# Investigation of Mechanical Behavior and Microstructure Analysis of AA7075/SiC/B4C-Based Aluminium Hybrid Composites

Authors: HassabAlla M. A. Mahmoud; P. Satishkumar; Yenda Srinivasa Rao; Rohinikumar Chebolu; Rey Y. Capangpangan; Arnold C. Alguno; Mahesh Gopal; A. Firos; Murthi C. Saravana
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

The microstructure and mechanical properties of an MMC based on AA 7075 and strengthened through silicon carbide (SiC) as well as boron carbide (B4C) elements were studied. The (SiC + B4C) combination was used in various weight percentages of 4, 8, 12, and 16% to create the hybrid composites utilizing the traditional stir casting procedure. XRD and SEM measurements were used to investigate the dispersion of the reinforced particles. For example, microhardness, impact strength, and ultimate tensile strength were measured on hybrid composites at room temperature. The density and porosity of the materials were also studied. The researchers found that increasing the weight percentage of the (SiC + B4C) mixture resulted in a small drop in % elongation. However, hybrid composites comprising 16% (SiC + B4C) weight reduction showed some decrease in hardness and tensile strength. Equated to unreinforced alloys, the hardness and tensile strength of hybrid composites rise by 8% and 21%, respectively. Reinforcement also resulted in a decrease in impact strength and density, as well as an increase in porosity.


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## Body

## 1. Introduction

Metal matrix composites (AMCs) made of aluminium have gained popularity in recent decades because of their amazing qualities such less weight, higher strength, modulus of elasticity, exceptional restraining, and good wear resistance. When the number of reinforced particles in a matrix composition grows, ductility often suffers [1]. In transportation and structural applications, where high-stress resistance is critical, 6082 T6 tweaked AA provides good mechanical qualities and high strength [2]. Aluminium composites have undergone a great deal of development in the last few decades to improve their qualities [3].Hybrid aluminium AMCs are the next generation of AMCs, and they have the ability to fulfill the growing demands of high-tech applications in the future [4]. Additionally, researchers have experimented with creating hybrid metal matrix composites by combining two or more reinforcing materials, in an effort to get better mechanical qualities, such as increased dimensional stability and improved heat and corrosion resistance for the final invention [5]. A number of researchers have explored the mechanical properties of a range of hybrid composites. As per the proportion of strengthening in the metal matrix increases, tensile strength, stiffness, and porosity all improve. However, when the proportion of reinforcement rises, the composite’s impact energy and density both fall significantly. Ultrasonic cavitation solidification was used in [6] to create a hybrid composite utilizing AA6061 as a base metal and (SiC + B4C) as reinforcement. They found that the porosity boosted the hardness and tensile strength of the alloy. When [7]used a traditional stir casting method to create a hybrid composite, they used an aluminium alloy containing boron carbide (B4C) and graphite reinforcing particles (Gr). For better strength, hardness, and wear resistance, researchers added B4C to the matrix, but the material became more brittle as a result. Alumina nanoparticles (Al2O3) were created via powder metallurgy, and the strengthening mechanism was discovered to be the most important strength mechanism [8, 9]. The solidification of a substance is linked to the program of dislocations inside that material. Strengthening mechanisms must be introduced to limit dislocation movement and thus boost the material’s strength in order to improve material attributes like yield strength. Researchers evaluated the wear as well as the mechanical characteristics of reinforcement combinations on the surface of composites for wear [10]. An increase in microhardness is attributed to the occurrence of silicon carbide and alumina particles in hybrid composites made of Al, SiC, and Gr. SiC and Al2O3 reinforcement added to aluminium hybrid composites boosted tensile strength and hardness while decreasing the elongation percentage, according to a study by Davis et al. [11]. It was found that the ultimate tensile and hardness of hybrid composites made with boron carbide particles and calcium carbide with the main alloy of AA 6063 were improved, while the impact strength was somewhat reduced. A two-step stir casting procedure was used to create a dual-reinforced particle AA composite in [12]. LM-13 AA was used in the experiments. Silicon carbide and zircon sand (ZrSiO4) particles were used in the study. The composites outperform the unreinforced alloy in terms of wear resistance, according to the authors.It is stated in the literature that several researchers have evaluated the mechanical and structural properties of composite materials using SiC, Gr. Ca2O3, ZrSiO4, TiC, and Al2O3. There has been no study done on AA6082 to make hybrid composites employing (SiC + B4C) as reinforcement. Aluminum and silicon carbide (SiC) particles are chemically compatible and create strong bonds in the matrix [13]. There are a number of advantages to using SiC as a reinforcement in AMCs because of its outstanding workability, easy machining, and inexpensive cost. B4C must be added to aluminium composites in order to increase their mechanical qualities. B4C is a great reinforcement material because of its high rigidity and hardness, as well as its low density. Because of B4C and aluminum’s similar densities, the settling problem is reduced while solidifying a molten matrix due to its low density [14]. An initial investigation of the (SiC + B4C)-reinforced AA6082 hybrid composites’ microstructure and mechanical characteristics was carried out. Many different techniques, including liquid state production, stir casting, intrusion, and squeeze casting, can be utilized to make composites. The stir casting process is the most commonly used technique for composite manufacturing because it can generate complex shapes at a low cost. Using a graphite crucible to melt a molten matrix metal requires 10–15 minutes of vigorous stirring in order to produce a homogeneous composite [15]. When it comes to liquid state manufacturing, stir casting is the most easy and cost-effective process. Another benefit of the stir casting technology is its capacity to produce composites with a volume proportion of up to 30%. [16–18]. The swirling motion of the particles in the stir casting process enhances the chemical interactions between the matrix and reinforcing particles [19]. Experimental data on microhardness, impact strength, elongation percentage, and tensile strength of stir-cast hybrid metal matrix composites were collected [20].


