Characterization and Experimental Investigation on Mechanical Behavior of B₄C and RHA reinforced Aluminium Alloy 7075 hybrid Composite using Stir Casting

 

Nishant Verma¹, P.S. Rao², S.C.Vettivel³

^1,2Department of Mechanical Engineering, National Institute of Technical Teachers Training and Research (NITTTR), Chandigarh, India -160019

³Department of Mechanical Engineering, Chandigarh College of Engineering and Technology (Degree Wing)

Chandigarh, India -160019

 

ABSTRACT:

This paper is going to deal with the effect of Boron Carbide (B₄C) and Rice Husk Ash (RHA) in AA7075 Hybrid Composite. To study the effect of the addition of reinforcement on AA 7075, the fabrication is done by using bottom pouring type stir casting machine.K₂TiF₆isadded as filler to avoid the wettability problem of liquid molten aluminium alloy 7075 and B₄C.The results shows that the hardness of the hybrid composite is increased with increase in the wt. % of reinforcements. Scanning Electron Microscopy is used to confirm the microstructure of composite and distribution of reinforcements. The results of Energy Dispersive Spectroscopy analysis is used to confirm the elements in Al 7075/B₄C/RHA hybrid composite and some useful conclusions are made.

 

 

1. INTRODUCTION:

Aluminium Alloys (AA) are the backbone of automobile industry due to its light weight. The weight reduction is basic demand of automotive industry in order to make the vehicle more fuel efficient[1]. AA are the primary material of aircraft industry due to their well established design methods, manufacturing method and reliable inspection techniques. In the current scenario of aircraft industry the use of Aluminium(Al) composite has been done in place of AA due to their high specific properties, reduced weight, increased strength, increase corrosion resistance[2].

 

The cost reduction of aircraft has becoming more challenging for aircraft industries[3]. Aluminium castings are applied to large no of components in the automobile. The material of engine block is replaced from cast iron to AA in order to reduce the weight of vehicle to make vehicle more fuel efficient[4].The aluminium copper alloys is primary used in structure applications of aircraft where design criteria is damage tolerance[5].

 

Baradeshwaram and Perumal[6] investigated the influence of graphite on Aluminium 7075/graphite/Al₂O₃ hybrid composite. The investigation had been studied the effects of addition of Al₂O₃ as reinforcement on base AA 7075.The fabrication of samples was done with liquid metallurgy route. The properties of composite was compared on different wt. % of Al₂O₃ by keeping the wt.% of graphite constant. It had been investigated that the hardness increases at all the composition of Al₂O₃ Ceramics. but with addition of graphite as reinforcement material there was decrease in hardness.

 

Chuandong et al. [7] studied the effect of parameters of plasma activated sintering on microstructure and mechanical properties of Al 7075/B₄C composite. The parameters were temperature range and holding time. The Al7075 with 7.5% B₄C were fabricated in composite by using Plasma activated sintering method. The effect of temperature was studies in the range 450°C to 540°C. The effect of porosity on mechanical behavior and microstructure had been studied. It was reported that the composite sintered at 530°C with holding time of 3 minutes leads to fully dense microstructure and strong interface between AA7075 and B₄C and consist of highest Vicker’s hardness.

 

Baradeswaran and Perumal.[8]Investigated the mechanical behavior of AA7075/graphite composite. The samples were prepared using conventional casting technique and subjected to heat treatment. The stirring was done at 500 rpm for 5 min by using electric motor driven impeller. The composite was fabricated at the percentage of 5, 10, 15 and 20. The all samples were treated up to T6 condition before testing. The hardness test was carried on Rockwell hardness testing machine using load of 100kg.It was concluded that there was decrease in hardness with increase in percentage of graphite due to increase in brittle nature of the composite.

 

Chuandong et al.[9]investigated the effect of particle size and spatial distribution of B₄C reinforcement on the microstructure and mechanical behavior of AA matrix composite. AA 7075 was used as matrix material. Boron carbide is used as reinforcement consists of three sizes (56.9 µm, 4.2 µm and2.0 µm). The wt. % of B₄C is kept constant. The composite with coarse reinforcement had homogeneous distribution of B₄C particles and the composite with fine reinforcement had agglomeration of theB₄C particles. The composite had smallest size reinforcement particle had highest yield strength and fracture strength.

 

Alaneme and Sanusi[10]investigated the Microstructural characteristics, mechanical and wear behavior of aluminium matrix hybrid composites reinforced with alumina, Rice Husk Ash(RHA) and graphite. AA 6063 was used as matrix material. Alumina consists of particle size of 30µm. RHA and graphite had particle size of greater than 50 µm. The liquid metallurgy route is used to fabricate the samples for various types of testings. SEM micrographs show that proper dispersion of reinforcement particles in the aluminium matrix. It was observed that hardness was decrease with increase in RHA and graphite in all composites.

