Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; a freshly exposed surface has a reddish-orange color. It is used as a conductor of heat and electricity, a building material, and a constituent of various metal alloys.

The metal and its alloys have been used for thousands of years. In the Roman era, copper was principally mined on Cyprus, hence the origin of the name of the metal as сyprium (metal of Cyprus), later shortened to сuprum. Its compounds are commonly encountered as copper(II) salts, which often impart blue or green colors to minerals such as azurite and turquoise and have been widely used historically as pigments. Architectural structures built with copper corrode to give green verdigris (or patina). Decorative art prominently features copper, both by itself and as part of pigments.
Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the respiratory enzyme complex cytochrome c oxidase. In molluscs and crustacea copper is a constituent of the blood pigment hemocyanin, which is replaced by the iron-complexed hemoglobin in fish and other vertebrates. The main areas where copper is found in vertebrate animals are liver, muscle and bone.[citation needed] In sufficient concentration, copper compounds are poisonous to higher organisms and are used as bacteriostatic substances, fungicides, and wood preservatives.

Type of Material CDA No. Primary Use
Copper-Cadmium C16200 Cadmium Copper is a general-purpose material for resistance welding use. The addition of Cadmium increases the metal’s hardness and give it high electrical and thermal conductivity. It is commonly used for spot welding aluminum alloys, magnesium alloys, coated materials, brasses, and bronzes. It is also used for spot welding electrodes, welding fixture components, seam welding wheels, seam welding shafts, and flash and butt welding dies.
Copper-Zirconium C15000 Zirconium Copper is used in spot welding electrodes and seam weld wheels. It is particularly useful when welding galvanized materials because of its high thermal conductivity, which prevents sticking.
Copper-Chromium C18200 Chromium Copper is the primary copper alloy for high level production spot and seam welding of clean mild steel, low alloy steels, stainless steel, low conductivity brasses and bronzes, nickel-silver, nickel, nickel alloys, and monel. It is also suitable for projection welding dies, seam welder shafts and bearings, flash and butt welding dies, and current-carrying structural members.
Copper-Chromium-Zirconium C18150 Chromium Zirconium Copper is used as an electrode material for welding galvanized steel and other metallic-coated materials. It has improved creep resistance at high operating temperatures.
Copper-Nickel-Silicon-Chromium C18000 This alloy is a very hard, heat-treatable copper with moderate electrical conductivity that is ideal for use as seam weld wheels, projection welding dies, flash and butt welding dies, current-carrying shafts and bushings, high stressed structural current-carrying members, electrode holders, and high pressure electrodes where the welded material has a high electrical resistance.
Copper-Nickel-Beryllium C17510 This alloy is heat-treatable with moderate electrical and thermal conductivity and high tensile strength. It is recommended for projection welding dies, flash and butt welding dies, current-carrying members, and heavy-duty offset electrode holders. It is also generally recommended for spot and steam welding steels with high electrical resistance, such as stainless steel.
Copper-Beryllium C17200 Beryllium Copper has extremely high hardness and tensile strength but less electrical conductivity than Class III alloys. It is recommended as the electrode material for special flash, upset-butt and projection welding applications where pressures are extremely high and wear is severe, but where heat is not excessive. They are used frequently in the form of inserts and facings and seam welding bushings.
Copper-Tungsten C74450 Class 10 Copper Tungsten is used for flash and butt welding electrodes in applications in which high heat resistance, higher electrical and/or thermal conductivity, high malleability, and low thermal expansion are required. This metal is created by combining 45% copper and 55% tungsten, resulting in a dense, hard metal with superior wear resistance and strength.
Copper-Tungsten C74400 Class 11 Copper Tungsten contains 25% copper and 75% tungsten. Like Class 10, it has superior wear resistance and strength and good thermal and electrical conductivity. However, it is harder than Class 10 and used in applications that require moderate pressure. Common uses include projection welding electrodes, flash and butt welding electrodes, light upsetting and seam welding bushings, and spot welding low conductivity steels. It is also widely used in chip carriers, substrates, flanges, and frames for power semiconductor devices.
Copper-Tungsten C74350 Class 12 Copper Tungsten contains 20% copper and 80% tungsten. Stronger than Class 10 and 11 Copper Tungsten, it is commonly used in heavy duty projection welding electrodes, electro-forming and -forging electrode facings for upsetting studs and rivets, and cross wire welding. IT is also used in the liners of some specialty shaped explosive charges for the defense and oil and gas industries.
Tungsten C74300 Tungsten has the second highest melting point of all elements. It is extremely dense and has low ductility. It is commonly used in cross wire welding copper and brass, resistance brazing, and welding of braided copper wire. It is also has many non-welding applications, such as filaments for incandescent light bulbs, x-ray filaments and targets, and penetrating projectiles.
Molybdenum C42300 Molybdenum has the sixth highest melting point of all elements and is used in high temperature and high pressure applications. It has similar welding applications as Class 13 Tungsten; however, it is not as hard, but it has a more stable price and can be machined into special contours.
Dispersion Strengthened Copper C42300 Dispersion Strength Copper contains copper and aluminum oxide, giving this metal electrical and thermal conductivity similar to copper but greater strength and resistance to softening at high temperatures. DSC electrodes are particularly useful when welding metallic coated metals, such as galvanized steel and terne plate. In its electrical applications, DSC is used in incandescent lamp lead wires.