## 2. Materials and Experimentation

### 2.1. Base Material

A 6 mm thick AA7075 plate was chosen as the basis material in this study. The matrix alloy’s chemical and mechanical properties are listed in Tables1 and 2. At a temperature of roughly 180°C, the alloy was artificially aged to achieve the T6 state. Table 3 lists the specifics of the SiC and B4C particles utilized as reinforcement in this study. The particles used in this investigation were 35 μm in diameter. By adding 4, 8, 12, and 16wt% of the (SiC + B4C) mixture in equal proportions, we were able to create Al-SiC-B4C hybrid composites.Table 1
Chemical arrangement of AA7075.
ComponentMagnesiumSiliconManganeseIronCopperZincAluminium(wt%)2.50.080.040.31.55.6RemainingTable 2
Mechanical properties of AA7075.
Tensile strength (MPa)Density (g/cm3)Vickers hardness (HV)% elongation (%)2282.8117517Table 3
Particulars ofSiC and B4C particulate.
ReinforcementMean particle sizeHardnessDensityMelting point(μm)(kg/mm2)(g/cm3)°CSiC352,8003.202,700B4C3524502.522,450


### 2.2. Composite Fabrication

The specimen was prepared employing the standard stir-casting method. Figure1 depicts the experimental setup employed in this study. For the production of each sample, a graphite crucible was used to melt 1000 grams of aluminium in an electric furnace with an argon environment at 8000°C. As a way to improve the matrix alloy’s wettability with reinforcements, magnesium (2 wt%) was infused into the molten metal. Magnesium is considered a better wettability agent for SiC. To oxidize the surface of the B4C particles, they were baked for 3–4 hours at a temperature of 2000°C in a baking oven. Using a graphite stirrer set to 400 rpm for roughly 10 minutes, this preheated powder was fed into the molten metal at a consistent feed rate using SiC. This ensured a uniform distribution of the powder throughout the metal. A 300 mm long, 80 mm wide, and 40 mm deep injection mold was utilized to pour the liquid combination.Figure 1
Diagram of experimental arrangement.The hybridized composite was allowed to harden at ambient temperature before being taken from the mold and subjected to various mechanical tests. Samples containing 4%, 8%, 12%, and 16% (SiC + B4) were prepared using the same procedure.


