}_{2}(0.50,0.75,1.00${\mathrm{ZrO}}_2(0.50,0.75,1.00$ and $1.25\mathrm{wt}\mathrm{\%})$$1.25\mathrm{wt}\mathrm{\%})$1.25wt%)1.25 \mathrm{wt} \%)$1.25\mathrm{wt}\mathrm{\%})$ and nano ${\mathrm{Al}}_2{\mathrm{O}}_3(0.50,0.75,1.00\mathrm{\&}1.25\mathrm{wt}\mathrm{\%}$${\mathrm{Al}}_2{\mathrm{O}}_3(0.50,0.75,1.00\mathrm{\&}1.25\mathrm{wt}\mathrm{\%}$Al_(2)O_(3)(0.50,0.75,1.00&1.25wt%\mathrm{Al}_{2} \mathrm{O}_{3}(0.50,0.75,1.00 \& 1.25 \mathrm{wt} \%${\mathrm{Al}}_2{\mathrm{O}}_3(0.50,0.75,1.00\mathrm{\&}1.25\mathrm{wt}\mathrm{\%}$ ) particles at ${250}^{\circ }\mathrm{C}$${250}^{\circ }\mathrm{C}$250^(@)C250^{\circ} \mathrm{C}${250}^{\circ }\mathrm{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}^{\circ }\mathrm{C}$${750}^{\circ }\mathrm{C}$750^(@)C750^{\circ} \mathrm{C}${750}^{\circ }\mathrm{C}$, which improves the fluidity of the molten liquid and boosts the wettability of nanoparticles to the matrix, as well as the flow ability of the molten metal, with increasing temperature [21]. Following 10 minutes of mechanical stirring, an ultrasonic vibrator (Probe) was employed to disperse the ceramic nanoparticles inside the metal pool for uniform mixing. The probe is positioned at three-quarters of the liquid's depth and permitted to vibrate. These vibrations generate high-energy waves, resulting in numerous cavitation bubbles within the molten pool. The cavitation bubbles exhibit elevated temperature and
pressure, which detonate within microseconds due to pressure differentials, fragmenting clusters and uniformly dispersing the agitated nanoparticles throughout the liquid metal. The molten material was thereafter put into the preheated $\left({400}^{\circ }\mathrm{C}\right)$$\left({400}^{\circ }\mathrm{C}\right)$(400^(@)C)\left(400^{\circ} \mathrm{C}\right)$\left({400}^{\circ }\mathrm{C}\right)$ mould to prevent stress concentration, and the cast substance was permitted to cool and solidify within the mould prior to its removal for further examination. SEM was used for the microstructural study of the produced composites; mechanical and wear criteria were also assessed. To minimize errors, three test specimens were evaluated for each test, and the average of the three readings was calculated.

Microstructural investigations were conducted using a scanning electron microscope (Model: Tescan Vega 3) to examine the distribution of reinforcing elements, specifically ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ particles, within the Al 6061 matrix. The device features electron cannon with a tungsten heated cathode, either in discrete stages or continuously, a resolution of 3.0 nm at 30 kV , magnification ranging from 4.5 X to $1,000,000\mathrm{X}$$1,000,000\mathrm{X}$1,000,000X1,000,000 \mathrm{X}$1,000,000\mathrm{X}$, and a scanning speed changeable from 20 ns to 10 ms per pixel. ASTM standard B311-22 is followed for determining the density of composite. This standard specifies the test methods for determining the density of aluminum and its alloys by the water displacement method. Density is assessed for each sample using a Mettler Toledo specific gravity measurement instrument. First, the weight of the specimen is measured in air, and then the same specimen is measured in water. The density is calculated based on the weight difference between the measurements in air and water.
To acquire test samples in accordance with ASTM requirements, the manufactured hybrid metal matrix composites of Al6061 containing 0.5, 0.75, 1, and $1.25{\mathrm{wt}}^{\mathrm{\%}}{\mathrm{Al}}_2{\mathrm{O}}_3$$1.25{\mathrm{wt}}^{\mathrm{\%}}{\mathrm{Al}}_2{\mathrm{O}}_3$1.25wt^(%)Al_(2)O_(3)1.25 \mathrm{wt}^{\%} \mathrm{Al}_{2} \mathrm{O}_{3}$1.25{\mathrm{wt}}^{\mathrm{\%}}{\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ were machined utilizing a wire EDM machine. The hardness of the Al 6061 composite, reinforced with nano ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and nano ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$, was assessed using a Vickers Hardness Tester (Mitutoyo HM). The test was performed as per ASTM E384-22 standard. The samples were polished to a smooth, reflective gloss to guarantee that surface flaws do not influence the hardness test. A Vickers hardness tester employing a diamond indenter is utilized for the assessment. The load is incrementally introduced to prevent shock and maintained for duration of 10 seconds at a force of 0.5 kgf (kilogram-force).
To examine the potential impact of the indenter on tougher particles, the test was performed at three distinct sites, and the hardness of the samples was ascertained by averaging three separate measurements. Tensile tests conducted in compliance with ASTM E8-22 utilizing an INSTRON-5980 computerized universal testing machine (UTM) with a maximum capacity of 50 kN and a minimum resolution of 1 N had We evaluated the fabricated nano hybrid composite's tensile characteristics-that of yield strength, ultimate tensile strength, and ductility. The SEM examination was utilized to investigate the shattered surfaces, ascertain the fracture mechanism, and conduct microstructural studies. The wear characteristics of the composite were evaluated by wear testing. The engineered composite specimens were subjected to dry sliding wear assessment with a pin-on-disc tribometer. The experiments were performed on cylindrical specimens measuring 10 mm in diameter and 25 mm in height. The ASTM G99-23 standard provided the framework for the wear testing conducted in this investigation. An EN-32 steel disc with an 80 mm track diameter served as the counter-face for specimen testing. This study examined the wear behaviour of the composites under various situations. The wear test was conducted by altering load, distance and velocity of sliding. Fractured specimens and abraded regions were examined using SEM to analyze wear and fracture.

