Magnesium Alloy EQ21A-T4
Temper
ASTM EQ21A · UNS M18330
T4 = solution heat treated and naturally aged
Intermediate condition between solution treatment and ageing; slightly more ductile but well below T6 strength — rarely sold as a final condition.
Values for the T4 condition
Other EQ21A tempers and conditions
EQ21A is listed in 4 conditions; see the grade overview at EQ21A.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
As fabricated | Foundry intermediate state only; use when the casting will be solution treated later or for non-structural trial parts. | 100 | 175 | 5 | 55 HB | 23 % IACS |
T4This page Solution heat treated and naturally aged | Intermediate condition between solution treatment and ageing; slightly more ductile but well below T6 strength — rarely sold as a final condition. | 110 | 215 | 8 | 60 HB | 21 % IACS |
T6Default Solution heat treated and artificially aged | Standard supply condition for all EQ21A aerospace castings; maximum strength and best creep resistance to ~200 °C. | 195 | 260 | 4 | 80 HB | 113 W/m·K |
hot isostatically pressed then solution treated and aged | For flight-critical castings where residual microporosity must be closed; gives the best fatigue life and ductility scatter. | 195 | 270 | 6 | 82 HB | 25 % IACS |
What is EQ21A-T4?
EQ21A-T4 is EQ21A in the T4 temper — intermediate condition between solution treatment and ageing; slightly more ductile but well below T6 strength — rarely sold as a final condition. EQ21A-T4 has a yield strength of 110 MPa (16 ksi) and a tensile strength of 215 MPa (31.2 ksi) — weaker than 83% of magnesium alloy grades. Elongation at break is 8% and the elastic modulus is 44 GPa (6.38 Msi). EQ21A-T4 has a density of 1.81 g/cm³ (0.0654 lb/in³), heavier than 58% of magnesium alloy grades. It melts at 550°C (1,022 °F). T6 is the default condition FabDigit quotes; T4 is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 19 MPa·√m (17.3 ksi·√in), better than 98% of magnesium alloy grades
- Readily welded — 78/100, better than 94% of magnesium alloy grades
Limitations
- Low strength — 110 MPa (16 ksi), worse than 83% of magnesium alloy grades
EQ21A-T4 properties
Typical room-temperature values for EQ21A-T4; 21 are specific to this condition. Other listed values are EQ21A reference data and may not represent this condition. Bars are the position among magnesium alloy grades.
Physical3
EQ21A-T4 has a density of 1.81 g/cm³ (0.0654 lb/in³), heavier than 58% of magnesium alloy grades. It melts at 550°C (1,022 °F).
Mechanical14
EQ21A-T4 has a yield strength of 110 MPa (16 ksi) and a tensile strength of 215 MPa (31.2 ksi) — weaker than 83% of magnesium alloy grades. Elongation at break is 8% and the elastic modulus is 44 GPa (6.38 Msi).
Thermal6
EQ21A-T4 is rated for continuous service to 150°C (302 °F). It conducts heat at 98 W/m·K (56.6 BTU/hr·ft·°F), better than 54% of magnesium alloy grades. Thermal expansion is 26.7 µm/m·K (14.8 µin/in·°F).
Electrical3
EQ21A-T4 conducts electricity at 21 % IACS, better than 55% of magnesium alloy grades.
Chemical & Environmental3
Corrosion resistance is poor (27/100), better than 75% of magnesium alloy grades.
Sustainability4
Producing a kilogram of EQ21A-T4 takes about 350 MJ of energy and emits 32 kg of CO₂ — more than 74% of magnesium alloy grades. Typical recycled content is 15%.
Manufacturability8
EQ21A-T4's machinability is excellent (88/100, worse than 99% of magnesium alloy grades); weldability very good (78/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with EQ21A-T4
Is EQ21A easy to machine?
Machines extremely easily at high speed with sharp positive-rake tools and no coolant mist — but fine chips are pyrophoric, so keep dry, use flood mineral oil or dedicated chip handling and Class D extinguishers on hand.
