Development and Characterization of Aluminium-Based Metal Matrix Composites ()
1. Introduction
A new material known as a composite is created by mixing two or more different suggested materials, such as metal, ceramic, or plastic, to provide qualities that are superior to those of the parent materials alone. Composites are now regarded as one of the most important tribes of engineered materials in the modern era. Due to their exceptional specific strength, stiffness, and high thermal and electrical conductivities, these composites have also drawn attention. In addition to its usage for structural purposes, composites are also used in electrical, thermal, tribological, and environmental applications. Because of their superior machining, joining, and processability, Al-based metal matrices are referred to as adaptable materials that may be employed for a wide range of engineering applications. Al alloys are better material for engineering applications due to their inexpensive cost, enhanced strength-to-weight ratio, high elastic modulus and other ecologically favorable features. The reinforcement consists of the discontinuous members silicon carbide (SiC) and aluminium oxide (Al2O3) used to strengthen the aluminum metal, while the continuous phase (aluminum or aluminum alloy) in molten form during casting is known as the matrix, which becomes solid after solidification. In this study, SiC and Al2O3 was used because of their diverse properties and availability. SiC is a commonly used and economical choice for reinforcement. SiC is hard, brittle but it can enhance ductility, density and hardness. SiC reinforced MMC is very cost effective and easy to cast. Like SiC, Al2O3 was chosen because of its versatile properties. Al2O3 is a hard ceramic particle that has high thermal conductivity and can supplement the mechanical and tribological properties. Alumina can also be helpful for weathering as metal aluminium can be reactive with the atmospheric oxygen. Depending on the need and application, many researchers created a variety of composite materials employing various matrices, reinforcement sizes, shapes, and volumes, as well as acceptable processing methods. According to Balasivanandha Prabu et al., by adjusting the stirring speed and duration, it was possible to improve the performance of the aluminum-Si-based composite by adding 10% silicon carbide [1]. Various effects on microstructure and other properties change with varying stirring speed and time. According to B. Roebuck et al.’s research, silicon carbide (SiCp)-reinforced aluminum metal matrix composites (MMC) outperform comparable non-reinforced matrix alloy systems in terms of yield strength, thermal expansion coefficient, elastic modulus, and wear resistance by up to 20% [2]. When the stirring speed and duration are changed, different impacts on the microstructure and other properties also change. According to Amit Raturi et al., yield strength constantly increases with an increase in Al2O3 particle concentration up to 1 weight percent, but when more particles are added—1.5 weight percent, yield strength decreases [3]. The ultimate tensile strength and yield strength of the composite increased by 37% and 81%, respectively, relative to the alloy matrix at the optimal concentration of nano-Al2O3 particulates (1 wt%). A359/Al2O3 composite was created by Abhishek Kumar et al. using the electromagnetic stir casting method [4]. The author noticed that compared to pure alloy, the hardness values increased to 72.8 HRC (46HRC). In addition, compared to pure alloy (103.7 N/mm2), the composite’s tensile strength increased to 148.7 N/mm2. The size of the Al2O3 particle affects wear behavior. Wear resistance also increases as particle size increases. According to the literature, there has been comparatively less research on the electrical and thermal properties of SiC and Al2O3 reinforced Al-MMC, but much more on the microstructure and mechanical properties (hardness, tensile qualities, friction). Therefore, using silica and alumina as reinforcement, we experimentally examined the composite’s electrical, thermal, and mechanical properties. Another fabrication technique, such as squeeze casting, powder casting, spray casting, etc., can be used to carry out the same experiment, and the results can then be compared to those of the stir casting technique. By using different reinforcement grains of the same particle, as in this experiment, the research can be furthered. A number of properties like thermal expansion coefficient, corrosion resistance etc. of the SiC/Al2O3 reinforced Al/Al alloys MMC are not well studied. This study focused on the different properties of SiC/Al2O3 reinforced Al/Al alloys MMC.
2. Experimental Procedure
2.1. Materials
All the raw materials (Pure Al, AA-6061, AA-4032, SiC) were collected from local market (chemical composition shown in Tables 1(a)-(c)). Table 2 shows the size distribution of the course and fine SiC particles. Table 3 shows composition of 7 samples of MMC.
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Table 1. (a) The chemical composition of pure Aluminium; (b) The chemical composition of AA-6061; (c) The chemical composition of AA-4032.
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Table 2. The Size of course and fine SiC.
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Table 3. Different types of sample.
2.2. Fabrication
A crucible furnace (VBF-1200×, MTI corporation, USA) to melt the metal/alloys used as matrix of the MMC. 40 min requires to raise the temperature 750˚C and then it was kept at 750˚C for 30 min. A local made stir casting set was used for making MMC (as shown in Figure 1). A motor was utilized to regulate the stirrer’s rotation. In order to control the motor’s rpm, we connected a dimmer to it. The controlled voltage range for the dimmer was from 0 to 250 Volts. The motor’s RPM range was 250. A steel frame that served as a hanger for the motor was placed in the center of the furnace.
2.3. Testing
Density is measured with the help of Archimedes’ principle using electronic balance (AS 220/C/2, RADWAG, Polland).
To determine the hardness of the material a micro-hardness tester (HMV-2T, Shimadzu Corporation, Japan) was used in this work. Samples with a 10 × 5 × 5 mm dimension were used for the hardness test. The specimens were polished using different grades of emery (400 to 1800). The samples were tested after being polished. The indentation was place for 10 seconds with 500 g of load. Five indentions were measured and the average was ultimately chosen.
The materials were cut into precise measurements for tensile testing after creating the appropriate samples. A computer operated UTM (H10KS, Hounsfield, UK) was used for tensile properties measurement. 5 samples were used for each set of sample. The arms moved at a 2 mm/second speed.
The impact test of the manufactured materials was measured using impact tester (QPI-IC-21J, Qualitest, USA). The experiment’s specimens were 40 × 10 × 10 mm in size with V-shaped notch at the center with 2 mm depth and 45˚ notch angle. 3 samples were used for each set of sample test.
3. Result and Discussion
3.1. Physical Properties
Physical properties are those properties that can be measured without changing the composition of the material. In our present work, we only measure density as the physical properties of the material.
3.1.1. Density Measurement
Results of calculated density are illustrated in Figure 2.
Figure 2(a) shows the effect of course SiC addition on the density of AA-6061 it shows that the density increases with the addition of SiC. It is because of denser particle (3.21 gm/cc) addition with lighter materials AA-6061 (2.70 gm/cc). According to mixer rule, the density of the MMC is 2.7255 which is very similar to obtained density of the MMC (2.703 gm/cc). The slight variation might be associated with voids. Figures 3(b)-(d) show the effect particulate additions (5% fine SIC, 5% Al2O3, and 5% Al2O3) on different matrix (AA-6061, pure Al and AA-4032). Both the reinforcements are denser than the pure Al/Al alloy. From the above bar charts, the density of the matrix is raised when a greater density reinforcement is used with a lower density matrix material. According to
Ozben T, Kilickap Erol et al. the average density of aluminium alloy is 2.6 and after adding reinforcement, the density increases [5]. The density of SiC and alumina are 3.21 and 3.95 gm/cc.
Very similar results were obtained by Balasubramanya et al. (2019).
3.2. Mechanical Properties
Different mechanical properties of the composites are discussed below:
3.2.1. Hardness Test
Figure 3(a) and Figure 3(b) show the effect SiC addition on AA-6061. It shows that with 5% course SiC addition enhances the hardness at 63.25%. For 5% fine SiC enhances the hardness 83.5% (Figure 1(b)). Finer particle increases hardness more because of more surface area to resist the slip. Figure 4(c) and Figure 4(d) show effect of 5% Alumina addition on pure Al and AA-4.32 alloy. The increase in hardness is 15.98%, and 61.03%, respectively. The base materials behave differently. AA-4032 yield more hardness than that of pure aluminium.
The material’s resistance to plastic deformation was boosted via particle reinforcement, which also increased the material’s hardness. From the results above, it can be inferred that adding reinforcement to the matrix material resulted in the manufactured material’s hardness being higher than the base material. The
test findings demonstrate that the composite’s hardness increases when hard particles are present inside the matrix. Balasubramanya HS obtained HV20.5 to 30 with the increase of SiC upto 20% SiC in pure Al.
3.2.2. Tensile Test
Figure 4(a) and Figure 4(b) show the effect SiC addition on UTS of AA-6061. It shows that with 5% course SiC addition enhances the UTS at 41.85%. For 5% fine SiC enhances the hardness 41.07% (Figure 4(b)). Figure 4(c) and Figure 4(d) show effect of 5% Alumina addition on pure Al and AA-4.32 alloy. The increase in hardness is 5.02%, and 72.42%, respectively. The base materials behave differently. AA-4032 yield more strength than that of pure aluminium.
