Magnesium is the 8th most abundant element in the earths crust. Most of it is disolved in sea water. The raw metal is never found in nature due to its high degree of reactivity. Magnesium alloys are light weight (two thirds that of aluminum), high strength, and posess exceptional vibration damping characteristics. Because of their low modulus of elasticity, magnesium alloys can absorb energy elastically. It is easy to machine and process with conventional methods although special considerations have to be made due to the risk of fires. Once ignited it is difficult to extinguish, being able to burn in both nitrogen (forming magnesium nitride), and carbon dioxide (forming magnesium oxide and carbon). At room temperature, magnesium work hardens rapidly, reducing cold formability. Casting temperatures are about the same as aluminum, and both hot chamber and cold chamber die casting processes are used as well as more traditional permanent molds and sand casting. Casting rates for magnesium are high because of its low specific heat. For the same reason, less energy is required to heat the metal to casting temperature.

Table 1: Alloying element properties

Element Effect
Aluminum (A)
  • If magnesium is alloyed with aluminium, manganese usually present at about 0.2% by weight to improve grain structure
  • aluminium-containing alloys are usually used for casting
Copper (A)
  • allows heat treatment
  • improves corrosion resistance
Rare earths (E)
  • added for applications exposed to temperatures over 95°C.
  • magnesium rare earth-zirconium alloys are common
Thorium (H)
  • thorium-containing alloys with a thorium content of more than 2% means a component has to be handled as a radioactive material.
  • thorium-containing alloys exhibit a greater tendency for oxidation
Zirconium (K)
  • used if aluminium and manganese are absent
  • greater tendency to oxidize is overcome by the use of specially developed melting processes.
  • Zirconium is a potent grain refiner for magnesium alloys
  • zirconium-containing alloys are often used in forgings
  • zirconium-based alloys can be used at higher temperatures and are popular in aerospace
Manganese (M)
  • increased resistance against corrosion
  • improve grain structure
  • prevent Soldering in magnesium alloy high pressure die casting
Lithium (L)
  • Adding 10% lithium to magnesium produces improved anode in batteries using a manganese-dioxide cathode
  • Magnesium-lithium alloys are generally soft and ductile
Silver (Q)
  • improves both room-temperature and elevated-temperature mechanical properties
  • increases alloy cost significantly
Silicon (S)
  • improved physical characteristics
  • improved electrical conductivity in wire conductors using aluminum magnesium-silicon
  • imparts high fluidity and low shrinkage for casting and weldability
Zinc (Z)
  • added to alloys used for squeeze casting
  • additional strength and creep resistant
  • allows heat treatment
Yttrium (W)
  • these alloys can operate without creep at up to 300°C
  • reasonably corrosion-resistant.

ANSI designation

The first two letters of the ANSI designation identify the alloying elements specified in the greatest amount. The letters are arranged in order of decreasing percentages or alphabetically if the elements are present in equal amounts. The letters are followed by element percentage rounded off to whole numbers, followed by a final serial letter. The serial letter indicates some variation in composition of minor alloying constituents or impurities.

Table 3: First two characters for magnesium alloys

Characters Classification
AExx Aluminum Rare Earth
  • Good strength
  • creep resistance to 150°C
AMxx Aluminum Manganese
  • Very good weldability
  • Usually cast
  • High ductility and impact strength
  • No longer widely used
ASxx

Aluminum Silicon

  • Excellent creep resistance
  • Used in high temperature applications
  • die cast structural automotive parts
AZxx

Aluminum Zinc

  • most widely used magnesium alloy
  • moderate strength
  • good ductility and toughness
  • can be cast, formed, and forged
EAxx

Rare Earth Aluminum

  • aerospace alloy
EQxx Rare Earth Silver
  • high yield strengths up to 200°C
  • sand and permanent-mold castings
EZxx Rare Earth Zinc
  • Sand and permanent mold cast
  • relatively free from microporosity
  • creep resistant to 245°C
QExx

