Shashi Prakash Dwivedi | Ashish Kumar Srivastava* | Nagendra Kumar Maurya | Rohit Sahu
© 2020 IIETA. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).
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In the present investigation, an attempt was made to utilize RHA in the development of aluminium based composite material. AA6061 alloy was melted in muffle furnace. Preheated RHA and SiC were added in the aluminium alloy. Composite material was fabricated by stir casting technique. Microstructure image showed proper wettability of reinforcement material with aluminium alloy matrix. Uniform distribution was observed of reinforcement particles in aluminium alloy. It has been observed that by using the RHA and SiC simultaneously in aluminium alloy, mechanical properties were improved significantly. However; toughness and ductility were reduced. Heat treatment of composite material was also carried out to observe the enhancement of mechanical property. Results showed that after the heat treatment process, mechanical properties were further improved.
hybrid composite, SiC, RHA, ductility, hardness, tensile strength
Nowadays, automobile industries as well as air craft industries are using light weight material with high strength material [1, 2]. In the selection of material, it was observed that ferrous metals have high strength but its density is much high. However, non-ferrous metal such as aluminium have low density, but its strength is very low as compared to iron. However, by increasing the mechanical properties of aluminium, it can be used in the automobile and air craft industries [3, 4].
Aluminium alloy is now currently using in the development of composite material. Aluminium based composite materials are using in various industrial application [5, 6]. Usually, composite is the combination of two or more than two materials. Here, one is matrix material and others are reinforcement materials. Reinforcement materials may be one or more than one. These reinforcement materials enhanced various properties of matrix material such as tensile strength, hardness etc. However, sometimes toughness and ductility are reduced [7-10].
Various authors have done their work on mechanical characterization and microstructural examinations of MMCs. Such as Srivastava et al. [11] has worked on the development of A359/B4C MMCs by stir casting route. They discussed about the improvement in the mechanical properties. Idrisi and Deva [12] has fabricated the MMC by aluminum alloy reinforced with SiC particles. They observed that the mechanical properties were increases as the percentage contribution of SiC particles were increases. Milos et al. [13] worked on the development of composite by Al5083 alloy reinforced with Al2O3 and graphite. The weight % and size of the reinforced particles was chosen as a variable to study the effect on mechanical properties. Further the tensile and compressive strength were studied by Idris et al. [14]. They also suggested that the liquid stirring processes is quite cheaper than the solid-state processing and liquid stirring has remarkable characteristics like improved wettability and chemical reaction between molten aluminum alloy and reinforcement particle. Meena et al. [15] has investigated the casting characteristics of Al6063/SiC composite produced by mechanical stir casting. Weight percentage of reinforcement such as 5%, 10%, 15% and 20% were taken for the study. Srivastava et al. [16] reviewed the work related to development and characterization of MMCs published by various authors. They also discuss the merits and demerits of various fabricated composites. Dwivedi et al. [17] has discussed the thermal behavior and microstructural examination of Aluminum based composite reinforced with SiC and MgO. Their results revels that the minimum expansion in dimension due to heat is observed at 5% of mixing of each reinforcements in the matrix alloy.
From the literature, it was observed that very few researchers are AA6061 matrix base composite material by using SiC as primary reinforcement material and Agro-waste RHA as secondary reinforcement material. Keeping these facts in the mind in the present investigation AA6061/SiC/RHA hybrid metal matrix composite material was developed. Further, mechanical properties of hybrid composite materials were investigated to observe the addition effect of SiC and RHA in AA6061 matrix material. Heat treatment process was also carried out to enhance further mechanical properties of hybrid composite material.
2.1 Matrix material
In the present investigation, AA6061 aluminium alloy was taken as reinforcement material. AA6061 aluminium alloy was broadly used in various application among the all aluminium alloys. AA6061 materials are used in the fabrication of wings and fuselages in aircraft structures. It is used in the yacht construction. AA6061 alloys were also used in fabrication of chassis of the Audi A8. AA6061 alloy was also very good wieldable material.
2.2 Reinforcement materials
In this study, ceramic particle SiC was used as primary reinforcement material. SiC particles have good wettability characteristics with aluminium alloy [18, 19]. Due to this reason, SiC is the most preferable ceramic particle with aluminium alloy. Agro-waste RHA (rice-husk ash) is agricultural waste materials which produce lots of soli pollution in agricultural land [20]. By utilizing this waste in the development of composite material, some pollution may be reduced. Further, by using RHA as secondary reinforcement material with AA6061 alloy, some mechanical properties can be improved.
2.3 Development of hybrid composite material
Figure 1. Schematic diagram of stir casting process [10]
Table 1. Composition selection
|
Sample No. |
Compositions |
Wt. % of SiC |
Wt. % of RHA |
|
1 |
AA6061+ 0 % SiC + 0% RHA |
0% |
0% |
|
2 |
AA6061+15% SiC + 0% RHA |
15% |
0% |
|
3 |
AA6061+12.5% SiC + 2.5% RHA |
12.5% |
2.5% |
|
4 |
AA6061+10% SiC + 5% RHA |
10% |
5% |
|
5 |
AA6061+7.5% SiC + 7.5% RHA |
7.5% |
7.5% |
|
6 |
AA6061+5% SiC + 10% RHA |
5% |
10% |
|
7 |
AA6061+2.5% SiC + 12.5% RHA |
2.5% |
12.5% |
|
8 |
AA6061+0% SiC + 15% RHA |
0% |
15% |
Figure 1 shows the line diagram of stir casting set-up. Hybrid metal matrix composites were fabricated by using the mechanical stir casting technique. First of all, AA6061 matrix material was melted in muffle furnace. Reinforcement particles SiC and RHA were preheated before mixing it in matrix material. Reinforcement materials were added in AA6061 matrix material at temperature 700ºC. Prepared composite material was removed from crucible after the solidification. Composition of hybrid composite material was shown in Table 1.
