7075 is one of the "difficult" to weld Al alloys.
I do know it is RSW regularly in the aerospace industry. It can be GTAW, but this process still requires some attention as it tends to crack if welding parameters are not dialed in and adhered to. It has a VERY narrow weldability range.
The welding engineer at one of the companys I worked for years ago told me something about corrosion susceptibility (with regards to our shielding gas and filler metal). Back then I had no clue what he was talking about, but it stayed in my hard drive and years later I now understand his statement.
CWIC is correct. 7075 is usually considered to be unweldable by arc welding processes. Some general and specific information on welding aluminum alloys is available using the following links: