Is bronze stronger for fillet brazing than brass? what kind should I use. Is the melting temp a bit higher?
I need to make the joints as strong as possible, because I am building a cargo bike.
"Brass" is the lay term for bronze copper-bearing brazing rods. Typically people use either RBCuZn-C, RBCuZn-B or RBCuZn-D. The melting temps and strengths vary slightly for each, but for practical application those are mostly academic distinctions. The differences are subtle, and a skilled brazer should be able to adapt to either quickly.
I'm not sure is "near settale" is "near Seattle", but if so I recommend hooking up with the local community collage for a welding and brazing module.
Go with RBCuZn-d like Crown 120 bare,
Crown Alloy 3/32 x 36" CROWN 120 BR.PKG. Bare Nickel-Silver ( RB CuZn-D) BRAZING 1 lb TUBE (CT120/TN-BP) - FREE SHIPPING - Welding Supplies from IOC
Melts about the same, great for cargo bikes and lots of others.
Walker Bicycle Company | | Walker Bicycle Company
Although Andy's recommendation is sound and appropriate for your question, I am skeptical of the "1400-1600" degree claim. Most Nickel Silver alloys have a solidus around 1690 degrees F and have a brazing temperature higher still. Nickel Silver is a high temperature alloy, so make sure your tube selection can handle the higher temperatures. That said, it is a wicked strong alloy. We sure to wear gloves when handling, and a respirator when brazing with nickel bearing alloys, Nickel is a bio-accumulating toxin.
Many brazers call (myself included) sometimes call Low Fuming Bronze Brass, technically they are not the same, and you will have much better luck with a Low Fuming Bronze alloy Like our LFB, or Hank's C-4.