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THE EFFECT OF HEAT TREATMENT ON THE MICROSTRUCTURE, MECHANICAL PROPERTIES AND DRY SLIDING WEAR BEHAVIOUR OF A356.O REINFORCED WITH GRAPHITE

Amith.D.Gangadhar1, M.H. Annaiah2, S. Linge Gowda3, T.G. Rajiv4, Harendra Kumar H.V5
 P G student, Department of Mechanical Engineering, Acharya Institute of Technology, Bangalore, Karnataka, India1
Professor and P G Coordinator, Department of Mechanical Engineering, Acharya Institute of Technology Bangalore, Karnataka, India2
Professor, Department of Mechanical Engineering, Acharya Institute of Technology, Bangalore, Karnataka, India3
Assistant Professor, Department of Mechanical Engineering, Acharya Institute of Technology, Bangalore, Karnataka, India4
P G student, Department of Mechanical Engineering, Acharya Institute of Technology, Bangalore, Karnataka, India5
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Abstract

In this study, A356.0 alloys were reinforced with varied percentage of Graphite by liquid metallurgy route, heat treated (T6) and tested for microstructure, mechanical properties. Wear tests were conducted using Pin-on-Disc apparatus at a constant sliding velocity of 1m/s and pressure of 0.35 MPa. Microstructure revealed uniform distribution of reinforcement in the matrix resulting in improved mechanical properties and wear resistance compared to un-reinforced material. The ceramic reinforced alloys were found to have improvement in mechanical properties and wear resistance compared to unreinforced alloy which may be attributed to the uniform distribution and improved bonding of reinforcement in the matrix.

Keywords
Composites, MMC’s, Microstructure, Mechanical behaviour, Heat treatment

INTRODUCTION
Aluminium-Silicon alloys possess light weight, high specific strength and good heat transfer ability which make them suitable material to replace components made of ferrous alloys. Al-Si alloys are widely used in all types of IC engines such as cylinder blocks, cylinder heads and Pistons. They find applications in aircraft pump parts, aircraft structure and control parts, automotive transmission, aircraft fittings, water cooled cylinder blocks and nuclear energy installations. Both hypoeutectic and hyper-eutectic alloys can be used as useful engine block materials on account of their adequate resistance and high strength to weight ratio. There are quite large numbers of studies made on the mechanical behavior of Al-Si alloys. Attempts are made to increase the strength of Al-Si-Mg by various manufacturing processes, heat treatment, reinforcement of hard and soft reinforcements etc. In this paper, an attempt is made to study the effect of heat treatment on microstructure, mechanical properties and dry sliding wear behavior of Graphite reinforced A356.0.

II. MATERIALS
A356.0 alloys were reinforced with Graphite and were cast using liquid metallurgy route in the form of cylindrical bars of length 300mm and diameter 25mm. They were heat treated (T6).

III. TESTING
A: Microstructure
The samples for microstructure examination were prepared by following standard metallurgical procedures, etched in etchant prepared using 90 ml water, 4ml of HF, 4ml H2So4 and 2g CrO3 and were examined using Optical Microscope.
Figures 2.1 to 2.4 show the Microstructures of Heat treated A356.0 and its Composites depicting uniform distribution of ceramic reinforcement (Graphite).
B: Hardness test
The hardness tests were conducted as per ASTM E10 norms using Brinell hardness tester. Tests were performed at randomly selected points on the surface by maintaining sufficient spacing between indentations and distance from the edge of the specimen.
Table III Shows the hardness values of A356.0 alloy and its composites. The hardness of 3G (3% Graphite) is found to be 97 compared to A356.0 alloy with hardness 57 indicating 70.17% increase in hardness. 5G (5% Graphite) has largest value of 98 indicating 71.9% increase in hardness and 10G has hardness of 77 indicating 35.08% increase in hardness when compared to A356.0.
C: Tension test
Table IV shows plot of UTS and % elongation values of A356.0 and its composites. It is clear from the table that UTS and Ductility increases with Graphite reinforcement for all composites such as G3, G5 and G10 compared to A356.0. G3 has highest UTS compared to A356.0 and it’s other composites. UTS of G3 is 277.73MPa which is 104.2% higher than UTS of A356.0. G10 has 195.54MPa showing 43.3% increase in strength. G5 has 246.88 showing 81.5% increase in strength. The Elongation of G3 is 3.60% which is 100% higher than that of A356.0. Composites G10 and G5 also have improved Ductility which are 102.2% and 42.2% respectively higher than A356.0.
Fig.3.2 shows the plot of Wear rate versus sliding distance of A356.0 and its composites. A356.0 has Wear rate of 1.75x10- 5 gm/m where as G3 has 1.28x10-5 showing 26.85% reduction in Wear rate. This reduction in wear rate may be attributed to the increase in hardness achieved due to uniform distribution and bonding of the ceramic in the composite. Composites G5 and G10 have wear rate 1.03x10-5gm/m and 1.58 x10-5gm/m respectively. The decreased wear rate of G5 may be attributed to higher percentage of graphite in the composite which act as solid lubricant results in reducing wear rate.

IV. CONCLUSION
Microstructure indicates uniform distribution of ceramics in the matrix resulting in good bonding of the particulates. The composite with 5% Graphite has highest hardness. Composite with 10% Graphite has highest ductility. The composite with 3% Graphite has highest UTS. The composite with 5% Graphite has lesser wear rate when compared to A356.0 and it’s other composites.

ACKNOWLEDGEMENT
We thank Dr. H. D. Maheshappa, Principal and Management of Acharya institute of Technology, Bangalore India for motivating and providing research facilities at the institute.

Tables at a glance
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Figures at a glance
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