Mechanics of Materials
Experimental Investigation of NanoB4C-NanoGr Reinforced AA7075 Alloy Hybrid Nanocomposites
2024 Volume 65 Issue 8 Pages 923-927
Details
2024 Volume 65 Issue 8 Pages 923-927
The purpose of this research is to experiment with different weight percentages of nanoB4C (5%, 10%, and 15%) in order to develop nano B4C/graphite-reinforced AA7075 alloy composites. An analysis of the morphological and mechanical behavior of the material was carried out using SEM in accordance with ASTM E8, E9, E23, and D790. All of the reinforcement particles are distributed uniformly throughout the matrix alloy, and there are no porous portions left over. Composite materials have a hardness of 30.18 percent, an ultimate tensile strength that is 40.93 percent higher, and a compressive strength that is 19.73 percent higher than the base material. The flexural strength of the material is improved by 26.75% when the matrix dislocation density and elastic modulus fluctuations are higher. There was a 66.21% increase in impact strength as a result of reduced porosity and grain refinement.
Over the past decade, functional applications, particularly in the automotive and marine industries, have relied on low-density materials. These applications favor metal matrix composites because to their lower cost and higher strength-to-weight ratio [1]. Aluminum and its alloys, among other metals, have many engineering uses due to their low density and durability. Due to their low hardness and wear resistance, such materials were limited for functional applications [2]. Adding enough ceramic-strengthening particles to parent materials improves their characteristics. Different studies have computed discrete strengthening particles on such alloys [3]. Cast metal matrix composites often incorporate micron-sized ceramic reinforcement. Such particles are tougher and less ductile. Also related to machining quality is tool wear. Nanocomposites reduce this weakness. Nanocomposites have some ductility and wear resistance, making them better for certain applications. Also, it increased tensile strength, hardness, and fracture toughness at low and high temperatures [4, 17]. However, particle aggregation due to the higher surface-to-volume ratio caused widespread problems. Adequate process settings and a flexible processing approach can fix this.
Recent hybrid composites have basic materials with two or more micro-ceramic particles, according to research. Specialized ceramic particles improve wear, corrosion, and oxidation resistance. Ceramic particles don’t improve hybrid composites either. Consider the production method, weight fraction, particle size, and reinforcing particle distribution with the base material [5]. Boron carbides, and nitrides are common solid lubricants and hardeners in base materials. Secondary reinforcement with hard ceramic strengthening particles uses solid lubricants such graphite, MoS2, CNTs, and graphene. Many metal matrix composites incorporate secondary reinforcements like this to resist fatigue, wear, corrosion, and tribology [6]. Tribo-layers in the sliding contact zone prevent the base matrix from having more solid lubricant weight. Therefore, hardness and wear rate are not lowered. In stir casting, aluminum and zinc composites were investigated with nano graphite (50 nm) ceramic particles. Graphite-boron carbide-reinforced aluminum alloy composites were liquid cast. Research shows that AA7075 strengthening particles outperform Al6061 [7]. Stir casting produced aluminum hybrid composites reinforced with boron carbide and graphite. Mechanically, aluminum hybrid composites outperformed the base material [8].
Aluminum hybrid composites with variable strengthening particles of different weights were made using liquid metallurgy. B4C/Gr composites have better physical qualities than SiC/Gr strengthened aluminum composites [9]. The literature review indicated that graphite as a solid lubricant makes it difficult to identify hybrid composites’ physical properties, which can be done using nano-sized particles [10]. Few nanoscale investigations have examined boron carbide and graphite, and their mechanical properties are unknown.
Stir casting synthesized B4C with different weight proportions (5, 10, and 15%) and unvarying graphite (3 wt%) to address inquiry disparities and analyze its physical properties for vehicle implications [11]. Two researchers disagreed that utilizing graphite as a solid lubricant makes it hard to determine hybrid composites’ physical features by imposing nano-sized graphite-strengthening particles. The hybrid reinforcement’s wettability in the aluminum matrix has not been investigated. Due to investigative discrepancies, stir casting was employed to manufacture B4C (5%, 10%, and 15%) and unvarying graphite (3 wt%) for automobile applications and evaluate its physical qualities [16]. Examinations are conducted to evaluate the hardness, tensile, compressive, flexural, and impact strength [15].
