7075 is an Aluminum alloy that is very light and very strong but it cannot be welded - the components of the alloy react and cause cracks at the weld zone. Airplanes are made from 7075 - this is why they are still rivited to this day.
From UCLA Samueli School of Engineering:
Nanotechnology enables engineers to weld previously un-weldable aluminum alloy
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 molecular structure creates an uneven flow of its constituent elements — aluminum, 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.
I use 6061 which can be welded with a simple TIG torch - it will be fun to add 7075 to the mix. Wonder how much the filler rods will cost? Probably nosebleed territory until the UCLA patent expires.
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