Metal Foams Matrices of Aluminium Composites - Properties, Production and Applications

Metal Foams Matrices of
Aluminium Composites
Contents
Literature Review..................................................................................................................................1
Properties..........................................................................................................................................1
Production.........................................................................................................................................1
Applications.......................................................................................................................................3
Aims and objectives...............................................................................................................................4
Research Methodology..........................................................................................................................4
Preliminary Development of the project...............................................................................................4
Timeline.............................................................................................................................................5
Resource requirements.....................................................................................................................5
References.............................................................................................................................................5
Literature Review
Aluminium composites consist of aluminium which is reinforced with other metals with an aim to
improve upon the properties of the metal. Metal foams can be produced from Aluminium
composites to further enhance its properties which widens its application. This section of the
research explores the properties of these metal foams of aluminium composite, various methods
that are used for producing them, and the applications of the same.
Properties
Aluminium matrix composites (AMCs) are the aluminium metals reinforced with other metals or
compounds for improving properties of aluminium. Different reinforcements have different impacts
on the composites. Carbide (SiC), Boron Carbide (B4C) and Aluminium Oxide (Al2O3) are two most
commonly used reinforcements. SiC increases the hardness, density and tensile strength of
aluminium, B4C increases its hardness and Al2O3 gives it a good compressive strength and wear
resistance. They can improve the strength, stiffness, and fatigue properties of aluminium. AMCs
have many applications because of their physical and mechanical properties (Ramnath, et al., 2014).
Metal foam consists of a metal which is filled with gas in its pores that form a large portion of the
metal. The gas either seals the pores in which case it is called closed-cell foam or is interconnected
which is called open-cell foam. A metal foam matrix would be the aluminium composite having
pores filled with gas. Metal foams retain some of the metal properties like its flammability and
thermal expansion coefficient while others are modified such as thermal conductivity.
Foams initially used micro-sized ceramic particles to promote stability in metals and to avoid non-
uniform pore formation but now, a liquid or gas is used for stabilizing bubbles and increasing the
viscosity. Ceramic particles could prevent the melted metal drain and bubble formation that

commonly cause non-uniformity in structures. Presence of ceramic particles at the gas or liquid
interface can retard liquid flow out of the metallic form to stop bubbles growth and make the
composite structure more uniform. Ceramic particles are used in foams for minimizing their
structural defects (Duarte & Ferreira, 2016).
Production
Foaming of aluminium or its alloys can be done using a variety of production methods that include
gas injection, using blowing agents, solidification, use of powder compacts, or foaming of ingots.
Foaming of Aluminium melt by gas injection melting of aluminium to form metal-matrix composite
and then injection of gas like nitrogen or argon through the use of vibrating nozzles or rotating
impellers. In this process, fine gas bubbles are formed in the melt and the resulting mixture floats up
on the liquid surface resulting into the formation of a dry liquid foam after draining out of the liquid
metal. The melts can also be foamed using blowing agent that is added to melt and which gets
decomposed because of heat propelling the foaming process. Melt is stirred to reach a level of
viscosity. A typical foaming process lasts for 15 minutes (Banhart, 2000).
Figure 1: Gas-Solid Euclectic Solidification (Drenchev, et al., 2005)
Gas-Solid Euclectic Solidification is a relatively new method of foaming aluminium in which
aluminium is melted under high pressure and is charged with hydrogen. When temperature is
lowered, the melt goes into an eutectic transition. As it solidifies, the pores of gas precipitate and get
trapped inside the metal. Foaming with powdered compacts involve mixing of metal powders with
blowing agents after which the compact is created from the mix forming a dense foam (Han, et al.,
2015).

Figure 2: Foaming of ingots (Srivastava & Sahoo, 2007)
Foaming of ingots involve a powder-compact melting process in which titanium-hydride particles are
pushed into aluminium for preparing the foamable material using a die cast material. The resulting
cast resulting from foamcasting is then added with powder with slow stirring creating stable foams, a
process which is called formgrip. Different rates of heat produce different varieties of pore
structures (Bodunrin, et al., 2015).