# Analysis and Experimental Investigation of A356 Aluminium Alloy Hybrid Composites Reinforced with Gr-FE3O4-B4C Nanoparticles Synthesised by Selective Laser Melting (SLM)

Authors: J. Anoop; Vijay Ananth Suyamburajan; P. Sekhar Babu; Sisay Addis Filketu
Journal: Journal of Nanomaterials
 (2022)

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## Abstract

Additive manufacturing techniques (AMTs) evolved quickly from simple prototype options to promising additive manufacturing techniques. The additive technologies, which include point-by-point material merging, full melting, and solidification of powder particles, provide potential unique braves and advantages with nanometal powders. In the fabrication of A356 aluminium alloy-based hybrid metal matrix nanocomposites, graphite (Gr), iron oxide (Fe3O4), and boron carbide (B4C) are used as nanoreinforcement. Famous AMTs like selective laser melting have created A356 hybrid nanocomposites (SLM). The ingot was made out of a cylindrical slot measuring 14×100 mm. The percentages 2%, 4%, and 6% are added to the reinforcements Gr, Fe3O4, and B4C. Microtensile and microhardness tests were used to determine the outcome of the reinforcement. Microtensile and microhardness parameters are assessed using microtensile test equipment and a Vickers hardness tester, with the specimen prepared in accordance with ASTM standards. A356 with 2, 4, and 6% reinforcing has a Vickers Hardness Number (VHN) of 144, 163, and 188, respectively. As the boron carbide reinforcement is increased, the load value of graphite and iron oxide (2, 4, and 6%) rises. The greatest ultimate tensile strengths are 260.10, 290.06, and 325.43 N/mm2, respectively. The bonding structure of nanocomposites is assessed using an OM, and then, microtensile specimens are assessed using a SEM. As a result of the superior effect of the diverse reinforcements Gr, Fe3O4, and B4C, more increased tensile and hardness qualities have been attained.


