Why is aluminum welded with AC?

When one or more of the constituent atoms loses electrons, the other atom gains electrons. This creates covalent bonding, which is a shared electron cloud by the entire molecule. Both covalent and ionic bonding have a constrained location of electrons and ions, which results in a bond that is characteristically fragile. A type of covalent bonding called metallic bonding is one in which all the constituent atoms of the atoms are the same type, and don't combine to form a chemical bonds. An array of positive ions will form when atoms lose one or more electrons. The electron cluster is made mobile by the fact that the electrons can move freely and are also shared by the lattice. It gives metals their characteristically high electrical and thermal conductivity, as well as being ductile.

Forge welding saw significant advances during the Middle Ages. In this era, blacksmiths beat heated metal repeatedly until it was fused. Vannoccio Biringuccio published De la pirotechnia (1540), which describes the forging process. This process was well-known among Renaissance craftsmen. The industry grew steadily over the centuries. Sir Humphry Davy was the first to discover the short-pulse electricity arc. His results were published in 1801. Vasily Petrov, an Russian scientist, created the continuous electrical arc in 1802. He also published "News of Galvanic-Voltaic Experiments" 1803, which described his experiments from 1802. The description of a stable discharge and indications of its potential use in many applications was of great importance to this work. Davy, unaware of Petrov’s work, discovered the continuous electrical arc in 1808. Stanislaw Olszewski, Polish inventor and Nikolai Benardos (Russian), created the first carbon arc welding method using carbon electrodes in 1881-82. With the invention of metal electrodes in late 1800s by a Russian named Nikolai Slavyanov (1888) and an American named C. L. Coffin (1990), arc welding has continued to advance. A. P. Strohmenger in Britain released a coated electrode metal electrode around 1900. It provided a more stable arc. Vladimir Mitkevich, an Russian scientist, proposed the use of a three-phase electrical arc for welding in 1905. C. J. Holslag, a 1919 inventor of alternating current welding, did not make it popular for over ten years.

GTAW can work on virtually all weldable metallics. However, it is most commonly applied to stainless and light metals. It is frequently used when high-quality welds need to be achieved, such a in aircraft, marine, and bicycle applications. Plasma arc welding uses a similar process but uses a plasma gas to create an arc. The arc is less concentrated than the GTAW arc. Because of this, transverse control becomes more important. Because the method has a stable current, it can work with a wider range material thicknesses and is quicker than the GTAW process. It can be used to all of the materials that GTAW except magnesium. The automated welding process of stainless steel, however, is one of its most important applications. A variant of this process is plasma cutting. This is an efficient way to cut steel.