Magnesium Alloy ZK40A
ASTM ZK40A · UNS M16400
ZK40A is a zirconium-grain-refined Mg-Zn sand casting alloy (UNS M16400) with no rare-earth additions, supplied as-cast (F) or aged to T5.
Reference datasheet — ZK40A 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 T5 condition
ZK40A tempers and conditions
ZK40A is supplied in 2 conditions, soft to hard. T5 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 |
|---|---|---|---|---|---|---|
As fabricated | Pick for lightly loaded castings where the T5 age is not economical; lower yield strength but the best as-cast ductility. | 120 | 220 | 6 | 55 HB | 27 % IACS |
T5Default Cooled from hot working and artificially aged | Standard supplied condition (ASTM B80): a simple single-step age that raises yield strength and stabilises dimensions with no solution treatment or quench distortion. | 145 | 250 | 5 | 65 HB | 117 W/m·K |
What is ZK40A?
ZK40A is a zirconium-grain-refined Mg-Zn sand casting alloy (UNS M16400) with no rare-earth additions, supplied as-cast (F) or aged to T5. Engineers pick it for good ductility at moderate strength — 145 MPa yield, 250 MPa tensile, 5% elongation, 65 HB — together with 117 W/m·K thermal conductivity and a machinability score of 95, in sand-cast brackets, housings and fittings. Service is capped at 120 °C, the Zn-rich chemistry is hot-crack sensitive so welded construction is avoided, and a conversion coating plus paint is mandatory for corrosion protection. ZK51A and ZK61A are the next steps up in strength. ZK40A has a density of 1.83 g/cm³ (0.0661 lb/in³), heavier than 81% of magnesium alloy grades. It melts at 550°C (1,022 °F). ZK40A has a yield strength of 145 MPa (21 ksi) and a tensile strength of 250 MPa (36.3 ksi) — stronger than 51% of magnesium alloy grades. Elongation at break is 5% and the elastic modulus is 45 GPa (6.53 Msi).
What is ZK40A used for?
- Sand-cast structural brackets
- Aerospace fittings
- Lightly loaded equipment housings
- Instrument mounting plates
- Accessory and gearbox covers
- Weight-critical non-pressurised castings
Advantages
- High electrical conductivity — 29 % IACS, better than 91% of magnesium alloy grades
- Conducts heat well — 117 W/m·K (67.6 BTU/hr·ft·°F), better than 80% of magnesium alloy grades
Limitations
- Hard to polish — 45/100, worse than 93% of magnesium alloy grades
- Difficult to weld — 30/100, worse than 90% of magnesium alloy grades
- Limited service temperature — 120°C (248 °F), worse than 78% of magnesium alloy grades
ZK40A properties
Typical room-temperature values for ZK40A-T5; bars are the position among magnesium alloy grades.
Physical3
ZK40A has a density of 1.83 g/cm³ (0.0661 lb/in³), heavier than 81% of magnesium alloy grades. It melts at 550°C (1,022 °F).
Mechanical13
ZK40A has a yield strength of 145 MPa (21 ksi) and a tensile strength of 250 MPa (36.3 ksi) — stronger than 51% of magnesium alloy grades. Elongation at break is 5% and the elastic modulus is 45 GPa (6.53 Msi).
Thermal6
ZK40A is rated for continuous service to 120°C (248 °F). It conducts heat at 117 W/m·K (67.6 BTU/hr·ft·°F), better than 80% of magnesium alloy grades. Thermal expansion is 27 µm/m·K (15 µin/in·°F).
Electrical3
ZK40A conducts electricity at 29 % IACS, better than 91% of magnesium alloy grades.
Chemical & Environmental3
Corrosion resistance is poor (20/100), worse than 77% of magnesium alloy grades.
Sustainability4
Producing a kilogram of ZK40A takes about 290 MJ of energy and emits 28 kg of CO₂ — less than 99% of magnesium alloy grades. Typical recycled content is 15%.
Manufacturability8
ZK40A's machinability is excellent (95/100, better than 54% of magnesium alloy grades); weldability poor (30/100); 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. ZK40A is highlighted; hover a dot for its name, or open the interactive family chart.
