Magnesium Alloy HK31A
ASTM HK31A · UNS M13310
Mg-Th-Zr wrought sheet alloy retaining strength up to about 350°C, historically used in aerospace heat-shield and elevated-temperature structural panels before thorium-bearing alloys fell out of favor.
Values for the H24 condition
HK31A tempers and conditions
HK31A is supplied in 4 conditions, soft to hard. H24 is the default FabDigit quotes; the values on this page are for it.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
As fabricated | As-cast condition used only for non-critical parts or as the starting state before T6 solution/aging. | 95 | 185 | 5 | 50 HB | 26 % IACS |
Solution heat treated and artificially aged | Cast HK31A per ASTM B80 for elevated-temperature housings and covers where creep resistance to ~350 °C matters more than absolute strength. | 105 | 220 | 8 | 55 HB | 92 W/m·K |
Annealed | Choose when maximum ductility for warm forming/deep drawing is needed; strength then restored partly by post-form stress relief. | 140 | 230 | 23 | 45 HB | 115 W/m·K |
H24Default Strain hardened and partially annealed, half hard | Standard supply condition for HK31A sheet and plate; best strength/creep combination for hot structures to ~315 °C. | 200 | 255 | 9 | 57 HB | 111 W/m·K |
What is HK31A?
Mg-Th-Zr wrought sheet alloy retaining strength up to about 350°C, historically used in aerospace heat-shield and elevated-temperature structural panels before thorium-bearing alloys fell out of favor. HK31A has a density of 1.79 g/cm³ (0.0647 lb/in³), lighter than 73% of magnesium alloy grades. It melts at 588°C (1,090 °F). HK31A has a yield strength of 200 MPa (29 ksi) and a tensile strength of 255 MPa (37 ksi) — stronger than 88% of magnesium alloy grades. Elongation at break is 9% and the elastic modulus is 45 GPa (6.53 Msi).
What is HK31A used for?
- Aerospace heat-shield panels
- Elevated-temperature structural skins
- Engine fittings
- Missile and airframe sheet components
- High-temperature sand castings
- Ducting and shroud panels
Advantages
- High service temperature — 315°C (599 °F), better than 100% of magnesium alloy grades
- High strength — 200 MPa (29 ksi), better than 88% of magnesium alloy grades
- Forms and bends easily — 35/100, better than 87% of magnesium alloy grades
- High electrical conductivity — 28 % IACS, better than 85% of magnesium alloy grades
HK31A properties
Typical room-temperature values for HK31A-H24; bars are the position among magnesium alloy grades.
Physical3
HK31A has a density of 1.79 g/cm³ (0.0647 lb/in³), lighter than 73% of magnesium alloy grades. It melts at 588°C (1,090 °F).
Mechanical11
HK31A has a yield strength of 200 MPa (29 ksi) and a tensile strength of 255 MPa (37 ksi) — stronger than 88% of magnesium alloy grades. Elongation at break is 9% and the elastic modulus is 45 GPa (6.53 Msi).
Thermal6
HK31A is rated for continuous service to 315°C (599 °F). It conducts heat at 111 W/m·K (64.1 BTU/hr·ft·°F), better than 68% of magnesium alloy grades. Thermal expansion is 26.1 µm/m·K (14.5 µin/in·°F).
Electrical3
HK31A conducts electricity at 28 % IACS, better than 85% of magnesium alloy grades.
Chemical & Environmental3
Corrosion resistance is poor (20/100), worse than 77% of magnesium alloy grades.
Sustainability4
Producing a kilogram of HK31A takes about 350 MJ of energy and emits 32 kg of CO₂ — more than 74% of magnesium alloy grades. Typical recycled content is 5%.
Manufacturability8
HK31A's machinability is excellent (95/100, better than 54% of magnesium alloy grades); weldability very good (70/100); formability fair (35/100).
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. HK31A is highlighted; hover a dot for its name, or open the interactive family chart.
Working with HK31A
Is HK31A easy to machine?
Machines extremely easily at high speed with sharp tools and generous rake, but fine chips are flammable — no water-based coolant, keep chips dry, ground and swept up; thorium content requires dust/swarf controlled as radioactive material.
Can HK31A be welded?
GTAW/GMAW in argon with HK31A or EZ33A filler gives good joints; preheat 150–260 °C for thick sections and stress relieve after welding to limit SCC and distortion.
Can HK31A be formed, bent or molded?
Form warm at 230–320 °C (O temper preferred); cold bending is limited to generous radii because of the hcp structure — sand castings are poured in dry sand with SF6-free inhibited cover gas.
Manufacturability
The process limits FabDigit's quote engine applies to HK31A. Design inside these and the part quotes instantly; outside them it routes to an engineer.
CNC machining
| Machinability | Excellent95 / 100 |
|---|---|
| ISO material group | N.7 |
| Cutting speed (rough / finish) | 400 / 460 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1.5 mm |
| Drill depth limit | 8× diameter |
| Best surface (machined / polished) | Ra 0.8 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair35 / 100 |
|---|---|
| Weldability | Good70 / 100 |
| Bendable | Yes |
HK31A 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 |
|---|---|---|
| Thradioactive alloying addition; source-material controls apply | 2.5 – 4 | 3.25 |
| Zrgrain refiner | 0.4 – 1 | 0.7 |
| Cuimpurity limit | ≤ 0.1 | |
| Niimpurity limit, corrosion critical | ≤ 0.01 | |
| Feimpurity limit | ≤ 0.01 | |
| Others (each)total others 0.30 max | ≤ 0.05 | |
| Mg | balance |
What surface finishes work on HK31A?
Chemical conversion coating (chrome-free or Dow 7) or HAE/Dow 17 anodizing followed by epoxy primer and topcoat is mandatory; isolate from steel, copper and carbon-fibre parts to avoid galvanic attack.
Surface treatments FabDigit runs on magnesium alloy parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Conversion Coating
Organic Coating
Equivalent designations
Standards and trade names that resolve to Magnesium Alloy HK31A in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- M13310
- Trade names
- Thorium Magnesium
- Also called
- HK31A-H24
How much does HK31A cost?
HK31A is a standard-cost magnesium alloy ($$), cheaper than about 59% 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.
HK31A — frequently asked
What is HK31A used for?
HK31A is typically used for aerospace heat-shield panels, elevated-temperature structural skins, engine fittings, missile and airframe sheet components, high-temperature sand castings and ducting and shroud panels. In short: heat-resistant magnesium plate.
What is the yield strength of HK31A?
HK31A has a typical yield strength of 200 MPa (29 ksi) and a tensile strength of 255 MPa (37 ksi) — stronger than 88% of magnesium alloy grades. Strength varies by condition: see the 4 listed tempers.
Is HK31A easy to machine?
Yes — machinability is rated excellent (95/100, better than 54% of magnesium alloy grades). Machines extremely easily at high speed with sharp tools and generous rake, but fine chips are flammable — no water-based coolant, keep chips dry, ground and swept up; thorium content requires dust/swarf controlled as radioactive material.
Can HK31A be welded?
Yes — weldability is rated very good (70/100). GTAW/GMAW in argon with HK31A or EZ33A filler gives good joints; preheat 150–260 °C for thick sections and stress relieve after welding to limit SCC and distortion.
What surface finishes work on HK31A?
Chemical conversion coating (chrome-free or Dow 7) or HAE/Dow 17 anodizing followed by epoxy primer and topcoat is mandatory; isolate from steel, copper and carbon-fibre parts to avoid galvanic attack.
Can HK31A be formed, bent or molded?
Form warm at 230–320 °C (O temper preferred); cold bending is limited to generous radii because of the hcp structure — sand castings are poured in dry sand with SF6-free inhibited cover gas.
What is the maximum service temperature of HK31A?
HK31A is rated for continuous use to about 315°C (599 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between HK31A-H24 and HK31A-F?
H24 is the default condition — standard supply condition for HK31A sheet and plate; best strength/creep combination for hot structures to ~315 °C. F: as-cast condition used only for non-critical parts or as the starting state before T6 solution/aging. Yield strength is 200 MPa in H24 versus 95 MPa in F.
How much does HK31A cost?
HK31A is a standard-cost magnesium alloy ($$), cheaper than about 59% 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.
Can FabDigit make parts in HK31A?
Yes — HK31A is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM B90/B90M — Magnesium-Alloy Sheet and Plate — ASTM International (2021)
- ASTM B80 — Magnesium-Alloy Sand Castings — ASTM International (2015)
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- ASM Specialty Handbook: Magnesium and Magnesium Alloys — ASM International (1999)
- ASM Handbook Vol.13B — Corrosion: Materials — ASM International (2005)
- MMPDS / MIL-HDBK-5 magnesium sheet allowables — FAA/Battelle (2019)
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.