Utilization of RHA in development of green composite material using RSM

Abstract In the present investigation, rice husk waste from rice mill was utilized in the development of aluminum based green metal matrix composite. Response surface methodology (RSM) was employed to develop green metal matrix composite by considering tensile strength as a response. Rice husk ash (RHA) was used as primary reinforcement material and B4C was used as a secondary reinforcement material in the development of composite. Microstructure results showed a uniform distribution of RHA and B4C in aluminum based matrix material. The optimum combination of reinforcement parameters was found to be RHA weight percentage of 7.8%, RHA preheats temperature of 231.12∘C, B4C preheats temperature of 435.24∘C and B4C wt.% of 6.67% respectively to achieve a tensile strength of 249.867 MPa.


Introduction
The development of low density and low-cost metal matrix composite using waste material is one of the most interesting research areas in the current scenario. Nowadays; in all over the world, most of the researchers are focussing on green manufacturing research-based technology. Green manufacturing is the regeneration of a manufacturing route which provides a healthy environment condition or gives the technique so that the environment can keep green by minimizing the pollution [1,2]. Aluminum alloys, due to having the automobile industry-relevant characteristics (such as lightweight, higher specific strength, higher specific stiffness), attracts more and more researchers. Secondly, aluminum alloys show excellent improvement in its properties on being reinforced by some selected materials. Metal matrix composites (MMCs) are a combination of matrix and reinforcement [3][4][5]. Matrices can be selected from several Al alloy depending on the application like AA6061, AA2024, A356, etc. These aluminum alloys are most commonly used in automobile industries [6][7][8][9][10][11][12]. Further, it was observed that rice husk produces lots of soil pollution around rice mill area as shown in Figure 1.
Though various researchers tried to utilize RHA in various fields, but those techniques were costly and not friendly. In this study, RHA waste was utilized to develop a green metal matrix composite. In the present investigation, an attempt was made to utilize RHA as primary reinforcement material with B 4 C as secondary reinforcement material in the development of Aluminium base composite using RSM.

Matrix material
In this study, Al 2024 is considered as a matrix material. AA2024 alloy is aluminum based alloy which has copper is   the main alloying element. Machining property of AA2024 alloy is average, while its corrosion resistance property is very low. It is very tough to weld. It is broadly used in aircraft industries in making wing and fuselage structures under simple tension due to its high fatigue and tensile strength. Its chemical compositions and mechanical properties are shown in Table 1 and Table 2 respectively.

Rice husk ash (RHA) as primary and B 4 C as secondary reinforcement material
In the present study, agro waste rice husk ash (RHA) was utilized as reinforcement material in the development of green aluminum based metal matrix composites. Rice husk powder (RHP) was burned to obtain Rice husk ash (RHA) after ball milling as shown in Figure 2. Ceramic par-  Electrical Conductive Electrical resistivity at 25 ∘ C is 0.1 -10 ohm-cm  ticle B 4 C was used as a secondary reinforcement material. Table 3 shows the RHA composition used in this study.

Development of composite material
Stir casting technique was used to develop composite material. RHA and B 4 C were utilized in the development of composite material as reinforcement with the AA2024 aluminum alloy matrix. Reinforcement particles were added into melt material when the temperature of melt material was reached about 600 ∘ C as shown in Figure 3. Stir casting parameters for the development of hybrid composite materials are shown in Table 5. Table 6 shows the process parameters with their ranges. The design matrix table is shown in Table 7.

Response surface methodology
Response surface methodology (RSM) is defined as a collection of mathematical and statistical methods that are used to develop or optimize a product or process.

Microstructure analysis
Microstructure image of green hybrid metal matrix composite reinforced with RHA and B 4 C is shown in Figure 5. Microstructure image shows a uniform distribution of RHA and B 4 C in aluminum base matrix. This microstructure results showed that B 4 C and RHA can be used simultaneously in the development of aluminum based hybrid metal matrix composite.

Mathematical modeling for development of green composites
ANOVA Table is indicated by Table 8 for mathematical modeling. From Table 8, it can be observed that the model term, as well as each independent input parameter, is significant. While "lack of fit" is insignificant. It was also observed from the ANOVA  Figure 6 shows normal percent probability graph and predicted v/s actual graph. Both graphs are falling in straight line. Hence, all the experiments conducted for tensile strength is fair, arbitrary and randomly.

