Soldering Bangles

Wondering if anyone can help. I am trying to solder together 9 carat
yellow gold bangles with a silver core.

The wall thickness of the gold is 0.3mm and the balance is a core of
solid fine silver. The outside diameter of the tube is 6mm round.

I am having great difficulty in finishing these items. Once the
solder is applied to join the two ends of the bangle we then polish
but pitt marks or hairline cracks are appearing.

Any suggestions in avoiding this would be appreciated.

Victor Donovic