Applied Mechanics and Materials Vols. 766-767

Abstract: Aluminium metal matrix composites (AMMCs) are being considered as a group of superior material for its lightness, strength, high specific modulus, low coefficient of thermal expansion and good wear resistance properties. Solid state and liquid state processing methods are used to fabricate AMMCs. Achieving a uniform distribution of reinforcement within the matrix is one such challenge, which affects directly on the properties and quality of composite material. Powder metallurgy route, one of the solid state processing methods can be effectively used to get uniform dispersion of reinforcements with aluminium metal matrix. This paper presents the summary of the ball milling and stir casting processes to fabricate the AMMCs and its applications. Major issues like ball milling time, dispersion of reinforcements, grain size, the stirring time and speed are discussed. Also the effect of different reinforcement for AMMCs on the mechanical properties is discussed in detail.

Abstract: ABSTRACTAluminium alloys are used in advanced applications because their combination of high strength, low density, and durability. However, the properties of this material can be improved by using aluminium matrix composite materials. By reinforcing hard ceramic particles like SiC, Al₂O₃and B₄C, TiO₂ etc the strength of the composite can be enhanced. In this paper an effort is made to enhance the property of AMCs by reinforcing steel slag particle with A356 matrix. By varying the weight percentage of the steel slag the composite material was prepared through stir casting method. The mechanical property like hardness and impact strength of A356 was investigated and compared with that of composite material. The result reveals that by increasing the reinforcement percentage of steel slag the impact strength decreases with the increase in hardness of the composite material. The density is also compared with that of A356 composite.

Abstract: Aluminium based Metal Matrix Composites (MMCs) with Aluminium matrix and non-metallic reinforcements are finding extensive applications in automotive, aerospace and defence fields because of their high strength-to-weight ratio, high stiffness, hardness, wear-resistance, high-temperature resistance, etc. Composite materials are frequently chosen for structural applications because they have desirable combinations of mechanical characteristics. Development of hybrid metal matrix composites has become an important area of research interest in Material Science. In this work, the Aluminium alloy is reinforced with 3,5,7,9 wt. % of Al₂O₃ and 2 wt. % of SiC to prepare the hybrid composite. The present study is aimed at evaluating the physical properties of aluminium 7075 in the presence of silicon carbide, aluminium oxide and its combinations. The compositions are added up to the ultimate level and stir casting method is used for the fabrication of aluminium metal matrix composites. The mechanical behaviours of metal matrix composites like tensile strength, and hardness test are investigated by conducting laboratory experiments. Mechanical properties like micro hardness and tensile strength of Al7075 alloy increase with the addition of SiC and Al₂O₃ reinforcements.

Abstract: The composite material is a combination of two or more materials with different physical and chemical properties. The composite has superior characteristics than those individual components. A hybrid composite is the one which contains at least three materials. When the matrix material is a metal, the composite is termed as metal matrix composites (MMC). The MMC is a composite material with two constituent parts, one being a metal. The other material may be another metal, ceramic or fiber. Among all the MMC’s, Aluminium is the most widely used matrix material due to its light weight, high strength and hardness. This paper deals with the fabrication and mechanical investigation of hybrid metal matrix composite Al - SiC. The fabrication is done by stir casting by adding the required quantities of additives into the stirred molten Aluminium. The results show significant effect of mechanical properties such as tensile strength, yield stress and flexural strength. The internal structure of the composite is observed using Scanning electron microscope (SEM) and found that are formation of pores in them.

Abstract: The aluminium based composites are increasingly being used in the transport, aerospace, marine, automobile and mineral processing industries. The widely used reinforcing materials for these composites are silicon carbide, aluminium oxide and graphite in the form of particles or whiskers. In this study Al6061-6 & 4wt% Al₂O₃ based metal matrix composite were produced by mechanical stir casting process. The obtained cast metal matrix composite is carefully machined to prepare the test specimens for hardness, tensile as well as fracture toughness studies as per ASTM standards. The hardness, tensile strength and fracture toughness properties of Al6061-Al₂O₃ composites are explored experimentally. Finally compare the material characterization with heat treatment process sample and compare the fracture toughness of sample with mathematical approach, experimental and finite element method.

Abstract: Metal matrix composite materials are finding increased applications in many fields due to their excellent properties. Adding of one more constituent in the metal matrix make the composites hybrid. Machining of these composite materials are important and is different from the conventional materials. In the present investigation, hybrid metal matrix composites is machined by using Polycrystalline Diamond tool and the effect of volume fraction on surface roughness in turning is evaluated and presented in detail.

Abstract: The tribological behaviour of hybrid aluminium matrix composites (AMCs) A356 reinforced with SiC , Gr and Tin particulate, fabricated by powder metallurgy route. In this experimental study, the mechanical and tribological properties are investigated. The results show that addition of more reinforcements reduce the hardness and also increase the wear rate of the composites. The addition of Gr beyond certain limit will decrease hardness and that of SiC will increase brittleness. In the hybrid composite with 15% weight SiC and 5% weight Gr reinforcement results show that great improvement under tribological condition. The wear loss of the hybrid composites decreased with increasing applied load and sliding distance. The SEM analysis shows the wear tracks results of the composite materials.

Abstract: Discontinuously reinforced SiCp/Al composites were extensively used in space applications including joints and attachment fittings for truss structures, electronic packages, thermal planes, mechanism housing and bushing. In this research work, the metal matrix composite of AA6061+ SiC_p 10% were produced by stir casting method with an aim to predict the mechanical properties of a Metal Matrix Composite (MMC) subjected to age hardening. The Ultimate tensile test and Vickers hardness test was carried on the both condition of produced MMC and Age hardened (HMMC). A comparative study of the mechanical properties of the MMC before and after age hardening has been reported.

Abstract: The presence of Hollow particles instead of gas porosity provides a closed cell structure called Syntactic foams. Syntactic foams have gained significant attention in recent years due to their low density, moisture absorption and thermal expansion coefficient compared to other cellular materials, such as open and closed cell structured foams. In terms of mechanical behavior, it is generally more insightful to compare metal matrix syntactic foams with metal foams and metal matrix composites. In comparison with metal foams, they have high compressive yield strength and more homogenous mechanical properties but usually higher densities and lower plasticity. In comparison with metal matrix composites, they have lower strength but offer compressibility, which is not existence in metal matrix composites. Syntactic foams have been extensively studied for aluminum based metal matricesand polymer matrices. Importance in magnesium foams is increasing in recent periods due to their very low density. Only a few studies are available on magnesium matrix syntactic foams processed through powder metallurgy techniques. This review presents an overview of hollow particle filled magnesium matrix (AZ91D/microballons) syntactic foams using powder metallurgy methods.

Abstract: Carbon Nanotubes (CNT’s) have recently been found to possess extraordinary mechanical, thermal and electrical properties. Extensive studies on the properties of CNT’s as a re-inforcing agent in Metal Matrix Composites are being investigated. In this study, powder metallurgy technique has been employed for the matrix material being Aluminium 6063 with CNT in varying concentrations as reinforcing agent. The powders are mixed thoroughly using ball milling and are compacted in a compacting die made of D-2 Steel to make green compact. It is then sintered at 350°C to 550°C at a rate of increase of 50°C per hour. Chemical, Microscopic examination, Compression and Hardness tests were performed on the specimens and were compared with pure aluminium specimens to show the effects of varying concentrations of CNT. The study indicated that there was no improvement in hardness of the composite on addition of CNT while there was an increase in compressive strength. The microstructure of pure aluminium and Al-CNT composite had fine grains of pure aluminium particles and Al-Si eutectic particles throughout the matrix phase.