### 2.3. Measurements

Microstructural investigation was performed by producing cylindrical samples with 6 mm diameters and 20 mm heights. The microstructure samples depicted in Figure2 were used in the research. An SEM was utilized to examine the microstructure of the Al-SiC-B4C mixture. Keller’s Reagent (HF/HF/HCl/HNO3/H2O) and Emery paper (400, 600, and 1000 grades) were utilized to etch samples using Keller’s Reagent (H2O). Nikon’s Eclipse MA-100 optical microscope and JOEL’s JSM-6510LV scanning electron microscope were utilized for the microstructure study.Figure 2
Samples for microstructure evaluation.All samples were subjected to a 15-second microhardness test on a Vickers hardness testing method and a force of 1 kg. The hardness of small cuboids was determined using an electric discharge machine. Samples were indented by a diamond indenter, which had square bases and an angle of 136° between them. The Charpy tests, which used specimens 56 × 10 × 10 mm in size, with notch depths of 3 mm, tip radius of 0.30 mm, and angles of 45°, were performed on impact testing machines using these specimens. As shown in Figure3, the samples used in this study are schematically depicted. All specimens were evaluated three times for hardness and impact strength in order to acquire an average result.Figure 3
Diagram of specimen for impact strength.The hybrid composites’ tensile behaviour was examined and tested in accordance with the ASTM-E8 standard. Temperatures ranged from 25°C to 30°C and relative humidity ranged from 40 to 60% during the tests on the universal testing equipment. Using the schematic diagram indicated in Figure4(a), the flat specimens with a thickness of 6 mm were machined to match the dimensions of the schematic diagram. Figure 4(b) shows the tensile test specimens.Figure 4
Tensile test. (a) Diagram and (b) sample.
(a)(b)The mass and volume of a sample were utilized to calculate the density of the specimen. Equation (1) can be used to determine the density by using the measurements of mass and volume:(1)densitygcm3=massvolume.The following equation can be used to determine the specimen’s porosity using a straightforward relationship:(2)porosity=1−dda,whereas d is the mass of the specimen and da is the density of the base material.It will be possible to account for even closed porosity using this straightforward approach.


## 2.1. Base Material

A 6 mm thick AA7075 plate was chosen as the basis material in this study. The matrix alloy’s chemical and mechanical properties are listed in Tables1 and 2. At a temperature of roughly 180°C, the alloy was artificially aged to achieve the T6 state. Table 3 lists the specifics of the SiC and B4C particles utilized as reinforcement in this study. The particles used in this investigation were 35 μm in diameter. By adding 4, 8, 12, and 16wt% of the (SiC + B4C) mixture in equal proportions, we were able to create Al-SiC-B4C hybrid composites.Table 1
Chemical arrangement of AA7075.
ComponentMagnesiumSiliconManganeseIronCopperZincAluminium(wt%)2.50.080.040.31.55.6RemainingTable 2
Mechanical properties of AA7075.
Tensile strength (MPa)Density (g/cm3)Vickers hardness (HV)% elongation (%)2282.8117517Table 3
Particulars ofSiC and B4C particulate.
ReinforcementMean particle sizeHardnessDensityMelting point(μm)(kg/mm2)(g/cm3)°CSiC352,8003.202,700B4C3524502.522,450


## 2.2. Composite Fabrication

The specimen was prepared employing the standard stir-casting method. Figure1 depicts the experimental setup employed in this study. For the production of each sample, a graphite crucible was used to melt 1000 grams of aluminium in an electric furnace with an argon environment at 8000°C. As a way to improve the matrix alloy’s wettability with reinforcements, magnesium (2 wt%) was infused into the molten metal. Magnesium is considered a better wettability agent for SiC. To oxidize the surface of the B4C particles, they were baked for 3–4 hours at a temperature of 2000°C in a baking oven. Using a graphite stirrer set to 400 rpm for roughly 10 minutes, this preheated powder was fed into the molten metal at a consistent feed rate using SiC. This ensured a uniform distribution of the powder throughout the metal. A 300 mm long, 80 mm wide, and 40 mm deep injection mold was utilized to pour the liquid combination.Figure 1
Diagram of experimental arrangement.The hybridized composite was allowed to harden at ambient temperature before being taken from the mold and subjected to various mechanical tests. Samples containing 4%, 8%, 12%, and 16% (SiC + B4) were prepared using the same procedure.


