Changing the chemical composition of alloys to obtain sustainable and stronger metals

To achieve metals with greater resistance, that cushion more shocks and are usable from elements that exist in nature, researcher Ismeli Alfonso López, from the Materials Research Institute (IIM) of the UNAM, works on aluminum alloys, which he mixes with nanostructures of silicon, copper, and magnesium.

"We are adding new combinations and creating new processes. We, as a research group, already have nine patents, of which seven have already been granted and two are pending. We are not only changing the chemical composition of the alloys, but we are also modifying the manufacturing process of the materials," he explained.

Aluminum in its pure state is used, for example, to manufacture windows and gates. But when it is to be used in car or airplane parts, it is mixed with other elements such as silicon, copper, zinc, and magnesium, which make it more resistant.

"Aluminum is known as the green metal because it is completely recyclable. Since it began to be used, almost everything has continued to be recycled and it is still used because it does not rust like iron, thanks to the fact that it is coated with a layer of alumina and protects itself, unlike iron, which is found in yards outdoors, all corroded and completely decomposed, and aluminum is not like that," explained the academic, who works at the IIM's Morelia Unit.

This metal has a long life, and although the one extracted from the deposits is expensive and polluting, the one used for remelting and recycling only requires 15 percent of the energy used to produce the original aluminum, so it is feasible to use it.

In the laboratory, Alfonso López uses aluminum alloys with copper, magnesium, and silicon to manufacture car monoblocks. "The silicon helps us make the mixture fill all the holes in the mold and flow smoothly, while the magnesium and copper give it high-strength properties thanks to the use of nanometer-sized particles."

Although various combinations are patented internationally with different contents, the expert and his group add new elements to see how they behave. "We add much more magnesium, which makes other phases form and has different properties. With them we manufacture metallic foams, which make the aluminum porous on the inside, which helps to absorb impacts for the automotive industry," he explained.

With the porous metal alloy, a sort of sandwich is created in the fenders of cars, with solid material on the edges and porous in the middle, so that the impact of a blow does not reach the driver. In addition, having this consistency lowers the density of the material and results in lower fuel consumption, a condition that makes it more sustainable.

Sustainability means working with what we have, without compromising the resources of future generations and using up everything ourselves, stressed the academic, who insisted on the need to consume less freshly extracted materials and fuels.

Aluminum can be recycled numerous times, there is no limit. "There are some losses when re-melting it, because there is evaporation and because it sticks to the mold, but it does not lose its properties when it is recycled," he clarified.

The expert in the characterization of materials by microscopy and mechanical properties said that nanoscience helps to increase the mechanical resistance of materials since the particles are so small that they oppose the passage of dislocations, which are deformations in the metal network.

The researchers recover materials from car engine parts, from the purchase of scrap metal, and do not use 100 percent pure inputs, with a few exceptions. "Almost all the research we do with these materials is with recycled aluminum alloys."

Of the nine patents, four are for devices to manufacture new materials, three for the processes to develop them, and two more for new alloying elements with nanostructured particles.

Alfonso López pointed out that there is a strong trend in metallurgy towards sustainability, as every day there are fewer extractable materials left in the deposits, and it is essential to recover those that exist, even as scrap on the planet.