Is it possible to weld a cracked head tube on an aluminum frame? The crack is about 1 1/2" ling and starts at the bottom on the right side parallel to fork.
Yes, I have had cast aluminum welded and it has held. But for a bike frame, I would not trust it at all, and would question it all the time. I think it is time for a new frame.
What make is the frame?
Depending on the type of aluminum you may have to heat treat the entire frame after welding. That means new paint all over, too. Makes the job too expensive for all but the priciest frames.
With new tires/brakes/chains /etc., bikes can last for many years: this however is something that puts and end to them. Hang it on your wall if it is a bike you treasured, if not strip the parts and put it in a dumpster- it is unsafe.