Stronger alloys are on the horizon thanks to new research

The research describes how microscopic crystals grow and change shape in molten metals as they cool. Credit: Maksim Gusev

In research that is breaking new ground in alloy research and prepares the way for enhancing the tensile strength of alloys used in casting and welding, scientists from the University of Birmingham have detailed how minute crystals develop and change shape in molten metals as they cool.

Their study, which was published in the journal Acta Materialia today, employed high-speed synchrotron X-ray tomography to ‘photograph’ the shifting crystal structures in molten alloys as they cooled.

The research indicates that as the aluminum-copper alloy cools, the solidification process begins with the creation of faceted dendrites, which are generated by layer-by-layer stacking of micrometer-sized basic units. These units start out as L-shaped building blocks that stack on top of one another, but as they cool, they change shape and convert into a U shape, then a hollowed-out cube, with some of them piled together to produce beautiful dendrites.

Dr. Biao Cai of the University of Birmingham’s School of Metallurgy and Materials conducted the research, which has previously shown how magnetic fields affect crystal development.

Dr. Cai had this to say: “The findings of this new study demonstrate the structure of the basic building blocks of crystals in molten alloys and provide a real insight into what happens at a micro level when an alloy cools. The strength of the final alloy is determined by the crystal form, and we can build stronger alloys by using finer crystals.”

“The findings are in direct opposition to the traditional concept of dendrite production in cooling alloys, and they open the door to creating new methodologies that can forecast and control the creation of intermetallic crystals,” he said.

Dr. Cai’s prior research resulted in a revolutionary approach for improving the quality of recycled aluminium by eliminating iron from molten alloy using magnets and a temperature gradient in a simple, low-cost process.

University of Birmingham Enterprise has filed a patent application for the technology. It has also received financing from the Midlands Innovation Commercialization of Research Accelerator and the EPSRC-Impact Acceleration Account, allowing Biao to construct a large-scale prototype capable of operating at 1000 degrees Celsius and employing a 1 Tesla magnet.

The prototype is now being tested using ingots given by Tandom Metallurgical Group, which manufactures aluminium alloys, master alloys, and recycles aluminium products, wastes, and drosses from its base in Congleton, Cheshire.

Before the end of the year, Dr. Cai hopes to publish the results of the testing and show the demonstrator to industry, with the goal of finding industrial collaborators ready to undertake tests in foundries alongside existing production lines.

Further information: Zihan Song et al, Revealing growth mechanisms of faceted Al2Cu intermetallic compounds via high-speed Synchrotron X-ray tomography, Acta Materialia (2022). DOI: 10.1016/j.actamat.2022.117903

Journal information: Acta Materialia

Source: University of Birmingham