I searched but did not find much info on this.
I will be using 16 or 20 oz. (.022-.027") copper sheet for upcoming jobs. The first job will be caps for 10 x 10 posts. I have done very little soldering and brazing so I trying to determine which will work best for me.
The pic is a test piece of 16oz copper brazed with B CuP-2 phosphorus copper rod and Oxy/Ace torch. The Phos in the copper acts as fluxing agent so no flux is required. This makes a good strong joint but because of the heat required the parent metal is annealed and weakened substantially.
I like copper filler because it will match the parent metal.
This is 7% phos like the rod I have but is only 1mm dia.(I called them). This is smaller than the flat rod in the pic, maybe this will melt at lower temp? https://shop.rings-things.com/cart/p...ire-p36120.htm
Hard solder is mostly silver; it's used to join silver and other metals for jewelry. But it needs just as much heat as the phos-copper, so you'll have the same problems with annealing. TIG would do the same thing, but over a smaller heat-affected zone, since the joint is formed quicker.
The amount of heat required for soldering varies by the amount of metal that's being heated and the type of solder used, but isn't affected much by the diameter of the solder wire; a thinner wire will just add less metal to the joint in the same amount of time. Your links didn't work for me, but for the kinds of things you're talking about a torch will work better than a heated iron.
Soft solders work in a much lower heat range than hard solder; they're typically made from tin and lead with admixtures of other metals like silver and zinc. While using them won't anneal your metal, they aren't nearly as strong either, so the joints are more likely to fail.
I like phos-copper best for joining copper; the joints are strong, the color's not bad, and I can usually live with whatever annealing happens (cooling copper slowly actually preserves hardness better than quenching it hot, unlike steel). But if strength is your primary consideration, have you thought of stamping out these post caps? I think that's normally how they're made.
There is a fellow here in my town that builds copper exhaust hoods for over the top of kitchen stove/ranges, as well as other copper sheet work for higher end kitchens.
He is got to be around 60 years old and came from Europe years ago that said this guy is a copper working master. Most of these hoods sell for thousands of dollars, and yes he is very busy.
Only uses solder and the old world soldering irons that are heated in a little natural gas fired brick heating oven made for the irons.
All his soldering is done in such a way that you will never see the actual solder. All joints are butts and laps etc.
For post caps, solder would work fine. My favorite flux is zinc chloride, the pink liquid at the hardware store. Tin both surfaces of the joint with solder, and press together while heating. A heavy soldering copper works the best for what you want to do. With a little practice you will have a tight joint, and won't see any solder.