Ed, It was black steel pipe - actually rusty steel pipe!
I do weld and/or braze galvanized metal after stripping it in dilute muriatic acid. In fact I strip black steel pipe as well. Otherwise it doesn't braze well. And certainly strip rusty stock!
Brass brazing rod contains zinc, btw. About 40% in order to lower melting point in relation to most brass and even copper, which is often brazed. It's important not to overheat while brazing not only for fume control, but for soundness of joint. I braze outdoors, and take precautions. You can braze with pure copper, too.
ps. the bearing boss on the twin was a piece of brass rod that was brazed onto the steel, as an experiment. Temperature control is important when trying that, since the melting points of the braze and part are close.