Working with ZK40A
Is ZK40A easy to machine?
Outstanding machinability at high speeds with sharp positive-rake tools and low forces; keep chips dry and never allow fine swarf to accumulate — use flood mineral-oil coolant, never water-based.
Can ZK40A be welded?
Poor: the Zn-rich, RE-free chemistry is hot-crack sensitive, so GTAW repair with EZ33A/ZK filler must be preheated and stress-relieved, and welded structures are generally avoided.
Can ZK40A be formed, bent or molded?
Sand or permanent-mould casting with zirconium-bearing melt practice; hold pouring temperature and grain-refinement carefully, add generous risering because of hot-tear tendency and a fairly narrow freezing range.
ZK40A 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 strengthener | 3.5 – 4.5 | 4 |
| Zrgrain refiner, 0.45 % minimum | 0.45 – 1 | 0.7 |
| Others (total)total impurities per ASTM B80 | ≤ 0.3 | |
| Mg | balance |
What surface finishes work on ZK40A?
No sulfuric anodizing — use chromate-free or Dow 17/HAE conversion/anodic coatings, then epoxy primer and topcoat; isolate all steel and copper-alloy fasteners to avoid galvanic attack.
Equivalent designations
Standards and trade names that resolve to Magnesium Alloy ZK40A in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- M16400
- ASTM
- ZK40A-T5
How much does ZK40A cost?
ZK40A is a premium-cost magnesium alloy ($$$), cheaper than about 51% 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.
ZK40A — frequently asked
What is ZK40A used for?
ZK40A is typically used for sand-cast structural brackets, aerospace fittings, lightly loaded equipment housings, instrument mounting plates, accessory and gearbox covers and weight-critical non-pressurised castings. In short: rare-earth-free Mg casting; ductile ZK-series grade; near-top magnesium machinability.
What is the yield strength of ZK40A?
ZK40A has a typical yield strength of 145 MPa (21 ksi) and a tensile strength of 250 MPa (36.3 ksi) — stronger than 51% of magnesium alloy grades. Strength varies by condition: see the 2 listed tempers.
Is ZK40A easy to machine?
Yes — machinability is rated excellent (95/100, better than 54% of magnesium alloy grades). Outstanding machinability at high speeds with sharp positive-rake tools and low forces; keep chips dry and never allow fine swarf to accumulate — use flood mineral-oil coolant, never water-based.
Can ZK40A be welded?
Not readily — weldability is rated poor (30/100). Poor: the Zn-rich, RE-free chemistry is hot-crack sensitive, so GTAW repair with EZ33A/ZK filler must be preheated and stress-relieved, and welded structures are generally avoided.
What surface finishes work on ZK40A?
No sulfuric anodizing — use chromate-free or Dow 17/HAE conversion/anodic coatings, then epoxy primer and topcoat; isolate all steel and copper-alloy fasteners to avoid galvanic attack.
Can ZK40A be formed, bent or molded?
Sand or permanent-mould casting with zirconium-bearing melt practice; hold pouring temperature and grain-refinement carefully, add generous risering because of hot-tear tendency and a fairly narrow freezing range.
What is the maximum service temperature of ZK40A?
ZK40A 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 ZK40A-T5 and ZK40A-F?
T5 is the default condition — standard supplied condition (ASTM B80): a simple single-step age that raises yield strength and stabilises dimensions with no solution treatment or quench distortion. F: pick for lightly loaded castings where the T5 age is not economical; lower yield strength but the best as-cast ductility. Yield strength is 145 MPa in T5 versus 120 MPa in F.
How much does ZK40A cost?
ZK40A is a premium-cost magnesium alloy ($$$), cheaper than about 51% 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 B80 — Standard Specification for Magnesium-Alloy Sand Castings — ASTM (2020)
- SAE/UNS M16400 alloy designation listing — SAE International (2017)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- ASM Specialty Handbook: Magnesium and Magnesium Alloys — ASM International (1999)
- MatWeb cast magnesium alloy datasheets — MatWeb LLC (2024)
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.