Jurgen J. Maerz probably can answer this…
Just to keep things interesting I want to do some mixed alloy
pieces using palladium and palladium/ruthenium. Weld it like
platinum or solder it? I’ll be soldering the resulting sections
to 18k yellow and 22k.
Richard D. Hamilton
A goldsmith on Martha’s Vineyard
USA
Fabricated 14k, 18k, 22k, and platinum Jewelry
wax carving, modelmaking, jewelry photography,
and sailing whenever I can…
http://www.rick-hamilton.com
Just to keep things interesting I want to do some mixed alloy
pieces using palladium and palladium/ruthenium. Weld it like
platinum or solder it? I’ll be soldering the resulting sections
to 18k yellow and 22k.
I would solder the pd/ru to the pd, as the alloyed piece will have a
different melting point then the pure palladium. Then I would be sure
that both the PGM and the Au is annealed before I join them with gold
solder, as ther is a different expansion rate between them, which may
cause cracking.
Hope that helps Have a platinum day sailing 
PLATINUM GUILD INTERNATIONAL USA
Jurgen J. Maerz
Mgr of Tech. Edu. JA Cert Master Bench Jeweler