No, Pistolwrench, I have not done a weld repair of a cracked aluminum frame. I'd hate to try it, even though I practically worship the guy that does my welding, I mean the guy can weld the edge of a razor blade... but not in aluminum. My aluminum welding experience comes from my prototype aluminum injection mold days. These were pretty much always 7075 T6, and welding was always a last resort because even on a good-sized, solid block, you got that Peanut Butter Syndrome as mentioned above. We welded when there was no choice or it didn't matter. Otherwise we made it over or inserted it.
BUT-- there was one little product I discovered and used the shXX out of... well, that is, I mean, on those RARE occasions when I made a mistake.... Lumiweld. I haven't had a call to mess with it for a long time. It was kinda finicky to apply. I did it with an oxy/acetylene rig, the Lumiweld was an uncoated rod. When it stuck, it stuck well, you could mill it, drill it, EDM it, whatever, but I often had to take two stabs at getting it to take. It either did or didn't, there was no in between. Once done, the Lumiweld itself was harder than the original base aluminum, but the 7075 was usually peanut-butterized by the heat. And I don't think it would be a good thing for crack repair anyway.. more like for building up where there's missing metal.
As to TIGing an alloy dust cover, George probably knows better than I, but with the amorphous nature of aluminum, and the thin section in question, I doubt that it can be done easily. I'd think there would be a large risk of just blowing the whole thing away with the arc-- or, George, am I just outta touch with what can be done?
Pistolwrench, your observation about slide contact with the top surface of the dustcover: brilliant! Never gave it any thought. Sounds totally viable and with what you have seen on cracked guns, I bet you're right. I think George had a good point too with Shok-buffs squishing out to the side, but I don't feel that would do it. A little high speed video could prove me wrong though, that material has to go somehwere when it's compressed.
[This message has been edited by Ned Christiansen (edited 11-07-2001).]