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## Body

## 1. Introduction

Nowaday’s rapid developments in engineering and technology have a huge demand for lightweight and high-strength materials with good tensile, wear, and hardness properties for particular use in aeronautical, automobile, medical, marine, and defence departments. Aluminium and their alloys are espoused in enormous applications, in particular aeronautical, automobile, medical, sports, defence, petrochemical engineering, and marine, outstanding to their superb properties like high strength, good thermal conductivity, high wear, and corrosion resistance [1–3]. Most of the researchers used casting [4, 5], powder metallurgy [6–8], and heat treatment techniques [9–11] to improve the mechanical properties of aluminium alloys. These traditional techniques are inadequate to meet technological demand. The application of modern advancement to the manufacturing of products and parts with high mechanical properties is the major intention of material processing.Metal matrix composites (MMCs) are an essential role in lightweight and high-strength materials that venture to coalesce the high solidness, stiffness, and sturdiness provided by a metal matrix [12–14]. Research shows that the formation of metal matrix composites with the addition of the different reinforcements into the matrix can improve the mechanical properties appreciably. Generally used reinforcements include particle, whisker, and fiber. When comparing whisker and fiber, particle reinforcement has more benefits produced in the matrix such as processing, uniform microstructure, and cost [15]. Consequently, particle reinforcement MMCs have been used in aeronautical industries, automotive industries, and medical and defence departments. Nanoparticles by adding a metal matrix improve the strength of MMCs extensively due to disarticulation and dispersal strengthening. Nanoparticles assist to enhance mechanical properties such as strength, wear resistance, and hardness of MMCs [16].When high strength is required, A356 aluminium casting alloys are employed in the manufacture of aviation components. The need for lightweight, high-strength components is expanding all the time. Aluminium matrix composites are being touted as a new generation of possible materials for a wide range of technical applications. For Aluminium Metal Matrix Composites (AMMCs), generally used nanoparticle reinforcement contains B4C, SiC, Gr, TiB2, Al2O3, and TiC [17–19].B4C is an elegant reinforcement material because of its superb strength, microhardness, wear resistance, high specific stiffness, good damping capacity, excellent thermal conductivity, chemical and thermal stability, high melting point, high wettability, low density, and good interfacial bonding property with aluminium comparable to Al2O3, TiB2, TiC, and SiC [20–22].Dirisenapu et al. [23] reported that the tensile strength of the nanocomposites increased with an increase in B4C nanoparticles and percentage of elongation; density is decreased.Chandrasekaran et al. [24] investigated Al-B4C cermet fabricated by additive manufacturing; the hardness of the composite reached as high as 80 Ra with an increase of 59.3 Vol% b4c particle.Poovazhagan et al. [25] studied the added Nanob4c in AMCs and enhanced its hardness, tensile strength, wear resistance, and good ductility, and impact resistance of the Al alloy was retained.Graphite is another important secondary reinforcement material because of its constructive dry sliding wear condition for AMCs. In the current research, graphite favoured in AMCs improved both wear resistance and machinability. The incorporation of graphite diminishes the surface porosity and enhances mechanical and tribological properties continuously [26–28].Saini et al. [29] observed that hardness of the hybrid composite had increased significantly to added nanosilica particles and graphite flake as reinforcements. These new hybrid composites can be used for various applications including engine piston, automobile components, and microelectronic devices.Zhang et al. [30] prepared two variety composites Al-Sic-graphite and Al-Sic-graphene and observed reinforcement and microstructure by using SEM, TEM, XRD, and Raman spectroscopy. The added graphite flake reinforcement is partly desquamated into thinner ones, and the clusters of graphite with a size as large as 10 μm can still be observed in the Al-graphite sample.Alaneme et al. [31] developed Al-Mg-Si alloy with steel and graphite particle composites prepared by stir casting. All the mechanical properties are reduced slightly with an augment in graphite content and trailed the composite reinforced with 8 wt.% steel.Fe3O4 is a third reinforcement, and it plays an important role in the aerospace industry. The addition of Fe3O4 nanoparticle reinforcements in the AMCs enhanced the magnetic permeability of composites and thermal properties lacking mechanical degradation [32]. Fereiduni et al. [33] used Fe3O4 nanoparticles in the welding process to Al-Fe intermetallics due to their small size and heat generated.AMCs produced with selective laser melting (SLM) have attracted all embracing attention in the lightweight application fields [34]. AMCs manufactured by SLM efficiently can accomplish greater mechanical properties compared to conventional manufacturing. Martin et al. [35] reported crack-free AA7075 elements achieved by mixing nano-ZrH2 particles with 7075 powder before SLM. All through solidification, the recently shaped Al3Zr phase obviously assisted granule modification, because of which the mechanical properties are enhanced. Gu et al. [36] discussed that the effect of nanoparticle reinforcement on the strength and ductility of materials is enhanced simultaneously as manufactured by SLM. Zhang et al. [37] fabricated SiC/AlSi10Mg composites by SLM technique, and the microstructure and mechanical properties of composites are investigated. The AMCs show the highest yield strength and modulus among values of 408 MPa and 90 GPa, respectively. In the current research work, the AMCs-B4C-Gr-Fe3O4 hybrid composite is fabricated by selective laser melting (SLM) and investigated tensile, hardness, and microstructure.


## 2. Experimental Details

### 2.1. Powder Preparation

The experiment’s matrix materials were A356 alloy powder (60 m, =2.662 g/cc) acquired from Bhoomi Metal & Alloys in Maharashtra. B4C powder (30 m, 2.25 g/cc), Gr powder (100 m, 2.26 g/cc), and Fe3O4 powder (60 m, 4.9 g/cc) were acquired from Intelligent Materials Private Limited in Punjab and Saveer Biotech Limited in Uttar Pradesh, respectively. In a planetary ball mill, three samples (2, 4, and 6) of the A356-B4C-Gr-Fe3O4 hybrid composite powder were prepared. The details of the sample powder are mentioned in Table 1.Table 1
Sample powder details.
Sample no.Composite powderA356B4CGrFE3O41A356-B4C-Gr-FE3O494222288444382666


