BMW April 2022

Researchers have developed a means of changing aluminium’s microstructure to boost ductility and produce strength equivalent to stainless steel, and the alloys might have ramifications on collision repair someday. “Most lightweight aluminium alloys are soft and have inherently low mechanical strength, which hinders more widespread industrial application,” Purdue School of Materials Engineering professor Xinghang Zhang said in a statement. “However, high-strength, lightweight aluminium alloys with strength comparable to stainless steels would revolutionise the automobile and aerospace industries.”

Zhang said in an interview that the team has yet to test the tensile strength of the new aluminium (the metric collision repairers typically reference when working on automotive steel), but compression strength has reached 1-1.5 gigapascals (1 000-1 500 megapascals). “We hope tensile strength will also be high,” he said.

The scientist said he saw both structural and nonstructural automotive applications, for the new aluminium is scratch- resistant as well as strong. “The coatings are very, very hard,” he said. If brought to market, that could make aluminium closures even more attractive than they’re already expected to be for OEMs over the next decade.

The crystal lattice of a metal involves repeating atomic layers; scientists call absent layers “stacking faults” and dual layers of stacking faults “twin boundaries,” according to Purdue. While copper and silver are receptive to stacking faults, aluminium’s higher stacking fault energy make it harder to artificially induce them.

“It has been shown that twin boundaries are difficult to be introduced into aluminium. The formation of the 9R phase (a type of stacking fault) in aluminium is even more difficult because of its high stacking fault energy,” Zhang said in a statement. “You want to introduce both nanotwins and 9R phase in nanograined aluminium to increase strength and ductility and improve thermal stability.” The team figured out how to do both.

“These results show how to fabricate aluminium alloys that are comparable to, or even stronger than, stainless steels,” Zhang said in a statement. “There is a lot of potential commercial impact in this finding. By using a laser-induced projectile impact testing technique, we discovered a deformation-induced 9R phase with tens of nanometers in width,” wrote Purdue postdoctoral research associate Sichuang Xue, the study’s lead author. The technique could be attractive to a manufacturer for its reduced cost, based on another statement by Zhang. “Say I want to screen many materials within a short time,” Zhang said, “this method allows us to do that at far lower cost than otherwise possible.”

The nanotwins Zhang referenced are delivered through a different technique described in Advanced Materials paper. This method creates 9R phases by introducing iron atoms into aluminium with”magnetron sputtering,” according to Perdue.

“Iron also can be introduced into aluminium using other techniques, such as casting, and the new finding could potentially be scaled up for industrial applications,” Purdue wrote. “The resulting ‘nanotwinned’ aluminium-iron alloy coatings proved to be one of the strongest aluminium alloys ever created, comparable to high-strength steels.”

“Molecular-dynamics simulations, performed by professor Jian Wang’s group at the University of Nebraska, Lincoln, showed the 9R phase and nanograins result in high strength and work-hardening ability and revealed the formation mechanisms of the 9R phase in aluminium,” Zhang said in a statement. “Understanding new deformation mechanisms will help us design new high strength, ductile metallic materials, such as aluminium alloys.” Purdue suggested one use might be “wear- and corrosion-resistant aluminium alloy coatings for the electronics and automobile industries.” The team is now scaling up for larger production quantities. “We’re still trying to do that,” Zhang said.