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, 2014a; Baradeswaran and Perumal, 2014b; Imran et al., 2016; Devaganesh et al., 2020; Alaneme et al., 2020; Çavdar et al., 2020) 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., 2017; Sharma et al., 2018). 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., 2013). 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., 2014).

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, 2015). 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, 2014). 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., 2015). 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., 2017). Heat treated Al 6061/red mud composites improved the surface property like reduction of the cracks on surfaces (Panwar et al., 2020). 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., 2021). 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) 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). 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., 2017). 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, 2021).

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, 2019). 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, 2014b). Corrosion tests were carried out according to ASTM standards. A salt spray test using NaCl was carried out according to ASTM B117-19 (2019) and immersion tests using NaCl and NaOH as corrodents were carried out according to ASTM G31-12a (2012) standards (Ravi Kumar et al., 2018). 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, 1997; Aravindan et al., 2015).

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.

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.

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).

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) 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) 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.

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.

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) 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%.

Testing results provided the following conclusions: