Fabrication, characterization and optimal selection of aluminium alloy 8011 composites reinforced with B 4 C-aloe vera ash

The aim of this study is to determine the use of B 4 C along with AVA as economical reinforcements to improve the mechanical properties of aluminium alloy 8011. The purpose of this investigation is the development of cost-effective hybrid metal matrix composites. The present investigation assessed the mechanical characteristics of Al-8011 alloy, Al-8011/3AVA, Al-8011/4B 4 C, Al-8011/2.5B 4 C/2.5AVA, and Al-8011/3B 4 C/3AVA composites, which were manufactured through stir-casting techniques. Scanning electron microscope (SEM) imaging with an energy-dispersive spectroscope (EDS) was performed on the fabricated composites to confirm the presence of reinforcements, and the images revealed a uniform distribution of reinforcements in the matrix. The density of the composite decreased with an increase in weight % of AVA-B 4 C in comparison with that of matrix aluminum alloy 8011. Results obtained for tensile strength and hardness exhibit the optimal results from adding 3 wt.% B 4 C with 3 wt.% AVA. The present paper also investigates the application of three multiple criteria decision-making (MCDM) methodological approaches to select the best option.


Introduction
Metal matrix composites (MMCs) are used increasingly frequently today owing to their excellent mechanical characteristics, such as high specific strength, high specific stiffness, and high wear resistance.Because of its high strength-to-weight ratio, MMCs are primarily used in the automotive industry, although they are also used in other industrial applications [1].Traditional materials have limitations in achieving good mechanical and physical property combinations.To compensate for these shortcomings, hybrid composites have recently become the preferred material [2].Manufacturing industries have expressed a growing desire in recent years to use low-cost reinforced aluminium metal matrix composites to meet production rates with the least cost considerations while retaining unique properties.The researchers made several attempts in this context to reinforce with various low-price materials like rice husk ash, bagasse ash, cow dunk ash, coconut shell ash, red mud, fly ash, and so on [3].Recently, researchers' attention has shifted to the application of agro-derivatives as a reinforcement material in AMMCs with a view to supplementing reinforcement with carbides or alumina, etc.A few agricultural byproducts, such as maize stalk ash, corn cob ash, groundnut shell, bamboo leaf, straw, and rice husk, were processed into ashes, and their potential for further use as reinforcement has been investigated.This agro-waste ash is primarily composed of silicon dioxide (SiO2), with varying amounts of Al2O3, Fe2O3, CaO, MgO, and C [4,5].However, during the conversion of agricultural waste to ashes, air pollutant gases may be produced, causing the destruction of the environment.
Researchers are increasingly focusing on the environmentally friendly manufacturing of new materials in order to preserve the resources that are available to humanity for use in the future.As a result of increasing ecological consciousness and increased demand for lightweight, low-cost materials, researchers are taking advantage of agricultural, poultry, and industrial wastewater to create composites.By using these wastes for benefits, we can reduce the risk of contaminating people, plants, and animals.Ash created by burning waste from natural sources can be used as reinforcement.The use of these wastes can assist in lowering industrial costs and environmental degradation.For instance, the Acheson method used for generating silicon carbide requires a lot of energy to generate the high temperature required to complete the reaction.Furthermore, the process releases CO into the atmosphere, threatening the ecosystem.Agricultural waste-derived reinforcements are an environmentally friendly, cost-effective, and energy-efficient filler resource for composite fabrication.Rice husk is a type of agricultural trash made when paddy is milled.Over 20% of paddy is made up of it; rice and bran make up the rest.This husk's burning and subsequent dumping may pose environmental problems.Bagasse is the fibrous by-product of crushing and squeezing sugarcane to get the juice.Because of this, a lot of bagasse must be burned.However, in the case of aloe vera leaf, this problem might not exist because this plant's leaves are widely used in the cosmetics sector and for medical purposes.
The physio-mechanical behavior of developed aluminium composites is addressed in this investigation for usage in engineering applications where cost and weight are considered the primary considerations.In this work, it is essential to identify environmentally friendly reinforcement fine particles for the manufacture of aluminum metal matrix composites.Aloe vera is a widely available, less dense, environmentally friendly natural fiber that is inexpensive and may be a better alternative to industrial waste, so this research attempted to employ it as a reinforcement for composite materials.Similar work was carried out by previous researchers [6].The experimental findings demonstrate that mechanical properties like hardness and tensile strength significantly increase when AVA and B 4 C are utilized as reinforcement materials.Aluminum-based composites reinforced with boron carbide are more likely to be recommended as an effective alternative as suggested by previous works [7].Due to their applicability to aerospace materials, many researchers have looked into the 7xxx and 6xxx series alloys.The mechanical behaviour of Aluminium 8011 alloy reinforced with synthetic materials such as ZrB2, Si3N4, SiC, TiC, WC, B 4 C, and ZrC has been studied by a previous researcher [7,8].However, there is very little literature available for the 8xxx series alloys [9] AA8011 is used as a matrix material in this work.According to a review of the literature based on the roles of various reinforcements (types & wt%), including synthetic and natural, table 1 illustrates that they achieve the maximum improvement in mechanical strength.Bannaravuri et al [10] obtained maximum tensile strength and hardness at 4 weight percent of bamboo leaf ash in the composite.Madhu et al [11] worked on hybrid composites containing Al7029-RHA-Fly ash using the double stir casting process.The composite comprises 6 wt.% B 4 C and 6 wt.% Gr ash was found to have the maximum level of hardness.The inclusion of reinforcing particles significantly increased hardness and UTS, according to Bannaravuri et al [12] with Al-4.5Cu and (10SiC + 4BLA) hybrid composite showing better toughness and UTS.Some researchers have worked on AMMCs containing a variety of reinforcements, and they have found that the mechanical strength increased by 15.2% MPa [13], 15.7% MPa [14], and 24.6% MPa [15], 16.32% BHN [16], 20.38% HRB [17], 24.19% HR [18] as compared to unreinforced alloy.The literature reveals that no studies have been published on the use of aloe vera with aluminium alloy 8011.An attempt is made in this paper to prepare a novel combination of AVA and B 4 C particles reinforced AA8011.This approach gives room for the possible reduction of cost coupled with property optimization in AMMCs.