## 2.3. Measurements

Microstructural investigation was performed by producing cylindrical samples with 6 mm diameters and 20 mm heights. The microstructure samples depicted in Figure2 were used in the research. An SEM was utilized to examine the microstructure of the Al-SiC-B4C mixture. Keller’s Reagent (HF/HF/HCl/HNO3/H2O) and Emery paper (400, 600, and 1000 grades) were utilized to etch samples using Keller’s Reagent (H2O). Nikon’s Eclipse MA-100 optical microscope and JOEL’s JSM-6510LV scanning electron microscope were utilized for the microstructure study.Figure 2
Samples for microstructure evaluation.All samples were subjected to a 15-second microhardness test on a Vickers hardness testing method and a force of 1 kg. The hardness of small cuboids was determined using an electric discharge machine. Samples were indented by a diamond indenter, which had square bases and an angle of 136° between them. The Charpy tests, which used specimens 56 × 10 × 10 mm in size, with notch depths of 3 mm, tip radius of 0.30 mm, and angles of 45°, were performed on impact testing machines using these specimens. As shown in Figure3, the samples used in this study are schematically depicted. All specimens were evaluated three times for hardness and impact strength in order to acquire an average result.Figure 3
Diagram of specimen for impact strength.The hybrid composites’ tensile behaviour was examined and tested in accordance with the ASTM-E8 standard. Temperatures ranged from 25°C to 30°C and relative humidity ranged from 40 to 60% during the tests on the universal testing equipment. Using the schematic diagram indicated in Figure4(a), the flat specimens with a thickness of 6 mm were machined to match the dimensions of the schematic diagram. Figure 4(b) shows the tensile test specimens.Figure 4
Tensile test. (a) Diagram and (b) sample.
(a)(b)The mass and volume of a sample were utilized to calculate the density of the specimen. Equation (1) can be used to determine the density by using the measurements of mass and volume:(1)densitygcm3=massvolume.The following equation can be used to determine the specimen’s porosity using a straightforward relationship:(2)porosity=1−dda,whereas d is the mass of the specimen and da is the density of the base material.It will be possible to account for even closed porosity using this straightforward approach.


## 3. Results and Discussion

### 3.1. XRD and Microstructural Study

By using XRD patterns, Figures5(a)–5(e) depict the matrix alloy and hybridized composites. The prominent peaks in the XRD data belong to aluminium, which is the parent material. Hybrid composites’ lower peaks show their SiC and B4C content. At the goniometer receiving slit station, the diffractometer uses a graphite curved single crystal monochromator to select CuK radiation (λ = 1.54A). During the XRD investigation, a diffraction angle (2θ) of 20–1100 was maintained. Figures 5(a)–5(e) depict the occurrence of Si, Al4C3, and Al3BC, all of which were found in the final samples. The hybrid composites’ Al3BC and Al4C3 maxima, on the other hand, were incredibly low. In an electric furnace, aluminium and boron carbide interacted directly to produce Al3BC and Al4C3 [21–23].Figure 5
X-ray diffraction forms of (a) 0%, (b) 4%, (c) 8%, (d) 12%, and (e) 16% of (silicon carbide + boron carbide) strengthened hybridized composites.
(a)(b)(c)(d)(e)Figures6(a) and 6(b) show scanning electron microscope images of silicon carbide and boron carbide particles, respectively. First-generation Al 7075 grains developing dendritically reveal the interdendritic zone between aluminium and silicon grains in the microstructure of the Al 7075 silicate eutectic. The temperature mismatch between the molten matrix and the reinforcing particles results in the formation of aluminium. Due to the ceramic particles’ weaker heat conductivity compared to Al 7075 melt, the molten matrix is hotter than the temperature of the ceramic particles.Figure 6
(a, b) SEM images of silicon carbide and boron carbide particles.As a result, the solidification process requires more time to cool hotter particles, which in turn heats the liquid alloy around them. When the hybrid composites were cooled during solidification, they formed dendritic regions. In regions where the dispersion of reinforced particles is not as good, the particle clusters were also detected. No cavities in the interface indicate that the interfacial connection between particles and matrix is strong. According to [20, 24], the reinforcing particulate can prevent dendritic development. Increasing the weight percentage of reinforcement leads to an increased degree of cluster agglomeration as well. In contrast, well-placed agglomerations in the composites can reinforce the composite [25].


