Not all 7005 gets post heat treatment. In fact, its probably only the boutique homegrown stuff that does, since 7005 will naturally age harden at room temperature over the course of about 30 days, or, approximately the journey time from the Far East to the UK/USA.
6061 will also age harden, but you can leave that at room temperature for a decade and it still won't reach T6 temper, Hence all 6061 frames require post weld heat treatment to harden the material up. 7005 takes a lot longer to anneal (soften) than 6061 when heated, far longer than this little weld will take, so a weld repair promptly completed and then left in a cupboard for a month to reharden will be fine. If the frame has sentimental value, then go for it. Get the crack drilled to prevent further propogation, ground out and welded up with the right filler wire, and it'll be good as new.
6061 will also age harden, but you can leave that at room temperature for a decade and it still won't reach T6 temper, Hence all 6061 frames require post weld heat treatment to harden the material up. 7005 takes a lot longer to anneal (soften) than 6061 when heated, far longer than this little weld will take, so a weld repair promptly completed and then left in a cupboard for a month to reharden will be fine. If the frame has sentimental value, then go for it. Get the crack drilled to prevent further propogation, ground out and welded up with the right filler wire, and it'll be good as new.
