Seems no one got back to ou. In general you are going to want to preheat the copper only because it has such high specific heat and conductivity that it's harder to heat up from room temp and tends to promote cold roll, at 1/8th" it wouldn't take much but I would recommend between 100-300F for a preheat to make things a little easier.
I unfortunately couldn't help you on the filler metal selection as i have not done any GMAW brazing of copper. I don't see why 100% Argon would be a problem.
Hi,
Good Evening All!
I am Ranjith Kumar from India and regarding Copper to Steel joining below are the alloy recommendation from my end.
In GTAW you can use Eutectic Castollin - CastoTIG 45704W
Please revert back with your E mail Id so that I can send Product literature or you can mail me at mittajith@gmail.com
Regards,
Ranjith
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