1. INTRODUCTION
⌅In recent times aluminium alloys play a major role in composite preparation. There are N no. of combination available in aluminium alloys, they are Al7075, Al6061, Al2024, Al8081, Al6063, A413, A380, A356, A535, etc. This is the reason why researchers move to aluminium composites. Due to its high strength to density ratio, high tensile strength, high yield strength and its high elongation during downtime is the reason for Al7075 has a large number of applications in the automotive, aerospace, machine and ship industries (Baradeswaran and Perumal, 2014aBaradeswaran, A., Perumal, A.E. (2014a). Study on mechanical and wear properties of Al 7075/Al2O3/graphite hybrid composites. Compos. Part B-Eng. 56, 464-471. https://doi.org/10.1016/j.compositesb.2013.08.013.; Baradeswaran and Perumal, 2014bBaradeswaran, A., Perumal, A.E. (2014b). Wear and mechanical characteristics of Al 7075/graphite composites. Compos. Part B-Eng. 56, 472-476. https://doi.org/10.1016/j.compositesb.2013.08.073.; Imran et al., 2016Imran, M., Khan, A.A., Megeri, S., Sadik, S. (2016). Study of hardness and tensile strength of Aluminium-7075 percentage varying reinforced with graphite and bagasse-ash composites. Resour.-Eff. Technol. 2 (2), 81-88. https://doi.org/10.1016/j.reffit.2016.06.007.; Devaganesh et al., 2020Devaganesh, S., Kumar, P.D., Venkatesh, N., Balaji, R. (2020). Study on the mechanical and tribological performances of hybrid SiC-Al7075 metal matrix composites. J. Mater. Res. Technol. 9 (3), 3759-3766. https://doi.org/10.1016/j.jmrt.2020.02.002.; Alaneme et al., 2020Alaneme, K.K., Bodunrin, M.O., Chown, L.H., Maledi, N.B. (2020). Flow stress behaviour and microstructural analysis of hot deformed Aluminium matrix composites reinforced with CuZnAlNi shape memory alloy particles. Rev. Metal. 56 (2), e170. https://doi.org/10.3989/revmetalm.170.; Çavdar et al., 2020Çavdar, U., Ulvi Gezici, L., Gül, B., Ayvaz, M. (2020). Microstructural properties and tribological behaviours of Ultra-High frequency induction rapid sintered Al-WC composites. Rev. Metal 56 (1), e163. https://doi.org/10.3989/revmetalm.163.) There are various methods for producing the particles reinforced MMC, including stir casting is one of the best method for production of MMC. Casting is very popular because of its simplicity and flexibility and is the most economical method for the production of large components (Sambathkumar et al., 2017Sambathkumar, M., Navaneethakrishnan, P., Ponappa, K., Sasikumar, K.S.K. (2017). Mechanical and corrosion behavior of Al7075 (hybrid) metal matrix composites by two step stir casting process. Lat. Am. J. Solids Stru. 14 (2), 243-255. https://doi.org/10.1590/1679-78253132.; Sharma et al., 2018Sharma, A., Belokar, R., Kumar, S. (2018). Dry sliding wear characterization of red mud reinforced aluminium composite. J. Braz. Soc. Mech. Sci. Eng. 40, 294. https://doi.org/10.1007/s40430-018-1223-4.). Composites consist of one or more discontinuous phases that are integrated in a continuous phase. The discontinuous phase is generally harder and stronger than the continuous phase and is called a reinforcing material, the continuous phase is called a matrix. The main function is to transfer and distribute the load to the fiber reinforcement. The matrix can be selected based on its resistance to oxidation and corrosion. Metallic matrix Composite materials (MMC) offer designers advantages, they are particularly suitable for applications good resistance to high temperatures, good structural rigidity, dimensional stability, and light (Prasad et al., 2013Prasad, N., Sutar, H., Mishra, S.C., Sahoo, S.K., Acharya, S.K. (2013). Dry sliding wear behavior of aluminium matrix composite using red mud an industrial waste. Int. Res. J. Pure Appl. Chem. 3 (1), 59-74. https://doi.org/10.9734/IRJPAC/2013/2906.). Red mud is one of the main wastes in the production of aluminium oxide from bauxite using the Bayer process. It is an insoluble product that is produced after the digestion of bauxite with sodium hydroxide at high temperature and pressure and is known as red mud or “bauxite residue”. It contains oxides of iron, titanium, aluminium and silica as well as other secondary components. Due to economic and ecological issues, enormous efforts have been made worldwide to solve problems of red mud management, i.e., the use, storage and disposal (Pradeep et al., 2014Pradeep, R., Kumar, B.P., Prashanth, B. (2014). Evaluation of mechanical properties of aluminium alloy 7075 reinforced with silicon carbide and red mud composite. Int. J. Adv. Res. Chem. Sci. (IJARCS) 2 (6), 1081- 1088. http://www.ijergs.org/files/documents/EVALUATION-152.pdf.).
Corrosion can affect the metal matrix composite in several ways, depending on its nature and the prevailing environmental conditions. Examination of the corrosion resistance of Al-based materials is important, especially for automotive and aerospace applications where the parts are exposed to corrosive media such as salt water solutions, acidic and alkaline media. The main advantages of AMMC compared to unreinforced materials are as follows: higher strength, improved rigidity, reduced density, good corrosion resistance, improved properties at high temperature, coefficient of controlled thermal expansion, thermal/thermal management, resistance to improved wear and improved damping capacities. Aluminium 6061-MMC with a volume percentage of 0 to 6 percent reinforced with red mud particles has been successfully manufactured using liquid molten metallurgy technology. The corrosion rate of the alloy and the composite material decreased with increasing time in seawater. The corrosion rate of the composite materials was lower than that of the corresponding matrix alloy in seawater Composite materials are better suited to marine environments than matrix alloys (Krupakara and Ravikumar, 2015Krupakara, P., Ravikumar, H. (2015). Corrosion Characterization of Aluminium 6061/Red Mud Metal Matrix Composites in Sea Water. Int. J. Adv. Res. Chem. Sci. (IJARCS) 2 (6), 52-55. Corpus ID: 201799168. https://www.arcjournals.org/pdfs/ijarcs/v2-i6/8.pdf.). It has also been observed that the addition of red mud under the current test conditions results are increase in hardness and a decrease in the yield strength and electrical conductivity. Here it is observed that as the size of the red mud particles decreases, the density, hardness, yield strength and electrical conductivity of the sintered compacts gradually increases (Sai, 2014Sai, N.V. (2014). Fabrication and Characterization of Copper-Red Mud Particulate Composites Prepared by Powder Metallurgy Technique. JJMIE 8 (5), 313-321.). Red mud, the waste from the Production of alumina, has been used successfully as reinforcement material based on an aluminium alloy Composites with better wear resistance. These composite materials can be used instead of the classic ones Aluminium-based alloys. Composites can replace expensive reinforcement materials like, SiC and Al2O3 with red mud, which leads to Reduce costs and use industrial waste (Singla et al., 2015Singla, Y.K., Chhibber, R., Bansal, H., Kalra, A. (2015). Wear behavior of aluminum alloy 6061-based composites reinforced with SiC, Al2O3, and red mud: A comparative study. JOM 67, 2160-2169. https://doi.org/10.1007/s11837-015-1365-0.). The results show that the specific wear rate of the composite increases with increasing temperature. The reason for an increase in the wear rate at high temperature may be a loss of wear resistance at high temperature by softening the matrix (Dabral et al., 2017Dabral, R., Panwar, N., Dang, R., Poonia, R., Chauhan, A. (2017). Wear Response of Aluminium 6061 Composite Reinforced with Red Mud at Elevated Temperature. Tribol. Ind. 39 (3), 391-399. https://doi.org/10.24874/ti.2017.39.03.14.). Heat treated Al 6061/red mud composites improved the surface property like reduction of the cracks on surfaces (Panwar et al., 2020Panwar, N., Chauhan, A., Pali, H.S., Sharma, M.D. (2020). Fabrication of Aluminum 6061 Red-mud Composite using Stir Casting and Micro Structure Observation. Mater Today- Proc. 21 (4), 2014-2023. https://doi.org/10.1016/j.matpr.2020.01.318.). Addition of cermet (WC-Co) in to the Al 7075 matrix improves the hardness around 10.52%. The cermet particles also improve yield strength (49%) and tensile strength (58%) of the Al 7075 composite (Guruchannabasavaiah et al., 2021Guruchannabasavaiah, N., Auradi, V., Nandeeshaiah, B., Boppana, S.B., Nishanth, B.N. (2021). Investigation on the Microstructure and Mechanical Properties of Aluminum 7075 Reinforced with Different Weight Percentage of Tungsten Carbide and Cobalt Metal Matrix Hybrid Composites. IOP Conf. Ser.