Micro structural characterization of $\mathrm{AlbO}61/{\mathrm{Al}}_2{\mathrm{O}}_3/\mathrm{ZrO}$$\mathrm{AlbO}61/{\mathrm{Al}}_2{\mathrm{O}}_3/\mathrm{ZrO}$AlbO 61//Al_(2)O_(3)//ZrO\mathrm{AlbO61} / \mathrm{Al}_{2} \mathrm{O}_{3} / \mathrm{ZrO}$\mathrm{AlbO}61/{\mathrm{Al}}_2{\mathrm{O}}_3/\mathrm{ZrO}$ h hybrid nano composite with different weight fractions

The microstructure of the SEM image of $\mathrm{Al}6061-1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-0.5\mathrm{\%}{\mathrm{ZrO}}_2,\mathrm{Al}6061-1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-1.25\mathrm{\%}{\mathrm{ZrO}}_2$$\mathrm{Al}6061-1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-0.5\mathrm{\%}{\mathrm{ZrO}}_2,\mathrm{Al}6061-1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-1.25\mathrm{\%}{\mathrm{ZrO}}_2$Al6061-1%Al_(2)O_(3)-0.5%ZrO_(2),Al6061-1%Al_(2)O_(3)-1.25%ZrO_(2)\mathrm{Al} 6061-1 \% \mathrm{Al}_{2} \mathrm{O}_{3}-0.5 \% \mathrm{ZrO}_{2}, \mathrm{Al} 6061-1 \% \mathrm{Al}_{2} \mathrm{O}_{3}-1.25 \% \mathrm{ZrO}_{2}$\mathrm{Al}6061-1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-0.5\mathrm{\%}{\mathrm{ZrO}}_2,\mathrm{Al}6061-1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-1.25\mathrm{\%}{\mathrm{ZrO}}_2$, and $\mathrm{Al}6061-1.25\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-1\mathrm{\%}{\mathrm{ZrO}}_2$$\mathrm{Al}6061-1.25\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-1\mathrm{\%}{\mathrm{ZrO}}_2$Al6061-1.25%Al_(2)O_(3)-1%ZrO_(2)\mathrm{Al} 6061-1.25 \% \mathrm{Al}_{2} \mathrm{O}_{3}-1 \% \mathrm{ZrO}_{2}$\mathrm{Al}6061-1.25\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-1\mathrm{\%}{\mathrm{ZrO}}_2$ depicted in Fig. 14 (a-c). EDS proved that the sample's real chemical makeup was present in certain areas. Fig. 13 shows the energy dispersive spectroscopy results for Al6061 that has been strengthened with $1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1%Al_(2)O_(3)1 \% \mathrm{Al}_{2} \mathrm{O}_{3}$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$ and $1\mathrm{\%}{\mathrm{ZrO}}_2$$1\mathrm{\%}{\mathrm{ZrO}}_2$1%ZrO_(2)1 \% \mathrm{ZrO}_{2}$1\mathrm{\%}{\mathrm{ZrO}}_2$. These results show that the reinforcements are present in the aluminium matrix. The stir casting process makes mixtures of $\mathrm{Al}6061,{\mathrm{Al}}_2{\mathrm{O}}_3$$\mathrm{Al}6061,{\mathrm{Al}}_2{\mathrm{O}}_3$Al6061,Al_(2)O_(3)\mathrm{Al} 6061, \mathrm{Al}_{2} \mathrm{O}_{3}$\mathrm{Al}6061,{\mathrm{Al}}_2{\mathrm{O}}_3$, and ZrO . The prepared composite had this even spread out texture because it was made with an ultrasonic-assisted stir casting method. When the stirring time ( 10 minutes) and speed ( 500 rpm ) are just right, the particles are spread out more evenly and the matrix and reinforcement stick together well. Fig. 14(b, c) shows areas of clustering and agglomeration, which is probably because there is a lot of reinforcing. As the weight percentage of reinforcement increases, the link between the soft matrix and hard ceramic reinforcement particles weakens. This causes the surface energy to rise, therefore influencing the clustering [23]. The $1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1%Al_(2)O_(3)1 \% \mathrm{Al}_{2} \mathrm{O}_{3}$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$ and $1\mathrm{\%}{\mathrm{ZrO}}_2$$1\mathrm{\%}{\mathrm{ZrO}}_2$1%ZrO_(2)1 \% \mathrm{ZrO}_{2}$1\mathrm{\%}{\mathrm{ZrO}}_2$ particles were spread out more evenly, as shown by SEM studies of the microstructures. Higher filled composites, on the other hand, showed that these particles separated and clumped together. This separation probably happens when solidifies, since dendrites form first. This lets extra particles move and group together in the spaces between the dendrites at the solid-liquid contact. Sample had $1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1%Al_(2)O_(3)1 \% \mathrm{Al}_{2} \mathrm{O}_{3}$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$ and $1.25\mathrm{\%}{\mathrm{ZrO}}_2$$1.25\mathrm{\%}{\mathrm{ZrO}}_2$1.25%ZrO_(2)1.25 \% \mathrm{ZrO}_{2}$1.25\mathrm{\%}{\mathrm{ZrO}}_2$, so the separation was more noticeable. The combination with $1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1%Al_(2)O_(3)1 \% \mathrm{Al}_{2} \mathrm{O}_{3}$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$ and $1\mathrm{\%}{\mathrm{ZrO}}_2$$1\mathrm{\%}{\mathrm{ZrO}}_2$1%ZrO_(2)1 \% \mathrm{ZrO}_{2}$1\mathrm{\%}{\mathrm{ZrO}}_2$ has strong bonds between the reinforcing ceramic particles and the Al6061 matrix, which means that load, is transferred efficiently and the structure is more stable. It's clear that the production process worked well because there are no major flaws like holes, cracks or particle agglomeration.

Figure 13: EDS spectrum and SEM image of $\mathrm{Al}6061-1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-1\mathrm{\%}{\mathrm{ZrO}}_2$$\mathrm{Al}6061-1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-1\mathrm{\%}{\mathrm{ZrO}}_2$Al6061-1%Al_(2)O_(3)-1%ZrO_(2)\mathrm{Al} 6061-1 \% \mathrm{Al}_{2} \mathrm{O}_{3}-1 \% \mathrm{ZrO}_{2}$\mathrm{Al}6061-1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3-1\mathrm{\%}{\mathrm{ZrO}}_2$.

Tab. 4 and Fig. 15 shows the theoretical and experimental densities of Al6061 alloys that have been strengthened with different amounts of nano ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ and nano ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ particles. When nano reinforced ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ are added to Al 6061 , the total density of the composite material goes up in a noticeable way. Theoretical density was found using the rule of
mixing. The actual densities are very close to the theoretical densities. This suggests that the methods used in the experiments were correct and reliable. The samples are likely to be homogeneous since the measured and estimated densities are very close to each other. This means that ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ were evenly spread out in the aluminium matrix, which is important for making sure that the material's qualities are the same all over. The actual density is sometimes lower than the theoretical density. This might be because of the pores that form during the manufacturing process. Porosity could be caused by the gas getting trapped during casting, the movement of hydrogen, or the material shrinking as it hardens [24]. Hence, the addition of nano ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ and nano ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ particles to Al6061 alloy resulted in increased density, indicating a homogeneous distribution of nanoparticles.

