Magnesium Alloy ZM21-O (Annealed)
Temper · default condition
ASTM ZM21 · EN MgZn2Mn1 · ISO ISO-WD32350
Pick for maximum room-temperature and warm press formability — deep drawn, stretch-formed or bent panels.
Values for the O condition
Other ZM21 tempers and conditions
ZM21 is listed in 3 conditions; see the grade overview at ZM21.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ODefaultThis page Annealed | Pick for maximum room-temperature and warm press formability — deep drawn, stretch-formed or bent panels. | 140 | 240 | 19 | 45 HB | 29 % IACS |
As fabricated | Default condition for extrusions and forgings where no post-work thermal treatment is applied. | 160 | 250 | 13 | 50 HB | 28 % IACS |
Strain hardened and partially annealed, half hard | Standard structural sheet temper: higher yield strength and stiffness-per-gauge with usable warm formability. | 195 | 265 | 9 | 58 HB | 27 % IACS |
What is ZM21-O?
ZM21-O is ZM21 in the O temper — pick for maximum room-temperature and warm press formability — deep drawn, stretch-formed or bent panels. ZM21-O has a yield strength of 140 MPa (20.3 ksi) and a tensile strength of 240 MPa (34.8 ksi) — weaker than 61% of magnesium alloy grades. Elongation at break is 19% and the elastic modulus is 44 GPa (6.38 Msi). ZM21-O has a density of 1.78 g/cm³ (0.0643 lb/in³), lighter than 78% of magnesium alloy grades. It melts at 605°C (1,121 °F).
Advantages
- Ductile — tolerates forming and impact — 19%, better than 98% of magnesium alloy grades
- Tough — resists crack growth — 19 MPa·√m (17.3 ksi·√in), better than 98% of magnesium alloy grades
- Conducts heat well — 128 W/m·K (74 BTU/hr·ft·°F), better than 93% of magnesium alloy grades
- High electrical conductivity — 29 % IACS, better than 91% of magnesium alloy grades
- Forms and bends easily — 42/100, better than 91% of magnesium alloy grades
Limitations
- High embodied carbon — 36 kg CO₂/kg, worse than 93% of magnesium alloy grades
- Limited service temperature — 120°C (248 °F), worse than 78% of magnesium alloy grades
ZM21-O properties
Typical room-temperature values for ZM21-O; 41 are specific to this condition. Other listed values are ZM21 reference data and may not represent this condition. Bars are the position among magnesium alloy grades.
Physical3
ZM21-O has a density of 1.78 g/cm³ (0.0643 lb/in³), lighter than 78% of magnesium alloy grades. It melts at 605°C (1,121 °F).
Mechanical14
ZM21-O has a yield strength of 140 MPa (20.3 ksi) and a tensile strength of 240 MPa (34.8 ksi) — weaker than 61% of magnesium alloy grades. Elongation at break is 19% and the elastic modulus is 44 GPa (6.38 Msi).
Thermal6
ZM21-O is rated for continuous service to 120°C (248 °F). It conducts heat at 128 W/m·K (74 BTU/hr·ft·°F), better than 93% of magnesium alloy grades. Thermal expansion is 26 µm/m·K (14.4 µin/in·°F).
Electrical3
ZM21-O conducts electricity at 29 % IACS, better than 91% of magnesium alloy grades.
Chemical & Environmental3
Corrosion resistance is poor (26/100), better than 74% of magnesium alloy grades.
Sustainability4
Producing a kilogram of ZM21-O takes about 350 MJ of energy and emits 36 kg of CO₂ — more than 74% of magnesium alloy grades. Typical recycled content is 30%.
Manufacturability8
ZM21-O's machinability is excellent (93/100, worse than 78% of magnesium alloy grades); weldability very good (72/100); formability fair (42/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with ZM21-O
Is ZM21 easy to machine?
Machines faster than any other structural metal — sharp tools, high speed, generous rake, no coolant mist on fine chips; collect and keep dry chips away from water and sparks (fire risk).
Can ZM21 be welded?
Aluminium-free chemistry gives good TIG/MIG weldability with ZM21 or AZ61/AZ92 filler; use argon, clean oxide, preheat thick sections and stress relieve to avoid distortion.
Can ZM21 be formed, bent or molded?
Cold-bend on generous radii only (≥5t); best results warm-forming at 200–300 °C where elongation exceeds 40 % — O temper for deep draws, H24 for shallow forms and rollforming.
What surface finishes work on ZM21?
Chromate-free conversion coating (ASTM D1732) or Mg anodize (HAE/Dow 17/PEO) plus epoxy primer and topcoat; never leave bare in humid or salt service and insulate all steel/CFRP joints.
ZM21 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 |
|---|---|---|
| Znprincipal solid-solution strengthener | 1.75 – 2.5 | 2 |
| Mniron control and corrosion improvement | 0.6 – 1.4 | 1 |
| Alimpurity limit | ≤ 0.05 | — |
| Siimpurity limit | ≤ 0.05 | — |
| Cuimpurity limit | ≤ 0.05 | — |
| Fecritical for corrosion | ≤ 0.01 | — |
| Nicritical for corrosion | ≤ 0.01 | — |
| Others (each)total 0.30 max | ≤ 0.05 | — |
| Mg | balance | — |
ZM21-O — frequently asked
What is ZM21-O used for?
ZM21-O is typically used for sheet stampings, extruded sections and formed components. In short: best-welding wrought magnesium; aluminium-free Zn-Mn sheet alloy; good warm formability.
What is the yield strength of ZM21-O?
ZM21-O has a typical yield strength of 140 MPa (20.3 ksi) and a tensile strength of 240 MPa (34.8 ksi) — weaker than 61% of magnesium alloy grades. Strength varies by condition: see the 3 listed tempers.
Is ZM21-O easy to machine?
Yes — machinability is rated excellent (93/100, worse than 78% of magnesium alloy grades). Machines faster than any other structural metal — sharp tools, high speed, generous rake, no coolant mist on fine chips; collect and keep dry chips away from water and sparks (fire risk).
Can ZM21-O be welded?
Yes — weldability is rated very good (72/100). Aluminium-free chemistry gives good TIG/MIG weldability with ZM21 or AZ61/AZ92 filler; use argon, clean oxide, preheat thick sections and stress relieve to avoid distortion.
What surface finishes work on ZM21-O?
Chromate-free conversion coating (ASTM D1732) or Mg anodize (HAE/Dow 17/PEO) plus epoxy primer and topcoat; never leave bare in humid or salt service and insulate all steel/CFRP joints.
Can ZM21-O be formed, bent or molded?
Cold-bend on generous radii only (≥5t); best results warm-forming at 200–300 °C where elongation exceeds 40 % — O temper for deep draws, H24 for shallow forms and rollforming.
What is the maximum service temperature of ZM21-O?
ZM21-O is rated for continuous use to about 120°C (248 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between ZM21-O and ZM21-H24?
O is the default condition — pick for maximum room-temperature and warm press formability — deep drawn, stretch-formed or bent panels. H24: standard structural sheet temper: higher yield strength and stiffness-per-gauge with usable warm formability. Yield strength is 140 MPa in O versus 195 MPa in H24.
Sources
- ISO 3116 — Magnesium and magnesium alloys, wrought products (MgZn2Mn1 / WD32350) — ISO (2019)
- ASM Specialty Handbook: Magnesium and Magnesium Alloys — ASM International (1999)
- ASM Handbook, Vol. 2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- Wrought magnesium sheet and extrusion alloy data (ZM21/AZ31B) — Magnesium Elektron / Luxfer MEL Technologies (2021)
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.