Silver Rare Earth

  • sand and permanent mold cast
  • weldable
QHxx Silver Thorium
  • Good castability
  • creep resistance and high yield strength to 250°C.
WExx Yittrium Rare Earth
  • sand and permanent mold cast
  • Excellent Creep resistance to 250°C
  • weldable
ZCxx Zinc Copper
  • Excellent castability
  • high strength
  • can be welded
ZExx Zinc Rare Earth
  • useful in thin-section castings
  • high mechanical strength
ZKxx Zinc Zirconium
  • used in highly stressed aerospace castings
  • suffers from microporosity and cracking due to shrinkage
  • high cost
  • not weldable
ZMxx Zinc Manganese
  • Good forgeability
  • medium strength
  • good damping capacity
ZWxx Zinc Yittrium

Table 4: third and fourth neumerical digit for magnesium alloys

second and third digit alloy content
AM60 Al 6%, Mn 0%
AS41 Al 4%, Si 1%
AZ61 Al 6%, Zn 1%
AZ91 Al 9%, Zn 1%
WE43 Y 4%, Nd 3%
WE54 Y 5%, Nd 4%

an alpha character following the four digit code such as the letters A, B and C signify alloys subsequently developed whose specified compositions differ slightly from the first and from one another but do not differ sufficiently to effect a change in the basic designation. There may also be a heat treatment code separated by a hyphen. Temper designations are in accordance with ASTM B296

Table 4: heat treatment suffix for magnesium alloys

suffix heat treatment
F as fabricated
O annealed
H cold worked
H1 strain hardened only
H2 strain hardened and then partially annealed
H3 strain hardened and then stabilized
T4 solution treatment
T5 artificial aging
T6 solution treatment and then artificial aged
T7 solution heat treated and stabilized
T8 solution heat treated, cold worked, and artificially aged

Some commonly used casting alloys

By far, casting is the most common method of producing usable parts from magnesium. Traditional sand and permanent mold casting techniques are used for larger or small production runs. Die casting is more suited to high volume parts including larger items like transmission housings and automotive wheels.

Although magnesium die castings are often used uncoated, they can be finished in a variety of ways to give increased protection against corrosion, wear, and to improve adhesion of other coatings such as paint. Common surface treatments include chemical dips, anodizing and plating. Organic coatings such as oil, wax, resin and paint are usually applied to seal surface porosity, increase corrosion protection and provide an attractive appearance.

Sand and permanent mold castings

AM100A-T61: Creates pressure tight castings with a good strength and ductility. This alloy is no longer widely used, typical uses were commercial and military structural castings with good combinations of tensile strength, yield strength, and elongation. Very good weldability.

AZ63A: Alloy with good room-temperature strength, ductility and toughness.

AZ81A-T4: An inexpensive alloy with good castability that makes tough, pressure tight parts with post casting heat treatment.

AZ91C and AZ92A-T6: Both are good general-purpose, moderate strength casting alloys that are often found in gearboxes.

EQ21A-T6: Although high priced, this alloy is noted for excellent short-time mechanical properties at high temperature.

EZ33A-T5: Good castability and damping capacity, pressure tight, creep resistant at 245°C

HK31A-T6: Good castability, pressure tight, creep resistant to 350°C

HZ32A-T5: Good castability, pressure tight, creep resistance to 260°C

QE22A-T6: Good castability, pressure tight, high yield strength to 200°C

QH21A-T6: Good castability, pressure tight, creep resistance and high yield strength to 250°C

WE43A-T6 and WE54A-T6: High strength at room and temperatures up to 290°C, good corrosion resistance but WE43A-T6 slowly loses ductility upon exposure to 150°C

ZC63A-T6: Pressure tight, stronger and more castable than AZ91C

ZE41A-T5 and ZE63A-T6: Pressure tight, medium-strength elevated-temperature alloy, improved castability over ZK51A. Especially useful for strong, thin-wall pore-free castings.