Can EQ21A be welded?
Readily TIG/GTAW repair-welded with matching EQ21/QE22 filler under argon; weld local zones require re-solution + re-age (or local re-age) to restore T6 properties.
Can EQ21A be formed, bent or molded?
Casting alloy only — sand and investment cast with Zr-refined melt under SF6-free cover gas; not cold-formable, section design should promote directional solidification.
What surface finishes work on EQ21A?
Chemical conversion coating (chromate-free Mg pretreatment) or anodic processes such as Dow 17/HAE/Tagnite, then epoxy primer and topcoat; insulate all steel/aluminium fastener interfaces to avoid galvanic attack.
EQ21A 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 |
|---|---|---|
| Agsilver, provides age-hardening response with Nd | 1.3 – 1.7 | 1.5 |
| REneodymium-rich rare earth (didymium) | 1.5 – 3 | 2.1 |
| Zrgrain refiner | 0.4 – 1 | 0.7 |
| Cuintentional addition | 0.05 – 0.1 | 0.07 |
| Siimpurity limit | ≤ 0.01 | — |
| Feimpurity limit | ≤ 0.01 | — |
| Niimpurity limit, critical for corrosion | ≤ 0.01 | — |
| Other, each | ≤ 0.01 | — |
| Mg | balance | — |
EQ21A-T4 — frequently asked
What is EQ21A-T4 used for?
EQ21A-T4 is typically used for aerospace gearbox castings, high-strength structural brackets and racing component castings. In short: highest-strength RE magnesium casting; stable to 200 °C; silver-bearing, high cost.
What is the yield strength of EQ21A-T4?
EQ21A-T4 has a typical yield strength of 110 MPa (16 ksi) and a tensile strength of 215 MPa (31.2 ksi) — weaker than 83% of magnesium alloy grades. Strength varies by condition: see the 4 listed tempers.
Is EQ21A-T4 easy to machine?
Yes — machinability is rated excellent (88/100, worse than 99% of magnesium alloy grades). Machines extremely easily at high speed with sharp positive-rake tools and no coolant mist — but fine chips are pyrophoric, so keep dry, use flood mineral oil or dedicated chip handling and Class D extinguishers on hand.
Can EQ21A-T4 be welded?
Yes — weldability is rated very good (78/100). Readily TIG/GTAW repair-welded with matching EQ21/QE22 filler under argon; weld local zones require re-solution + re-age (or local re-age) to restore T6 properties.
What surface finishes work on EQ21A-T4?
Chemical conversion coating (chromate-free Mg pretreatment) or anodic processes such as Dow 17/HAE/Tagnite, then epoxy primer and topcoat; insulate all steel/aluminium fastener interfaces to avoid galvanic attack.
Can EQ21A-T4 be formed, bent or molded?
Casting alloy only — sand and investment cast with Zr-refined melt under SF6-free cover gas; not cold-formable, section design should promote directional solidification.
What is the maximum service temperature of EQ21A-T4?
EQ21A-T4 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 EQ21A-T6 and EQ21A-F?
T6 is the default condition — standard supply condition for all EQ21A aerospace castings; maximum strength and best creep resistance to ~200 °C. F: foundry intermediate state only; use when the casting will be solution treated later or for non-structural trial parts. Yield strength is 195 MPa in T6 versus 100 MPa in F.
Sources
- ASTM B80 — Magnesium-Alloy Sand Castings — ASTM International (2015)
- ASTM B199 — Magnesium-Alloy Permanent Mold Castings — ASTM International (2019)
- ASTM B403 — Magnesium-Alloy Investment Castings — ASTM International (2020)
- ASM Specialty Handbook: Magnesium and Magnesium Alloys — ASM International (1999)
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- Elektron high-strength RE/Ag magnesium casting alloys — Magnesium Elektron (Luxfer MEL Technologies) (2019)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.