### 2.2. SLM Process

The A356-B4C-Gr-FE3O4 specimens were created on an SLM machine designed by ARCI in Hyderabad, India, as shown in Figure 1. An SLM machine is fitted with a fiber laser with a wavelength of 1076 nm. The entire experiment was carried out with a continuous-wave laser with a power of 400 W and a spot size of 110 m. To prevent the specimens from oxidising, the SLM procedure was carried out in a vacuum, as described in earlier literature reviews [25–27]. The pressure in the chamber was fixed at 6×10−3 Pa. In addition, an argon gas flow was incorporated into the experimental setting in order to evaluate the impact of atmospheric conditions on the make superiority. The chamber was emptied to the abovementioned pressure. During laser irradiation, the chamber pressure was adjusted to 1.5·103 Pa by using argon gas to produce flow. Table 2 and Figure 2 show the process parameters and SLM procedure. The experiment was carried out with each combination of process parameters to construct single-layer samples with a dimension of 14mm×100mm.Figure 1
The SLM experimental setup.Table 2
The list of SLM process machine specifications and laser process parameters.
Fiber laser400 WSpot sizes80-115μmScan processing speed10 m/sBuild area280×280×365 mmLayer thickness20-100μmPlatform heating200°CFigure 2
Flow chart of SLM process.


## 2.1. Powder Preparation

The experiment’s matrix materials were A356 alloy powder (60 m, =2.662 g/cc) acquired from Bhoomi Metal & Alloys in Maharashtra. B4C powder (30 m, 2.25 g/cc), Gr powder (100 m, 2.26 g/cc), and Fe3O4 powder (60 m, 4.9 g/cc) were acquired from Intelligent Materials Private Limited in Punjab and Saveer Biotech Limited in Uttar Pradesh, respectively. In a planetary ball mill, three samples (2, 4, and 6) of the A356-B4C-Gr-Fe3O4 hybrid composite powder were prepared. The details of the sample powder are mentioned in Table 1.Table 1
Sample powder details.
Sample no.Composite powderA356B4CGrFE3O41A356-B4C-Gr-FE3O494222288444382666


## 2.2. SLM Process

The A356-B4C-Gr-FE3O4 specimens were created on an SLM machine designed by ARCI in Hyderabad, India, as shown in Figure 1. An SLM machine is fitted with a fiber laser with a wavelength of 1076 nm. The entire experiment was carried out with a continuous-wave laser with a power of 400 W and a spot size of 110 m. To prevent the specimens from oxidising, the SLM procedure was carried out in a vacuum, as described in earlier literature reviews [25–27]. The pressure in the chamber was fixed at 6×10−3 Pa. In addition, an argon gas flow was incorporated into the experimental setting in order to evaluate the impact of atmospheric conditions on the make superiority. The chamber was emptied to the abovementioned pressure. During laser irradiation, the chamber pressure was adjusted to 1.5·103 Pa by using argon gas to produce flow. Table 2 and Figure 2 show the process parameters and SLM procedure. The experiment was carried out with each combination of process parameters to construct single-layer samples with a dimension of 14mm×100mm.Figure 1
The SLM experimental setup.Table 2
The list of SLM process machine specifications and laser process parameters.
Fiber laser400 WSpot sizes80-115μmScan processing speed10 m/sBuild area280×280×365 mmLayer thickness20-100μmPlatform heating200°CFigure 2
Flow chart of SLM process.


## 3. Testing of Composite

### 3.1. Microstructural Investigation

The optical microscope was used to examine the SLM specimens, as illustrated in Figure3. To produce a better disparity, the samples were ground with 220, 400, 600, and 1000 grades of emery paper, then refined with diamond suspensions of 6, 4, and 2 mm diameters, and etched using Kroll’s reagent (15 mL of HF, 40 mL of HNO3, and 60 mL of water, ASTM E407) for 30 seconds. Optical microscopy was used to investigate the microstructure (1000x magnifications, GX51, Olympus).Figure 3
Optical microscope.


### 3.2. Microhardness

When test samples are very small or thin in a composite sample, microhardness testing is a technique for estimating a material’s hardness on a microscopic scale. Microhardness was assessed on this specimen using UHL VMHT digital microhardness equipment, as illustrated in Figure4. Ranges of indents may be completed on the sample with the aid of computer control, and the hardness can be computed (load range from 0.3 to 30 kgf) for the purpose of detachment from an orientation point. This microhardness apparatus is very well suited to create fractures on the sample surface, allowing the rupture robustness to be assessed.Figure 4
Microhardness tester (UHL VMHT digital).