 

Saravanan and Kumar[11]reported the effect of RHA reinforcement on AlSi10Mg. The fabrication was done by using stir casting technique. The fabrication was done with different wt. % of RHA. The wt. %age of reinforcement was 3, 6, 9 and 12%.SEM was used to analyze the dispersion of RHA into AlSi10Mg. The hardness of composite increased with increase in the RHA contents.

 

Narasaraju and Lingaraju[12] characterized the Hybrid RHA and fly ash-Reinforced Composites. AlSi10Mg was used as matrix material. RHA and fly ash was used as reinforcement material consists of particle size between 0.1 to 100µm.The mixture of reinforcement was 5% fly ash 15% RHA, 10% fly ash 10% RHA and 15% fly ash 5% RHA respectively. The stir casting technique was used to fabricate the samples. The hardness increased with increase in wt. % of RHA and fly ash. But beyond10% RHA and 10% fly ash in composite, the hardness starts decreasing. It can be concluded that the 10% RHA and 10% fly ash were the optimized value for this composite.

 

Baradeswaran and Elaya Perumal[13]studied the effects of B₄C on tribological and mechanical properties of AA7075/B₄C composites. The febrications was done by using stir casting technique, K₂TiF₆ was used as flux to overcome the wettability problem between B₄C and liquid melted AA7075.The sample of AA7075/B4C composite was subjected to hardness, tensile and wear test. The results revealed that the hardness of composite increase with increase in B₄C content due to increase in ceramic phase.

 

Literature confirms that no work has been reported with B₄C and RHA as reinforcement in AA 7075. RHA is agricultural waste product and it is very cheap and easily available. So it is used as reinforcement for improving the properties. This paper is focused to prepare a AA7075 with B₄C and RHA hybrid composite and their effect in mechanical behaviour.

 

2. MATERIALS AND METHODS:

2.1 Material:

The experimentation was based on AA 7075 matrix composite so AA 7075 was used as matrix material and B₄C with RHA was used as reinforcement material to improve the properties of hybrid composite.

 

(a)                                                                                                                                       (b)

 

(c)

Figure 1 Details of Al 7075:(a) Aluminium 7075 rods (b) SEM of Aluminium 7075(c) EDS of Aluminium 7075

 

2.1.1 Matrix material:

The AA7075 is used as matrix material. AA 7075 was purchased from Ozair Tradelink, Gujrat India. The purchased material was in the form of rods having different lengths. The Fig.1 (a) shows the purchased AA 7075 material in the form of rods. Fig.1 (b) shows the SEM of AA 7075 at 500µm.The Fig.1(c) shows the EDS of AA 7075. EDS test confirms the purchased material was AA 7075having various alloying elements. The identified elements are Al, Zn, Cu, Mg, Si, Mn, Cr and Ti.

 

2.1.2 Reinforcement material:

The B₄C and RHA were used as reinforcement materials. The B₄C was purchased from Geepax industries, New Delhi, India and Rice husk ash was obtained from local sources.

 

2.1.2.1 Boron Carbide:

The fine particles of B₄C having size 50µm is used as reinforcement material. The hardness of B₄C is 2900 to 3580 HKN [14]. The wt. % of B₄C is kept constant during the fabrication of Composite. Fig.2 (a) shows the purchased B₄C in the form of powder. Fig.2 (b) shows the SEM of B₄C powder at 500µm.Fig.2(c) shows the EDS of B₄C powder. The results of EDS confirmed that the purchased material was B₄C.Theelements identified are only Boron and Carbide.

 

2.1.2.2 Rice Husk ash:

The rice husk was collected from local sources of Punjab, India. It is washed with fresh water in order to remove dust particle from the rice husk and dried it at room temperature for one day. The washed rice husk is then heated at 250°C for 1hour in order to remove moisture and oxides. Then it is heated at 600°C for 24 hours. The obtained silica ash is used as reinforcement material. Fig. 3(a) shows the RHA reinforcement without temperature treatment. Fig.3 (b) shows the detail of RHA reinforcement with temperature treatment. Table 1 shows the composition of RHA.