Hybrid composites are made via stir casting with AA7075 alloy. Analyzed in Table 1 shows the chemical combinations. When a light load is required, this alloy is a good choice for the transportation sector. It outperforms competing aluminum alloys in terms of its physical characteristics. It is believed that reinforcing ceramic particles in parent materials do not increase composite density due to the fact that weight reduction characteristics are not balanced for practical use. Graphite (2.16 g/cm3) and B4C (2.25 g/cm3), two commercially available nano-ceramic strengthening particulates with particle sizes of 80 nm and 60 nm, respectively, were utilized in this work (Merck). The main hard ceramic strengthening particle of B4C is used to homogenize the mixture. Boron carbide (B4C) exhibits enhanced properties such as increased hardness, flexural strength, elastic modulus, wear resistance, chemical and thermal stability, as well as reduced density [12]. Graphite is also suggested as a supplementary reinforcement in this study.
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The process of casting hybrid composites made of aluminum alloys via stir casting is illustrated in Fig. 1. As the slurry cools and solidifies, pressure is applied to it. The nucleation momentum is revealed as the solidification temperature drops and cooling speeds up. The prevention of air passage between the mold and the molten composites improves the heat diffusion and grain refinement of hybrid composites. Furthermore, it results in composites with reduced deformation [13]. AA7075 alloy was melted at 993 K for 15 minutes in a resistive heating furnace. To melt the alloy completely, stirring was kept at 450 rpm. Heating nano graphite (nGr) and nano boron carbide (nB4C) reinforcing particles in 5, 10, and 15% weight proportions at 548 K, 3% nGr reinforcement particles increase matrix-reinforcement particulate wettability and eliminate moisture [14]. The melt was heated to 1048 K and ceramic reinforcing particles were added via sprue. To prevent particle aggregation, the molten slurry is stirred at 550 rpm.
Experimental setup of stir casting.
The chemical process of the matrix-reinforcement particle dissolves, resulting in the formation of vortex that hinders the accumulation of strengthening nanoparticles. The even dispersion of reinforcement in the molten slurry is impacted. By increasing the temperature of the molten metal to 1073 K, the composite slurry exhibited reduced viscosity, causing the ceramic reinforcement particles to rise to the surface during stirring. An increase in stirring speed and duration was achieved by adding 600 rpm and extending the time to 20 minutes. The study revealed that the addition of a higher concentration (15 wt%) of nano boron carbide leads to the formation of agglomerates in the ceramic particles, despite the implementation of effective processing techniques. Consequently, a lower concentration (10 wt%) was selected instead. Studies indicate that the inclusion of secondary nano graphite reinforcement diminishes the tensile characteristics, while simultaneously augmenting the proportion of these particles in the aluminum matrix. Due to the flat and brittle nature of these ceramic particles, there is a weak binding between the parent material alloys. To restrict this, the present practice involves maintaining graphite at a concentration of 3 wt%. Prior to introducing the molten slurry into the die chamber, the die was subjected to heating in order to eliminate any trapped gas, hence reducing the occurrence of matrix porosity. The die cavity was filled with molten slurry and allowed to cool at ambient temperature.
ASTM E8, E9, E23, and D790 were used to measure aluminum alloy hybrid composite performance. An optical microscope was utilized in order to gather information regarding the microstructure of aluminum hybrid composites. To investigate the morphology of the reinforcement particle dispersion in the matrix alloy, a scanning electron microscope (SEM) study was carried out. A study is conducted to investigate the tensile, compressive, flexural, and impact resistance of hybrid composites made of aluminum alloy.
This work examined nano boron carbide-nanographite reinforced aluminum hybrid composite microstructures with an optical microscope. Figure 2–4 etched composites with different weights. Nano boron carbide and nano graphite-strengthening particles are dispersed throughout the micrograph. These particles are evenly distributed in the matrix. Entrapping strengthening particles at grain boundaries thickens them. Ceramic particles in smaller amounts reduce density dispersion. Near grain boundaries are eutectic alloy particles precipitated. Multiple eutectic particles were found in primary aluminum solid solution grains.
