Characterization of Aluminium Alloy AA2219 Reinforced with Graphite by Stir Casting Method

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Characterization of Aluminium Alloy AA2219 Reinforced with Graphite by Stir Casting Method1 V. Bhuvaneswari¹, a, G. Yuvaraj¹, b, Dr. A. Saravanakumar¹, c, L. Rajesh Kumar¹, d, R. Kiruthiha¹, e 1 – KPR Institute of Engineering & Technology, Coimbatore, India a – bhuvaneswari.v@kpriet.ac.in b – yuvarajg75@gmail.com c – saravanakumar.a@kpriet.ac.in d – l.rajeshkumar@kpriet.ac.in e – rkiruthu@gmail.com DOI 10.2412/mmse.79.48.932 provided by Seo4U.link

Keywords: aluminium alloy, graphite, mechanical properties, stir casting method.

ABSTRACT. Aluminium alloy has been accepted in the world wide for the fabrication of lightweight structures requiring a high strength to weight ratio, such as aerospace, automotive and structural components resulting in savings of materials and energy. In this work, mechanical properties like porosity test and surface roughness test of Aluminium Alloy AA2219 is reinforced with graphite powder in the ratio of 1%, 3%, 4.5% (in terms of weight) was done. It is fabricated with different composition of graphite using stir casting method and maintained at the temperature of 1023 K, and running speed at 500 rpm. The proposal work is aimed at obtaining a composite material with good surface finish and with less casting effects. By testing, we obtained the increase in surface roughness values of 3.83 µm at 4.5% of graphite and found porosity is increased up to 0.04%.

INTRODUCTION. Nowadays for the light weight applications, aluminium-matrix composites are extensively used in all mechanical fields for pre-existing structure that have to be retrofitted to make them seismic resistant, or to repair damage caused by seismic activity. Aaron Lam et al. [1] did the experimental studies on aluminium alloy 2219 have been formed the creep-aged at 175ºC for 18 h.

Using the CAF material constants determined for this alloy, corresponding finite element models have been developed and experimentally validated using the measured profiles. Suresh et al., [2] investigate the Aluminium composites have been produced with copper-coated cenospheres of fly ash as reinforcement. The results indicate that with increasing percentage of reinforcement, the tensile strength, impact strength and wear resistance of composites increases up-to 10%. Dunia Abdul Saheb [3] study the modest attempt has been made to develop aluminium based silicon carbide particulate MMCs. An increasing of hardness and with increase in weight percentage of ceramic materials has been observed. The best results (maximum hardness) have been obtained at 25 % weight fraction of SiC and at 4% weight fraction of graphite. Rajasekaran, & Sampath [4] Aluminium alloy AA2219 was reinforced with TiB particles introduced in-situ by the salt- metal reaction technique and the results proved that the addition of TiB particles results in increased mechanical properties, such as 0.2%YS, UTS and hardness. Chunlin He et al.,[5] Analysed the corrosion protection from sulphuric acid anodized coatings on 2024 aluminium and SiC particle reinforced 2024 aluminium metal matrix composite (SiCp/2024Al MMC) The results show that the anodized coating on 2024Al provides good corrosion protection to 3.5 wt. % NaCl. Krupinski et al., [6] investigated AlSi7Cu3Mg aluminium cast alloy was performed for samples cooled with different cooling rate settings. Results observed that phase morphology changes increase in relation to the cooling rate for the Al-Si-Cu alloy. The 1

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

amount of the pores increases together with the cooling rate. Hashim et al., [7] Combining high specific strength with good corrosion resistance, metal matrix composites (MMCs) are materials that are attractive for a large range applications. Vijayaramnath et. al. [8] studied the effect of reinforcements of aluminium by the addition of different metals. Suryanarayana et. al. [9] studied the SiC reinforced particles with aluminium for aerospace applications. Rupa Dasgupta [10] investigate the effect of dispersing SiC in 2014 base alloy adopting the liquid metallurgy route on different wear modes like sliding, abrasion. P.B. Pawar et.al studied [11] investigate the composite prepared by stir casting technique, conducted Mechanical tests such as hardness test, microstructure test find out the properties. Manoj Singla et.al.[12] modest attempt has been made to develop aluminium based silicon carbide particulate MMCs with an objective to develop a conventional low cost method of producing MMCs. C. Saravanan et.al. [13] studied the combined effect of reinforcements on Aluminium Metal Matrix composites with individual and multiple particulate reinforcements like Hybrid Metal matrix composites are finding increased applications in aerospace. Michael oluwatosin et.al. Reviewed the different combination of metals along with aluminium alloy and investigate the change in properties.

In the present work, we reinforced the graphite in different percentage that it was not done before in the previous work and we obtained the good results in surface roughness and porosity.

Properties of aluminium values 

Density (g/cc) 2.84



Hardness (BHN) 49.5



Ultimate tensile strength (Mpa) 455



Modulus of elasticity (Gpa) 73.1



Poisson’s ratio 0.33



Shear strength (Gpa) 285



Thermal conductivity (W/m-K) 120



Melting point (◦C) 643-750

Table 1. Properties of graphite.

Bulk Density (g/cm3)

1.3-1.95

Porosity (%)

0.7-53

Modulus of Elasticity (GPa)

8-15

Compressive strength (MPa)

20-200

Coefficient of Thermal Expansion (x10-6 °C)

1.2-8.2

Thermal conductivity (W/m.K)

25-470

Specific heat capacity (J/kg.K)

710-830

Experimental work. 

Fabrication of the project



Fabrication of composite bar.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954



Specimen preparation.



Testing of the specimen

Fabrication of composite bar.

Stir casting. Stir casting is a liquid state method of composite materials fabrication, (is shown in fig.

