The specific aim of this stage is to manufacture Aluminum/Ceramic Foams. Two manufacturing processes will be used to produce the Aluminum/Ceramic composite Foams. One is powder metallurgical process. Aluminum alloy powders, flyash particles and Foaming agent particles (TiH2) will be used as starting materials in this process.
This process consists of four steps as preparing starting ingredients, mixing, forming of precursors, and heat treatment for Foaming. The schematic illustration of the manufacturing steps is shown in Fig. 2. The process begins with the mixing of starting materials of metal powders and Ceramic particles with a Foaming agent (titanium hydride), after which the mixture is compacted to yield a dense green precursor. In principle, the compaction can be done by any technique that ensures that the Foaming agent is embedded into the metal matrix without any notable residual open porosity.
Examples of such compaction methods are hot uniaxial or isostatic compression, rod extrusion or powder rolling. Compaction method is chosen depending on the required shape of the precursor material. In the present study, uniaxial compression and extrusion will be used because they are the most economical methods at the moment and are therefore the preferred ways. The manufacture of the precursor will be carried out very carefully because any residual porosity or other defects will lead to poor results in further processing.
Fig. 2 Schematic illustration of the experimental procedures for the powder metallurgical process
Heat treatment at temperatures near the melting point of the matrix material is the following step. The Foaming agent titanium hydride, which is homogeneously distributed within the dense metallic matrix, begins to decompose at 465oC. The released gas forces the compacted precursor material to expand, thus forming its highly porous structure.
The time needed for full expansion depends on the temperature and the size of the precursor and ranges from a few seconds to several minutes. The degree of maximum expansion, and therefore, the density of the solid metal/Ceramic composite Foam, can be controlled by adjusting the content of Foaming agent and several other Foaming parameters, such as temperature and heating rates. In the present study, Aluminum alloys and various contents of Ceramic particles and Foaming agent will be selected for obtaining the optimum porous structure and mechanical properties.
Another process is the so-called gas-injection process . The schematic illustration is shown in Fig. 3. Pure liquid metals cannot easily be caused to Foam by bubbling a gas into them. Drainage of liquid down the walls of the bubbles usually occurs too quickly to create a Foam that remains stable long enough to solidify. However, 10-30% of small flyash particles raises the viscosity of the Aluminum melt and impedes drainage in the bubble membrane, stabilizing the Foam. In this project, Aluminum/Ceramic composite Foams will also be produced by this process. However, tubular component structures of Foam filling tubes or frames cannot be produced directly by this process. Composite Foams produced by this process will be machined to the shape to match that of the outside tube or frame. Adhesive will be used to bond the Foam and the tube or frame together.
The mechanical properties and the energy absorption capability of the tubular component filled with Foams produced by the two processes will be evaluated and compared. The best combination of the tube and Foam will be developed based on the research of this project.
Fig. 3 Schematic illustration of the manufacturing process of a composite Foam by gas-injection method.