From literature evaluations, numerous instances of a similar outcome were seen. According to Mohamed et al. MMC made of AA-6061 and 5% SiC has an approximate 70 MPa tensile strength and a 55% elongation [6]. Chiga et al. found that AA-6061 with 5% SiC had an elongation of 17.5% and a tensile strength of 52.08 MPa [7].
Figure 5 shows that the elongation of Al and Al alloys with the addition 5% particulate materials. It shows that the % of elongation increases for all except for AA-4032. From Figure 5(c), the pure Al + 5% Al2O3 sample shows more ductile than any other alloys (Figures 5(a)-(c)). According to the third sample’s
elongation %, it has ductile properties as found in Figure 5(c). The AA-4032 + 5% Al2O3 composite, on the other hand, has very little elongation and is hence a brittle material.
Based on extensive literature reviews, instances of similar outcomes were seen. According to Mohamed et al., MMC of AA-6061 and 5% SiC had an elongation of 55% [6]. Additionally, Chiga et al. found that AA-6061 with 5% SiC had an elongation of 17.5% [7].
3.2.3. Impact Test
Results of Izod impact test measurements are illustrated in below.
Figure 6 shows the impact energy of Al and Al alloys with the addition 5% particulate materials From the preceding figure, it can be inferred that the AA-4032 + 5% Al2O3 sample fractures at a maximum energy of 24.08 J. The all-fabricated composites’ impact energy is raised in this instance. Figure 6(a) and Figure 6(b) show that sample 1 and 2 have the most increased impact energy than its base materials.
Ozden et al. noticed the attributes of AA-6063 reinforced with approximately 5% SiC (511 m2) heat treated at 515˚C and liquid cooled for 2 hours had an impact strength of 13.08 J. This was used as a comparison. Compared to the publication, these results were more favorable [8].
Electrical Properties:
Electrical Conductivity (% IACS):
Figure 7 shows the effect of particulate addition on the electrical conductivity of MMC. It depicts that electrical conductivity increases with addition of particles. Cui X et al. concluded in their study that Al-0.5Mg-0.35Si and Al-0.5Fe- 0.2Si can reach electric conductivity of 52.4% and 51.8% IACS [9]. Zhukov I et al. iterated in their paper that aluminum alloy with reinforced Al2O3 can reach electric conductivity of 36.03% ± 1.38% IACS [10]. Tokutomi J et al. stated in their paper that pure al has electric conductivity of 63.2% IACS [11]. From the few papers stated above, it is evident that the results of this study are similar.
Thermal Properties:
Thermal Expansion Co-efficient (TEC):
Figures 8(a)-(d) show the effect on particulate materials addition on TEC of Al/Alloy MMC. It shows TEC increases with the increase of particulate additions. But the increases in TEC are 9.69, 10.37, 1.52 and 17.87 × 10−6/˚C for the alloys. Hashihuchi D. et al. published in their study that Al-6061, Al-2124A (17% SiC), Al-6061B (40% SiC) has a TEC of 23.17 × 10−6/˚C and 13.4 × 10−6/˚C respectively [12]. Huber T et al. have expressed in their study that A359 alloy with
10% SiC reinforcement can reach co-efficient of thermal expansion of approximately 25 × 10−6/˚C [13]. The aforementioned papers confirm the results of this study.
TGDTA
Figure 9 shows the DTA of pure Al, AA 6061, and AA-4032. These are obtained at 20˚/min heating rate. The following Table 4 shows different thermal data of the three materials, it shows that with the increase of alloying element particularly Si, the melting point peak temperature decreases, but heat of fusion increase. The melting point of Aluminium is slightly less than that of pure Aluminium, because it is commercially pure containing 0.55% Si and 0.13% Fe. The melting points/solidus temperatures are 658.7˚C, 642.6˚C and 582.0˚C.
For AA6061, containing 0.85% Si, from phase diagram (Al-Si) it is found that at room temperature it is a single-phase solid solution having 1.65% Si maximum solubility at 577˚C eutectic temperature. But Al-0.85% Si alloy crosses two lines (solidus and liquidus), consequently two temperatures 642.6˚C and 672.3˚C are obtained as solidus and liquidus temperatures. There is existed one 2nd phase melted at 686.3˚C.