### 3.3. Tensile Test

Microtension tests are used to measure the strength and ductility of nanocomposites under uniaxial tensile stresses in the development of novel alloys for quality control, commercial shipment acceptance testing, and structural design assistance. It was validated in accordance with ASTM B-557M standards using three specimens, each measuring 100 mm in length and 14 mm in diameter, as illustrated in Figure5 for each AMC family. The microtension was customary in any form at room temperature specifically the methods of determination of yield strength, yield point, elongation, tensile strength, and reduction of area. The multipurpose microtensile testing machine type (Max. static load±3000 N and Max. dynamic load±2500 N) among dutiful seize is used to hold the tensile specimen as shown in Figure 6.Figure 5
Microtensile test specimen.Figure 6
Multipurpose microtensile testing machine.


### 3.4. SEM

In the microanalysis and failure analysis of nanocomposites, scanning electron microscopy (SEM) is used very professionally. It is done at high exaggerations, produces high-resolution pictures, and precisely measures very small facial features and objects. By rastering a focused electron beam across the surface and distinguishing between generated and backscattered electron signals, SEM offers comprehensive high-resolution images of the material. Figure7 shows the SEM.Figure 7
Scanning electron microscopy (SEM).


## 3.1. Microstructural Investigation

The optical microscope was used to examine the SLM specimens, as illustrated in Figure3. To produce a better disparity, the samples were ground with 220, 400, 600, and 1000 grades of emery paper, then refined with diamond suspensions of 6, 4, and 2 mm diameters, and etched using Kroll’s reagent (15 mL of HF, 40 mL of HNO3, and 60 mL of water, ASTM E407) for 30 seconds. Optical microscopy was used to investigate the microstructure (1000x magnifications, GX51, Olympus).Figure 3
Optical microscope.


## 3.2. Microhardness

When test samples are very small or thin in a composite sample, microhardness testing is a technique for estimating a material’s hardness on a microscopic scale. Microhardness was assessed on this specimen using UHL VMHT digital microhardness equipment, as illustrated in Figure4. Ranges of indents may be completed on the sample with the aid of computer control, and the hardness can be computed (load range from 0.3 to 30 kgf) for the purpose of detachment from an orientation point. This microhardness apparatus is very well suited to create fractures on the sample surface, allowing the rupture robustness to be assessed.Figure 4
Microhardness tester (UHL VMHT digital).


## 3.3. Tensile Test

Microtension tests are used to measure the strength and ductility of nanocomposites under uniaxial tensile stresses in the development of novel alloys for quality control, commercial shipment acceptance testing, and structural design assistance. It was validated in accordance with ASTM B-557M standards using three specimens, each measuring 100 mm in length and 14 mm in diameter, as illustrated in Figure5 for each AMC family. The microtension was customary in any form at room temperature specifically the methods of determination of yield strength, yield point, elongation, tensile strength, and reduction of area. The multipurpose microtensile testing machine type (Max. static load±3000 N and Max. dynamic load±2500 N) among dutiful seize is used to hold the tensile specimen as shown in Figure 6.Figure 5
Microtensile test specimen.Figure 6
Multipurpose microtensile testing machine.


## 3.4. SEM

In the microanalysis and failure analysis of nanocomposites, scanning electron microscopy (SEM) is used very professionally. It is done at high exaggerations, produces high-resolution pictures, and precisely measures very small facial features and objects. By rastering a focused electron beam across the surface and distinguishing between generated and backscattered electron signals, SEM offers comprehensive high-resolution images of the material. Figure7 shows the SEM.Figure 7
Scanning electron microscopy (SEM).


## 4. Result and Discussion

### 4.1. Microstructure

Figure8 shows the fascia microstructures of A356 with 2, 4, and 6% B4C-Gr-Fe3O4 at magnifications of 100. The nanocomposite specimen remained sophisticated in terms of removing particles from the surface. Optical microscopes are expected to support particle distribution vestiges. The additive manufacturing process was inspected under an optical microscope to determine the specimen reinforcement pattern. The homogeneous dispersion of nanoparticles in the matrix material of the A356 alloy was clearly visible. The presence of nanoparticles leads to the formation of cracks, which leads to elastic deformation with increases in load. Composite rupture is represented by dimples, voids, clusters, and cracks. Fragile composite fracture in the form of cracks and rupture is due to the strong interfacial bonding between the reinforcements and the A356 matrix.Figure 8
Microstructure of A356 with reinforcement B4C-Gr-Fe3O4.


### 4.2. Microhardness

The specimen for the microhardness test was prearranged with a length and diameter of10mm×12mm. The surface to be examined should have a metallographic finish; hence, emery sheets of various grit sizes (100-1000) were used to finish the surface.Equation (1) calculates the microhardness:
(1)MH=MALAI,where,MH is microhardnessMAL is maximum applied load, andAI is the area of indentation.The Vickers Hardness Number (VHN) for A356 with 2, 4, and 6% reinforcement is 144, 163, and 188, respectively. With the reinforcement of 4% graphite and 3% ferrous oxide, the microhardness value of LM25 was 112. As the percentage of graphite (Gr) in the composites increases, the hardness of the normal particles falls [38]. When compared to matrix A356 alloy, the combined BHN value of A356/Gr/B4C is 63.1 and the hardness value of the hybrid composite increased by roughly 56.1 percent. The harder B4C ceramic particles are responsible for the increased hardness [39–41]. The research used A356 nanoparticles and reinforcements to achieve the better improvement in microhardness demonstrated in Figure 9 and Table 3.Figure 9
The microhardness values.Table 3
Microhardness value of A356 with B4C-Gr-Fe3O4 hybrid composites.
Microhardness value (VHN)A356 with 2% B4C-Gr-Fe3O4144A356 with 4% B4C-Gr-Fe3O4163A356 with 6% B4C-Gr-Fe3O4188


### 4.3. Tensile Test

The ultimate tensile strength and stress-strain of the composites are improved with increased reinforcement, as shown in Figure10. The variance in ultimate tensile strength with the AMMCs is shown in Table 4. The load value of graphite and iron oxide (2, 4, and 6 percent) increases as the boron carbide reinforcement is increased. 260.10, 290.06, and 325.43 N/mm2 are the maximum ultimate tensile strengths, respectively [40, 41].Figure 10
Stress vs. strain (UTS value in N/mm2).Table 4
Ultimate strength value of A356 with B4C-Gr-Fe3O4 hybrid composites.
Ultimate strength value (N/mm2)A356 with 2% B4C-Gr-Fe3O4260.10A356 with 4% B4C-Gr-Fe3O4290.06A356 with 6% B4C-Gr-Fe3O4325.43


### 4.4. FESEM

When the manufactured composite material was subjected to fracture analysis, the results were as indicated in Figure11. The FESEM image of the broken surface shows the mixing behaviour of ductile fracture, brittle fracture, and ploughing of reinforced material. Ductile fracture behaviour is caused by plastic deformation of the material prior to fracture, which results in the creation of a hollow. The quick and sudden fracture under stress causes brittle fracture behaviour. Transverse ruptures cause the ploughing fracture, which results in a deep hole-like cavity. All of these point to the fracture mixing behaviour [41].Figure 11
FESEM of tensile specimen (fracture analysis).


## 4.1. Microstructure

Figure8 shows the fascia microstructures of A356 with 2, 4, and 6% B4C-Gr-Fe3O4 at magnifications of 100. The nanocomposite specimen remained sophisticated in terms of removing particles from the surface. Optical microscopes are expected to support particle distribution vestiges. The additive manufacturing process was inspected under an optical microscope to determine the specimen reinforcement pattern. The homogeneous dispersion of nanoparticles in the matrix material of the A356 alloy was clearly visible. The presence of nanoparticles leads to the formation of cracks, which leads to elastic deformation with increases in load. Composite rupture is represented by dimples, voids, clusters, and cracks. Fragile composite fracture in the form of cracks and rupture is due to the strong interfacial bonding between the reinforcements and the A356 matrix.Figure 8
Microstructure of A356 with reinforcement B4C-Gr-Fe3O4.


