27-10-2016, 12:25 PM
Hardness and Tensile behavior of Al-4.5%Cu-Sic-Gr particulates Reinforced hybrid composites
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Abstract
Aluminium hybrid composites are a new generation of metal matrix composites that havethe potentials of satisfying the recent demands of advanced engineering applications. Thesedemands are met due to improved mechanical properties, amenability to conventionalprocessing technique and possibility of reducing production cost of aluminium hybrid composites. present work we are investigating effects of adding Sic and Gr particulates to Al 4.5%Cu alloyOn the mechanical properties of the composites .The Al-4.5%Cu alloy reinforced with 6wt % Sic and 6wt% of Gr particulate composites were fabricated by stir casting method . microstructure and mechanical properties such as hardness and ultimate tensile strength, yield strength were examined . microstructure of the samples has been investigated by using optical microscope to know the uniform distribution of reinforcement particulates in the matrix .it was absorbed that the hardness , ultimate tensile strength and yielding strength of the Al-4.5%Cu alloy increased with the addition of 6wt %of Sic and Gr particulates .
Introduction:-
Metal matrix composites (MMCs) offer designers requirements, they are particularly suited for applications requiring high strength to weight ratio at high temperature, good structural rigidity,
dimensional stability, and light weight. The inadequacy of metals and alloys in providing both strength and stiffness to a structure has led to the development of various composites particularly metal matrix composites (MMCs) [1-3]. Composite materials are used extensively as their higher specific properties (properties per unit weight) of strength and stiffness, when compared to metals, offer interesting opportunities for new product design. MMCs are metals reinforced with other metal, ceramic or organic compounds. They are made by dispersing the reinforcements in the metal matrix [4]. Reinforcements are usually done to improve the properties of the base metal like strength, stiffness, conductivity, etc. The particle distribution plays a very vital role in the properties of the Al MMC and is improved by intensive shearing[5]. Addition of hard ceramic particles like SiO3, SiC, Al2O3, TiB2, B4C etc. to Al matrix lead to strengthening of the matrix with improved properties. Ceramic particles such as Al2O3 and Sic are the most widely
used materials for reinforcement with aluminium.
One of the major challenges processing MMCs is achieving a homogeneous distribution of reinforcement in the matrix as it has a strong impact on the properties and quality of the material[6].MMCs are generally processed with liquid metal routes such as stir casting and infiltration .a powder metallurgy route is also used for the specific application,however an stir casting route is the most commonly used method by industry and accounts for the latest volume in primary production[7]
Dunia[8] has developed aluminium silicon carbide and aluminium graphite particulate composites. The author has revealed that,there is increase of hardness with increase in weight percentage of ceramic materials.
Materials and Experimental details
Matrix material
The matrix material used in experimental investigation is aluminium 4.5%Cu alloy. the theoretical density is taken as 2.8 gm/cm3.
Reinforcement material
The main advantage of introducing reinforcement material to base metal or alloy is to increase the properties their by enhancing the mechanical and tribological properties of composites .In the current research Sic particulates of size 40microns and Gr particulates were used as a reinforcement material which was procured from speedfam (India) Pvt Ltd, chennai
Preparation of aluminium 4.5%Cu Sic-Gr composites
In the engineering materials , the MMCs can be manufactured by a unique technique such as casting , has it is inexpensive and suitable for mass production of components the synthasis of matrix composites used in study was carried out by liquid metallurgy route in particular stir casting technique. Initially Sic and Gr particulates were pre heated for 400-500oC in the present work, an attempt has been made to study the mechanical properties of cast Al-4.5%Cu andAl-4.55%Cu –Sic-Gr particulate composites.the composites containing 6wt.% of Sic and 6wt.% of Gr particulates were pre-heated. Initially required mount of charge of matrix material was placed in electric resistance furnace at a temperature around 800o C after complete melting ofAl-4.5%Cu alloy matrix, Magnesium was added in small quantity during stirring to increase the wetting, degasing was carried out by using Solid HexaChloroethane[9], which helps to remove unwanted adsorbed gases from the melt.once degasing is over,the pre heated ceramic reinforcement particles were introduced into the matrix in a novel way which involves two stages addition of reinforcement during melt stirring. This novel two stages addition of reinforcement into matrix Al-4.5%Cu will increases wettability of the matrix and reinforcement particulates and further, which helps in uniform distribution of the particles. A continuous stirring process was carried out during addition of reinforcement into matrix. Normally for all composite preparation, stirring speed maintained at 300rpm after 10 minutes of continuous stirring entire molten metal was poured into cast iron die. The prepared composites were machined and tested for microstructural studies. After reveling uniform distribution of Sic and Gr particulates in a matrix, tensile behavior of cast Al-4,5Cu alloy and its composites were evaluated as per ASTM standards.figure 1 showing the cast iron die and stir casting setup used to prepare the composites for the present study.
Specimen Testing
The microstructure of the cast Al-4.5%Cu alloy and its composites reinforced with 6wt.% of Sic and 6wt.% of Gr particulates were examined by using optical microscope.the sample of cast and Al-4.5%Cu with Sic and Gr composites for microstructural study were cut from casted rods and ground by means of abrasive papers followed rotating disc cloth polishing. Keller’s reagent was used has an etching agent and examined with optical microscope. Hardness test were performed on as cast Al-4.5%Cu alloy and Al-4.5%Cu with Sic and Gr composites to know the effect of Sic and Gr particulates in the matrix material. The polished specimens were tested there hardness, using Brinell Hardness testing machine having ball indentor for 62.5kg load and dwell time of 15sec.5 sets of readings were taken at different places of the specimen and an average value was used for calculation.
Tensile testing of the prepared samples were conducted in accordance with the ASTM E8 std on round tension test specimens of guage diameter 9mm and guage length is 45mm.tension test was conducted by using instron made servo hydraulic machine, with cross head speed set at 0.280mm per minute. The experiments were conducted at room temperature. Stress versus strain graph was plotted to know the effect of Sic and Gr particulates on tensile behavior of Al-4.5%Cu alloy.