Aluminum-Zinc Grain Decay Anisotropy

That's not a real problem, just a mishmash of half-knowledge. With AlZnMgCu alloys, the high-strength wrought aluminum alloys, you always have to expect microstructural changes in the heat-affected zone when welding. The strength that the material has from precipitation hardening breaks down in the heat zone – that's called overaging. That has nothing to do with 'anisotropy'; it's simply a loss of strength. If you have to weld the parts, the right strategy is: position the weld so it removes as little as possible of the high-strength structure, and if in doubt, after welding, solution heat treat and re-age the parts completely. Just welding away and hoping it holds is not the way with this stuff. The risk is that after welding you have a part that looks hard on the outside but is soft in the heat zone and breaks there.