Purdue announced last month researchers have developed a means of changing aluminum’s microstructure to boost ductility and produce strength equivalent to stainless steel, and the alloys might have ramifications on collision repair someday.
“Most lightweight aluminum 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 aluminum alloys with strength comparable to stainless steels would revolutionize the automobile and aerospace industries.”
Zhang said in an interview Wednesday that the team has yet to test the tensile strength of the new aluminum (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 aluminum is scratch-resistant as well as strong.
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, aluminum’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 aluminum. The formation of the 9R phase (a type of stacking fault) in aluminum 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 aluminum to increase strength and ductility and improve thermal stability.”
The team figured out how to do both.
“These results show how to fabricate aluminum 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.”
A November 2017 Nature Communications paper describes a “shock-induced” 9R phase in aluminum, according to Perdue. Rice University researchers who also worked on the project used a laser to shoot microscopic silicon dioxide particles into thin aluminum film at 1,342.16 miles per hour (600 meters per second).
“Here, by using a laser-induced projectile impact testing technique, we discover 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 a Jan. 22 Advanced Materials paper. This method creates 9R phases by introducing iron atoms into aluminum with”magnetron sputtering,” according to Perdue.
“Iron also can be introduced into aluminum using other techniques, such as casting, and the new finding could potentially be scaled up for industrial applications,” Purdue wrote.
“The resulting ‘nanotwinned’ aluminum-iron alloy coatings proved to be one of the strongest aluminum 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 aluminum,” Zhang said in a statement. “Understand new deformation mechanisms will help us design new high strength, ductile metallic materials, such as aluminum alloys.”
Purdue suggested one use might be “wear- and corrosion-resistant aluminum 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.