### 3.2. Impact Strength and Microhardness

Samples of substrate metal AA7075 and hybridized composites are shown in Table4. Hybrid composites have higher hardness values than their unreinforced counterparts, and this hardness rises in direct proportion to the weight percentage of reinforcement added. This is in accordance with the investigation that took place previously [26]. The matrix’s hardness and resistance to plastic deformation are both improved by the inclusion of hard reinforcing particles [27]. As shown in Figure 7, the hardness increases up to 12%wt fraction, which is shown in the graph. Increasing the density of the particulate mixture within the matrix reduces the hardness of the SiC and B4C particles [28]. The ideal hardness of reinforced composites with a (SiC + B4C) mixture of 12%wt is 8% greater than the hardness of unreinforced alloys.Table 4
Results on microhardness.
Terms of specimenHardness1Hardness2Hardness 3Average hardnessAA7075170172168170AA7075 + 4% (SiC + B4C)168169170173AA7075 + 8% (SiC + B4C)171173175173AA7075 + 12%(SiC + B4C)170172173172AA7075 + 16% (SiC + B4C)168173172171Figure 7
Hardness of unreinforced alloy and hybridized composites.Table5 summarizes the impact test findings for unreinforced alloys and hybrid composites. As shown in Figure 8, as compared to the unreinforced alloy, the impact strength of composites falls as the weight percentage of particles rises in the metal matrix. However, despite the fact that hybrid composites’ impact strength tends to decrease, the reduction amount was quite small. One possible explanation for the decrease in strength is the modest change in material properties from ductile to brittle caused by the reinforcement of hard particles [29].Table 5
Impact tests results.
Terms of specimenTest 1(Nm)Test 2 (Nm)Test 3 (Nm)Mean impactAA 70759.59.89.59.6AA 7075 + 4% (SiC + B4C)9.49.49.29.33AA 7075 + 8% (SiC + B4C)8.78.758.88.75AA 7075 + 12% (SiC + B4C)8.48.48.28.33AA 7075 + 16% (SiC + B4C)7.97.957.97.92Figure 8
Impact strength on variant wt% of (SiC + B4C) mixture.Cracking and decohesion of reinforcing particles lead to the loss of impact strength in composites because of microstructural defects. A reduction in impact strength occurs as a wt% increase in reinforcement occurs, which leads to a rise in failure rates.


### 3.3. Tensile Behavior of Hybrid Composites

Hybrid composites exhibited a surge in UTS with an increasing weight percentage of the (silicon carbide + boron carbide) mixture in the tensile behavior when the reinforcing mixture was present. Table6 shows the tensile values as well as the % elongation. Figure 4(b) shows that all samples, even the unreinforced ones, did not break at the center of the gauge length. Because the midsection of a tensile specimen is the weakest when subjected to tensile stresses, it is common for the specimen to shatter. Due to particle concentration, defects, or minute impurities, the center may not be shattered in some cases. For example, the UTS went from 319 MPa at 0% addition to 386 MPa at 12% addition, an increase of 21%. In terms of UTS, the hybrid composite with 12%wt of reinforcement outperforms its 16%wt counterpart. The increased porosity and excessive aggregation of reinforcing particles in the microstructures could be the cause [30]. Porosity in hybrid composites that have been cured reduces material strength, which is caused by the aggregation of tiny particles.Table 6
Results of tensile strength along with % elongation.
Terms of specimenUltimate tensile strength (MPa)% enhancement% elongationAA 7075319—8.42AA 7075 + 4% (SiC + B4C)3354.87.91AA 7075 + 8% (SiC + B4C)35812.317.32AA 7075 + 12% (SiC + B4C)38621.076.89AA 7075 + 16% (SiC + B4C)37216.76.9The % elongation of hybrid composites declines as the weight percentage of reinforcement increases in comparison to AA7075. Figure9 demonstrates how the UTS and elongation percentage change when the wt% of strengthening in the aluminium matrix increases. With the inclusion of strengthening particles and a decrease in the ductility of Al 7075 composition, the percentage elongation decrease may be attributed to these factors.Figure 9
Ultimate tensile strength and % elongation for different weight percentages of (SiC + B4C) mixture.


### 3.4. Density and Porosity

Figures10 and 11 show the outcome of the measurements of density and porosity. Hybrid composite density decreased after 2.7 g/cm3 at 0% (silicon carbide + boron carbide) towards 2.61% at 16% (SiC + B4C) addition, indicating that the inclusion of reinforcing particles in the metal matrix has little influence on density. There was a recorded 5.2% reduction in density. With the addition of strengthening, the porosity ranges of the strengthened hybridized composites marginally rise. There is an increase in value from 0.35 to 2.14 when adding 16% (SiC + B4C) to the mixture. The authors in [31, 32] found similar results in terms of density and porosity.Figure 10
Density with variant weight percentage of (SiC + B4C) mixture.Figure 11
Porosity with variant wt% of (SiC + B4C) mixture.