Materials and MCDM methods
2.1.AA8011 (Al-Fe-Si) Aluminium alloy 8011 was employed as the base metal, and it was initially obtained from the market in billet form with the dimensions of 145 × 20 × 5 mm, as shown in figure 3. The high-quality AA8011 aluminum-based alloy is developed, with the main alloying constituents being iron (Fe) and silicon (Si).The base matrix chosen is AA 8011 aluminium, which has a density of 2.71 g/cc, a melting point of 670C, and a CTE of 23.This alloy is primarily used to fabricate heat exchanger fins for a variety of cooling systems found in air conditioners, vehicles, ships, aeroplanes, and other types of cooling equipment [35].AA8011 is emerging as a promising material for modern engineering applications requiring improved hardness, tensile strength, wear, and corrosion resistance [36].The samples were moulded and machined in accordance with the requirements for the universal testing machine, Brinell hardness tester(SE-RAB-1) and Charpy tester.The presence of major elemental components such as Al, Si, and Fe was confirmed in alloy by laboratory test and it is depicted in table 2. The SEM with EDS imaging of AA8011 is shown in figure 4(a)-5(a) respectively.Figure 1 depicts the methodical flow of the investigation.To accomplish the objective(s) of this innovative research, the flow comprises the selection of materials for reinforced composites as well as the characterization and analysis of composite materials.

