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The Effect of Heat treatment on Microstructure, Mechanical properties and Damping behaviour of hybrid composite of A356.0

Vinayak Janiwarad1, Shadakshari R2, M.H. Annaiah3,Dr.Mahesha K4 ,Harendra kumar H.V5
 P G student, Department of Mechanical Engineering, Acharya Institute of Technology, Bangalore1 Asst Professor, Department of Mechanical Engineering, Acharya Institute of Technology, Bangalore2, Professor and P G Coordinator, Department of Mechanical Engineering, Acharya Institute of Technology3, Professor and Head, Department of Mechanical Engineering, Acharya Institute of Technology, Bangalore 4 , P G student, Department of Mechanical Engineering, Acharya Institute of Technology, Bangalore, Karnataka, India5
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International Journal of Innovative Research in Science, Engineering and Technology

Abstract

In this study, Al-Si-Mg alloys A356.0 were stir cast by liquid metallurgy route with varied percentage of Alumina and Graphite. The composites were T6 treated and tested for microstructure and mechanical properties. Microstructure revealed uniform distribution of reinforcement in the matrix resulting in improved bonding of reinforcement in the matrix which in turn improved mechanical properties and Damping behaviour compared to un-reinforced material. The ceramic reinforced alloys were found to have improvement in Mechanical properties and Damping behaviour which may be attributed to the uniform distribution and bonding of reinforcement in the matrix.

Keywords
Composites, MMC’s, Damping ratio, Microstructure, Mechanical behaviour

INTRODUCTION
Aluminium-silicon alloy and its composite possess light weight, high specific strength and good heat transfer ability which make them suitable material to replace components made of ferrous alloys. Estimating damping characteristics in structures made of different materials remains as one of the biggest challenges. Aluminium, its alloys and its composites is one such pioneer material which is being used extensively in Aerospace, Automotive and the manufacturing industries. The damping capacity of a material refers to its ability to convert mechanical vibration energy in to thermal energy. Passive damping is critically important material property from the view point of vibration suppression in aerospace and submarine structures. Attempts are made to increase the strength of Al-Si-Mg by various manufacturing processes, heat treatment and reinforcement of hard and soft reinforcements etc. In this paper, an attempt is made to study the effect of reinforcement of Alumina and Graphite on microstructure, mechanical properties and damping behaviour of A356.0.

II. MATERIALS
A356.0 alloys were reinforced with Alumina and Graphite and were cast using liquid metallurgy route in the form of cylindrical bars of length 300mm and diameter 25mm.Cantilever beams of cross section 15mm X 3mm X 180mm for Damping test were machined from the cylindrical bars.

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 2.6 show the uniform distribution of ceramic reinforcements namely, Alumina and Graphite in A356.0 matrix.
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 As cast A356.0 alloy and its composites. The hardness of A3 (3% Alumina + 5% Graphite) is found to be 58 compared to as cast alloy with hardness 51 indicating 13.73% increase in hardness. A5 (5% Alumina + 5% Graphite) has least value of 39. G10 has hardness of 46.
C: Tension test
Fig 2.9 shows plot of UTS of as cast and its composites. Alloys 3A, 5A have UTS 87.99 M Pa and 79.79 M Pa indicating 12.74% and 2.22% increase respectively compared to as cast alloy with UTS 78.05 MPa. Composites 10A, 3G and 10G have lower strength compared to A356.0.
Fig 3.1 to 3.5 shows the free vibration response of SDOF of A356.0 reinforced with varied percentage of Alumina and Graphite particulates, where best damping ratio was observed for composite with 10% Graphite +5% Alumina

IV CONCLUSION
Microstructure indicates uniform distribution of ceramics in the matrix resulting in good bonding of the particulates. The composite with 3% Alumina & 5% Graphite has highest hardness and UTS. Composite with equal % of Alumina and Graphite (5%) has highest ductility. The composite with 10% Graphite +5% Alumina showed highest damping ratio and is a good damping material compared to as cast alloy and its Composites. Graphite particles are better reinforcement compared to Alumina reinforced composite.

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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