Mechanical Characteristics of AA7075 Reinforced with Tungsten Carbide Produced by Stir Casting

Home , Casting (metalworking)

International Journal of Pure and Applied Mathematics Volume 119 No. 15 2018, 2015-2029 ISSN: 1314-3395 (on-line version) url: http://www.acadpubl.eu/hub/ Special Issue http://www.acadpubl.eu/hub/

Mechanical Characteristics of AA7075 reinforced with Tungsten carbide produced by stir casting

Arun Prakash S2, Shaikh Anis Abdul Razzak2 Ajay Christan F2,Logesh M1

1 Assistant Professor, 2 Final year students Department of Mechanical Engineering Vel Tech Multi Tech Dr.Rangarajan Dr.Sakunthala Engineering College Abstract

The present works shows about the fabrication of composites and its characterization of Aluminium metal matrix composites (AMCs) AA7075 T6 base metal base with Tungsten carbide (WC) particulate with various reinforcements 2.5%, 5.0%.7.5%, 10%, 12.5% was produced by stir casting technique. WC particle size of 3-4 µm was used as reinforcement to disperse in matrix. Mechanical properties and Micro-structure was studied. Increased reinforcement percentage gives higher hardness value and tensile strength.

Keywords Aluminium metal matrix composites, Tungsten carbide, stir casting

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1.Introduction

A particle-reinforced composite was widely used in used in automotive, aerospace, opto- mechanical assembly’s components.They are used in metals, polymers and ceramics.Composites are generally contains equiaxed ceramic reinforcements with an aspect ratio less than about 5.

Ceramic reinforcements are generally oxides or carbides or borides (Al2O3 or SiC or TiB2) and present in volume fraction less than 30% when used for structural and wear resistance applications [2]

2. Experimental

2.1 Material

Aluminium 7075 alloy was selected due its excellent strength and hardness especially it was used in aerospace industries so it was selected has base metal chemical composition is shown in Table 1

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Table 1 Chemical composition of Aluminium 7075

Weight% Al Si Fe Cu Mn Mg Cr Zn Ti

7075 Rem 0.4 0.5 2 0.3 2.9 0.28 6.1 0.2

Many researches investigated with various reinforcements like SiC, B4C.Al2O3 etc out of which WC was hardest one due to its unique property it was selected.The properties of WC was presented in Table 2

Table 2 Properties of WC[1]

Density Expansion Young’s Modulus

669 GPa (240C)

15.63x10-3 kg m-3 5.09 10-6 oC -1

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Fig.1 Tungsten carbide particle size 4µm

2.2 Fabrication of Composites

In this present work AA7075 was used has base metal and reinforcement of WC(4µm) was fabricated by stir casting technique.So many casing techniques was there like squeezee casting,investment casting etc., out of which stir casting was economical one for fabrication of plates.Typical stir casting technique (bottom pouring )experimental setup was shown in Fig.2

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Fig.2 Stir casting Machine (bottom pouring)

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Initially AA 7075 base metal was bought in the form of rod and WC in the form of powder (4µm) Initially Tungsten carbide powder was heated upto 200̊ C to remove the moisture present in the particles. After that AA7075 is heated in the stir casting furnace upto 800̊ C then the Tungsten carbide is added to the molten metal by weight percentage ratio with a constant stirring speed of 400 rpm for 5 min .The following weightpercentage is carried out for preparing composites.The various reinforcements are 2.5%, 5.0%.7.5%, 10%, 12.5%The reason for the selection of low % addition is to obtain good weld ability. Otherwise, formation of fine particles or flaws can be occur.

After adding Tungsten carbide to the molten metal, molten metal must be stirred properly for the even distribution of the reinforcement particles.Mould was prepared in each mould 5 plates the dimension of 100 x 50 x5 mm then the molten metal was poured in sand mould thus plates was produced . Repeated this process various plates were fabricated plates was shown in figure 3.

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Fig.3 Fabricated composite plate with various reinforcements

2.3 Hardness and tensile strength

Hardness and tensile test specimen was prepared as per ASTM standards 5X3 mm plates was polished finely then then Vickers and Brinell hardness was carried out HV 10kg and BHN (5mm ball/250kg) the trends in the result shows that when the reinforcement percentage was increase hardness value also increased gradually the result shows in the figure 4 and 5.

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Vickers Hardness (HV)

100 97.2 98 96.7

94 92 91.5 92

88 86.8

Vickers Hardness (HV) 86

82 2.5 5 7.5 10 12.5 Tungsten carbide (WC %)

Fig.4 Vickers Hardness value for various reinforcements

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Brinell Hardness (BHN)

100 97.2 98 96 95 94 92 90 87.7 87.7 88 86

Brinell Hardness (BHN) Brinell 84 81.3 82 80 2.5 5 7.5 10 12.5 Tungsten carbide (WC %)

Fig.5 Brinell Hardness value for various reinforcements

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Tensile test specimen was prepared by machining the plate gauge length100mm length and thickness 5mm.The test was performed using ultimate tensile test machine the test samples was shown in figure 6.

Fig.6 Tensile test specimen

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EFFECT OF UTS

160 152 148 149 150 142 140 132 130

120 ULTIMATE STRENGTH (MPA) ULTIMATE 110

100 2.5 5 7.5 10 12.5 TUNGSTEN CARBIDE (WC ) %

Fig.7 Ultimate Tensile stress with varying reinforcements

The above Figure 7 shows by varying the reinforcement UTS was increased at 12.5% it was decreased this would be due to more particles presence.

2.4 Optical Microscopic Structure of Composite Plates

OM was performed after etching with Nital reagent for various samples result shows the presence of tungsten carbide and various casting defects was observed like porus,voids,unfused shown in figure 8 Magnification of 100X.

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a b

Fig.8 Typical Optical micro structure after etching with Nital reagent a) 2.5% WC b)5%WC c)12.5%

3. Result and Discussion

Thus the composite was fabricated successfully with various WC reinforcement percentage

 By increasing the reinforcement hardness value was increased due to the presence of tungsten carbide.

 In ultimate tensile stress(Mpa) the value was increased gradually up to sample 4 at 12.5% addition tungsten carbide strength was decreased.

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 Optical Microscopic result shows that there are so many casting defects was observed like voids, due to uneven fusion inter metallic defects,cracks was observed this shows their effect in tensile strength.

 Present work shows for preparing composites sand casting technique was not preferable.

References

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