Space Shuttle main tank friction stir welded aluminum

Boeing used friction stir welding for external tank components around 1990 — the first major aerospace adoption.

No, friction stir welding had not been developed. Actually it had been developed as a research thing about 1975 at the British Welding Institute. It was still sort of a curiosity. For aluminum it wasn't until about 1990 that Boeing built some parts of the space shuttle with it — not the main space shuttle but some of the external tanks or something. Boeing built some aerospace components with friction stir welding of aluminum. People have tried steel. The problem with steel for friction stir welding is you just don't have a stirrer rod with high temperature strength. There's really no good material that will go to the types of temperatures you need without just wearing away very rapidly. They have done it with titanium, but titanium is very reactive with a lot of metals and you can't tolerate the impurities that you get in there. Aluminum is the sweet spot for friction stir welding.

Brief reference. NASA's Michoud friction-welding program for aluminum structures, post-shuttle-retirement.

For spacecraft, they're trying to move toward friction welding — friction welding of things like aluminum and titanium. Friction welding of aluminum is what friction welding was invented for. The space shuttle main tank, they were looking at friction welding that — the big tank that goes into the ocean afterwards. Since they're not making that anymore, NASA has now got a big program at Michoud, in Mississippi or Louisiana, where they used to build the space shuttle, for friction welding of aluminum structures. And Boeing had a big program for friction welding because you don't get the distortion you get when you arc-weld aluminum, and it should be a better structure.