Handbook-Non-Ferrous Metals

Silicon-bronze plate and sheet contain only 1.75 to 3.0% silicon, though the silicon may go as high as 14% in a

casting alloy. The silicon bronzes can be welded by almost any process, including oxy-acetylene. Silicon bronze has high strength and good corrosion resistance, but lower heat conductivity than pure copper. The aluminum bronzes (7-11% aluminum) have high tensile strength. Oxy-acetylene welding is not recommended. Welding of Copper-Zinc Alloys (Brasses). To oxy-acetylene weld brass is not difficult if you know what to do about the problems created by the zinc content. These are the things to remember: (1) You must use a flux; either a braze-welding flux (such as OXWELD BRAZO flux) or a flux formulated for oxy- acetylene welding of stainless steel may be used. The flux should be mixed with water to form a paste, which should then be painted on the rod and on the surfaces to be welded. (2) You must use an oxidizing flame. In fact, it must be quite strongly oxidizing. If you apply a neutral flame to brass, before actual melting has been observed zinc fumes will start coming off; and the surface of the metal will get quite bright. If you then start to make the flame oxidizing (by cutting back on the acetylene flow) you will find that at a certain point a distinct coating forms on the surface of the brass, and the fuming is virtually eliminated. An oxidizing flame that is just sufficient to create a visible coating on the surface of the base metal is what you want. Too much oxygen will increase the thickness of the coating and make welding more difficult. (3) You can use a high-quality braze welding filler metal (such as OXWELD 25M rod) on almost any copper-zinc alloy, if precise color match is not essential. In the case of a low-zinc alloy (5% zinc) the melting point of the base metal will be so much higher than that of the rod (OXWELD 25M or equivalent) that you can actually braze weld rather than fusion weld. With most brasses, however, the difference in melting points will be far less. (4) Use a welding tip at least one size larger than you would normally use on steel of the same thickness, because of the high heat conductivity of the metal. Otherwise, generally follow the forehand welding technique used for steel welding.