Nanotechnology enables engineers to weld previously un-weldable aluminum alloy

January 25, 2019 by Matthew Chin, University of California, Los Angeles
Two pieces of aluminum alloy 7075 welded together using a nanoparticle-enhanced filler wire. Credit: Oszie Tarula/UCLA

An aluminum alloy developed in the 1940s has long held promise for use in automobile manufacturing, except for one key obstacle. Although it's nearly as strong as steel and just one-third the weight, it is almost impossible to weld together using the technique commonly used to assemble body panels or engine parts.

That's because when the alloy is heated during welding, its creates an uneven flow of its constituent elements—, zinc, magnesium and copper—which results in cracks along the weld.

Now, engineers at the UCLA Samueli School of Engineering have developed a way to weld the alloy, known as AA 7075. The solution: infusing titanium carbide nanoparticles—particles so small that they're measured in units equal to one billionth of a meter—into AA 7075 welding wires, which are used as the filler material between the pieces being joined. A paper describing the advance was published in Nature Communications.

Using the new approach, the researchers produced welded joints with a tensile strength up to 392 megapascals. (By comparison, an known as AA 6061 that is widely used in aircraft and automobile parts, has a tensile strength of 186 megapascals in welded joints.) And according to the study, post-welding heat treatments, could further increase the strength of AA 7075 joints, up to 551 megapascals, which is comparable to steel.

Graduate student Maximilian Sokoluk; laboratory mechanician Travis Widick, holding a demonstration bike frame welded using aluminum alloy 7075; and Professor Xiaochun Li. Credit: Kenny Stadelmann/UCLA

Because it's strong but light, AA 7075 can help increase a vehicle's fuel and battery efficiency, so it's already often used to form airplane fuselages and wings, where the material is generally joined by bolts or rivets rather than welded. The alloy also has been used for products that don't require joining, such as smartphone frames and rock-climbing carabiners.

But the alloy's resistance to welding, specifically, to the type of welding used in , has prevented it from being widely adopted.

"The is just a simple twist, but it could allow widespread use of this high-strength aluminum alloy in mass-produced products like cars or bicycles, where parts are often assembled together," said Xiaochun Li, UCLA's Raytheon Professor of Manufacturing and the study's principal investigator. "Companies could use the same processes and equipment they already have to incorporate this super-strong aluminum alloy into their , and their products could be lighter and more energy efficient, while still retaining their strength."

The researchers already are working with a bicycle manufacturer on prototype bike frames that would use the alloy; and the new study suggests that nanoparticle-infused filler wires could also make it easier to join other hard-to-weld metals and metal .

Explore further: Superstrong Al alloys may change manufacturing processes for automobiles, aerospace devices

More information: Maximilian Sokoluk et al. Nanoparticle-enabled phase control for arc welding of unweldable aluminum alloy 7075, Nature Communications (2019). DOI: 10.1038/s41467-018-07989-y

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5 / 5 (6) Jan 25, 2019
Discoveries like this may not look like much, but they're very important. Being able to weld this alloy means structures built with it are likely to be stronger and lighter than they would otherwise be with fasteners.
Da Schneib
3 / 5 (4) Jan 25, 2019
This illustrates the difference between science and technology. Science made this alloy; technology will now make it useful.
2 / 5 (2) Jan 25, 2019
i'm probably missing a point, because alu 7075 bike frames exists from long time ago
Da Schneib
2.3 / 5 (3) Jan 25, 2019
They made the frames out of 7075 because they could weld it. These will be 10-pound mountain bikes. They might be able to make 1000-pound (half a tonne, for those who think in metric) cars as strong as the ones we have now that weigh twice or three times as much. Think what that will do to the range of electric cars.
5 / 5 (5) Jan 25, 2019
i'm probably missing a point, because alu 7075 bike frames exists from long time ago

They were bonded:
5 / 5 (1) Jan 25, 2019
This is the sort of progressive creativity that proves my maxim:
"Conservative is an action.
Not a political slogan."
3 / 5 (2) Jan 25, 2019
I have a salamagundi bike with a metal matrix frame. Tubes are joined with gussets or lugs? Perhaps some 7075 frames were made this way.
Da Schneib
3.3 / 5 (3) Jan 25, 2019
Thanks @pntaylor, I had no idea. The problem with 7075 apparently is brittleness and cracking, along with the welding problem. Learn something new every day.
not rated yet Jan 26, 2019
Is this kind of joint sensitive to fatigue? As far as aircraft are concerned a loss of fatigue strength compared to the parent metal makes this kind of joint unacceptable.
5 / 5 (1) Jan 26, 2019
Think what that will do to the range of electric cars.

Doesn't affect it as much as you would think. For an ICE car it's about 6% extra fuel consumption per additional 100kg. For an EV it's only 0.6% per additional 100kg (according to tests performed on Tesla Model S)

Makes sense if you think about it: ICE cars convert all the energy they use to accelerate into heat when braking. EVs, however, use regen.

Heavier EVs need more energy to accelerate but also recoup more - for the same reason. Most energy is used to stay at a specific speed - and that isn't dependent on weight at all* according to Newton but only on aerodynamics.

*there exists a weight-dependent factor: tire deformation. But that is relatively minor in the overall energy calculation.

So saving, say, 200kg on the weight of a car would net you (in an EV) just over 1% more range.
not rated yet Jan 28, 2019
Sounds like titanium carbide nanoparticles would be an excellent candidate for 3D printing. If it forms joints that strong, then it could be powdered, along with the welding wire material, and fed into a 3D deposition process.
not rated yet Jan 28, 2019
7075 Aluminum alloy has a tensile strength of about 70 KSI compared to a reasonable low carbon steel after heat treatment of at least 180 KSI. That shows that your statement about them having similar strengths is inaccurate. It might be applicable if one is comparing this aluminum (after heat treatment of course) with the basic steel that has not yet been so treated! If we compare the strength/weight of these two materials when used correctly there is a small advantage in aluminum providing fatigue considerations are not included.

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