3.1 Microstructure analysis
Figure 2 shows the microstructure image of AA6061/SiC/RHA hybrid metal matrix composite. Microstructure image shows some agglomeration of RHA particles inside the AA6061 matrix material. However, SiC particles were distributed uniformly inside the matrix material. From the microstructure image, it can be concluded that mechanical properties enhanced due to the presence of SiC and RHA in AA6061 matrix material.
Figure 2. Microstructure of hybrid metal matrix composite
3.2 Tensile strength analysis
Figure 3 shows the microstructure image of AA6061/SiC/Agro-waste RHA hybrid metal matrix composite. Maximum tensile strength was found to be 165 MPa for composition AA6061+12.5% SiC+2.5% RHA hybrid metal matrix composite. Tensile strength of AA6061+12.5% SiC+2.5% RHA hybrid metal matrix composite was further improved after the heat treatment process. Result showed that after the heat treatment process about 65.71% tensile strength was improved with respect to base AA6061 matrix material as shown in Figure 3. Enhancement of tensile strength of composite is due to the presence of hard phases in RHA such as SiO2, CaO, Fe2O3, K2O, TiO2, MnO, CuO. Silicon carbide (SiC) was also fully responsible in enhancing the tensile strength of composite.
Figure 3. Tensile strength of hybrid metal matrix composite
3.3 Hardness
Figure 4 shows the hardness of hybrid metal matrix composite material. Results showed that addition of ceramic particle enhanced the hardness of composite material. Maximum hardness was found to be 88 BHN for composition AA6061+15% SiC+0% RHA. Hardness of the hybrid metal matrix composite was further improved after the heat treatment process. Results showed that after the heat treatment process, 95 BHN was observed of AA6061+15% SiC+0% RHA composite material. Low porosity in the composite was fully responsible in the enhancement of hardness of AA6061+15% SiC+0% RHA composite. However, Silicon carbide is a very hard particle. Reinforcement of SiC particles in the AA6061 matrix material, improved the hardness significantly.
Figure 4. Hardness of hybrid metal matrix composite
3.4 Fracture toughness
Figure 5 shows the fracture toughness of hybrid metal matrix composite. Fracture toughness of hybrid composite material was continuously decreased by adding the SiC and RHA particles in AA6061 matrix material. However, fracture toughness was improved after the heat treatment process. Hard phases in RHA such as SiO2, CaO, Fe2O3, K2O, TiO2, MnO, CuO are always enhanced the tensile strength and hardness of composite. Presence of hard phases in composite material, energy required to cause a crack to grow to fracture decreases, resulting fracture toughness decreases.
Figure 5. Toughness results of hybrid metal matrix composite
3.5 Ductility (percentage elongation)
Ductility of the composite material was identified by observing the percentage elongation of composite material. Percentage elongation was observed from the tensile samples of hybrid composite material. Figure 6 shows the ductility of hybrid composite material. Results showed that by adding the ceramic particle in AA6061 matrix material, ductility was continuously decreasing. When hard particles are added in the matrix material, deformation before fracture is reduced. Low deformation before fracture reduced the ductility of composite.
Figure 6. Ductility of hybrid metal matrix composite
3.6 Corrosion behaviour
The durability of the material in the moisture or acid surrounding is one of the most important factors in the selection of material for different application. Corrosion behaviour of the hybrid composite material reinforced with SiC and RHA has been observed to identify the reinforcement particle addition effect on aluminium alloy. Corrosion behaviour of the composite was observed in 3.5 wt. % NaCl for 120 hours. Weight of each sample before the test was kept 15 gm. Corrosion behaviour of AA6061+7.5% SiC+7.5% RHA hybrid composite material observed before heat treatment and after heat treatment. Silicon Carbide is a ceramic particle. Addition of SiC particles in the aluminium alloy with minimum porosity reduced the weight loss of the aluminium based composite material. It has been observed that after the heat treatment process, weight loss of the composite material reduced as shown in Figure 7.
Figure 7. Corrosion behaviour of composite
3.7 Thermal expansion behaviour
Thermal Expansion Behaviour of hybrid composite material has been identified to observe the material durability in a high-temperature environment. Thermal expansion behaviour of AA6061+7.5% SiC+7.5% RHA hybrid composite material as cast and as heat treated has been observed to identify the heat treatment effect on the composite material. The dimension of the sample has been kept 2500 mm3 (25 X 10 X 10) before the test. Results showed that after the heat treatment process, thermal expansion of the composite material has been significantly improved (Figure 8).
Figure 8. Thermal expansion behaviour of composite
Following conclusions may be drawn from the exhaust analysis.
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