Preparation of aloe vera ash
The Asphodelaceae family comprises the perennial, drought-tolerant succulent plant known as aloe vera.Aloe vera is an evergreen, greasy, xerophytic plant having tissue in its leaves that allows it to store a significant amount of water and endure in dry areas with little rainfall.As a result, it may be grown without the use of pesticides even in dry and/or marginal areas, making it a very sustainable agricultural execution.Therefore, it follows that there are minimal adverse environmental repercussions from aloe cultivation.As a result, burning aloe vera leaves has a smaller impact on the environment [37][38][39][40][41].This plant is widely employed in the pharmaceutical and cosmetics.It emerged in tropical Africa and is now grown in tropical climates across America, Asia and Europe.The major producers of this crop in India are Chhattisgarh, Rajasthan, Andhra Pradesh, Tamil Nadu, Gujarat, Kerala, and Maharashtra[ [42]].Aloe vera plant has a higher capacity of water retention and primarily contains potassium (4.06%), sodium (3.66%), calcium (3.58%), magnesium (1.22%), copper (0.06%), iron (0.1%), phosphorous (0.02%), and zinc (0.02%)[ [43]].It is a succulent plant with no stems or very short stems that can reach heights of 80 to 100 cm and spread through offsets and root sprouts.Aloe vera leaves have a contact angle of 96.89 degrees [44], and so they possess significant iron (0.1%),.It is a widely available, less dense, easily cultivable, and environmentally friendly material [45].
Fresh aloe vera leaves were obtained from a nursery.The leaves were cut into small pieces, cleaned with warm water to remove unwanted dust and debris, and then dehydrated in hot air to remove any excess moisture.The chopped leaves were then processed into a fine powder with a micron size.The leaves were allowed to burn AA8011 Achieved maximum strength 5% B 4 C-Al2O3 Alaneme et al [30] Al-Mg-Si HRV 64, UTS 150MPa SiC-GSA (1:0) Groundnut shell ash-SiC Alaneme et al [31] Al-Mg-Si UTS 160MPa RHASiC (0:1) Rice hush ash-SiC Poovazhagan et al [32] Al6061 UTS 281MPa, 84 BHN 2.5vol% 2.0vol% B 4 C Imran et al [5] Al7075 UTS 299.4 MPa, 99.6BHN 5Gr-6BA Graphite-Bagasse ash Manu et al [33] Al6082 70BHN, 32J 4%B4C-4%CCA B 4 C-Corn Cob ash Alaneme et al [34] Al-Mg-Si UTS-125.5 MPa, 78.6BHN 0%Rice Husk ash-10%Al2O3 completely before the ashes were removed 24 hours later.The ashes were removed one day later after the leaves had burned completely.After that, the ash was conditioned by being heated at 650 C for 240 minutes to remove its volatile and carbonaceous.After complete burning, the average weight of the leaves was only reduced to 20% of the original weight of ash taken.These outcomes are in line with the previous investigator's findings.[46,47].A digital weight balance was used to determine the sample's weight before and after each test.By calculating the difference between the sample's original and final masses, the mass loss was ascertained.Figure 3  The purpose of this investigation is to convert the aloe vera leaf into aloe vera ash and make it a useful reinforcing material by obtaining silica (SiO 2 ) and then investigated the mechanical characterization of materials.Table 3 depicts the aloe vera's thermal properties.

Boron carbide (B 4 C)
Boron carbide can be used to develop hard materials with greater strength, hardness, and ionising radiation stability at a low density.It is used in the production of bulletproof vests and armour tanks vehiles, and acts as a shield in nuclear power plants.The boron carbide powder chemical composition report is as depicted in table 4.

MCDM methods
The basic steps of MCDM methodologies are described below 1. Developing a set of criteria and alternatives.

Fabrication Routes for AMMCs
In stir casting, the alloy and reinforcements are blended in a crucible using a stirrer.Small alloy pieces were added to the furnace and calcined at 800 C to allow the metal to melt.The aloe vera ash was preheated for a few hours in a separate furnace at 750 C.Then, with each stirrer stroke, the measured quantity of the reinforcement particles was slowly added to the molten alloy. 1 wt.% magnesium was used to minimize the voids, and 3 wt.% of the degassing agent C2Cl6 was utilized to enhance the wettability.Even after the ash particles had been fed, the stirring continued for another 10 minutes.To achieve homogeneous solidification, the mixture was put into a warmed mould.The method was repeated for different reinforcing particle weight fractions.Figure 3 shows the procedure for fabricating an aluminium composite and this fabricated structure reveals that the casting had no voids, shrinkage, or slag presence.The composition of hybrid metal matrix composites with varying weight percentages as shown in table 5.
The quality of specimens produced during the stir-casting process depends on the number of process variables including pouring temperature, stirring time, stirring speed, holding time, and the impeller's size & position.By controlling those factors, the wettability and porosity of cast aluminium metal matrix composites can be enhanced.Therefore, a composite with a variety of mechanical characteristics can be produced by adjusting the manufacturing conditions as well as the relative amount of reinforcement material.Previous studies used identical manufacturing methods to minimise processing problems by regulating the crucial variables [50,51].

Microstructure
The high-resolution field emission scanning electron microscope (HR FESEM) is from Zeiss, model name ULTRA Plus was employed to examine the microstructural characteristics of the composites.An energydispersive spectroscope attached to a Zeiss-ULTRA Plus extreme resolution analytical field emission scanning electron microscope was also used to determine the elemental composition (EDS) of mono and hybrid composites.SEM was employed to examine the surfaces and confirm that the reinforcement particles in composite was distributed properly.Figure 4 shows the microstructures of the prepared AMCs containing various weight fractions of reinforcement particles.The elemental analysis of cast alloy, mono composites, and hybrid composites was conducted using a spectroscope and the EDS spectra also show the peaks of Al (aluminium), Si (silicon), Fe (iron), Mg (magnesium), O (oxygen) B (Boron) and C (carbon).These elements are present, which is evidence that SiO 2 and B 4 C are the main reinforcement.Figure 4(a-e) depicts the microstructure of the Al 8011 alloy and hybrid composites.The SEM imaging distinctly displays no discernible micro-cracks within the matrix.Each imaging of the hybrid reinforcements clearly shows the homogeneity or uniformity of the particles within the ductile matrix, which can be ascribed to the process variables used the two step stir casting process.In order to have the clear view of AVA, B4C morphology and distribution, SEM examinations was carried out.Figure 4(a)-(e) shows the microstructure for Al8011 alloy and hybrid composites.Mark the reinforcements particles which are uniformly distributed throughout the matrix as presented in figure 4(a)-(e), however, agglomeration of particles has also taken place as seen at few places.With an increase in the weight percentage of the particles, the grain improvements of the second discontinuous phase precipitates were fully evident along the grain boundaries.Figure 5(a), which displays the EDS image of main components of AA8011, makes this clear presence of (Al-Si-Fe).Figure 5(a-e) illustrates the elemental analysis of results for samples number as M1-M5.Figure 6 shows the elemental mapping of the M-5 sample.The sample typically contained O, Al, B, C, Si, Fe, Ca, Mg, Zn, and Mn.

Effect of B 4 C and AVA on density
Density measurements were conducted to see how the AVA-B 4 C wt% proportions affected the densities of the composites that were created.The archimedes principle [52] was used to estimate the experimental density of composites, and the rule of mixture approach was employed to measure the theoretical density.The density fluctuation of an unreinforced and reinforced alloy is depicted in figure 7. The density of the composite decreased as more AVA-B 4 C was incorporated.The addition of 3.0 wt.% AVA and 3.0 wt.% B 4 C particles to the AA8011 alloy resulted in the lowest density of all synthesized composites, as indicated in figure 7.
It is apparent that density decreases as reinforcement levels increase.The addition of low-density AVA particles caused a decrease in the densities of the hybrid composites.AVA and B 4 C powder have lower densities than aluminium alloys.Therefore, the density of the composite decreases as a result of blending high density alloy and low density reinforcement materials.Consequently density reduces as the value of reinforcement increases.In earlier studies, the same trends were also found by [17,18].On the basis of experimentally and theoretically defined densities, the porosity of the composites (M5 3.0064%) and the alloy (M1 1.0697%) was measured using equation (% of porosity=(1-ρ rd )x100) and it was found that the porosity increases with the amount of reinforcement employed.The observation stated by Prasad et al [53] is an additional one.Gas entrapment, shrinkage, and air bubbles that either enter the slurry on their own or surrounding the reinforcing particles are some of the causes that might increase porosity.As a result, hybrid composites decrease density while increasing porosity and hardness as the amount of reinforcement increases.Table 6 displays the sample's physical properties.

