Magnesium alloy
Encyclopedia
Magnesium alloys are mixtures of magnesium
with other metals (called an alloy
), often aluminium
, zinc
, manganese
, silicon
, copper
, rare earth
s and zirconium
. Magnesium is the lightest structural metal. Magnesium alloys have a hexagonal lattice
structure, which affects the fundamental properties of these alloys. Plastic deformation of the hexagonal lattice is more complicated than in cubic latticed metals like aluminum, copper and steel
. Therefore magnesium alloys are typically used as cast alloys, but research of wrought alloys has been more extensive since 2003.
Cast magnesium alloys are used for many components of modern cars, and magnesium block engines have been used in some high-performance vehicles; die-cast magnesium is also used for camera bodies and components in lenses.
Magnox (alloy)
, whose name is an abbreviation for 'magnesium non-oxidising', is 99% magnesium and 1% aluminium, and used in the cladding of fuel rods in some nuclear power stations.
Magnesium alloys tend to be referred to by short codes (defined in ASTM 275) denoting the approximate chemical composition by weight: for example, AS41 has 4% aluminium and 1% silicon; AZ81 is 7.5% aluminium and 0.7% zinc. If aluminium is present, manganese is almost always also there at about 0.2% by weight to improve grain structure; if aluminium and manganese are absent, zirconium is usually present at about 0.8% for the same purpose.
aluminum and 1 weight percent zinc. Exact composition should be confirmed from the standards.
135-285 MPa and elongation 2-10%. Typical density
is 1800 kg/m3 and Young's modulus
is 42 GPa. Most common cast alloys are:
Wrought magnesium alloys have a special feature. Their compressive proof strength is smaller than tensile proof strength. After forming, wrought magnesium alloys have a stringy texture in the deformation direction, which increases the tensile proof strength. In compression the proof strength is smaller because of twinning, which happens more easily in compression than in tension in magnesium alloys because of the hexagonal lattice structure.
(codes: A=Aluminium
C=Copper
E=Rare earths, usually provided by adding mischmetal
to the melt, H=Thorium
K=Zirconium
L=Lithium
M=Manganese
O=Silver
S=Silicon
T=Tin
W=Yttrium
Z=Zinc
)
The thorium-containing alloys tend not to be used since a thorium content of more than 2% means a component has to be handled as a radioactive material.
Magnesium alloys are used for both cast and forged components, with the aluminum-containing alloys usually used for casting and the zirconium-containing ones for forgings; the zirconium-based alloys can be used at higher temperatures and are popular in aerospace. Magnesium+yttrium+rare-earth+zirconium alloys such as WE54 and WE43 (the latter with composition Mg 93.6%, Y 4%, Nd 2.25%, 0.15% Zr) can operate without creep at up to 300C and are reasonably corrosion-resistant.
and gadolinium
have been tried as alloying elements; an alloy with 1% manganese, 0.3% scandium and 5% gadolinium offers almost perfect creep resistance at 350C. The physical composition of these multi-component alloys is complicated, with plates of intermetallic compounds such as Mn2Sc forming. Erbium has also been considered as an additive.
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...
with other metals (called an alloy
Alloy
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...
), often aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, zinc
Zinc
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...
, manganese
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...
, silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, rare earth
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...
s and zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
. Magnesium is the lightest structural metal. Magnesium alloys have a hexagonal lattice
Hexagonal lattice
The hexagonal lattice or equilateral triangular lattice is one of the five 2D lattice types.Three nearby points form an equilateral triangle. In images four orientations of such a triangle are by far the most common...
structure, which affects the fundamental properties of these alloys. Plastic deformation of the hexagonal lattice is more complicated than in cubic latticed metals like aluminum, copper and steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
. Therefore magnesium alloys are typically used as cast alloys, but research of wrought alloys has been more extensive since 2003.
Cast magnesium alloys are used for many components of modern cars, and magnesium block engines have been used in some high-performance vehicles; die-cast magnesium is also used for camera bodies and components in lenses.
Magnox (alloy)
Magnox (alloy)
Magnox is an alloy—mainly of magnesium with small amounts of aluminium and other metals—used in cladding unenriched uranium metal fuel with a non-oxidising covering to contain fission products in nuclear reactors....
, whose name is an abbreviation for 'magnesium non-oxidising', is 99% magnesium and 1% aluminium, and used in the cladding of fuel rods in some nuclear power stations.
Magnesium alloys tend to be referred to by short codes (defined in ASTM 275) denoting the approximate chemical composition by weight: for example, AS41 has 4% aluminium and 1% silicon; AZ81 is 7.5% aluminium and 0.7% zinc. If aluminium is present, manganese is almost always also there at about 0.2% by weight to improve grain structure; if aluminium and manganese are absent, zirconium is usually present at about 0.8% for the same purpose.
Designation
Magnesium alloys names are often given by two letters following by two numbers. Letters tells main alloying elements (A = aluminum, Z = zinc, M = manganese, S = silicon). Numbers tells nominal compositions of main alloying elements respectively. Marking AZ91 mean magnesium alloy where is roughly 9 weight percentConcentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
aluminum and 1 weight percent zinc. Exact composition should be confirmed from the standards.
Cast alloys
Magnesium casting proof stress is typically 75-200 MPa, tensile strengthTensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
135-285 MPa and elongation 2-10%. Typical density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
is 1800 kg/m3 and Young's modulus
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...
is 42 GPa. Most common cast alloys are:
- AZ63
- AZ81
- AZ91
- AM50
- ZK51
- ZK61
- ZE41
- ZC63
- HK31
- HZ32
- QE22
- QH21
- WE54
- WE43
- Elektron 21
Wrought alloys
Magnesium wrought alloy proof stress is typically 160-240 MPa, tensile strength is 180-440 MPa and elongation is 7-40%. The most common wrought alloys are:- AZ31
- AZ61
- AZ80
- Elektron 675
- ZK60
- M1A
- HK31
- HM21
- ZE41
- ZC71
Wrought magnesium alloys have a special feature. Their compressive proof strength is smaller than tensile proof strength. After forming, wrought magnesium alloys have a stringy texture in the deformation direction, which increases the tensile proof strength. In compression the proof strength is smaller because of twinning, which happens more easily in compression than in tension in magnesium alloys because of the hexagonal lattice structure.
Aluminium alloys with magnesium
- BirmabrightBirmabrightBirmabright is a trade name of the former Birmetals Co. for various types of lightweight sheet metal in an alloy of aluminium and magnesium. The constituents are 7% magnesium, sometimes 1% manganese, and the remainder aluminium...
- MagnaliumMagnaliumMagnalium is an aluminium alloy with 1.5 to 2% magnesium and small amounts of copper, nickel, and tin. Some alloys, intended for particular uses at the cost of poor corrosion resistance, may consist of up to 50% magnesium...
(codes: A=Aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
C=Copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
E=Rare earths, usually provided by adding mischmetal
Mischmetal
Mischmetal is an alloy of rare earth elements in various naturally occurring proportions. It is also called cerium mischmetal, rare earth mischmetal or misch metal. A typical composition includes approximately 50% cerium and 25% lanthanum, with small amounts of neodymium and praseodymium...
to the melt, H=Thorium
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....
K=Zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
L=Lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
M=Manganese
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...
O=Silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
S=Silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
T=Tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
W=Yttrium
Yttrium
Yttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and it has often been classified as a "rare earth element". Yttrium is almost always found combined with the lanthanides in rare earth minerals and is...
Z=Zinc
Zinc
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...
)
The thorium-containing alloys tend not to be used since a thorium content of more than 2% means a component has to be handled as a radioactive material.
Magnesium alloys are used for both cast and forged components, with the aluminum-containing alloys usually used for casting and the zirconium-containing ones for forgings; the zirconium-based alloys can be used at higher temperatures and are popular in aerospace. Magnesium+yttrium+rare-earth+zirconium alloys such as WE54 and WE43 (the latter with composition Mg 93.6%, Y 4%, Nd 2.25%, 0.15% Zr) can operate without creep at up to 300C and are reasonably corrosion-resistant.
Further alloy development
ScandiumScandium
Scandium is a chemical element with symbol Sc and atomic number 21. A silvery-white metallic transition metal, it has historically been sometimes classified as a rare earth element, together with yttrium and the lanthanoids...
and gadolinium
Gadolinium
Gadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. It is found in nature only in combined form. Gadolinium was first detected spectroscopically in 1880 by de Marignac who separated its oxide and is credited with...
have been tried as alloying elements; an alloy with 1% manganese, 0.3% scandium and 5% gadolinium offers almost perfect creep resistance at 350C. The physical composition of these multi-component alloys is complicated, with plates of intermetallic compounds such as Mn2Sc forming. Erbium has also been considered as an additive.