Hi there apres,
One process I can think of is brazing-we fabricate guttering/spouting for Agricultural buildings and we've found that brazing with a low melting point filler rod
acheives great results and no corrosion(some of the gutters
have been in place now for 4 years and there is no reports
of corrosion).However this may not be practical in your
application.
Try this link  http://galvanizingconsulting.com/plant.html
they might be able to help.
Best of luck-TWWeld.

Thanks for the suggestion but, in this application, we need a high weld speed and parent metal strenght.

Unfortunately when you weld pre-coated steels the coating oxides and you loose your corrosion protection.  Although with zinc and aluminium there is a degree of sacrificial protection of the underlying base metal, depending on environment.  Suggest you clean the welded area mechanically and apply a zinc rich primer or inorganic zinc silicate.

Good luck

The only thing that may help is to go back with a coat of cold galvanizing spray. to get a strong weld bond, of course you have to get to the base metal which isn't protected.
And from my experience paint itself doesn't bond well to zinc.
I thing the label of cold galv. states close to a 90% zinc content. The only possible option is to hot dip the part.