Magnesium Alloy AS21
ASTM AS21 · EN MC21310, MgAl2Si
AS21 (AS21A, UNS MC21310, MgAl2Si) is a Mg-Al-Si die-casting alloy in which fine Mg2Si particles raise creep resistance for lightly loaded powertrain parts, supplied as F and F-GRAV.
Reference datasheet — AS21 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the F condition
AS21 tempers and conditions
AS21 is supplied in 2 conditions, soft to hard. F is the default FabDigit quotes; the values on this page are for it.
Compare all 2 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
F | Rare, prototype-oriented condition: slower cooling coarsens the Mg2Si eutectic, so strength, ductility and creep performance all fall below HPDC values. | 90 | 150 | 5 | 48 HB | 15 % IACS |
FDefault As fabricated | Standard commercial condition: hot-chamber/cold-chamber HPDC parts used as cast, with rapid solidification giving fine Mg2Si for creep resistance to ~150 °C. | 120 | 220 | 13 | 55 HB | 68 W/m·K |
What is AS21?
AS21 (AS21A, UNS MC21310, MgAl2Si) is a Mg-Al-Si die-casting alloy in which fine Mg2Si particles raise creep resistance for lightly loaded powertrain parts, supplied as F and F-GRAV. It offers 120 MPa yield, 220 MPa tensile, 13 % elongation, 55 HB, 68 W/m·K conductivity and service to 150 °C, with a machinability rating of 95. Silicon lowers fluidity so very thin ribs are difficult, weldability scores 55 and corrosion resistance only 33, so coating and fastener isolation are required. AM60 or AZ91 are the alternatives when creep resistance is not the driver. AS21 has a density of 1.76 g/cm³ (0.0636 lb/in³), lighter than 94% of magnesium alloy grades. It melts at 565°C (1,049 °F). AS21 has a yield strength of 120 MPa (17.4 ksi) and a tensile strength of 220 MPa (31.9 ksi) — weaker than 77% of magnesium alloy grades. Elongation at break is 13% and the elastic modulus is 45 GPa (6.53 Msi).
What is AS21 used for?
- engine covers
- transmission housings
- creep-resistant brackets
Advantages
- Good corrosion resistance — 33/100, better than 99% of magnesium alloy grades
- Ductile — tolerates forming and impact — 13%, better than 80% of magnesium alloy grades
Limitations
- Hard to polish — 45/100, worse than 93% of magnesium alloy grades
- Poor heat conductor — 68 W/m·K (39.3 BTU/hr·ft·°F), worse than 81% of magnesium alloy grades
- Low strength — 120 MPa (17.4 ksi), worse than 77% of magnesium alloy grades
AS21 properties
Typical room-temperature values for AS21-F; bars are the position among magnesium alloy grades.
Physical3
AS21 has a density of 1.76 g/cm³ (0.0636 lb/in³), lighter than 94% of magnesium alloy grades. It melts at 565°C (1,049 °F).
Mechanical13
AS21 has a yield strength of 120 MPa (17.4 ksi) and a tensile strength of 220 MPa (31.9 ksi) — weaker than 77% of magnesium alloy grades. Elongation at break is 13% and the elastic modulus is 45 GPa (6.53 Msi).
Thermal6
AS21 is rated for continuous service to 150°C (302 °F). It conducts heat at 68 W/m·K (39.3 BTU/hr·ft·°F), worse than 81% of magnesium alloy grades. Thermal expansion is 26.1 µm/m·K (14.5 µin/in·°F).
Electrical3
AS21 conducts electricity at 16 % IACS, worse than 54% of magnesium alloy grades.
Chemical & Environmental3
Corrosion resistance is poor (33/100), better than 99% of magnesium alloy grades.
Sustainability4
Producing a kilogram of AS21 takes about 340 MJ of energy and emits 32 kg of CO₂ — more than 59% of magnesium alloy grades. Typical recycled content is 25%.
Manufacturability8
AS21's machinability is excellent (95/100, better than 54% of magnesium alloy grades); weldability good (55/100); formability poor (20/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the magnesium alloy family
Yield strength against density for every magnesium alloy grade FabDigit runs. AS21 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with AS21
Is AS21 easy to machine?
