Materials

"Faulty" aluminum alloys sport the strength of stainless steel

Purdue University researchers have developed new aluminum alloys that are as strong as stainless steel
Purdue University researchers have developed new aluminum alloys that are as strong as stainless steel
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Two researchers on the project, (left) Sichuang Xue and Qiang Li, prepare a sample for study
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Two researchers on the project, (left) Sichuang Xue and Qiang Li, prepare a sample for study
A sample of the aluminum alloy being prepped for analysis by a transmission electron microscope, to study its crystal structure
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A sample of the aluminum alloy being prepped for analysis by a transmission electron microscope, to study its crystal structure
Purdue University researchers have developed new aluminum alloys that are as strong as stainless steel
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Purdue University researchers have developed new aluminum alloys that are as strong as stainless steel

Aluminum is nice and light, but as an easily crushable soft drink can shows, that comes at the cost of strength. By introducing faults into the metal's crystalline structure, researchers at Purdue University have now developed new aluminum alloys that are about as strong as stainless steel, and they could be put to work in corrosion-resistant coatings.

On the microscopic level, metals are made up of crystal atoms in repeating cycles of layers stacked on top of each other. A "stacking fault" occurs when a layer is missing from the pattern, and two layers of these faults are known as "twin boundaries" or "nanotwins." When these faults create a structure that repeats over nine layers, it's called a 9R phase.

These stacking faults can actually make a material stronger, so Purdue researchers wanted to introduce both nanotwins and 9R phase into aluminum. The problem is that the metal has a "high stacking fault energy" – essentially, that means aluminum tends to correct the faults itself.

"It has been shown that twin boundaries are difficult to be introduced into aluminum," says Xinghang Zhang, an author on two studies describing the new material. "The formation of the 9R phase in aluminum is even more difficult because of its high stacking fault energy. You want to introduce both nanotwins and 9R phase in nanograined aluminum to increase strength and ductility and improve thermal stability."

The scientists invoked 9R phase in the material using two different techniques. One was "shock-induced," created by using a laser to bombard ultrathin sheets of aluminum 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.

A sample of the aluminum alloy being prepped for analysis by a transmission electron microscope, to study its crystal structure
A sample of the aluminum alloy being prepped for analysis by a transmission electron microscope, to study its crystal structure

The second study used a process called magnetron sputtering to introduce iron atoms into the aluminum's crystal structure. This aluminum-iron alloy was found to be one of the strongest ever made, and the team says the process could be scaled up to an industrial scale, for eventual applications as corrosion-resistant coatings for electronic devices and vehicles.

"These results show how to fabricate aluminum 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 shock-induced alloy was described in research published in the journal Nature Communications, while the magnetron sputtering technique was published in Advanced Materials.

The team describes the alloys in the video below.

Source: Purdue University

Super-strong Aluminum Alloy

1 comment
YuraG
I'm not a pro on the subject, but from my experience an AISI 430 sheet appears to be less strong than some grades of aluminum. All in all, there are various sorts of strength and there are various stainless steels and alu grades, the devil is in their specific properties.