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is the common name for a range of magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s containing thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
that are used in aerospace engineering
Aerospace engineering is the primary branch of engineering concerned with the design, construction and science of aircraft and spacecraft. It is divided into two major and overlapping branches: aeronautical engineering and astronautical engineering...
. These alloys commonly contain manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, but there are other combinations known. Some common alloys are named HK31, HM21, HM31, HZ32, ZH42, ZH62; where the "H" indicates that the alloy contains thorium. Magnesium alloy names are often given by two letters following by two numbers. The two letteres indicate the main elements present in the alloy where A = aluminum, Z = zinc, M = manganese, S = silicon, etc. the numbers tell percentage compositions of the two elements. So, AZ45 would indicate that there is 4% aluminum and 5% zinc in the alloy.
Magnesium-thorium alloys have been used in several military applications, particularly in missile construction. The most noted example of this is the CIM-10 Bomarc missile, which implemented thoriated magnesium in its construction. This is due to thoriated magnesium alloys being lightweight, having high strength, and creep resistance
In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material....
up to 350° C. But, these alloys are no longer used due to radiation concerns involving thorium's radioactivity. This has resulted in several missiles being removed from public display. Another concern for the thoriated magnesium alloys is the low melting point and rapid oxidation of the metal. This can result in dangerous flash fires during the production of the alloys. Additionally, thorium-free magnesium alloys have been developed that exhibit similar characteristics to mag-thor, causing currently used magnesium-thorium alloys to be cycled out of use.