Welding is a process that bonds two pieces of metal together by melting the points on each piece of metal where the two pieces are to be joined. Along with the metal being melted, there is also a filler material that is melted and blended in with the melted metal. This filler material is called a welding alloy. There are many types of welding alloys used and widely available, including alloys made from aluminum, bronze, cast iron, cobalt, copper, magnesium, nickel, steel, titanium, and zirconium. Alloys are also made from a number of different combinations of these metals, and any blend is referred to as an alloy.
Welding alloys have different metal compositions as well as varying forms, properties and electrode types. Some of the forms available include composite, paste, powder, solid wire, sheet, foil, thermite mix and tubular wire. Each of the different fillers has a different strength and melting range. Universal tensile strength (UTS) is the breaking load of the alloy, or the point at which the allow will not hold strong anymore. The yield strength refers to the point at which the alloy begins to deform under stress and pressure.
When choosing welding alloys, the first thing to consider is the type of metal that will be welding. You should always choose an alloy that bonds especially well with that type of metal to ensure quality and strength of your weld. If two dissimilar pieces of metal are being welded, such as copper to steel, then alloys like aluminum bronze or nickel aluminum bronze are appropriate to use as they are more generally suited for multiple types of metals.
Due to the variety of alloys which will work with each type of metal, there are a number of additional factors to evaluate aside from metal compatibility. One of these considerations is how easy the type of alloy is to weld. You should also consider the application and required performance specifications for the specific piece of metal or project that is being welding. If a welded joint is going to be exposed to extreme heat, for example, then the filler alloy should have a high melting point in order to make the weld successful and strong.
Joints which will be subjected to higher stress require stronger welding alloys. Low fuming bronze nickel and aluminum bronze alloys are both recommended for high strength metals as they both create very high strength welds. Joints which will be exposed to water will need a welding alloy that has a higher corrosion resistance, such as naval bronze, aluminum bronze, nickel aluminum bronze, and copper nickel alloys.
Some alloys may work well, but are not physically attractive. If a joint is going to be visible, such as a weld on a metal handrail or outside of a building, another consideration when picking an alloy is the color match between the alloy and the metal being welded. Most welding suppliers can provide charts which will show the post-weld color of welding alloys for matching purposes. Nickel silver and low fuming bronze nickel alloys are both good color matches when welding stainless steel. Silicon bronze alloy is often used in metal sculptures, where weld appearance is very important.