Magnesium, with a specific gravity of only 1.74, is the lowest-density metal available for engineering
use. It is produced either by electrolytic reduction of MgCl2 or by chemical reduction of MgO by Si
in the form of ferrosilicon. MgCl2 is obtained from seawater, brine deposits, or salt lakes. MgO is
obtained principally from seawater or dolomite. Because of the widespread, easy availability of
magnesium ores (e.g., from the ocean), the ore supply is, in human terms, inexhaustible.
Magnesium is used both as a structural, load-bearing material and in applications that exploit its
chemical and metallurgical properties.
7.2.1 Nonstructural Applications
Because of its high place in the electromotive series, magnesium is used as a sacrificial anode to
protect steel from corrosion; some examples are the protection of buried pipelines and the prolon-
gation of the life of household hot-water tanks. Alloys used for this purpose are produced by per-
manent-mold castings and by extrusion.
Magnesium in powder form is added to gray cast iron to produce ductile, or nodular, iron, an
alloy that has many of the producibility advantages of cast iron but is ductile and strong.
A significant use for magnesium powder is its addition to the iron tapped from blast furnaces to
remove sulfur prior to converting to steel, thereby increasing the efficiency of the blast furnace and
improving the toughness of the steel.
Magnesium powder is also used to produce the Grignard reagent, an organic intermediate used
in turn to produce fine chemicals and Pharmaceuticals.
Magnesium sheet and extrusions are used to produce photoengravings.
Magnesium in ingot form is one of the principal alloying additions to aluminum, imparting
improved strength and corrosion resistance to that metal.
7.2.2 Structural Applications
Magnesium structures are made from sand, permanent-mold, investment, and die casting, and from
sheet, plate, extrusions, and forgings. The base forms produced in these ways are fabricated into