Nanoparticles solve tricky welding problem

February 9, 2019 | 06:04
Nanoparticles solve tricky welding problem
Nanoparticles solve tricky welding problem
A particular alloy of aluminium — first produced in the 1940s — is almost as strong as steel but only one-third the weight. Its properties make it an ideal material for a wide range of applications. Unfortunately, up till now, it’s not been possible to weld the material successfully.

When aluminium alloy AA 7075 is melted during welding, its molecular structure creates an uneven flow of its constituent elements —aluminum, zinc, magnesium and copper — producing cracks along the weld joint. Now, engineers at the Samuell School of Engineering at UCLA (University of California, Los Angeles) have developed a novel process that achieves very good weld strength. The solution was to introduce tiny titanium carbide nanoparticles with diameters in the μm range into the welding rods made from AA 7075 alloy.

Results

Using the improved welding rods, joints with a tensile strength of up to 392 megapascals were possible. By comparison, the alloy AA 6061, commonly used in aluminium vehicle and aircraft construction, is significantly less strong, achieving a tensile strength of only 186 megapascals in welded joints. According to the researchers, additional post-weld heat treatment can increase the tensile strength of AA 7075 welds to as much as 551 megapascals, enabling the new process to build thin lightweight alloy structures which have a strength comparable to steel.
 
From left to right: Student Maximilian Sokoluk, Technician Travis Widick (holding a AA 7075 cycle frame) and Professor Xiaochun Li. Photo: Kenny Stadelmann/UCLA
Because AA 7075 is both very strong and lightweight it is ideal for the construction of vehicles and aircraft to make them significantly more fuel efficient. AA 7075 is already used in the construction of aircraft fuselages and wings, but components made from it can only be joined by bolting or riveting. It is also used to make smartphone frames and climbing carabiners. The difficulties of welding the alloy have prevented more widespread use, especially in automotive engineering.

Vehicles

Thanks to the breakthrough in the welding technology, a broad application of this high-strength aluminium alloy in mass-produced products such as cars or bicycles could now result. Lightweight and robust structures can be fabricated from AA 7075 alloy using traditional production methods. A prototype cycle frame design is already undergoing development with a commercial cycle manufacturer. It is hoped that the addition of nanoparticles to other types of welding rods could produce more stable welds in other hard-to-weld metals and alloys.

Source: UCLA
 
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