I've got some alloy hinges that have some holes which need to be welded up and redrilled & tapped to M6. Is it ok to tig them?

A friend who used to race a 70's Laverda motorbike broke the cast aluminium headstock in a fairly big off. They aren't available from anywhere so he had it TIGed and carried on racing and passed scruitineering.

So I believe the answer is it's ok to weld castings.

Not sure how a tapped hole in a Al weld will perform though.

Aluminium casting can be successfully TIG welded and you will have no problems tapping a new thread. I have just TIG welded up a cast flange on a Delage radiator fan. Part of the flange was missing so needed building up. Always at the back of my mind was that the part was irreplaceable so there was a certain amount of buttock clenching during the operation! I am lucky enough to have a foot pedal so the process is mega controllable.

John