 

 (b)

 

 

(c)EDS of boron carbide

Figure 2 Details of B₄C:(a)Normal image of B₄C Fig.(b) SEM of B₄C Fig(c) EDS of B₄C

 

  (b)

Figure 3 Details of RHA: (a) RHA without temperature treatment(b) RHA with temperature treatment

 

Table 1 Shows the Composition of Rice Husk Ash[12]

 

2.2 Stir Casting

The AA7075 was used as matrix material and B₄C and RHA with different wt. % is used as reinforcement material in order to produce Al7075/B₄C/RHA hybrid composite. The fabrication was done by bottom pouring Stir Casting machine (Swami Equipment Chennai, India). It is shown in Fig. 4 (a).The AA charged into graphite crucible. The matrix material heated up to melting point by setting furnace temperature of 712⁰C as shown in Fig 4(b). The B₄C and RHA were separately placed in muffle furnace for preheating Figure 4(c). The B₄C and RHA were preheated at 300°C for 30 minutes. The venting of mould was done by various tight screws in order to create perfect vaccum in mould as shown in Fig.4 (d). The B₄C and RHA were poured afterK₂TiF₆ used as flux to remove the oxides. The stirring was done at 415 rpm for 10 minutes. The four samples with different wt. % of reinforcement are fabricated. The temperature control of molten metal and mould die is done by the wt. % of reinforcement in different samples are shown in table 4. The fabricated samples are shown in Fig. 5(a-d)

 

Fig. (a)                                                                                                                               Fig. (b)

 

Fig.(c)                                                                                                                                Fig.(d)

 

Figure 4 Details of Stir Casting: (a) Stir Casting machine(b) Melting of metal(c) Muffle furnace (d) Permanent mould.

 

Table 2 Wt. % of different reinforcement

 

2.3 Characterization:

2.3.1 Scanning Electron Microscope with EDS:

SEM (Jeol JSM-IT100 In Touch Scope™) was used to characterize the Al7075 based hybrid composite. The range of the resolution SEM varies from 1µm to 500 µm. The maximum value of voltage was 20KV. The electric conductive carbon tape is used to mount the specimen for observation.

 

2.3.1.1 Specimen preparation for SEM:

The specimens were cut from the centre of the casted samples consist of length 15-20mm. The surfaces of the specimen are clean by emery papers of various grades. Less then 100 Grit size papers are used for roughing.100-200 Grit size paper is used for medium finish and 220 to 330 grit size papers are used for good finish. The specimens were dipped in ethanol in order to avoid the error in EDS. The dipped samples are placed in normal environment to remove the ethanol particles.

(a)                                                                 (b)

  (c)                                                                         (d)

Figure 5 Details of Casted Samples :

(a) Pure AA 7075 (b) AA7075+5%B₄C

(c) AA7075+5%B₄C+3% RHA.(d)AA7075+5%B₄C+5% RHA

 

2.4 Hardness Testing:

The hardness of the specimen was checked on Mitutoyo HM 100 series. Vicker’s cum Rockwell Hardness tester at the load of 0.5 kgf. The range of load varies from 0.1 Kgf to 1Kgf. The indentation time varies from 5 seconds to 20 seconds. The diamond type indenter was used to produce indentation on material.

 

2.4.1Specimen preparation for SEM:

The specimen for hardness testing was cut from casted samples. Plaining of samples are done by grinding process. Plaining is necessary to avoid the damage of lens of camera in Vicker’s hardness test. The plain sample was clean by emery paper then polishd by sample policing machine. The diamond paste is used for polish the sample upto mirror finish.

 

4 RESULTS AND DISCUSSION:

4.1 Characterization of casted samples:

The SEM of hybrid composite can be shown in figure. The figure shows that there are proper dispersion of matrix material and reinforcement material without any defects. The B₄C and RHA properly mixed in the base material of AA 7075.

 

Fig.6 (a) shows the SEM image of pure AA7075. It shows there is less porosity and formation of oxides is also less. Fig.6 (b) shows the EDS image of pure AA 7075 which confirmed the major alloying elements like Zn, Mg, Si, Mn, Cu, Ti, Fe in AA7075.

 

Fig.6(c) shows the SEM image of AA7075/B₄C composite. it confirms the most of B₄C particles mixed uniformly in pure AA 7075. Fig.6 (d) shows the elemental analysis of AA7075/B₄C composite which confirms the elements like Boron, Magnesium, Silicon and Oxygen. The presence of Boron confirm the dispersion of Boron in AA7075 and the presence of oxygen confirms the formation of oxides are little more as compare to pure AA 7075.

 

Fig.6(e) shows the SEM image of AA7075/B₄C/RHA the wt% of B₄C was 5% and the wt% of RHA was 3% Fig.6(f) shows the EDS image of AA7075/B₄C/RHA which confirms the various elements in composite like Mg, Si, C, B, presence of Silicon confirms the dispersion of Silica ash in the composite. and the presence of oxygen confirms formation of oxides are more as compare to AA7075/B₄C.and there is little increase in porosity of composite.

 

Fig. 6(g) shows the SEM image of AA7075/B₄C/RHA. The wt% of B₄C was 5% and wt% of RHA was 5%. The image shows the proper dispersion of RHA in composite. Fig. 6(h) shows the elemental analysis by EDS which confirms the elements like B, C, Al and Mg. The results of SEM Shows the worn surfaces and proper mixing of matrix material and reinforcement. The results of EDS shows the composition of casted samples.

