Handheld electronics
Camera bodies, laptop chassis, professional video gear, drone frames. Light + EMI shielding + thermal management in one alloy.
Mg-Al-Zn alloy · UNS M11311
Magnesium AZ31
The lightest commercial structural metal — 1.78 g/cc, about 2/3 the density of aluminum. AZ31 is the workhorse magnesium alloy for aerospace, electronics housings, optical fixtures, and racing applications where every gram matters. Requires special machining precautions due to chip flammability.
UTS
285 MPa
Density
1.78 g/cc
Modulus
45 GPa
Mach.
100 /100
Fire safety
Solid magnesium is safe to handle — bulk material is hard to ignite. Fine chips, dust, and shavings are highly combustible and burn at 3,100 °C. NEVER use water-based coolant — water + burning Mg = hydrogen explosion. We machine magnesium with mineral oil or air-only, dedicated chip collection, separate dust collector, and Class D extinguishers (sand or NaCl) on hand. Roughing may run dry on light cuts; fine finishing operations use a light mineral-oil mist.
When to use
Pick magnesium when grams matter most.
AZ31 is roughly 35% lighter than aluminum, 80% lighter than steel. Combined with reasonable strength (UTS 285 MPa) and fast machining, it’s the go-to alloy for handheld electronics housings (cameras, laptops, drones), aerospace structural elements where pounds count, optical fixtures (excellent damping), and motorsport hardware.
The drawbacks: lower modulus than aluminum (more flex per pound), poor corrosion resistance (galvanic risk + atmospheric oxidation), and the machining safety overhead. For applications where corrosion or galvanic compatibility is critical, magnesium often loses to aluminum despite the weight savings.
Strengths
Why every gram counts.
- Lightest structural metal1.78 g/cc — 2/3 of aluminum, 1/4 of steel. Best strength-to-weight in this strength range.
- Mach 100/100Cuts faster than aluminum. Cycle times drop with light DOC and high feed.
- Excellent dampingDampens vibration far better than aluminum or steel. Used in optical fixtures and audio applications.
- EMI shieldingEffective electromagnetic shielding for electronic enclosures.
- Cast and wrought formsAZ31 commonly available as plate, bar, sheet (wrought). Cast variants (AZ91) for complex shapes.
- RecyclableFully recyclable, lower energy than aluminum to recycle once collected.
Trade-offs
Where you give up.
- Fire / safety overheadFine chips ignite at temperature. Special coolant, ventilation, dust handling, fire suppression. Real ongoing cost.
- Poor corrosion resistanceOxidizes in atmosphere; galvanically incompatible with most other metals. Always anodized, painted, or coated.
- Low modulusModulus 45 GPa = 65% of aluminum. Parts deflect more for given load.
- Galvanic catastrophe vs steel/CuMagnesium is the most anodic engineering metal. Direct steel contact in moisture causes rapid corrosion of the magnesium.
- Limited service temperatureMechanical properties degrade above ~150 °C. Avoid hot environments.
- CostStock cost ~$15-25/lb. More expensive than aluminum per pound — but parts are 35% lighter.
Specs
Mechanical, physical & chemical data.
Mechanical
Properties (H24 extruded bar)
| Ultimate tensile strength | 285 MPa (41 ksi) |
|---|---|
| Yield strength (0.2% offset) | 200 MPa (29 ksi) |
| Elongation at break | 15% |
| Modulus of elasticity | 45 GPa |
| Shear modulus | 17 GPa |
| Hardness (H24) | 73 HB |
| Compressive yield strength | 165 MPa |
| Endurance limit 5×10⁸ cycles | 100 MPa |
Source: ASTM B107. Cast AZ91 grades reach UTS 240 MPa. AZ31B-O (annealed sheet): UTS 220 MPa, more formable.
Physical & thermal
At room temperature
| Density | 1.78 g/cc (0.0643 lb/in³) |
|---|---|
| Melting range | 605 – 630 °C |
| Specific heat | 1.04 J/g·°C |
| Thermal conductivity | 96 W/m·K |
| CTE (20–100 °C) | 26 µm/m·°C |
| Electrical conductivity | 18 – 19% IACS |
| Magnetic | Non-magnetic |
| Ignition (chip) | ~482 °C |
High specific heat is one of the few favorable safety factors — large parts absorb heat slowly. Fine chips don't have that protection.
Composition
Chemistry, weight %
| Aluminum (Al) | 2.5 – 3.5 |
|---|---|
| Zinc (Zn) | 0.6 – 1.4 |
| Manganese (Mn) | 0.20 min |
| Silicon (Si) | 0.10 max |
| Copper (Cu) | 0.05 max |
| Iron (Fe) | 0.005 max |
| Nickel (Ni) | 0.005 max |
| Magnesium (Mg) | balance (~95%) |
Strict limits on Cu, Fe, and Ni — these elements dramatically accelerate corrosion of magnesium. AZ31B specification is widely standardized.
Specifications
Common purchase specs.
ASTM B107
Bar, rod — extruded magnesium
ASTM B90
Sheet, plate — magnesium alloy
AMS 4377
Sheet, plate — AZ31B-H24
AMS 4375
Sheet, plate — AZ31B-O (annealed)
MIL-M-44067
Forgings
UNS M11311
Unified numbering — AZ31B
DIN MgAl3Zn1 / 3.5312
European equivalent
ASTM B275
Codification of magnesium alloys
Machining
How we cut it — safely.
Magnesium machines beautifully if handled correctly. Sharp tools, high speeds, no water. Chip handling is the central concern — small chips hot from the cutter can ignite if they accumulate. Dedicated machine cell, dedicated chip collection, dry process or mineral-oil mist only.
Cutting speed
1,500 – 5,000 SFM with carbide. Spindle-limited on most CNC mills.
Feed rate
Aggressive constant feed. Magnesium doesn’t work-harden.
Tooling
Polished carbide with positive rake. Sharp edges critical for chip control.
NO water-based coolant
Critical safety rule. Burning Mg + water → H₂ explosion. Use mineral oil mist or air only.
Mineral oil mist or dry
Light mineral oil mist for finishing; aggressive roughing often runs dry. Plan for chip cooling.
Chip control & collection
Coarse chips preferred (light DOC = fine chips = ignition risk). Frequent cleanup, dedicated dust collector.
Class D fire extinguishers
Required on hand. Sand or sodium chloride based — water and CO₂ make Mg fires worse.
Surface finish
Gleaming machine finish at 32 µin Ra easily. 16 µin achievable with sharp finishing tool.
Applications
Where AZ31 shows up.
Aerospace & defense
Helicopter gearbox housings, missile fins, satellite structural elements. Where every gram saves fuel or extends range.
Optical & instrumentation
Telescope frames, microscopy fixtures, vibration-critical mounts. Excellent damping properties.
Compare
Related materials.
Standard alt.
Aluminum 6061 →
~50% heavier but no special machining safety. The cost-effective alternative.
Stronger lightweight
Aluminum 7075 →
2× UTS at ~60% more weight than AZ31. When strength matters more than absolute light weight.
High-strength light
Ti-6Al-4V →
2.5× heavier but 3× the strength. For structural elements that need both.
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