## 4.2. Microhardness

The specimen for the microhardness test was prearranged with a length and diameter of10mm×12mm. The surface to be examined should have a metallographic finish; hence, emery sheets of various grit sizes (100-1000) were used to finish the surface.Equation (1) calculates the microhardness:
(1)MH=MALAI,where,MH is microhardnessMAL is maximum applied load, andAI is the area of indentation.The Vickers Hardness Number (VHN) for A356 with 2, 4, and 6% reinforcement is 144, 163, and 188, respectively. With the reinforcement of 4% graphite and 3% ferrous oxide, the microhardness value of LM25 was 112. As the percentage of graphite (Gr) in the composites increases, the hardness of the normal particles falls [38]. When compared to matrix A356 alloy, the combined BHN value of A356/Gr/B4C is 63.1 and the hardness value of the hybrid composite increased by roughly 56.1 percent. The harder B4C ceramic particles are responsible for the increased hardness [39–41]. The research used A356 nanoparticles and reinforcements to achieve the better improvement in microhardness demonstrated in Figure 9 and Table 3.Figure 9
The microhardness values.Table 3
Microhardness value of A356 with B4C-Gr-Fe3O4 hybrid composites.
Microhardness value (VHN)A356 with 2% B4C-Gr-Fe3O4144A356 with 4% B4C-Gr-Fe3O4163A356 with 6% B4C-Gr-Fe3O4188


## 4.3. Tensile Test

The ultimate tensile strength and stress-strain of the composites are improved with increased reinforcement, as shown in Figure10. The variance in ultimate tensile strength with the AMMCs is shown in Table 4. The load value of graphite and iron oxide (2, 4, and 6 percent) increases as the boron carbide reinforcement is increased. 260.10, 290.06, and 325.43 N/mm2 are the maximum ultimate tensile strengths, respectively [40, 41].Figure 10
Stress vs. strain (UTS value in N/mm2).Table 4
Ultimate strength value of A356 with B4C-Gr-Fe3O4 hybrid composites.
Ultimate strength value (N/mm2)A356 with 2% B4C-Gr-Fe3O4260.10A356 with 4% B4C-Gr-Fe3O4290.06A356 with 6% B4C-Gr-Fe3O4325.43


## 4.4. FESEM

When the manufactured composite material was subjected to fracture analysis, the results were as indicated in Figure11. The FESEM image of the broken surface shows the mixing behaviour of ductile fracture, brittle fracture, and ploughing of reinforced material. Ductile fracture behaviour is caused by plastic deformation of the material prior to fracture, which results in the creation of a hollow. The quick and sudden fracture under stress causes brittle fracture behaviour. Transverse ruptures cause the ploughing fracture, which results in a deep hole-like cavity. All of these point to the fracture mixing behaviour [41].Figure 11
FESEM of tensile specimen (fracture analysis).


## 5. Conclusion

SLM successfully created hybrid nanocomposites of B4C-GFe3O4 with varied reinforcements (2, 4, and 6). The microstructural analysis demonstrated that particles were distributed uniformly throughout the matrix material. Fractographic analysis was used to examine the tensile characteristics of the produced MMCs. The following are the results and conclusions of the hardness and tensile test:
(i)
The microhardness of nanocomposite A356 with 2, 4, and 6% reinforcement is 144, 163, and 188 VHN, according to the findings of a microhardness test(ii)
Tensile testing of nanocomposite A356 with 2, 4, and 6% reinforcement yielded 260.10, 290.06, and 325.43 N/mm2, respectively(iii)
The fractographic images reveal a combination of ductile and brittle fracture behaviours, as well as ploughing of reinforced material(iv)
Ductile fracture behaviour is caused by plastic deformation of the material prior to fracture, which results in the creation of a hollow. The quick and sudden fracture under stress causes brittle fracture behaviour. Transverse ruptures cause the ploughing fracture, which results in a deep hole-like cavity



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