Grille Restoration

I am restoring the grille on my 67. One of the 'bars' has broken off in the grille. I have the missing piece. I tried to solder the piece back onto the grille using solder for sweating copper pipes. This does not seem to work. Anyone have any ideas on how to put the missing bar back into the grille? I don't know if the grille is made out of tin or aluminum, tough to tell.

Any ideas?
Glenn