- Mat. Sci 1013, 012021. https://doi.org/10.1088/1757-899X/1013/1/012021.). Samples of the Al 7075 hybrid metal matrix composites are fabricated by two step stir casting process. Theoretical densities are calculated by using rule of mixture concept and experimental densities are calculated by using Archimedes principle. Phases of the composite was analyzed by using the method X-Ray diffraction (XRD) in Rigaku Ultima IV. Hardness of the composite is measured by using Vickers hardness tester in the standard of ASTM E384-11 (2011)ASTM E384-11 (2011). Standard Test Method for Knoop and Vickers Hardness of Materials. ASTM International, West Conshohocken, PA, USA. by using diamond indenter. Microstructure of the composites are studied by using the optical photomicrographs. Tensile test of the specimen is carried out by using universal tensile testing machine in the standard of ASTM E8/E8M-13a (2013)ASTM E8/E8M-13a (2013). Standard Test Methods for Tension Testing of Metallic Materials. ASTM International, West Conshohocken, PA, USA.. Corrosion test for the composite is done with 3.5% NaCl solution by using potentiodynamic polarization method. Finally studied the fractography and severity of corrosion by using SEM (Sambathkumar et al., 2017Sambathkumar, M., Navaneethakrishnan, P., Ponappa, K., Sasikumar, K.S.K. (2017). Mechanical and corrosion behavior of Al7075 (hybrid) metal matrix composites by two step stir casting process. Lat. Am. J. Solids Stru. 14 (2), 243-255. https://doi.org/10.1590/1679-78253132.). Addition of 15wt.% of SiC particles into the matrix improved the composite hardness and also showed better wear resistance compared to base alloy. Percentage of SiC and load play a significant role in the wear loss and coefficient of friction (Surya and Prasanthi, 2021Surya, M.S., Prasanthi, G. (2021). Effect of SiC Weight Percentage on Tribological Characteristics of Al7075/SiC Composites. Silicon 1-10. https://doi.org/10.1007/s12633-020-00885-5.).
The samples were subjected to wear and mechanical properties tests according to ASTM standards. It has been found that the microhardness, tensile strength, compressive strength and impact resistance of smaller composites have been increased Red mud particles were added to the composite (Geetha and Ganesan, 2019Geetha, B., Ganesan, K. (2019). Experimental investigation on influence of particle size on mechanical properties and wear behaviour of A356-red mud metal matrix composite. AIP Conf. Proc. 2128 (1), 020017. https://doi.org/10.1063/1.5117929.). The addition of graphite to an aluminium alloy is known to reduce hardness, tensile strength, compressive strength and flexural strength, and has been overcome by the addition of Al2O3 in hybrid composites. The presence of graphite in the hybrid composites has shown a tendency to maintain wear, less due to the formation of a thin layer of graphite on the surface of the tribo (Baradeswaran and Perumal, 2014bBaradeswaran, A., Perumal, A.E. (2014b). Wear and mechanical characteristics of Al 7075/graphite composites. Compos. Part B-Eng. 56, 472-476. https://doi.org/10.1016/j.compositesb.2013.08.073.). Corrosion tests were carried out according to ASTM standards. A salt spray test using NaCl was carried out according to ASTM B117-19 (2019)ASTM B117-19 (2019). Standard Practice for Operating Salt Spray (Fog) Apparatus. ASTM International, West Conshohocken, PA, USA. and immersion tests using NaCl and NaOH as corrodents were carried out according to ASTM G31-12a (2012)ASTM G31-12a (2012). Standard Guide for Laboratory Immersion Corrosion Testing of Metals. ASTM International, West Conshohocken, PA, USA. standards (Ravi Kumar et al., 2018Ravi Kumar, D., Seenappa, Rao, C.P., Bharat, V. (2018). Corrosion Behavior of Cenosphere Reinforced Al7075 Metal Matrix Composite-An Experimental Approach. JMMCE 6 (3), 424-437. https://doi.org/10.4236/jmmce.2018.63030.). In a two-step stir casting method, the structural defects such as wettability, interfacial reactions, particle cluster, porosity and oxide inclusions were overcome compared to the conventional casting technique (Zhou and Xu, 1997Zhou, W., Xu, Z. (1997). Casting of SiC reinforced metal matrix composites. J. Mater. Process. Technol. 63 (1-3), 358-363. https://doi.org/10.1016/S0924-0136(96)02647-7.; Aravindan et al., 2015Aravindan, S., Rao, P., Ponappa, K. (2015). Evaluation of physical and mechanical properties of AZ91D/SiC composites by two step stir casting process. J. Magnes. Alloy 3 (1), 52-62. https://doi.org/10.1016/j.jma.2014.12.008.).
Based on the literature survey, studies on mechanical and corrosion behaviour of Al 7075 composite reinforced with (5, 10, 15 Vol. %) red mud particle is not available. The main objective of the present study is to fabricate of Al7075/red mud composites and to investigate their mechanical and corrosion behaviour.
2. MATERIALS AND METHODS
⌅The base matrix is Al 7075 and the reinforcement material is Redmud for this present study of different composition of metal matrix composite. The chemical composition of the matrix and the properties of the matrix and the reinforcements are given in Table 1 and Table 2. Samples of the metal matrix composites are made using the two-stage stir casting technique. The amounts of matrix material and reinforcements were determined by calculating the volume percentages.
| Chemical Composition | Si | Fe | Cu | Mn | Mg | Cr | Zn | Ti | Al |
|---|---|---|---|---|---|---|---|---|---|
| Al 7075 | 0.4 | 0.5 | 1.6 | 0.3 | 2.5 | 0.15 | 5.5 | 0.2 | Rest |
| Properties | Density g·cm-3 | Specific gravity g·cm-3 | Hardness | Tensile strength MPa | Poisson’s ratio | PH value | Particle size |
|---|---|---|---|---|---|---|---|
| AL 7075 | 2.81 | 2.73 | 60 (HB500) | 220 | 0.33 | - | - |
| REDMUD | 3.26 | 2.77 | - | - | - | 10-13 | 6 µm |
The configuration of the stirring of moulding process consists of the furnace, the fire resistance stirring motor and the speed controller. The melting was carried out in the oven at 700 °C and the stirring was completed using a stirring motor and a speed controller. This setup is showen in Fig. 1a. The Redmud was preheated before being added to the aluminium matrix. The aluminium material was first heated to complete melting above the temperature of the liquid and converted to liquid form. It was then cooled below the liquid temperature to keep the molten metal in a semi-solid state. The preheated reinforcement (Redmud) was placed in the molten metal and stirred manually. The oven was then turned on to return the molten mixture to the liquid state. This was stirred mechanically for about 10 to 15 min at an average stirring speed of 150 to 200 rpm. The final temperature was maintained at 750 °C ± 100 °C.
Finally, the molten metal matrix composite was transferred to a metal of die. The die is made of mild steel with dimensions 150 x 60 x 50 mm3. Volume % of the matrix and the reinforcement in the metal matrix composite are shown in Table 3. The die used for preparing composite and produced composites are illustrated in Fig. 1 (b and c).
| S.No. | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| NAME | ALR0 | ALR5 | ALR10 | ALR15 |
| Vol. % of AL 7075 | 100 | 95 | 90 | 85 |
| Vol. % of Redmud | 0 | 5 | 10 | 15 |
Archimedes’ principle was used to calculate the experimental density and the mixing rule to calculate the theoretical density. The porosity of the composites produced is calculated using the theoretical and experimental densities calculated. The Vickers microhardness of the composites produced is measured using a Wilson microhardness tester. The Vickers microhardness of the cast base material Al 7075 and its composites (ALR0, ALR5, ALR10, ALR15) was determined according to ASTM standard E384-11 (2011)ASTM E384-11 (2011). Standard Test Method for Knoop and Vickers Hardness of Materials. ASTM International, West Conshohocken, PA, USA. using a diamond penetrator with an applied load of 500 g with a time of 10 s nominal stay. The microstructure of the polished and mirror polished samples is examined using an inverted metallurgical microscope to obtain optical microphotographs.
The samples are prepared for tensile tests in accordance with ASTM E8/E8M-13a (2013)ASTM E8/E8M-13a (2013). Standard Test Methods for Tension Testing of Metallic Materials. ASTM International, West Conshohocken, PA, USA. as shown in Fig. 1d. These samples are tested in the universal tensile testing machine (Instron) at an elongation speed of 1 mm/min. Seven tensile test pieces were tested and the mean value of the tensile strength of each pieces was shown graphically. Figure 1e each shows the tensile test pieces tested. Tensile test provides different kind of results they are, peak load, elongation and Ultimate tensile strength.
