Engineers at the UCLA Samueli School of Engineering developed a method for welding AA7075 alloy. Developed in the 1940s for the automotive industry, the alloy that is nearly as strong and one-third its weight, but traditionally has been almost impossible to weld together using the techniques commonly used by auto makers for the assembly of body panels or engine parts. This is because when the alloy is heated during the welding process, its molecular structure creates an uneven flow of its constituent elements — aluminum, zinc, magnesium, and copper — which results in cracks along the weld.
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 instead of welding. 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 automobile manufacturing, has prevented it from being widely adopted.
The solution developed by the UCLA engineers involves infusing titanium carbide nanoparticles (particles so small that they’re measured in units equal to one billionth of a meter) into the 7075 welding wires, which are used as filler material between the pieces being joined. In this way researchers were able to weld 7075 alloy parts, producing welded joints with a tensile strength of 392 MPa. They also showed that with post-welding heat treatments, the joint could achieve 551 MPa, which is comparable to steel. (In comparison, 6061 aluminum alloy, which is widely used in aircraft and automobile parts, only has a tensile strength of 186 MPa in welded joints.)
“The new technique 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 manufacturing processes, 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 alloys.
The study was published in Nature Communications, with UCLA graduate student Maximilian Sokoluk as lead author. The other authors are Chezheng Cao, who earned a doctoral degree from UCLA in December; Shuaihang Pan, a current UCLA graduate student; and Li who holds faculty appointments in mechanical and aerospace engineering and in materials science and engineering.