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Table 4. Thermal data of three base metal/alloys from differential thermal analysis.
For AA4032, containing 13.6% Si, it is a near eutectic alloy. The melting point is 582.0˚C which very near to equilibrium eutectic temperature 577˚C. It is slightly higher because higher heating rate. There is existence of another phase melt at 647.0˚C.
Figure 10(a) shows the comparative DTA curve of commercially pure Al, AA 6061 and AA4032. The most right on is for commercially pure Al and most left on is for AA-4032. AA6061 is in between the two curves. Figure 10(b) shows the comparative DTA curve of AA6061, AA 6061 with 5% course SiC and AA 6061 with 5% fine SiC. It reveals that SiC addition increase the thermal stability. The peak temperatures are 664.1˚C, 669.0˚C and 667.6˚C. Figure 10(c) show the comparative DTA curve of pure Al and pure Al with 5% Al2O3. It reveals that Al2O3 addition increase the thermal stability. The peak temperatures are 677.4˚C
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Figure 9. (a) Pure Aluminium; (b) AA6061; (c) AA4032.
and 682.7˚C. Figure 10(d) shows the comparative DTA curve of AA4032 nd AA 4032 with 5% Al2O3. It reveals that Al2O3 addition increase the thermal stability. The peak temperatures are 591.9 and 598.6˚C.
3.3. Chemical Properties
3.3.1. Corrosion Test
4% NaCl solution was used for creating environmental conditions. Gamry Reference 3000 Potentiostat/Galvanostat/ZRA machine have been used to perform the corrosion test. Through this test, we investigate Icorr and corrosion rate. Figure 11 and Figure 12 show the findings for the corrosion test that all of the samples Icorr values and corrosion rates have risen with the incorporation of reinforcement compared to the base metal and alloy. This is because the alloy matrix’s reinforcement content condenses the cathodic zones to a small number of impurities, porosities, and reinforcements. The favored sites for dissolving and pitting are also thought to be the residual stresses in the matrix that result from the disparity in thermal and mechanical characteristics between the matrix and reinforcement [14]. Additionally, the areas where pits first form are more likely to experience galvanic corrosion at the junction of hard ceramic particles and soft matrix alloy [15]. Figure 11 and Figure 12 depict that Icorr and corrosion rate have been increased more for the reinforced particles with finer size,
indicating more susceptibility to pitting corrosion. These findings concur with those of other studies [16]. This is because composite materials have a high surface area content of reinforcements, which speeds up the growth of pits into the metal.
3.3.2. Microstructure
The microstructure of the samples was under an optical microscope. SiC particles with a deep golden color and wedge shapes were seen in and around the interdendrite regions, leading to an increased aspect ratio. It is obvious that the coarser SiC particle distribution is less even than that of the finer SiC particle. There’s some dendritic growth seen on the AA-6061 + 5% coarse SiC. A little cracking can be seen on the AA-6061 + 5% finer SiC sample. The matrix of the composite with alumina particles showed even dispersion without any discontinuities. The grain disparity between the pure aluminium and aluminium alloy is clearly seen in Figure 3 and Figure 4. The discontinuity and issues in the samples can be seen because of the inconsistency in stirring, low wettability, presence of air trapped on the furnace etc. (Figure 13).
4. Conclusions
The following conclusions can be taken from the development and experimental analysis:
• The stir casting method has been successfully used to fabricate the metal matrix composite with an aluminum basis.
• A few variables can influence the manufacture of the MMC to produce better outcomes. The parameters include the casting process, the stirrer design, the size of the stirrer, the rpm and time of the stirring, the temperature of the preheating process, the uniform distribution of the particles, etc. In this example, changing parameters may result in various outcomes.
• Every sample created in this experiment displayed improved qualities, except for the third sample (pure aluminum + 5% Al2O3). The third sample, Pure Aluminium + 5% Al2O3, had a poor outcome in the hardness test since the sample’s hardness reduced. The aforementioned variables may be able to explain why the third sample’s hardness was reduced.
• During the corrosion test, it is found that the samples’ corrosion rate and Icorr were higher than those of the basic matrix materials. The materials will erode more quickly than the underlying materials as the corrosion rate and Icorr rise. This experiment’s bad outcome is that the samples’ corrosion rate and Icorr have increased.