A Vickers Hardness Tester (Mitutoyo HM) was used to check the hardness of a metal called Al6061 that had different amounts of ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ nanoparticles added to it ( $0.5,0.75,1$$0.5,0.75,1$0.5,0.75,10.5,0.75,1$0.5,0.75,1$, and $1.25\mathrm{wt}.\mathrm{\%}$$1.25\mathrm{wt}.\mathrm{\%}$1.25wt.%1.25 \mathrm{wt} . \%$1.25\mathrm{wt}.\mathrm{\%}$ ). Tab. 5 shows the effects of different compositions on hardness, and Fig. 16 shows a graph of those effects. It is clear that the mixture gets harder as the amounts of ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ in it go up. Pure aluminium has a hardness of 60.8 Hv , which is not very high because it is soft and easy to shape. The incorporation of nano ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ and nano ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ particles significantly improved the hardness of Al6061 alloy, with a maximum hardness of 90.9 Hv achieved at $1\mathrm{\%}{\mathrm{ZrO}}_2$$1\mathrm{\%}{\mathrm{ZrO}}_2$1%ZrO_(2)1 \% \mathrm{ZrO}_{2}$1\mathrm{\%}{\mathrm{ZrO}}_2$ and $1.25\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1.25\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1.25%Al_(2)O_(3)1.25 \% \mathrm{Al}_{2} \mathrm{O}_{3}$1.25\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$. Hence, increase in wt. $\mathrm{\%}$$\mathrm{\%}$%\%$\mathrm{\%}$ of nano reinforced particulates enhances the hardness of the produced composites. Similar trends were observed [7]. Also, there are hard ceramic nanoparticles called ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ in the aluminium alloy core. These particles stop dislocations from moving, which makes the material harder. The second reason is that the ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ nanoparticles have a big stabilizing effect on the movement of grain boundaries. This makes the grains more uniform and strengthens the grain boundaries, which makes the material harder.

Tensile tests were used to evaluate elongation, Young's Modulus (YM), Ultimate Tensile Strength (UTS), and Yield Strength (YS). Tab. 6 summarizes the tensile parameters of aluminium composites with varying weight percentages of nano zirconium dioxide ( ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ ) and nano aluminium oxide ( ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ ). The investigation underscores the influence of additives on the mechanical properties of composite materials. Pure aluminium demonstrates inferior mechanical capabilities coupled with considerable elongation, signifying excellent ductility. Augmenting the concentrations of ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ has improved the YM, YS, and UTS of aluminium composites. Sample 3, which contained 1 wt. $\mathrm{\%}$$\mathrm{\%}$%\%$\mathrm{\%}$ of ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and $1\mathrm{wt}.\mathrm{\%}$$1\mathrm{wt}.\mathrm{\%}$1wt.%1 \mathrm{wt} . \%$1\mathrm{wt}.\mathrm{\%}$ of ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ nanoparticles as reinforcement, exhibited the highest Young's modulus ( 70.8 MPa ), yield strength ( 120.5 MPa ), and ultimate tensile strength ( 194.8 MPa ), demonstrating an optimal synergy of these additives for enhanced strength while preserving adequate ductility. The percentage of elongation constantly diminishes with the incorporation of ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$. Pure aluminium has the greatest ductility ( $14.20\mathrm{\%}$$14.20\mathrm{\%}$14.20%14.20 \%$14.20\mathrm{\%}$ ), which markedly diminishes with the increased ceramic content in sample 7 containing $1\mathrm{\%}{\mathrm{ZrO}}_2$$1\mathrm{\%}{\mathrm{ZrO}}_2$1%ZrO_(2)1 \% \mathrm{ZrO}_{2}$1\mathrm{\%}{\mathrm{ZrO}}_2$ and $1.25\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1.25\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1.25%Al_(2)O_(3)1.25 \% \mathrm{Al}_{2} \mathrm{O}_{3}$1.25\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$, signifying a compromise between strength and ductility.
The enhancements in mechanical properties may stem from a low degree of porosity and uniform distribution of nanoparticles. The integration of nanoparticles into the matrix offers limited heterogeneous nucleation sites during solidification, leading to refined grains, which enhances the tensile strength of the nano composite. The addition of nano ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ and nano ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ has enhanced grain boundary integrity by refining the grain structure, leading to improved yield and tensile strengths. The thermal mismatch between the aluminium matrix ( $23\times {10}^{\wedge }-6/{}^{\circ }\mathrm{C}$$23\times {10}^{\wedge }-6/{}^{\circ }\mathrm{C}$23 xx10^-6//^(@)C23 \times 10^{\wedge}-6 /{ }^{\circ} \mathrm{C}$23\times {10}^{\wedge }-6/{}^{\circ }\mathrm{C}$ ) and the ceramic ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ particles ( $10.5\times {10}^{\wedge }-6/{}^{\circ }\mathrm{C}$$10.5\times {10}^{\wedge }-6/{}^{\circ }\mathrm{C}$10.5 xx10^-6//^(@)C10.5 \times 10^{\wedge}-6 /{ }^{\circ} \mathrm{C}$10.5\times {10}^{\wedge }-6/{}^{\circ }\mathrm{C}$ ) and Al 2 O 3 particles ( $8.2\times {10}^{\wedge }-6/{}^{\circ }\mathrm{C}$$8.2\times {10}^{\wedge }-6/{}^{\circ }\mathrm{C}$8.2 xx10^-6//^(@)C8.2 \times 10^{\wedge}-6 /{ }^{\circ} \mathrm{C}$8.2\times {10}^{\wedge }-6/{}^{\circ }\mathrm{C}$ ) results in an increase in dislocation density, independent of the entrapment of dislocations in the matrix by the second phase ceramic ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ particles during deformation [22, 25]. Figs. 17, 18, 19, and 20 indicate that the composite Al 6061 reinforced with $1\mathrm{\%}{\mathrm{ZrO}}_2$$1\mathrm{\%}{\mathrm{ZrO}}_2$1%ZrO_(2)1 \% \mathrm{ZrO}_{2}$1\mathrm{\%}{\mathrm{ZrO}}_2$ and $1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1%Al_(2)O_(3)1 \% \mathrm{Al}_{2} \mathrm{O}_{3}$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$ (Sample 3) exhibits the greatest balanced improvement in mechanical properties, surpassing those of the as-cast 6061 Al alloy.

