Crystal growth control in aluminium alloys

In engineering alloys, it is not just the alloy composition, but also the size and morphology of crystals that control the final alloy properties. In Al-Si alloys that are extensively used in automotive sector, additions of trace amount of metal elements such as Na and Sr, known as modifiers, can lead to dramatic modification of eutectic Si crystals from elongated flake-like to fibrous morphology, improving the alloy ductility and toughness.   Modifiers are also commonly employed in other metal systems: for example, Mg is added to cast iron to spheroidize graphite. Nevertheless, all additions were serendipitous discoveries and sufficient understanding to design new modifiers for a wider range of alloys does not exist.

The program will begin by studying the well-known case of Si in Al-Si alloys to gain a mechanistic understanding of the phenomena and then use the acquired knowledge to develop new modifiers for a selection of deleterious secondary phases in aluminium alloys. This will include extending the use of modifiers to manipulate the morphology of secondary intermetallic phases in aluminium alloys. The work will use a suite of advance electron microscopy techniques, including scanning and transmission electron microscopy, , combined with molecular dynamic simulations to understand the effect of the additions on the crystallography of the solid phase. I­n-situ X-ray imaging at synchrotron will also be used to investigate crystal growth dynamics and segregation phenomena at solid liquid interfaces.

  

d overall 2024 crystal growth control in aluminium alloys

Example of growth modification in of Fe-rich intermetallic phases in Fe-containing aluminium alloys

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