The hardest part of this project is baked into the material itself: 7075-T651 has a reputation for splitting when you melt it. The maker went at that problem directly with a workshop experiment that pitted several filler choices against one another to find out whether a sound joint on this alloy is even possible. That is exactly the right way to answer the question, in my view, rather than trusting hearsay either way.
The build itself was methodical. Coupons were cut on a metal-cutting bandsaw, then came autogenous TIG butt welds with no filler at all, plus rapid spot welding attempts. Filler joints followed, using standard rod, cut 7075 strips, 4943 rod, and 3003 sheet strips. An Alumiweld low-temperature brazing rod joined the lineup too. Two machines were in play, a Primeweld TIG welder and a Miller Dynasty 350, both run with Miller torches. One heavy fillet on thick 7075 blocks was run at 325 amps, which is serious current.
The details that stand out are the testing methods. Joints were bent in a bench vise using an adjustable wrench, the 325-amp fillet was struck repeatedly with a 4-pound sledgehammer, and a base material comparison pitted untreated 7075-T651 against an annealed, heat-affected sample, where the untreated piece snapped brittle and the annealed piece bent with some give.
The trade-off shows in the outcomes: every conventional welded joint broke at the weld line during bending, the brazed joint held without separating, and the fillet sheared off under the hammer. The conclusion drawn was that welding this alloy yields fragile, crack-prone joints, and 6061 stated client work involving 7075 welding will be declined. Given these results, that seems like a fair stance to me.
Project by 6061. Watch it on their YouTube channel: