Aluminium is a lightweight metal. However, being lightweight also makes it a soft metal. Soft drink cans can be crushed by our bare hands so you can guess it is not big on strength. Researchers at Purdue University discovered a way to make aluminium alloys stronger by introducing faults in the metal’s structure.
When you observe a metal under a microscope you see that it is made up of crystal atoms in repeating layers and cycles stacked on top of each other. One fault occurs when a layer is missing from the boundary and is known as stacking fault. The two layers of the faults are known as twin boundaries or nanotwins. When the fault creates such a structure that it repeats over nine layers, it is called a 9R phase.
Even though it is a fault, it can make a material stronger. Researchers at Purdue wanted to incorporate these faults into aluminium alloys to introduce the 9R phase but owing to the high stacking fault energy of aluminium, it continued to correct the faults itself.
“It has been shown that twin boundaries are difficult to be introduced into aluminium,” says Xinghang Zhang, an author on two studies describing the new material. “The formation of the 9R phase in aluminium is even more difficult because of its high stacking fault energy. You want to introduce both nanotwins and 9R phase in nanograined aluminium to increase strength and ductility and improve thermal stability.”
The scientists used two different techniques to invoke the 9R phase in the material. One of these techniques involved inducing a shock by using a laser to bombard ultrathin sheets of aluminium with particles of silicon dioxide. “Here, by using a laser-induced projectile impact testing technique, we discover a deformation-induced 9R phase with tens of nanometers in width,” says Sichuang Xue, lead author of this study.
The second process is called magnetron sputtering and introduces iron atoms into the aluminium’s crystal structure. This aluminium-iron allow was found to be one of the strongest ever made. The team says that this process could be scaled up to an industrial scale.
“These results show how to fabricate aluminium alloys that are comparable to, or even stronger than, stainless steels,” says Zhang. “There is a lot of potential commercial impact in this finding.”
The team describes the alloys in the video below: