| dc.description.abstract | Metal foams have found increasing applications in a wide range of structural and functional products, due to their exceptional mechanical, thermal, acoustic and electrical properties and offer great potential for lightweight structures for energy absorption in packaging during impact at high velocities. Metal foam structures have densities only fractions of that of a solid structure and have high specific strength and higher stiffness than other contemporary packaging materials. Therefore, the metal foam in particular “Aluminium Foam” has an important application as packaging material for transportation of Reactor fuels and Radioactive samples. Nuclear materials are transported in packages which should meet stringent safety standards like impact resistance, thermal shock etc. Therefore, in the transportation of the above materials, aluminium foam can play a key role in providing a cushion for absorption of shock and impact. The aim of this work is to develop a process for fabrication of aluminum foam. Two methods are experimented to manufacture metal foams. The first method involves mixing of a foaming agent in a liquid aluminium pool and the subsequent cooling of the melt while hydrogen is released from the foaming agent. The second method of metal foaming process is based on a procedure consisting of a base metal and a foaming agent, which are milled for homogeneous mixing and then pre-compacted by cold isostatic pressing. This is followed by cold/warm extrusion. The extruded piece is then heated up to a certain foaming temperature. The heating process leads to partial metal melting as well as to the release of the hydrogen gas and consequently to the formation of metal foam in the semi-solid state. In this thesis, the technology for fabrication of Al foam having a density of around 0.2-0.3 g/cm3 has been made & discussed in detail. The effects of various fabrication parameters like compaction pressure, extrusion ratio and foaming temperature on the formation of the Al foam are discussed.
The quality of fabricated Al foams is characterized in terms of density, microstructure, porosity content etc. The various mechanical properties like yield strength, tensile strength and impact energy of the Al foams are evaluated in order to understand their behavior under different conditions. The typical values of Young’s modulus, plateau stress, densification strain and energy absorbed for the foam tested are tabulated. The observations, which are made from the data, can be briefly quoted as under:
a) As the length of the specimen increases, plateau stress increases which increases the energy absorption.
b) The energy absorption for Al-20% Mg alloy has been found to be minimum. The foam exhibited brittle behaviour and crumbled under load application.
c) Young’s modulus varies in the range of 0.057 – 0.13 GPa for the foam.
d) As density increases, Young’s modulus also increases and correspondingly the energy absorption value increases for Al-foam.
It is found that the variation in the plateau stress with density is marginal. But the strain value was found to be dependent on the alloy composition and the density. The strain obtained for all cases was found to be very near to 75-90%. Al-20%Mg alloy showed an inferior behaviour compared to pure Al. It showed a lesser plateau stress and crumbled while testing. This shows that this alloy is highly brittle in nature. Also, the Al-Mg foam obtained did not exhibited good luster. | en |
