Metal is a chemical element that is a good conductor of heat and electricity. Metals have varying degrees of hardness, density, malleability and ductility. Malleability means its ability to be rolled out and hammered. Ductility has to do with being drawn out, as into wire. Metal has a definite melting point and will fuse with other metals to form alloys. Unlike pure metals, most alloys do not have a single melting point. Instead, they have a melting range in which the material is a mixture of solid and liquid phases.

Carbon and low-alloy steels are by far the most widely used materials in welded construction. Carbon content largely determines the weldability of plain carbon steels.  There are many grades of steel available, and their weldability varies.

Aluminium and its alloys are also generally weldable. Sometimes the oxide film on aluminium tends to prevent good metal flow. There are welding techniques to get around this, such as fusion welding which is more effective with alternating current when using the gas-tungsten arc process to enable the oxide to be removed by the arc action.

Copper and its alloys are weldable, but the high thermal conductivity of copper makes welding difficult.

Other metals such as zirconium, niobium, molybdenum, tantalum, and tungsten are usually welded by the gas-tungsten arc process. Nickel is the most compatible material for joining, is weldable to itself, and is extensively used in dissimilar metal welding of steels, stainlesses, and copper alloys.

Alloys

Many metals, when they are in the pure state, have properties that are undesirable. This is why most of the metals commonly used today are alloys. Pure iron is too soft to be of much value, so it is used most frequently as steel, which is an alloy.

An alloy is a metal consisting of a mixture of two or more materials. One of these materials must be a metal. Alloys usually have different properties from those of the component elements. Alloying one metal with another metal or non metal often enhances its properties.

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