Identifying Weldable Metals in the Field

When you are making use of a portable welder, you will occasionally find yourself preparing to weld some kind of metal that is not readily identifiable visually. Often, you will be able to identify a metal either by its appearance – copper is usually unmistakable, for example – or its use. Identifying by use is easier in some circumstances than others; for example, bundles of very fine, braided wire inside a rubber or plastic sheath and connecting a device to a power supply are probably copper.

On other occasions, though, metal may be so dirty, tinged with contaminants, oxidized, and so on that it is hard to tell if you are looking a piece of steel, a piece of aluminum, or something else. Nevertheless, it is important to identify metals before welding or cutting so that the proper torch tip, gases, settings, temperatures, and filler metal can be employed for joining them together.

When confronted by an unknown metal, you can establish whether or not it is ferrous by applying a magnet to its surface. The magnet itself should be clean, and tested under controlled conditions (that is, by sticking it to your refrigerator) to make sure that it has sufficient “grab” for testing. If the magnet is attracted to the metal, then the metal is ferrous – either iron or carbon steel. If it does not stick, then the metal could be nearly anything else – including stainless steel, which usually is non-magnetic and therefore indistinguishable from aluminum by the magnet test.

For distinguishing between the various types of steel, you can also make use of an angle grinder, grinding some part of the metal and seeing what sparks are produced. Aluminum produces no sparks at all, and will fill your grinding disc with debris. Stainless steel sparks are sparse and bright red, and show a few forks but not many. Manganese steel, by contrast, produces thick showers of brilliant white sparks, which spray out in a long stream and show many bursts. Carbon steel also makes very long white spark patterns, with small forks showing when the carbon is .3% or less and more and more bursts appearing as carbon content increases.

Cast iron spawns very short, faded red sparks with a few bursts and forks, while wrought iron emits long fans of straw-tinted sparks with white forks at the furthest point of the spark stream from the point where the angle grinder is touching the metal.

In the event that metal defies identification by appearance, magnetism, and the angle grinder test, you will likely need to fall back on one of two solutions. The first is to simply experiment – set your welding rig up to handle the type of metal that you deem the workpiece most likely to be, and hope for the best. Alternatively, you can research, either by inquiring of people who know of this particular piece of metal what it is, or by finding a description of the specific object you are about to weld and learning the composition directly from that.