## 3.1. XRD and Microstructural Study

By using XRD patterns, Figures5(a)–5(e) depict the matrix alloy and hybridized composites. The prominent peaks in the XRD data belong to aluminium, which is the parent material. Hybrid composites’ lower peaks show their SiC and B4C content. At the goniometer receiving slit station, the diffractometer uses a graphite curved single crystal monochromator to select CuK radiation (λ = 1.54A). During the XRD investigation, a diffraction angle (2θ) of 20–1100 was maintained. Figures 5(a)–5(e) depict the occurrence of Si, Al4C3, and Al3BC, all of which were found in the final samples. The hybrid composites’ Al3BC and Al4C3 maxima, on the other hand, were incredibly low. In an electric furnace, aluminium and boron carbide interacted directly to produce Al3BC and Al4C3 [21–23].Figure 5
X-ray diffraction forms of (a) 0%, (b) 4%, (c) 8%, (d) 12%, and (e) 16% of (silicon carbide + boron carbide) strengthened hybridized composites.
(a)(b)(c)(d)(e)Figures6(a) and 6(b) show scanning electron microscope images of silicon carbide and boron carbide particles, respectively. First-generation Al 7075 grains developing dendritically reveal the interdendritic zone between aluminium and silicon grains in the microstructure of the Al 7075 silicate eutectic. The temperature mismatch between the molten matrix and the reinforcing particles results in the formation of aluminium. Due to the ceramic particles’ weaker heat conductivity compared to Al 7075 melt, the molten matrix is hotter than the temperature of the ceramic particles.Figure 6
(a, b) SEM images of silicon carbide and boron carbide particles.As a result, the solidification process requires more time to cool hotter particles, which in turn heats the liquid alloy around them. When the hybrid composites were cooled during solidification, they formed dendritic regions. In regions where the dispersion of reinforced particles is not as good, the particle clusters were also detected. No cavities in the interface indicate that the interfacial connection between particles and matrix is strong. According to [20, 24], the reinforcing particulate can prevent dendritic development. Increasing the weight percentage of reinforcement leads to an increased degree of cluster agglomeration as well. In contrast, well-placed agglomerations in the composites can reinforce the composite [25].


## 3.2. Impact Strength and Microhardness

Samples of substrate metal AA7075 and hybridized composites are shown in Table4. Hybrid composites have higher hardness values than their unreinforced counterparts, and this hardness rises in direct proportion to the weight percentage of reinforcement added. This is in accordance with the investigation that took place previously [26]. The matrix’s hardness and resistance to plastic deformation are both improved by the inclusion of hard reinforcing particles [27]. As shown in Figure 7, the hardness increases up to 12%wt fraction, which is shown in the graph. Increasing the density of the particulate mixture within the matrix reduces the hardness of the SiC and B4C particles [28]. The ideal hardness of reinforced composites with a (SiC + B4C) mixture of 12%wt is 8% greater than the hardness of unreinforced alloys.Table 4
Results on microhardness.
Terms of specimenHardness1Hardness2Hardness 3Average hardnessAA7075170172168170AA7075 + 4% (SiC + B4C)168169170173AA7075 + 8% (SiC + B4C)171173175173AA7075 + 12%(SiC + B4C)170172173172AA7075 + 16% (SiC + B4C)168173172171Figure 7
Hardness of unreinforced alloy and hybridized composites.Table5 summarizes the impact test findings for unreinforced alloys and hybrid composites. As shown in Figure 8, as compared to the unreinforced alloy, the impact strength of composites falls as the weight percentage of particles rises in the metal matrix. However, despite the fact that hybrid composites’ impact strength tends to decrease, the reduction amount was quite small. One possible explanation for the decrease in strength is the modest change in material properties from ductile to brittle caused by the reinforcement of hard particles [29].Table 5
Impact tests results.
Terms of specimenTest 1(Nm)Test 2 (Nm)Test 3 (Nm)Mean impactAA 70759.59.89.59.6AA 7075 + 4% (SiC + B4C)9.49.49.29.33AA 7075 + 8% (SiC + B4C)8.78.758.88.75AA 7075 + 12% (SiC + B4C)8.48.48.28.33AA 7075 + 16% (SiC + B4C)7.97.957.97.92Figure 8
Impact strength on variant wt% of (SiC + B4C) mixture.Cracking and decohesion of reinforcing particles lead to the loss of impact strength in composites because of microstructural defects. A reduction in impact strength occurs as a wt% increase in reinforcement occurs, which leads to a rise in failure rates.