Microstructure of 5 wt% of nB4C + 3 wt% graphite strengthened AA7075 alloy composite.
Microstructure of 10 wt% of nB4C + 3 wt% Gr strengthened AA7075 alloy composite.
Microstructure of 15 wt% of nB4C + 3 wt% Gr strengthened AA7075 alloy composite.
The scanning electron microscopy (SEM) analysis of Aluminum hybrid composites in Fig. 5(a), Fig. 5(b) reveals that the strengthening particles accumulate as a result of an augmentation in ceramic particulates, even with an escalation in the process parameter. The needle-shaped boron carbide particles exhibit insolubility at elevated temperatures. During the solidification process, the graphite particles, which act as secondary strengthening agents, form a bond with aluminum. This interaction results in the formation of an aluminum dendritic pattern, which improves the strength and structure of the aluminum grains. The formation of secondary ceramic particles occurs as a nucleus, leading to the crystallization of this grain. The presence of these secondary particles hinders the growth of aluminum grains, resulting in the elevation of grain boundaries in the hybrid composite. This overlaying of the AA7075 alloy restricts the movement of dislocations and limits the size of the grains.
(a) SEM images of 10 wt% of nB4C + 3 wt% n-graphite strengthened Aluminum-Zinc-Magnesium alloy composite, (b) Emphasizes on Boron carbide.
The hardness test, which is based on ASTM E381 guidelines is used to find out how hard an AA7075 alloy hybrid composite is by looking at an average of 5 depressions in Vickers hardness. Because there were more hard ceramic strengthening particles in the aluminum alloy hybrid composites, they were much harder 30.18% than the parent material is shown in Fig. 6. The addition of B4C in the matrix material acts as an extra base during solidification. Because the nuclear rate has gone up, the grain size has shrunk. This makes the resistance higher and the dislocation movement slower during pressing.
Hardness of hybridized AA7075 alloy nanocomposites.
Tensile strength of aluminum hybrid composites was evaluated with 5 samples as per the ASTM E8 standards, at room temperature using a universal testing machine with a maximum load capacity of 10 tons and a crosshead speed of 0.5 mm/min. The ultimate tensile strength of the hybridized composites increased by 40.93% when compared to the original AA7075 alloy shown in Fig. 7. The basic matrix includes a higher concentration of nanoceramic strengthening particles (B4C), robust bonding between the components, reduction in grain size, increased dislocation density, and a virtual method for transferring load between the matrix alloy and nano-ceramic particles.
Ultimate tensile strength of AA7075 hybrid composites.
As shown in Fig. 8, the ASTM E9 standards were used to test the compression strength of hybridized aluminum nanocomposites. Compression strength increased 19.73% above base material. 5 indentations were manufactured specifically to conduct compression tests as per ASTM norms.
Compressive strength of nano AA7075 hybrid composites.
Figure 9 demonstrates that including hybrid composites with enhanced grain refinement significantly improves the flexural strength of the material by 26.75% compared to the AA7075 alloy. This improvement is attributed to the improved elastic modulus and toughness of the composites, which effectively prevent disruption. The Composite’s plastic flow is limited by uniform ceramic strengthening particle distribution. This greatly improves hybrid composites’ flexural behavior.
Flexural strength of hybrid composites.
As shown in Fig. 10, synthesized composites had a maximum impact strength of 66.21% higher than base alloy material due to stir casting’s reduction in porosity, uniform distribution of ceramic strengthening particulates in the matrix alloy, increased yield strength, and Mg2Si interface. Secondary reinforced particles also reduce void nucleation, decreasing composite cracking.
Impact strength of Aluminum hybrid composites.
This work studied the microstructure mechanical properties of stir-cast nano B4C (5%wt, 10%wt, 15%wt) and nanographite (3%wt) enhanced AA7075 alloy hybrid composites for automobile and marine applications.
In order to carry out the tests, the writers would like to express their gratitude to the Madras Institute of Technology at Anna University in Chennai.