Effect of B 4 C and AVA on tensile strength
The ASTM standard procedure was followed while using the universal tensile testing machine to determine the ultimate tensile strength of the samples.According to the plots, the ultimate tensile strength improves with the addition of AVA-B 4 C to the molten metal.M5 was found to be stronger, as indicated in figure 8, with a UTS of 157.92 MPa.
The improved in hardness and strength of manufactured hybrid composites is due to fundamental strengthening mechanisms.These include density generation due to mismatch in CTE and elastic modulus between alloy and reinforcements [54], Orowan mechanism [55], and load transfer [56].The strengthening may occur due to the movement of dislocations obstructed or delayed in the composites.Indirect strengthening arises due to high thermal mismatch occurring from irregular cooling between the alloy and reinforcement particles.Strengthening of fabricated composites may be characterized by a higher difference in CTE of the base alloy and the particles where CTE of Al-8011 alloy is 21.8X10 −6 K −1 [57] and CTE of B 4 C is 6.0X10 −6 K −1 [58].The larger differences in CTE put up strain fields around reinforcement particles in solidification process.The movement of dislocations may be obstructed by strain fields when applied to the tensile load.The CTE of the individual component particles varies remarkably.This difference could increase the strength of composite materials by producing geometrically necessary dislocations (GNDs) near to the matrix-reinforcement boundary.Thus, similar trends were also observed in previous research indicating that strengthening mechanisms are responsible for strength enhancement in composites [59,60].

Effect of B 4 C and AVA on hardness
In this work, the hardness of the synthetic materials was determined using a Brinell hardness tester (SE-RAB-1) equipped with a circular indentor (1.16 mm carbide).Prior to testing, metallographic surface operations were performed to develop a flat and smooth surface finish on the composite test specimens (f:15 mm, length: 10 mm).The specimens were then subjected to a 10 Kgf load for 10 seconds.After that, each sample was examined five times at various locations, with the average reading values being recorded.Figure 9 depicts the variation of microhardness values for M1 to M5 samples.The hardness recorded is 55.23 BHN when the reinforcement is 0%, 56.51 BHN when it is 5%, and 67.27 BHN when it is 20%.M5 was discovered to have the highest hardness.This illustrates that the improvement in the hardness number is proportional to the wt% of reinforcement.4.5.Effect of B 4 C and AVA on impact strength Figure 10 illustrates the effect of reinforcement on the impact strength of the prepared composites.The impact strength of hybrid composites decreases as the proportion of two reinforced materials increases.

Optimization by MCDM
In this investigation, the weighting of each attribute was determined using the standard deviation method.Then, the selection of optimal material was chosen using various MCDM approaches.The best alternative material, as well as the rating order, were found to be different.All of the attributes of composites were compared and measured the ranked using different MCDM methods.The ranking was determined using a variety of decision  making techniques and the efficacy of the WPM, WSM and PROMOTHEE-II are contrasted in tables 7, 8 and 9) in terms of computing duration, simplicity, and clarity.Figure 11 compares the optimal performance of each of these MCDM methods.WPM and PROMETHEE-II methods suggested that the M5 formulation for having the optimum properties based on the rank.Similarly, the M1 was selected as the best alternative by WSM.The ranking order 4-5-3-2-1 and 1-2-3-4-5 by WPM and WSM respectively.The PROMETHEE-II method recommends a rating order of 5-4-3-2-1.The suggested material as M5 is the best alternative, based on the findings from the prior material selection.The second choice M4 while M1 is the last choice.
In this study, three different techniques are used for solving multicriteria decision-making problems.In this case, we were selecting the best material out of all five available alternatives based on four criteria: density, tensile strength, hardness, and impact strength.Table 10 shows the decision matrix table.Firstly we did normalizing the data and we obtained table 11 of the normalisation decision matrix.

Weighted sum model (WSM)
WSM is a multi-criterion decision-making method in which there will be multiple alternatives and we have to determine the best alternative based on multiple criteria.WSM, it was previously stated, should only be employed when the decision criteria can be specified in the same units of measurement.On the other hand, can be used for any type and number of attributes if all of the decision tables entries are normalized.A beneficial attribute indicates that higher measures are more preferable for the particular decision-making problem.In contrast, non-beneficial attribute is that for which the lower measurement is preferred.WPM method is similar to WSM.The main difference is that instead of addition in the model there is multiplication.Here we keep the weight in the power of the performance value.We take the product of each value in each cell and we get the preference code.Based on the preference code we can rank of the alternatives.The overall or composite performance score of an alternative would be calculated with the help of the given equation.Alternative A5 is the best option (in the condition of maximization) since it has the highest WSM score, which is equal to 0.929 24.It can be used for any type and number of attributes if all of the decision table's entries are normalised.In this case the equation form as follows where, ( ) m ij normal implies the normalized value of m ij , and P i is the aggregate composite score of the alternative A i .The alternative with the highest P i value is considered to be the best option.