Cuts extremely freely with sharp, high-rake carbide tools and high speeds; run dry or with mineral oil (never water-based) and manage fine chips/dust as a fire hazard.
Can AS21 be welded?
GTAW/GMAW with AZ61/AZ92 or matching Mg filler works on gravity castings; HPDC AS21 welds poorly due to entrapped gas porosity — prefer mechanical joining or FSW.
Can AS21 be formed, bent or molded?
HPDC alloy: pour ~680–700 °C with fast fill and high cooling rate to keep Mg2Si fine; Si reduces fluidity so avoid very thin ribs, and protect the melt with SF6-free cover gas (SO2/HFC-134a).
AS21 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Alkept low to suppress Mg17Al12, the phase that causes AZ91 creep | 1.4 – 2.5 | 2.2 |
| Siforms Chinese-script/fine Mg2Si for grain-boundary pinning | 0.7 – 1.2 | 1 |
| Mniron control for corrosion resistance | 0.2 – 0.6 | 0.4 |
| Zn | ≤ 0.25 | 0.1 |
| Cuhigh-purity limit | ≤ 0.01 | |
| Nihigh-purity limit | ≤ 0 | |
| Fehigh-purity limit, Fe/Mn ratio controlled | ≤ 0 | |
| Others (each) | ≤ 0.01 | |
| Mg | balance |
What surface finishes work on AS21?
Not anodizable in the aluminium sense — use chromate-free conversion coating (ASTM D1732), Dow 17/HAE or PEO, then epoxy e-coat/powder; isolate all steel and aluminium fasteners to prevent galvanic attack.
Equivalent designations
Standards and trade names that resolve to Magnesium Alloy AS21 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- AS21A
- EN / DIN / Werkstoff-Nr.
- MC21310MgAl2Si
How much does AS21 cost?
AS21 is a standard-cost magnesium alloy ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
AS21 — frequently asked
What is AS21 used for?
AS21 is typically used for engine covers, transmission housings and creep-resistant brackets. In short: creep-resistant Mg die casting; 150 °C service, above AZ91; lower fluidity than AZ91.
What is the yield strength of AS21?
AS21 has a typical yield strength of 120 MPa (17.4 ksi) and a tensile strength of 220 MPa (31.9 ksi) — weaker than 77% of magnesium alloy grades. Strength varies by condition: see the 2 listed tempers.
Is AS21 easy to machine?
Yes — machinability is rated excellent (95/100, better than 54% of magnesium alloy grades). Cuts extremely freely with sharp, high-rake carbide tools and high speeds; run dry or with mineral oil (never water-based) and manage fine chips/dust as a fire hazard.
Can AS21 be welded?
Yes — weldability is rated good (55/100). GTAW/GMAW with AZ61/AZ92 or matching Mg filler works on gravity castings; HPDC AS21 welds poorly due to entrapped gas porosity — prefer mechanical joining or FSW.
What surface finishes work on AS21?
Not anodizable in the aluminium sense — use chromate-free conversion coating (ASTM D1732), Dow 17/HAE or PEO, then epoxy e-coat/powder; isolate all steel and aluminium fasteners to prevent galvanic attack.
Can AS21 be formed, bent or molded?
HPDC alloy: pour ~680–700 °C with fast fill and high cooling rate to keep Mg2Si fine; Si reduces fluidity so avoid very thin ribs, and protect the melt with SF6-free cover gas (SO2/HFC-134a).
What is the maximum service temperature of AS21?
AS21 is rated for continuous use to about 150°C (302 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between AS21-F and AS21 F-GRAV?
F is the default condition — standard commercial condition: hot-chamber/cold-chamber HPDC parts used as cast, with rapid solidification giving fine Mg2Si for creep resistance to ~150 °C. F-GRAV: rare, prototype-oriented condition: slower cooling coarsens the Mg2Si eutectic, so strength, ductility and creep performance all fall below HPDC values. Yield strength is 120 MPa in F versus 90 MPa in F-GRAV.
How much does AS21 cost?
AS21 is a standard-cost magnesium alloy ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM B94 — Standard Specification for Magnesium-Alloy Die Castings — ASTM International (2018)
- ASM Specialty Handbook: Magnesium and Magnesium Alloys — ASM International (1999)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.