Study of aluminium alloys addressing aspects of manufacturing, oxide formation, and recycling

Aluminium (Al) and its alloys have been applied in various industry sectors, such as construction, energy, packaging, marine, aerospace and automotive. Al has a unique combination of attractive properties: (i) Al is lightweight with a specific density of 2.70 gcm-3, about a third that of steel (7.83 gcm-3), and the continuous demand for lower energy consumption has made it an ideal candidate to substitute for heavier alloys in components (ii) can be cast and machined; (iii) the strength of Al can be adapted to different applications by modifying the composition and hence the microstructure of its alloys. Some novel Al alloys and Al matrix composites have recently been receiving considerable attention due to their potential ability to cope with extreme conditions, such as elevated temperatures and high pressures. This can be achieved by alloying additions, tailoring the alloy compositions for desired precipitates and adding suitable reinforcements. The ultimate aim of the project is to bond together these very specialist, high strength, lightweight nano-quasicrystalline aluminium alloys which have very good high temperature strength, with a more conventional aluminium alloy. This is to enable the use of minimum quantities of the very expensive nano-quasicrystalline alloy, by placing this alloy only in the locations in a component which require these properties. An example would be the top surface of a piston for an automotive engine. In order to do this we need an improved understanding of the thermodynamics and kinetics of the oxidation of aluminium alloys as a function of composition and processing.

Aluminium oxidises very readily and can take the form of a number of different oxides, amorphous and crystalline, in particle or film morphologies or in combinations. The presence of an oxide inhibits bonding but manipulation of the nature of the oxide can improve the bonding. The Department of Materials here at the University of Oxford has access to a number of sophisticated analysis techniques which can be used to investigate the rate of oxidation, the thickness of the oxides formed and the crystalline-types, compositions and morphologies of the oxides formed. We are perhaps the first laboratory in the world to have successfully dissolved away the aluminium from the oxide, so allowing detailed observation of the three-dimensional morphology of both sides of the oxide layer using electron microscopy techniques.

The overall aim of the work is to provide a comprehensive understanding of the role of oxidation on the bonding of different Al alloys through advanced characterization techniques and simulating the results from thermodynamic and kinetic points of reference. This will lead to the prediction of stable oxides and the nature and integrity of the interfacial bond, i.e., oxide bilayer, which will facilitate the tailoring of oxides and the interfacial oxide bilayers in order to achieve the desired bond.

This project falls within the EPSRC Manufacturing the future research area.