Fig. 20 displays the percentage elongation for produced composites, which indicates that as particle content increases, the elongation decreases, similar trends were seen [11]. The reason for decrease in elongation is the lower flexibility of the ceramic reinforcement with the matrix. The unshaped ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ particles may induce localized pressure around them, and over time, the accumulation of particles near the grain boundaries intensifies this pressure concentration. Overall, the addition of nano ${\mathrm{Al}}_2{\mathrm{O}}_3$${\mathrm{Al}}_2{\mathrm{O}}_3$Al_(2)O_(3)\mathrm{Al}_{2} \mathrm{O}_{3}${\mathrm{Al}}_2{\mathrm{O}}_3$ and nano ${\mathrm{ZrO}}_2$${\mathrm{ZrO}}_2$ZrO_(2)\mathrm{ZrO}_{2}${\mathrm{ZrO}}_2$ particles enhanced the tensile properties of Al 6061 alloy, with optimal results obtained at $1\mathrm{\%}{\mathrm{ZrO}}_2$$1\mathrm{\%}{\mathrm{ZrO}}_2$1%ZrO_(2)1 \% \mathrm{ZrO}_{2}$1\mathrm{\%}{\mathrm{ZrO}}_2$ and $1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1%Al_(2)O_(3)1 \% \mathrm{Al}_{2} \mathrm{O}_{3}$1\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$, demonstrating a balanced improvement in strength and ductility.

Figure 18: YS of Al6061 alloy and its reinforced composites.

Figure 19: UTS of Al6061 alloy and it's reinforced composites.

