22-08-2013, 04:50 PM
EXPERIMENTAL STUDY OF ALUMINIUM AND STAINLESS STEEL METAL MATRIX COMPOSITE
EXPERIMENTAL STUDY OF ALUMINIUM.docx (Size: 321.22 KB / Downloads: 56)
ABSTRACT
The aluminium composites are widely used in various applications. Aluminium (Al1060) has some major utilization in engineering filed so, Al1060 is concentrated in the project. Aluminium is a soft material and wears easily. It is very temperature sensitive and expands and contracts with temperature change. Aluminium is widely used because it is light weight, flexible and has improved strength. This work is focused on improve the tensile strength of metal matrix composite. Al1060 is selected in this project because of its various advantages. The reinforcement is given in unidirectional. To increase the strength of aluminium plate stainless steel wire is used as reinforcement. Therefore the Aluminium alloy matrix of Al1060 is added to stainless steel of AlSI304 as fibre. The 3mm thick aluminium plate has to be kept one above and one below. The stainless steel wire (AlSI1304) 0.7mm diameter has to be kept in the grooved path. The laminated composite has aluminium alloy of Al1060 and unidirectional continuous stainless steel fibre of AISI304 as metal matrix. The unidirectional fibre is increased the aluminium martial matrix. As these fibres where placed in between the grooves to obtain uniform distribution of reinforcements.
Introduction to AMCs
Composites
The possibility of taking advantage of particular properties of the constituent materials to meet specific demands is the most important motivation for the development of composites. A composite is a material made with several different constituents intimately bonded. This definition is very large, and includes a lot of materials such as the Roman ways (constituted of different layers of stones, chalk and sand), wood, human body etc... A more restrictive definition is used by industries and materials scientists: a composite is a material that consists of constituents produced via a physical combination of pre-existing ingredient materials to obtain a new material with unique properties when compared to the monolithic material properties. This definition distinguishes a composite from other multiphase materials which are produced by bulk processes where one or more phases result from phase transformation ("in-situ" composites).
The terms matrix and reinforcement are often used. The matrix is a percolating “soft” phase (with in general excellent ductility, formability and thermal conductivity) in which are embedded the “hard” reinforcements (high stiffness and low thermal expansion). The reinforcements can be continuous or discontinuous, orientated or disorientated. The composites are classified by: (1) their matrix (polymer, ceramic, metal), (2) their reinforcement, which includes the chemical nature (oxides, carbides, nitrides), shape (continuous fibers, short fibers, whiskers, particulates) and orientation, (3) their processing routes.
Aluminium Matrix Composites (AMCs)
Aluminium is the most popular matrix for the metal matrix composites (MMCs). The Al alloys are quite attractive due to their low density, their capability to be strengthened by precipitation, their good corrosion resistance, high thermal and electrical conductivity, and their high damping capacity. Aluminium matrix composites (AMCs) have been widely studied since the 1920s and are now used in sporting goods, electronic packaging, armours and automotive industries. They offer a large variety of mechanical properties depending on the chemical composition of the Al-matrix. They are usually reinforced by Al2O3, SiC, C but SiO2, B, BN, B4C, AlN may also be considered. The aluminum matrices are in general Al-Si, Al-Cu, 2xxx or 6xxx alloys. As proposed by the American Aluminum Association the AMCs should be designated by their constituents: accepted designation of the matrix / abbreviation of the reinforcement’s designation / arrangement and volume fraction in % with symbol of type (shape) of reinforcement. For example, an aluminum alloy AA6061 reinforced by particulates of alumina, 22 % volume fraction, is designated as "AA6061/Al2O3/22p".
Fabrication of the AMCs
There are many processes viable to fabricate AMCs; they can be classified in: solidstate, liquid-state and deposition processes. In solid-state processes, the most spread method is powder metallurgy PM; it is usually used for high melting point matrices and avoids segregation effects and brittle reaction product formation prone to occur in liquid state processes. This method permits to obtain discontinuously particle reinforced AMCs with the highest mechanical properties .
These AMCs are used for military applications but remain limited for large scale productions. In liquid-state processes, one can distinguish the infiltration processes where the reinforcements form a preform which is infiltrated by the alloy melt (1) with pressure applied by a piston (squeeze-casting SQC described in section3.2) or by an inert gas (gas pressure infiltration GPI) and (2) without pressure. In the last case, one can distinguish (a) the reactive infiltration processes using the wetting between reinforcement and melt obtained by reactive atmosphere, elevated temperature, alloy modification or reinforcement coating (reactive infiltration) and (b) the dispersion processes, such as stir-casting, where the reinforcements are particles stirred into the liquid alloy. Process parameters and alloys are to be adjusted to avoid reaction with particles.
DIFFUSION BONDING
In the last three decades, the development of advanced materials with superior mechanical properties has underpinned rapid progress in manufacturing of new products. The ever increasing demand for high performance materials has spurred research into the development of advanced alloys and composites. Transport industries, particularly aerospace and more recently car manufacturers, have been interested particularly in materials with high strength-to-weight ratios as these can provide significant performance benefits. Since the development of the first heat-treatable aluminium alloy in the early years of this century, aluminium alloys have been of interest because of their high strength-toweight ratio, formability, corrosion resistance and long-term durability. The first allaluminium aeroplane was manufactured in 1920 and since then, despite significant advances in non-metallic composites and titanium-based materials, aluminium alloys are still the major materials for aerostructures, Staley et al. (1997).
Aluminium metal matrix composites (Al-MMCs) possess even better mechanical properties compared to un-reinforced aluminium alloys (especially their high stiffness, strength and wear resistance). Following the recent development of low cost manufacturing processes, Al- MMCs with silicon carbide or alumina particle reinforcement (i.e. discontinuously reinforced aluminium, DRA) are now available commercially. The use of Al/SiC composites has reduced the production costs and improved the performance of aircraft components, Materials Progress (1997).
Theoretical aspects of solid-state diffusion bonding
The aim, when diffusion bonding, is to bring the surfaces of the two pieces being joined sufficiently close that interdiffusion can result in bond formation. In practice, because of inevitable surface roughness greater than an atomic scale, it is not possible to bring the surfaces of two pieces within interatomic distances by simple contact. Even highly polished surfaces come into contact only at their asperities and the ratio of contacting area to faying area is very low. Thus the mechanism of solid-state diffusion bonding can be classified into two main stages.
During the first stage, the asperities on each of the faying surfaces deform plastically as the pressure is applied. These asperities arise from the grinding or polishing marks that have been produced in the surface finishing stage. The microplastic deformation proceeds until the localised effective stress at the contact area becomes less than the yield strength of the material at the bonding temperature.