ZH62A-T5: High room-temperature yield strength

ZK51A-T5, ZK61A-T5 and ZK61A-T6: Similar properties including good room-temperature strength and ductility. increasing yield strength

Die-castings

AE42-F: Good strength, good creep resistance to 150°C

AM20-F: High ductility and impact strength

AM50A-F: Excellent ductility and energy-absorbing properties

AM60A-F: Similar to AM50A-F, but slightly higher strength

AS21-F: Similar to AE42-F

AS41A-F: Similar to AS21-F, but with decreased ductility and creep resistance, and

increased strength and castability

AZ91A, B and D-F: Excellent castability, good strength

AM60 Series Alloy

Die casting alloy used as-cast (F) temper for production of automotive wheels and other parts requiring good elongation and toughness combined with reasonable yield and tensile properties. These alloys are not weldable

Two new magnesium die casting alloys AM-lite and AM-HP2 have been developed as a light weight die casting alloy with good surface finish qualities. it improves many of the limitations of AZ91D and is competitive with zinc and aluminum die casting alloys. AM-lite has more than double the elastic limit of AZ91D This means that the stiffenss of critical parts is considerably higher. AM-HP2 has been specially developed to provide a die casting alloy that is creep resistant. this is suitable for powertrain components such as engine blocks, structural sumps, engine covers and automatic transmission housings.  AM-HP2 has the similar die castability of AZ91D and has a creep resistance similar to the aluminum alloys commonly used in these components. It is been specially adapted for high pressure die casting process. It can be realily electroplated

AZ Series Alloys

Although there has been, and still is, a large volume of castings for aerospace applications being produced in the older, conventional AZ-type alloys, the trend is toward the production of a greater proportion of aerospace castings in the newer zirconium types. For example, zirconium containing alloys such as EZ33 and ZE41 offer a specific combination of elevated temperature and room temperature properties which are not readily achievable with the AZ series alloys

This group of magnesium alloys are roughly 90% magnesium with aluminum as it's major other component. Small amounts of copper, nickel and iron contribute to corrosion resistance and silicon for strength. These alloys are used extensively for automotive castings. AZ91C and AZ91E can be readily welded by the gas-shielded arc process using AZ91C or AZ92A rod; stress relief required. AZ91A, AZ91B and AZ91D not weldable. Magnesium casting alloy AZ91B costs less per unit volume than any other die casting alloy.

AZ 63 mostly a sand casting alloy, Good room temperature strength, ductility, and toughness. Commonly used for parts in commercial and military structural applications requiring moderate strength and good ductility and toughness. Not typically used anymore - largely superseded by AZ91.

AZ91HP (high purity) alloy has been developed for die casting parts subject to corrosive environments. Because of lower levels of nickel, iron, copper and silicon versus AZ91B, this alloy is finding applications in automobiles, computers and peripheral equipment, and in other applications where paint or coatings are either undesirable or expensive. the high cost of surface finishing this alloy is a major issue and elecroplating is impractical. surface defects casting yeilds are low adn many parts are rejected

Magnesium AZ61A is a magnesium extrusion alloy appropriate for hollow and solid shapes. Stronger than AZ31B-F. Magnesium AZ80A performs well for extrusions and formings that resist creep and demand high fatigue strength. Stronger than AZ61A-F, AZ80A possesses an excellent machinability rating and can be readily heat treated. Applications of Magnesium AZ80A * Aircraft engine parts * Screw machine components * Hydraulic cylinders * Supercharger components WE43 A high strength magnesium alloy with good properties at elevated temperatures. Excellent corrosion resistance due to addition of yttrium. TIG weldable and usually heat treated. Typically used for military and aerospace sand castings used in the solution-heat-treated and artificially aged condition (T6 temper). Castings retain properties at elevated temperatures (under 250°C) for periods of time greater than 5000 hrs, and they are pressure tight and weldable. WE54 A high strength magnesium alloy close to WE43 in composition but with superior mechanical properties. Corrosion resistance and weldability are excellent. Usually heat treated. AS41A Used in as-cast condition (F) for automotive structural die casting parts in operating temps of up to 350°F. Creep resistance is superior to AZ91A, AZ91B, AZ91D, AM60A. Tensile strength, tensile yield strength, and elongation are good. ZC-63A Commercial and military sand castings used in the solution heat treated and artificially aged (T6 temper) condition. Superior properties to AZ91C-applications with better castability. Useful in pressure tight applications. Can be welded.