1) in which a dispersed phase (ceramic particles, short fibres) is mixed with a molten matrix metal by means of mechanical stirring. The liquid composite material is then cast by conventional casting methods and may also be processed by conventional metal forming technologies.

Fig. 1. Mechanical stirring machine.

Aluminium Stir Casting Equipment. In a stir casting process, the reinforcing phases are distributed into molten matrix by mechanical stirring. An interesting recent development in stir casting is a two-step mixing process. In this process, the matrix material is heated to above its liquids temperature so that the metal is totally melted.

Adding of Graphite with Melted Aluminium alloy. The melt is then cooled down to a temperature between the liquids and solidus points and kept in a semi-solid state. At this stage, the preheated particles are added and mixed. The slurry is again heated to a liquid state and mixed thoroughly. This two-step mixing process has been used in the fabrication of aluminium.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

a)

B)

Fig. 2. Cast Piece (a) of the Composite Bar (b) Cast Piece of the Composite Bar. Among all the well-established metal matrix composite fabrication methods, stir casting is the most economical. The distribution of the particles in the molten matrix depends on the geometry of the mechanical stirrer in the melt, melting temperature, and the characteristics of the particles added.

Parameters used in stir casting. There is various process parameters if they properly controlled can lead to the improved characteristic in composite material. · Stirring speed - 500rpm · Stirring temperature - 1023K · Stirring time - 10min · Preheating time of WC - 30min · Preheating temp of WC - 473K Composition of the specimen prepared.

Total weight is 750grams required to fabricate the composite bar (100%).

1. Aluminium – 738.75gm with 1.5% of WC- 11.25gm.

2. Aluminium – 727.5gm with 3% of WC- 22.5gm.

3. Aluminium – 716.25gm with 4.5% of WC-33.75gm.

Specimen preparation. Here the specimens are prepared as per the size requirement for the mechanical testing to be carried out for these materials.

Hardness test. Hardness is defined as the ability of the material to resist plastic deformation, usually by indentation. Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. Some materials, such as metal are harder than others. Resistance of a material to deformation, indentation, or penetration by means such as abrasion, drilling, impact, scratching, and/or wear, measured by hardness tests such as Brunel, Knoop, Rockwell, or Vickers. Since there is no standard hardness scale, each test expresses its results in its unique measure.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Brunel hardness test. Method of measuring the hardness of a material by pressing a chromium-steel or tungsten-carbide ball (commonly one centimetre or 0.4 inch in diameter) against the smooth material surface under standard test conditions. The hardness is expressed in Brunel Hardness Number (BHN) computed by dividing the load in kilograms by the area of indentation made by the ball measured in square millimetres. American Society for Testing and Material’s standard BH test is ASTM E10. For measurement up to BHN 500, Brunel hardness is equal to 0.96 times the Vickers hardness.

Fig. 3. Brunel hardness Equipment Table 2. Tests results. % of Graphite

Force Applied

Intender (dia) mm

(N)

Trial

Trial

Trial

Average

I

II

III

(dia)

mm

mm

mm

mm

Brunel Hardness Number (BHN)

1.

250

5.0

2.8

2.8

2.8

2.8

37.14

3.

250

5.0

2.9

2.8

2.9

2.845

34.8

4.

250

5.0

3.1

2.9

2.9

2.965

32.65

Surface roughness test. Surface roughness often shortened to roughness, is a component of surface texture. It is quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth. It is often necessary to know both amplitude and frequency to ensure that a surface is fit for a purpose.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Fig. 4. Surface roughness tester.

Table 3. Rockwell tests results.

Type Insert Spindle Used Speed (rpm)

Feed Rate

Depth of Cut (mm)

Al Alloy (%)

Graphite (%)

Trial I

Trial II

Trial III

Average Surface Roughness (µm)

Triangular Insert

750

0.06

4

98.5

1.5

1.45

1.1

1.2

1.25

Triangular Insert

750

0.06

4

97.0

3.0

2.5

2.4

2.7

2.53

Triangular

750

0.06

4

95.5

4.5

3.8

3.9

3.8

3.83

Porosity. Porosity or void fraction is a measure of the void or empty spaces in the material, and is a fraction of the volume of void over the total volume, between 0 and 1, or as a percentage between 0 and 100%. Strictly speaking, some tests measures the “accessible void”, the total amount of void space accessible from the surface.

Table 4. Porosity tests results.

Composition of Graphite

Volume

Mass ( gm)

1.5

5.4

14.966

14.966

3.0

5.4

13.731

13.737

2.54217 2.54388

0.02

4.5

5.4

15.267

15.270

2.82722

0.04

Before

After

Density(kg/cm³) Before 2.77

Porosity

After 2.77 2.8277

-

Summary The following conclusions were drawn from the AA2219 metal matrix composite after conducting the experiments and analysing the results:

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– Based on hardness test results, the sample A (Al 98.5% & graphite 1.5%) is having maximum hardness of 37.14 BHN. – Based on the porosity test results, the sample A (Al 98.5% & graphite 1.5%) is having minimum casting defect.

– Based on the surface roughness results, the sample A (Al 98.5% & graphite 1.5%) is having minimum surface roughness value of 1.25µm.

It is concluded, that the minimum amount of graphite percentages (1% to 2%) is preferable for many applications such as clutches, piston, spoilers, flight controls etc.

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[4] Koteswara Rao, S.R. Ph.D. Thesis. 2005. “Effects of welding processes, thermo mechanical treatments and scandium additions on the mechanical properties of AA 2219 welds”. Indian Institute of Technology Madras, Chennai, India, [5] A. Mahamani Procedia Materials Science “Effect of In-Situ TiB2 Particle Addition on the Mechanical Properties of AA 2219 Al Alloy”, Composite” 6, 2014, 950 – 960.

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