Frogbutter's idea of forming a collar sounds good - I would really want to know more about how this came to be - As in the condition of the rest of the bike - What ever the case I think it will be worth it - And yes - I'll ride it if you want...

Thanks to all for input, answers to some of the questions raised.
I have no idea who made the frame the only other words on the frame are on the seat tube with the word liyang on the carbon. The word liyang is also on the bottom bracket on the aluminium facing the road.
The "shells" on the bottom bracket have the letters SKF on the outside edge and near the centre there is thum, a size lettering, and germany.
I was informed by the charity centre that this is a mountain bike frame 18 inch and that someone had tried to force a 1 1/8 fork into the 1 inch headtube.
I will be at the centre later on this week if i can find out more I will add it later.
Thank you cheers.

Hello again I have just done a google on liyang it would appear to be a hit on the maker?
I will need to follow up later sorry no time at present. Cheers.

https://www.liyangbikes.com/ --company website

The heat required to weld aluminum would set the frame on fire. The collar will not work on that frame. Email the MFG, I am sure a new one can be had at little to no cost.

Email sent will keep you posted Cheers

The issue with an airframe, they get regular inspections, if a crack like that were found in an airframe, it would be repaired even if expensive to repair, because a replacement airframe means a new aircraft, and that means millions of dollars, in the case of a DC3 it's often a small airline where millions of dollars for new aircraft are not going to happen.

With a bicycle frame, when you can replace the frame with a new one for $500 - $1,000 it makes a lot less sense. The frame in question, needs to be partly disassembled, a new head tube found or made, then reassembled. You would need a frame shop that is experienced at this kind of thing, and the part needs to be available, and they haven't made that style of frame in over a decade, so you might need an AL machine shop to make one out of aluminum stock, if it's a cast part then you may be into casting costs and machining costs, it's not hard to spend the cost of a replacement frame on making the part. Welding isn't always a solution, AL needs a different welding rod for each alloy, which is fine if you know what alloy it is, sometimes you do, sometimes you don't.

To answer the OP's question, I vote, ornament.

Hello all received an Email from Liyang global who informed me that this frame was made in 1994 however the warranty is up and they are unable to help with a replacement head tube. I have considered all the alternatives including the good info. on this site and to answer my own question I will pass this frame on to a mountain biker who will give it pride of place as a wall hanging.Thanks again for input Cheers.