ZK60A Similar to but higher ductility than AZ60A-T5. ZM21 Good forgeability, medium strength, good damping capacity.

Forging, extruding and cold forming

Magnesium is easily formed to net shape by forging, extruding and cold forming.

Forging alloys

AZ31B-F: Good forgeability, medium strength, can be hammer forged, seldom used

AZ61A-F: Stronger than AZ31B-F

AZ80A-T5: Stronger than AZ61A-F

AZ80A-T6: Better creep resistance than AZ80A-T5

M1A-F: Good corrosion resistance, low to medium strength, can be hammer forged, seldom used

ZK31-T5: High strength, medium weldability

ZK60A-T5: Strength similar to AZ80A-T5, but higher ductility

ZK61-T5: Similar to AZ60A-T5

ZM21-F: Good forgeability, medium strength, good damping capacity

Extruded bars and shapes

AZ10A-F: Low cost, moderate strength

AZ31B and C-F: Medium strength

AZ61A-F: Moderate cost, good strength

AZ80A-T5: Stronger than AZ61A-F

M1A-F: Low to medium strength, good corrosion resistance and damping capacity

ZC71-T6: Medium cost, good strength and ductility

ZK21A-F: Moderate strength, good weldability

ZK31-T5: High strength, medium weldability

ZK40A-T5: High strength, more extrudable than ZK60A, not weldable

ZK60A-T5: High strength, not weldable

ZM21-F: Good formability and damping capacity, medium strength

Sheet and plate

AZ31B-H24: Medium strength

ZM21-0: Good formability and damping capacity

ZM21-H24: Medium strength

Table 1: Magnesium Alloy Mechanical Properties

Property AM-lite AZ91D
Yield stress (0.2% proof), MPa 160-170 120-150
Ultimate tensile strenght, MPa 230-250 180-205
Young's modulus, GPa 45 44
Elastic limit, MPa ~100 ~40
Tensile elongation, % 3-4 3-4

Table 2: Magnesium Alloy Composition

Alloy Al Mn Zn Si Cu Fe Ni Other
AZ31B 2.8-3.2% 0.35% max 1.0% -- -- -- -- --
AZ61A 5.8-7.2% 0.15 max 0.40-1.5% 0.10% max 0.05% max 0.005% max 0.005% max 0.30% max
AZ80A 7.9-9.2% 0.15 min 0.2-0.8% 0.05% max 0.05% max 0.005% max 0.005% max 0.30% max
AZ91A 8.3-9.7% 0.13 max 0.35-1.0% 0.50% max 0.10% max 0 0.03% max 0.30% max
AZ91B 8.3-9.7% 0.13% max 0.35-1.0% 0.50% 0.35% max --- 0.03% max 0.30% max.
AZ91C 8.1-9.3% 0.13% min 0.4-1.0% 0.30% max 0.10% max --- 0.01% max 0.30% max
AZ91D 8.3-9.7% 0.15% min 0.35-1.0% 0.10% max 0.03% max 0.005% max 0.002% max Other
AZ91E 8.1-9.3% 0.17-0.35% 0.4-1.0% 0.20% max 0.015% max 0.005% max 0.001% max 0.30% max
AM60A 5.5-6.5% 0.13% max 0.22% max 0.50% max 0.35% max -- 0.03% max ---
AM60B 5.5-6.5% 0.25% max 0.22% max 0.10% max 0.10% max 0.005% max 0.002% max 0.003% max

UNS numbers