Nanoparticles Advance Aluminum Alloy Welding

Aluminum alloy AA 7075 is almost as strong as steel but weighs only a third as much—a dream material to use for lightweighting, you might think. And in the decades since it was developed in the 1940s it has seen use in airplane wing skins because it can be riveted. But its use in other industries has been curtailed by the fact that the same molecular structure that gives it a great strength-to-weight ratio has also made it notoriously difficult to weld. Until now, that is.

The problem is that when the alloy is heated during welding, its constituent elements—aluminum, zinc, magnesium and copper—flow unevenly, melting and resolidifying at different rates, which results in cracks along the weld.

Researchers at the UCLA Samueli School of Engineering (samueli.ucla.edu) have now found a way to weld the alloy using traditional arc welder technology.

Their solution: infusing titanium carbide nanoparticles into AA 7075 welding rods, which are then used as the filler material between the pieces being joined. The presence of the nanoparticles causes the liquified alloy’s elements to solidify together much more uniformly as it cools, eliminating cracks.

Using this approach, the researchers produced welded joints with a tensile strength of 392 megapascals (MPa). By comparison, the widely used aluminum alloy AA 6061 has a tensile strength of 186 MPa in welded joints. The researchers posit that post-welding heat treatments could further increase the strength of AA 7075 joints—up to 551 MPa, which is comparable to steel. The team has published their findings in the journal Nature Communications (nature.com).

“The new technique is just a simple twist, but it could allow widespread use of this alloy in mass-produced products like cars or bicycles,” said UCLA professor of manufacturing Xiaochun Li, the study’s principal investigator. “Companies could use the same processes and equipment they already have to incorporate this alloy into their manufacturing processes, and their products could be lighter and more energy efficient, while still retaining their strength.”