3. RESULTS AND DISCUSSION
⌅3.1. Density and porosity
⌅The theoretical density of the metal matrix composite produced was calculated using the concept called as rule of mixture. The experimental density of this composite was measured using the principle of Archimedes. The porosity of the composite was calculated using theoretical and experimental densities. Porosity or void proportion is a measure of voids in a material. These values obtained are presented in Table 4. During the analysis of Table 4, it can be observed that the theoretical and experimental density and porosity of the composites are higher than the base matrix Al 7075. The theoretical, experimental values of density and porosity of the composites are increased while increasing the Vol. % of the reinforcement during the stirring casting process. The reason for the increased porosity is the formation of pores on the surfaces of the reinforcing particles. This increases the generation of gas bubbles and the flow of liquid metal in the composite materials. The maximum permissible degree of porosity for die-cast aluminium composite materials is within the limit of 4%.
| S.No. | Name | Density (g·cm-3) | Porosity (%) | |
|---|---|---|---|---|
| 7. | ALR0 | Theoretical | 2.810 | 1.067 |
| 8. | Experimental | 2.780 | ||
| 9. | ALR5 | Theoretical | 2.8325 | 1.64 |
| 10. | Experimental | 2.786 | ||
| 11. | ALR10 | Theoretical | 2.855 | 2.10 |
| 12. | Experimental | 2.795 | ||
| 13. | ALR15 | Theoretical | 2.8775 | 2.73 |
| Experimental | 2.799 | |||
3.2. Microhardness and microstructure
⌅The microstructure optic of the composite is used taking into account the quality and an assessment of the efficiency of the technology used by the composite. Figure 2 and Fig. 3 show the photomicrographs and the corresponding microhardness of the composite. From the images of the light microscope, we can see that the reinforcements were evenly distributed in the matrix material and also clearly show the increased content of reinforcement in the composite material.
The effect of Redmud on the microhardness of the composite materials obtained from the hardness test. The hardness measurements are carried out on a Vickers microhardness testing machine. From the microhardness test, it has been observed that the hardness of the Al7075 + Redmud metal matrix composite increases with the addition of Redmud. It was higher than that of the base alloy Al 7075. The hardness of all the metal matrix composites was significantly higher than that of the base alloy.
Table 5 shows that the hardness measurement of metal matrix composites reinforced with Redmud in 5 times. From the measurement of the 5 times, the average is taken as a hardness of the metal matrix composite reinforced with red mud.
| Trails | ALR0 | ALR5 | ALR10 | ALR15 |
|---|---|---|---|---|
| 1st trail | 142.5 | 175.0 | 179.3 | 183.6 |
| 2nd trail | 134.1 | 176.5 | 181.0 | 179.8 |
| 3rd trail | 140.7 | 173.2 | 176.3 | 180.1 |
| 4th trail | 138.4 | 176.0 | 175.2 | 177.4 |
| 5th trail | 136.1 | 177.1 | 181.6 | 185.0 |
| Average | 138.36 | 175.56 | 178.68 | 181.18 |
3.3. Tensile strength
⌅Due to the low density of aluminium, the material is suitable for applications in the aerospace and automotive industries. The lower resistance of the aluminium alloy limits their applications. Table 6 shows that the values obtained tensile strength values of Al 7075 metal matrix composites reinforced by redmud. The Al 7075 metal matrix composites reinforced with red mud show that the tensile strength increases compared to the base alloy. To increase the strength of the composite, the presence of hard reinforcing particles is used. The addition of Redmud particles mainly improves the impact on the rupture and the tensile strength of the composite material by transferring the stresses of the aluminium matrix (ductile) to the reinforced particles (brittle).
| Name | UTS in MPa | Peak Load in kN | Elongation in % |
|---|---|---|---|
| ALR0 | 87 | 3.115 | 6.40 |
| ALR5 | 326 | 11.720 | 12.0 |
| ALR10 | 272 | 9.800 | 10.20 |
| ALR15 | 223 | 8.040 | 10.0 |
The elongation of the metal matrix composite was also measured in the tensile test. The elongation in tension is the elongation that a material undergoes when it is pulled under tension. The ductility of the material is measured from the percentage of elongation. Table 6 shows that the elongation values and peak load values of the metal matrix composites reinforced by Redmud. Here is the discussion on the peak load of the metal matrix composite, it is the maximum load that the test object can support during the test. The higher the tension required to create a certain stretch, the more rigid the material.