A critical step in understanding material failure involves examining the fractured surfaces of alloys and their composites. Fig. 21 (a-f) displays the fractured surfaces of the fabricated composites with different weight fractions of reinforcement. The base matrix, Fig. 21(a) exhibited a smooth and consistent surface with shallow, evenly distributed depressions, indicating a fracture that stretches without breaking. In contrast, the composite material showed depressions oriented in two directions. Larger depressions absorbed the reinforcing particles, while smaller depressions were due to the breakdown of the stretchable matrix. SEM analysis of the damaged composite surfaces (Figs. 21(b-d)) revealed fine cracks in the $\mathrm{n}-{\mathrm{Al}}_2{\mathrm{O}}_3$$\mathrm{n}-{\mathrm{Al}}_2{\mathrm{O}}_3$n-Al_(2)O_(3)\mathrm{n}-\mathrm{Al}_{2} \mathrm{O}_{3}$\mathrm{n}-{\mathrm{Al}}_2{\mathrm{O}}_3$ and $\mathrm{n}-{\mathrm{ZrO}}_2$$\mathrm{n}-{\mathrm{ZrO}}_2$n-ZrO_(2)\mathrm{n}-\mathrm{ZrO}_{2}$\mathrm{n}-{\mathrm{ZrO}}_2$ particles, partial separation between the matrix and reinforcement, and even matrix fracture. Generally, the fracture surfaces displayed smooth particles, indicating particle fracture rather than separation, which suggests strong interfacial bonds in these composites.
The Al6061 matrix composites with elevated filler content (Fig. 21(e) and (f)) exhibited both large and tiny dimples, indicating that the failure mechanism was attributable to the growth, coalescence, and eventual rupture of ductile voids. The incorporation of $\mathrm{n}-{\mathrm{Al}}_2{\mathrm{O}}_3$$\mathrm{n}-{\mathrm{Al}}_2{\mathrm{O}}_3$n-Al_(2)O_(3)\mathrm{n}-\mathrm{Al}_{2} \mathrm{O}_{3}$\mathrm{n}-{\mathrm{Al}}_2{\mathrm{O}}_3$ and $\mathrm{n}-{\mathrm{ZrO}}_2$$\mathrm{n}-{\mathrm{ZrO}}_2$n-ZrO_(2)\mathrm{n}-\mathrm{ZrO}_{2}$\mathrm{n}-{\mathrm{ZrO}}_2$ modified the fracture characteristics of the Al 6061 matrix, transitioning from ductile to brittle modes, and subsequently to a hybrid ductile mode. The $\mathrm{n}-{\mathrm{Al}}_2{\mathrm{O}}_3$$\mathrm{n}-{\mathrm{Al}}_2{\mathrm{O}}_3$n-Al_(2)O_(3)\mathrm{n}-\mathrm{Al}_{2} \mathrm{O}_{3}$\mathrm{n}-{\mathrm{Al}}_2{\mathrm{O}}_3$ and $\mathrm{n}-{\mathrm{ZrO}}_2$$\mathrm{n}-{\mathrm{ZrO}}_2$n-ZrO_(2)\mathrm{n}-\mathrm{ZrO}_{2}$\mathrm{n}-{\mathrm{ZrO}}_2$ particles had minor dimples alongside the matrix and hairline fractures. Fractography studies demonstrate a significant correlation between reinforcement and the matrix, resulting in improved mechanical properties of hybrid nano composites. Consequently, the results of UTS, YS, and % elongation can be correlated with fractographic analyses and are suitably relevant.

The wear tests were performed by altering load, speed, and sliding distance. Tab. 7 presents the exact wear rate values as a function of changing load, while maintaining constant speed and sliding distance. Loads of $10\mathrm{N},20\mathrm{N},30\mathrm{N}$$10\mathrm{N},20\mathrm{N},30\mathrm{N}$10N,20N,30N10 \mathrm{~N}, 20 \mathrm{~N}, 30 \mathrm{~N}$10\mathrm{N},20\mathrm{N},30\mathrm{N}$, and 40 N were applied at a speed of $4\mathrm{m}/\mathrm{s}$$4\mathrm{m}/\mathrm{s}$4m//s4 \mathrm{~m} / \mathrm{s}$4\mathrm{m}/\mathrm{s}$ across a distance of 4000 meters, and the results were recorded. Fig. 22 illustrates the wear rate in relation to different loads at ambient temperature. The wear rate was shown to grow progressively with the elevation of load. The highest wear rate is noted in the as-cast Al6061 alloy. Al6061 reinforced with $1\mathrm{wt}.\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$$1\mathrm{wt}.\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$1wt.%Al_(2)O_(3)1 \mathrm{wt} . \% \mathrm{Al}_{2} \mathrm{O}_{3}$1\mathrm{wt}.\mathrm{\%}{\mathrm{Al}}_2{\mathrm{O}}_3$ and 1 $\mathrm{wt}.\mathrm{\%}{\mathrm{ZrO}}_2$$\mathrm{wt}.\mathrm{\%}{\mathrm{ZrO}}_2$wt.%ZrO_(2)\mathrm{wt} . \% \mathrm{ZrO}_{2}$\mathrm{wt}.\mathrm{\%}{\mathrm{ZrO}}_2$ exhibited the lowest wear rates, indicating its exceptional wear resistance. The enhancement in wear resistance can be ascribed to the substantial adhesive metal-metal contact that facilitated surface shear strain [26].