Engineering news
Scientists at the University of Birmingham have been studying how microscopic crystals grow and change shape in these metals using high-speed synchrotron X-ray tomography to capture images of these cooling structures.
The study, which was published in the journal Acta Materialia, shows that as aluminium copper-alloy cools, the solidification process begins with the formation of faceted dendrites. These are formed in layers from basic units just micrometres in size, stacking on top of each other like building blocks: first L-shaped, then U-shaped, and then a hollowed out cube.
“The findings from this new study provide a real insight into what happens at a micro level when an alloy cools, and show the shape of the basic building blocks of crystals in molten alloys," says the study's lead author, Dr Biao Cai, from the University of Birmingham’s School of Metallurgy and Material. "Crystal shape determines the strength of the final alloy, and if we can make alloys with finer crystals, we can make stronger alloys.”
He added: “The results are in direct contrast with the classical view of dendrite formation in cooling alloys, and open the door to developing new approaches that can predict and control the formation of intermetallic crystals.”
In the past, Cai's work has created a new technology that improves the quality of recycled aluminium by removing iron in a simple, inexpensive process involving magnets and a temperature gradient.
The technology is the subject of a patent application filed by University of Birmingham Enterprise. It has also attracted funding from the Midlands Innovation Commercialisation of Research Accelerator and the EPSRC-Impact Acceleration Account, which has enabled Cai to build a large-scale prototype that runs to 1000 degrees C, and uses a 1 Tesla magnet.
The prototype is currently being tested using ingots provided by the Tandom Metallurgical Group, which operates an international trading operation from its base in Congleton, Cheshire, where they produce aluminium alloys, master alloys and recycle aluminium products, scraps and drosses.
Dr Cai expects to publish the results of the testing and showcase the demonstrator to industry before the end of the year, with the aim of finding industrial collaborators willing to run tests in foundry settings in combination with existing production lines.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.