Weighted product model (WPM)
Bridgman invented the WPM in 1920.It serves as a substitute for the weighted sum model.It apply a product instead of a sum, in contrasting to the weighted sum approach.Since alternative A5 has the highest WPM score, it is the optimal option (in the maximization situation).The overall or composite performance score of an  alternatives would be calculated with the help of the given equation. [ Each alternatives normalized value in respect to an attribute, represented by ( ) m ij normal is raised to the power of the relevant attribute's relative weight.The alternative with the maximum P i is regarded as the best option.4.9.Preference ranking organization method for enrichment evaluations (PROMETHEE-II) Preference functions are used to compare alternatives pairwise for each criterion in order to determine the ranking.The aggregated preference function leaving & entering were calculated then ranking would be decided on the basis of net flow values.In case of PROMETHEE-II technique there are Preference functions which is used to compare alternatives pairwise for each criterion in order to determine the ranking.The steps that constitute the PROMETHEE-II technique are as follows.
• Compute the normalised decision matrix.

Conclusion
From the present investigation it can be concluded that the alloy and composites was synthesized successfully by stir casting fabrication techniques.SEM images illustrate that the AVA with B 4 C is uniformly distributed throughout the matrix and clear interface was revealed between alloy and reinforcement particles.The density of the synthesised composites diminished with an increase in reinforcement weight in comparison with the Al-8011 matrix, conversely increasing the porosity.It was determined that with the inclusion of reinforcing particles, hardness and tensile strength increased significantly while impact strength decreased.The hybrid composite containing Al-8011 and (3B 4 C + 3AVA) presented a higher tensile strength and hardness.The hybrid composite, M5 had a 21.86% strength and 20.86% hardness improvement over the unreinforced aluminum alloy 8011.In accordance with the optimization techniques, it was determined that the hybrid composite M5, which had the highest ranking by WPM and PROMETHEE-II, and the alternative M1, which was ranked highest by the WSM method.
illustrated the details picture showing to obtaining an aloe vera ash from aloe vera leaf.Energy Dispersive x-Ray analysis (EDS) is a technique used to determine elemental composition of materials and SiO 2 and Fe 2 O 3 being the major constituents have been found and the SEM images of low and high magnification of aloe vera ash is represented in figure 2(a)-(b).The fine powder has a density of 1.22 g cc .

2 .
Determined the relative importance weight of each attribute.

Figure 1 .
Figure 1.A schematic representation of the methodologys flow diagram.

Figure 6 .
Figure 6.Elemental mapping of AA8011%-3%B4C-3%AVA (a) Image (b) distribution of oxygen (c) distribution of aluminium (c) distribution of boron (c) distribution of carbon (c) distribution of silicon (c) distribution of iron (c) distribution of copper (c) distribution of magnesium (c) distribution of zinc (c) distribution of manganese.

Figure 7 .
Figure 7. Effect of reinforcement on density.

Figure 8 .
Figure 8.Effect of reinforcement on tensile strength.

••
Compute the evaluate difference of ith difference with respect to other alternatives.Compute the preference function, P j (a, b).

j[
[if R aj < R bj D(M a − M b ) 0] if R aj > R bj D(M a − M b ) 0]• Compute the aggregated preference function,

Table 1 .
Role of reinforcements on the mechanical behaviour of AMMCs.

Table 4 .
Chemical composition of boron carbide.

Table 3 .
Thermal properties of aloe vera.

Table 5 .
Composition of hybrid metal matrix composites.

Table 6 .
Physical properties of samples.Figure 10.Effect of reinforcement on impact strength.

Table 7 .
Preference score & Ranking table for WSM.

Table 8 .
Preference score & Ranking table for WPM.