## 3.3. Tensile Behavior of Hybrid Composites

Hybrid composites exhibited a surge in UTS with an increasing weight percentage of the (silicon carbide + boron carbide) mixture in the tensile behavior when the reinforcing mixture was present. Table6 shows the tensile values as well as the % elongation. Figure 4(b) shows that all samples, even the unreinforced ones, did not break at the center of the gauge length. Because the midsection of a tensile specimen is the weakest when subjected to tensile stresses, it is common for the specimen to shatter. Due to particle concentration, defects, or minute impurities, the center may not be shattered in some cases. For example, the UTS went from 319 MPa at 0% addition to 386 MPa at 12% addition, an increase of 21%. In terms of UTS, the hybrid composite with 12%wt of reinforcement outperforms its 16%wt counterpart. The increased porosity and excessive aggregation of reinforcing particles in the microstructures could be the cause [30]. Porosity in hybrid composites that have been cured reduces material strength, which is caused by the aggregation of tiny particles.Table 6
Results of tensile strength along with % elongation.
Terms of specimenUltimate tensile strength (MPa)% enhancement% elongationAA 7075319—8.42AA 7075 + 4% (SiC + B4C)3354.87.91AA 7075 + 8% (SiC + B4C)35812.317.32AA 7075 + 12% (SiC + B4C)38621.076.89AA 7075 + 16% (SiC + B4C)37216.76.9The % elongation of hybrid composites declines as the weight percentage of reinforcement increases in comparison to AA7075. Figure9 demonstrates how the UTS and elongation percentage change when the wt% of strengthening in the aluminium matrix increases. With the inclusion of strengthening particles and a decrease in the ductility of Al 7075 composition, the percentage elongation decrease may be attributed to these factors.Figure 9
Ultimate tensile strength and % elongation for different weight percentages of (SiC + B4C) mixture.


## 3.4. Density and Porosity

Figures10 and 11 show the outcome of the measurements of density and porosity. Hybrid composite density decreased after 2.7 g/cm3 at 0% (silicon carbide + boron carbide) towards 2.61% at 16% (SiC + B4C) addition, indicating that the inclusion of reinforcing particles in the metal matrix has little influence on density. There was a recorded 5.2% reduction in density. With the addition of strengthening, the porosity ranges of the strengthened hybridized composites marginally rise. There is an increase in value from 0.35 to 2.14 when adding 16% (SiC + B4C) to the mixture. The authors in [31, 32] found similar results in terms of density and porosity.Figure 10
Density with variant weight percentage of (SiC + B4C) mixture.Figure 11
Porosity with variant wt% of (SiC + B4C) mixture.


## 4. Conclusion

In summary, the stir casting process was employed to create AA7075 reinforced with 4, 8, 12, and 16 weight percentages of (SiC + B4C) particulates, and experimental results led to the conclusions listed below:(1)
The existence of Al 7075, silicon carbide (Sic), aluminum carbide (Al4C3), ternary alumina-boron carbide (Al3BC), boron carbide(B4C), and silicon (Si) in the hybridized composites was confirmed by XRD, and SEM micrographs showed good dispersion of the reinforced particles. As the weight percentage of strengthening rises, so does the particle agglomeration.(2)
It went from 170 HV for an unreinforced alloy to 175 HV for a hybridized component with 12wt% of strengthening in microhardness. An 8% increase in hardness was seen. There was also a minor drop in hardness over 12%wt of reinforcing.(3)
The impact strength of hybridized composites steadily decreases as reinforcement is added at a marginal rate.(4)
The ultimate tensile strength of hybrid composites is significantly improved by the addition of reinforcement. When equated to unreinforced alloy, the UTS increases in strength by 21%, from 318 to 386 MPa. With the addition of 16%wt strengthening, however, the hybridized composite’s strength decreased slightly.(5)
With increasing AA matrix composition, the % elongation was identified to be decreased as the strengthening percentage improved.(6)
A decrease in density and an increase in porosity were noted when reinforcing particulate was added. At 0% SiC + B4C adding to 16% Silicon Carbide + Boron Carbide in the metal matrix, the density decreases between 2.7 g/cm3 and 2.61 g/cm3, and the porosity increases between 0.4% and 2.21%.



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*Source: 2411848-2022-07-22.xml*