Researchers have created a super-strong aluminium alloy that rivals the strength of stainless steel, an advance with potential industrial applications. "Most lightweight aluminium alloys are soft and have inherently low mechanical strength, which hinders more widespread industrial application," said Xinghang Zhang, a professor at Purdue University in the US. "However, high-strength, lightweight aluminium alloys with strength comparable to stainless steels would revolutionise the automobile and aerospace industries," said Zhang. New research published in the journals Advanced Materials and Nature Communications shows how to alter the microstructure of aluminium to impart greater strength and ductility. The new high-strength aluminium is made possible by introducing "stacking faults," or distortions in the crystal structure. While these are easy to produce in metals such as copper and silver, they are difficult to introduce in aluminium because of its high "stacking fault energy," researchers said. A metal's crystal lattice is made up of a repeating sequence of atomic layers.
If one layer is missing, there is said to be a stacking fault. Meanwhile, so-called "twin boundaries" consisting of two layers of stacking faults can form. One type of stacking fault, called a 9R phase, is particularly promising, Zhang said. "It has been shown that twin boundaries are difficult to be introduced into aluminium. The formation of the 9R phase in aluminium is even more difficult because of its high stacking fault energy," Zhang said. "You want to introduce both nanotwins and 9R phase in nanograined aluminium to increase strength and ductility and improve thermal stability," said Zhang. Now, researchers have learned how to readily achieve this 9R phase and nanotwins in aluminium. "These results show how to fabricate aluminium alloys that are comparable to, or even stronger than, stainless steels," he said. "There is a lot of potential commercial impact in this finding," said Zhang.
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