UNN physicists produce aluminium alloys with record superplasticity

Physicists at Lobachevsky University have developed aluminium alloys with record superplasticity, which can be used in mechanical and electrical engineering.

Superplastic forging makes it possible to produce metal products of complex shapes in a few seconds, while avoiding loss of material, which cannot be achieved by traditional machining methods.

According to Nizhny Novgorod scientists, ultra-fine grains in aluminium alloys ensure maximum hardness under normal conditions, but when heated, such an alloy can be elongated several times and becomes superplastic. At 450-500°C, samples of aluminium alloyed with magnesium and scandium were elongated 9-10 times and regained their original properties on cooling.

"The non-trivial task of preserving the submicron size of aluminium grains while exposed to elevated temperatures and strain has been solved by microalloying the metal with magnesium and scandium. This preserves the mechanical properties and increases the corrosion resistance of the alloy, and we have managed to significantly reduce the magnesium content  - from 6% in commercial alloys to 0.5% in our case," says Alexey Nokhrin, Head of the Materials Diagnostics Laboratory at Lobachevsky University.

As a result, the electrical conductivity of the alloys has been further increased, which is very important for electrical engineering applications. However, the introduction of scandium into the alloy leads to the formation of large pores when the alloy is superplastic, which can trigger premature failure of the alloy. These pores occur on large needle-shaped particles formed at elevated temperatures.

 "To avoid this undesirable effect, we have performed  low-temperature annealing of the alloys, after which the nanoparticles acquire a spherical shape. This technology has made it possible to create aluminium alloys with better superplasticity characteristics," notes Alexey Nokhrin.

New aluminium alloys with extremely low magnesium and scandium content have record superplasticity characteristics: elongation of the samples exceeds 10 times at deformation rates of  10^{-2 __} 10^-1 s^-1.

This work was supported by the Russian Science Foundation (grant No. 20-19-00672).

The results have been published in Materials, a leading international journal, and the applied part of the research is protected by know-how.