3.4. Fractography
⌅Figure 4 shows that the fracture surface of base Al 7075 and Al 7075 metal matrix composites. In this study of fractography from the aluminium composites, with the higher percentage of reinforcement used matrix cracks are adjacent to the Redmud particles and the limited amount of material flow is observed in the fractography. The following SEM images are in 1200x and 2500x magnifications and scale of 40 µm and 20 µm.
4. POTENTIODYNAMIC POLARIZATION TEST
⌅Electrochemical behaviour of Al 7075 metal matrix composites in 3.5% NaCl solution at room temprature is shown in Fig. 5. Corrosion current density and potential (Icorr & Ecorr), betta cathodic (ßc), betta anodic (ßa) slopes and the corrosion rate are obtained from the cathodic and anodic region of the TAFEL scan and the results are tabulated in Table 7. In potentiodynamic polarization testing, values of potential started from -1.3 V and for all the metal matrix composites result for Ecorr values are in between the range of -700 mV to -800 mV, which is higher than base alloy Al 7075.
| Composition | ßa e-3V/decade | ßc e-3V/decade | Icorr µA | Ecorr mV | Corrosion Rate mpy |
|---|---|---|---|---|---|
| ALR0 | 148.5 | 596.9 | 8.590 | -996.0 | 3.925 |
| ALR5 | 42.00 | 763.9 | 5.910 | -771.0 | 2.701 |
| ALR10 | 41.10 | 405.0 | 4.970 | -708.0 | 2.273 |
| ALR15 | 40.20 | 540.9 | 3.270 | -756.0 | 1.496 |
The corrosion current density (Icorr) values were decreased, while increasing the volume percentage of reinforcement (Redmud) particles. Naturally sand particles are corrodable, but here the addition of redmud into the Al 7075 alloy can increase the corrosion resistance by the physical properties of reinforcement.
Increasing the volume percentage of reinforcement particle (redmud) increases the corrosion resistance of the Al 7075. Possibilities of corrosion is reducing due to the bonding between the reinforcement and matrix, while increasing the vol percentage of reinforcement. Uniform flow of reinforcement is the reason behind increasing the corrosion resistance. From Table 7, it has been found that the Al7075 composites show better corrosion resistance when compared with the base alloy Al7075.
Shimizu et al. (1995)Shimizu, Y., Nishimura, T., Matsushima, I. (1995). Corrosion resistance of Al-based metal matrix composites. Mater. Sci. Eng. A 198 (1-2), 113-118. https://doi.org/10.1016/0921-5093(95)80065-3. developed an Al7075/SiC metal matrix composite (MMC) using a squeeze casting process and investigated heat-treated MMC to increase the potential for pitting and resist stress corrosion cracking in NaCl solution at 3.5%.
4.1. SEM Analysis
⌅Figure 6 shows that the corrosion of Al 7075 base alloy and Al 7075 metal matrix composites in different volume percentages. 3.5% of NaCl solution is used for the potentiodynamic polarization testing process. NaCl is a highly corrosive medium for the both Al 7075 base alloy and Al 7075 metal matrix composites. Here, ALR5 composition is highly corroded when compare to the ALR15 composition. The reason behind the corrosion rate reduction is, Redmud was acting as a cathodic sites with the galvanic action.
5. CONCLUSIONS
⌅Testing results provided the following conclusions:
Experimental density of the fabricated composite was calculated by using Archimedes principle, which is higher than base matrix.
Highest level of porosity for the fabricated composite is not exceeded 3%.
The fabricated composite provide high hardness and tensile strength while compare to the base matrix.
Microhardness of the composite was increased while increasing the reinforcement from 0% to 15%.
Ultimate tensile strength of the composite is high at 5% of reinforcement addition, which is 326 MPa. It is higher than the base matrix.
Elongation and Peak load both are more over same, increases up to 5% addition of reinforcement. Afterwards, slightly decreases.
Al 7075 metal matrix composites provided lower corrosion rate than the base matrix in 3.5% NaCl solution. Increasing the volume percentage of redmud reduces the corrosion rate of the composites.