Process parameters effects on tensile strength
It was observed from the past analysis that very good mechanical properties can be obtained by considering the appropriate reinforcement parameters combination in the matrix material. Keeping these facts in the mind, various combinations of reinforcement parameters were taken by applying CCD (Central composite design) technique. By us-ing CCD, an attempt was made to find out the appropriate combination of reinforcement parameters achieve maximum tensile strength. Figure 7 (a) shows that by increasing the weight percentage of RHA up to center value, the tensile strength of hybrid composite increases, but beyond the center point tensile strength began to decreases. Figure 7 (b) displays that the tensile strength of hybrid green metal matrix composite also increases when RHA preheat temperature  Figure 8 (a-f) shows the three-dimensional (3D) interaction parameters effect on tensile strength of hybrid composite materials. It can be easily observed from Figures 7 (a) that when weight percent of RHA increases up to the center limit and RHA preheat temperature increases simultaneously then the tensile strength of composite also increases. In the same way, other interaction parameters effects can also be discussed.
Ramp function graph was plotted to obtain the optimum combination of reinforcement parameters to achieve maximum tensile strength. ramp function graph (Figure 9) shows that when RHA weight percentage, RHA preheat temperature, B 4 C preheat temperature and B 4 C wt.% are 7.8%, 231.12 ∘ C, 435.24 ∘ C and 6.67% respectively then the optimum value of tensile strength of the composite is 249.867 MPa with desirability one.

Mechanical properties of composite at optimum parameters
A confirmation experiment was carried out to see the effects of reinforcement addition on the mechanical properties of hybrid composites. Tensile strength was found to be 238.5 MPa at optimum parameters (RHA weight percentage of about 7.8%, RHA preheat temperature of about 231.12 ∘ C, B 4 C preheat temperature of about 435.24 ∘ C and B 4 C wt.% of about 6.67%). Tensile strength results showed that there is only a 4.4% error in the developed model and experimental result. However, hardness was also increased by about 35.41%. Though, toughness and ductility were reduced with respect to the base metal as shown in Figure 10.

Corrosion behaviour of hybrid composite at optimum reinforcement parameters
Corrosion test of all the samples was carried out to identify the durability (life) of developed composite materials concerning surrounding moisture and environment. The corrosion test of all the samples was carried out in 3.5 wt.% NaCl for 120 hours. The weight of each sample was taken 9 gm to make uniformity for the corrosion test. Corrosion be-  haviour of a hybrid composite at developed at optimum reinforcement parameters (RHA weight percentage of about 7.8%, RHA preheat temperature of about 231.12 ∘ C, B 4 C preheat temperature of about 435.24 ∘ C and B 4 C wt.% of about 6.67%) was investigated. Weight loss of hybrid composite after the corrosion test was found to be 8.98 mg. There was only 0.02 mg material of hybrid composite was corroded as shown in Figure 11.

Thermal expansion behavior of hybrid composite at optimum reinforcement parameters
The thermal expansion property of each green composite material was identified to observe the appropriateness of material in a high-temperature environment. Dimension (Volume: 2700 mm 3 (27 × 10 × 10)) of each sample was kept constant. The thermal expansion of all prepared samples was carried out in mu e furnace at 450 ∘ C constant temperature for 48 hours. The thermal expansion behaviour of the hybrid composite at optimum reinforcement parameters was investigated as shown in Figure 12. The volume Figure 12: Thermal expansion behavior of hybrid composite at optimum reinforcement parameters of the hybrid composite after the thermal expansion was found to be 2680 mm 3 , which is acceptable.

Conclusions
The following conclusions can be drawn from the analysis.
1. Soil pollution can be reduced by using rice husk ash as reinforcement material in the development of green composite material. 2. Al2024 aluminum alloy is one of the most demanding materials in automobile industries due to its light weight and good strength. 3. Green metal matrix composite with RHA and B 4 C as reinforcement materials and Aluminium as matrix material can be successfully developed using a stir casting technique. 4. Microstructure results showed a uniform distribution of B 4 C and RHA in Al2024 based matrix material. 5. The optimum combination of reinforcement parameters was found to be RHA weight percentage of 7.8%, RHA preheat temperature of 231.12 ∘ C, B 4 C preheat temperature of 435.24 ∘ C and B 4 C wt.% of 6.67%, respectively to achieve the tensile strength of 249.867 MPa with desirability one. 6. The mechanical properties of hybrid composites were investigated at optimum reinforcement parameters. Mechanical properties were enhanced significantly at optimum reinforcement parameters.

Corrosion loss and thermal expansion results
showed that material is stable in a moisture environment and high-temperature surrounding.