(a)	(b)
(c)	(d)
(e)	(f)
(g)	(h)

 

Fig.6 SEM image of casted Samples (a)SEM image ofPure AA 7075 (b) EDS of pure AA 7075 (c) SEM of AA7075+5% B₄C (d) EDS of AA7075+5% B₄C (e) SEM of AA7075+5% B₄C+3%RHA(f) EDS of AA7075+5% B₄C+3%RHA, Fig.(g) SEM of AA7075+5% B₄C+5%RHA Fig.(h) EDS image of AA7075+5% B₄C+5%RHA

4.2 Effect on Hardness:

The hardness of the hybrid composite increased with the wt.% of B₄C. The wt.% of B₄C kept constant at 5%. After that effect of RHA was studied with increase in wt.% of RHA. The hardness start increases it is more than base material at all wt.% of reinforcement material. The effect of the addition of prepared hybrid composite samples are shown in Fig 7. The result of hardness shows that there is rapid increase in hardness of the hybrid composite due to increase the wt.% B₄C. This is due to increase the ceramic phase and the hardness of B₄C is greater than the base material. The results show that there is less increase in hardness due to the addition of RHA as compare to B₄C. This is due to the fact that hardness of RHA is less than B₄C.

 

Fig.7 Effect of hardness

 

5. CONCLUSIONS:

·        The AA 7075/B₄C/RHA hybrid was successfully fabricated by liquid metallurgy stir casting route.

·        The SEM and EDS results confirmed that there is proper mixing of matrix material and reinforcement material.

·        The hardness of the hybrid composite higher at all wt.% of reinforcement as compare to base material

·        The addition of B₄C provides more hardness as compare to the addition of RHA.

 

6. REFERENCES:

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2.       Tolga Dursun, Costas Soutis, “Recent developments in advanced aircraft aluminium alloys” mat and design pp 862–871, 2014

3.       Campbell FC. Manufacturing technology for aerospace structural materials. Elsevier; 2006

4.       G. Cole, A. Glove, R. Jeryan, G. Davies, Steel World 2 (1) (1997) 75–83

5.       Williams JC, Starke EA. Progress in structural materials for aerospace systems. Acta Mater 2003; 51:5775–99.

6.       Baradeswaran and Elaya Perumal, “Study on mechanical and wear properties of Al 7075/Al₂O₃/graphite hybrid composites,” Compos. Part B Eng., vol. 56, pp. 464–471, 2014.

7.       ChuandongWua., Pan Fang, Guoqiang Luo, Fei Chen, Qiang Shen, Lianmeng Zhang, Enrique J. Lavernia “Effect of plasma activated sintering parameters on microstructure and mechanical properties of Al-7075/B4C composites, ” J. Alloys Compd., vol. 615, pp. 276–282, 2014.

8.       A. Baradeswaran and A. E. Perumal, “Wear and mechanical characteristics of Al 7075/graphite composites,” Compos. Part B Eng., vol. 56, pp. 472–476, 2014.

9.       Chuandong Wu, Kaka Ma, Jialu Wu, Pan Fang, Guoqiang Luo, Fei Chen, Qiang Shen, Lianmeng Zhang, Julie M. Schoenung, Enrique J. Lavernia “Influence of particle size and spatial distribution of B₄C reinforcement on the microstructure and mechanical behavior of precipitation strengthened Al alloy matrix composites, ” Mater. Sci. Eng. A, vol. 675, pp. 421–430, 2016.

10.     K. K. Alaneme and K. O. Sanusi, “Microstructural characteristics, mechanical and wear behaviour of aluminium matrix hybrid composites reinforced with alumina, rice husk ash and graphite, ” Eng. Sci. Technol. an Int. J., vol. 18, no. 3, pp. 1–7, 2015.

11.     S. D. Saravanan and M. S. Kumar, “Effect of mechanical properties on rice husk ash reinforced aluminum alloy (AlSi10Mg) matrix composites”, Procedia Eng., vol. 64, pp. 1505–1513, 2013.

12.     G. Narasaraju and D. Linga Raju, “Characterization of Hybrid Rice Husk and Fly ash-Reinforced Aluminium alloy (AlSi10Mg) Composites,” Mater. Today Proc., vol. 2, no. 4–5, pp. 3056–3064, 2015.

13.     A. Baradeswaran and A. Elaya Perumal, “Influence of B₄C on the tribological and mechanical properties of Al 7075-B₄C composites,” Compos. Part B Eng., vol. 54, no.1, 2015, pp.192-195.

14.     Retrieved from http://www.azom.com/article.aspx?ArticleID=75

 

 

 

 

Received on 10.07.2017                             Accepted on 25.08.2017        

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