Cast Magnesium Alloys
Cast magnesium alloys are Mg-Al based: 9 % aluminum with 1 % zinc in AZ91D for fluidity and strength, 5–6 % aluminum without zinc in AM50A and AM60B for ductility, and aluminum with silicon in AS41B for creep resistance. AZ91D die castings yield about 150 MPa with 3 % elongation, AM60B about 130 MPa with 8 %, and both fill walls of 1–1.5 mm in hot-chamber machines at faster cycles and longer die life than aluminum because magnesium does not solder to steel. The "D" and "B" suffixes mark the high-purity versions (iron, nickel and copper capped) that corrode an order of magnitude slower than the older grades — the only ones worth specifying today.
Popular cast magnesium grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| AZ91D | 160 | 230 | 1.81 | Excellent | Fair | The default die-casting alloy; housings and brackets |
| AM60B | 130 | 225 | 1.8 | Excellent | Fair | Ductile crash structures; steering wheels, seat frames |
| AM50A | 125 | 230 | 1.77 | Excellent | Poor | Thin, high-elongation impact parts |
| AS41B | 140 | 215 | 1.77 | Excellent | Fair | Creep-resistant die castings to 150 °C |
| AZ91E | 145 | 275 | 1.81 | Excellent | Very good | High-purity aerospace sand castings, T6 |
| AZ92A | 145 | 275 | 1.82 | Excellent | Good | Stronger sand and permanent-mold castings |
| AM100A | 152 | 275 | 1.81 | Excellent | Good | Pressure-tight permanent-mold castings |
Choose cast magnesium for
Thin-wall housings and structural frames in volume — laptop and camera bodies, power-tool housings, steering wheels, seat and instrument-panel structures, transmission and clutch housings, drone and e-bike frames — where a 30 % weight saving over an aluminum die casting, thinner walls and longer die life pay for the conversion coating and the galvanic design rules.
Look elsewhere when
The casting runs wet, salty or bolted bare to steel (A380 aluminum), it carries sustained load above about 120–150 °C (WE43 or EV31A for magnesium, A356-T6 aluminum otherwise), it needs more than about 160 MPa yield or real fatigue life (A356-T6 or a forged ZK60A), it is a large or thick casting where magnesium loses its cycle-time advantage, or the volume is too low for a die — then machine the prototype from AZ31B plate.
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Cast magnesium by application
- Electronics and tool housings
- AZ91D hot-chamber die cast at 1–1.5 mm walls, or thixomolded to 0.6 mm for laptop and camera shells; AM60B where the housing must survive a drop test without cracking.
- Automotive structure and safety parts
- AM60B and AM50A for steering-wheel armatures, seat frames, cross-car beams and door inners that must deform rather than shatter; AZ91D for covers, brackets and mounts that are not crash-loaded.
- Powertrain covers at temperature
- AS41B or AS21 for valve covers, oil pans and gearbox housings at 120–150 °C where AZ91D bolted joints relax; for 200 °C and above the rare-earth alloys EV31A and WE43 take over.
- Aerospace and low-volume castings
- AZ91E-T6 sand or investment castings for gearbox and accessory housings, with corrosion resistance far ahead of the older AZ91C; AZ92A-T6 and AM100A-T61 for permanent-mold housings that must hold pressure.
Working with cast magnesium
- Die casting
- Hot-chamber for AZ91D, AM60B, AM50A and AS41B: walls 1–1.5 mm (0.6 mm by thixomolding), draft 0.5–1.5 °, as-cast tolerance about ±0.1 mm on the first 25 mm, and cycle times 20–30 % shorter than aluminum because the melt is at 650–680 °C and does not attack the die. Dies last two to three times longer than for A380. Sand, investment and permanent-mold casting handle AZ91E, AZ92A and AM100A with zirconium-free grain refinement and protective fluxes or cover gas.
- Machining
- Light and fast — die castings need only facing, drilling and tapping, done dry or with mineral oil at high speed, sharp tools and coarse chips. Tap threads rather than cast them; roll-formed thread inserts or coarse pitches hold better in the soft alloy, and steel inserts must be isolated from the casting.
- Heat treatment
- Die castings are used as cast (F) — the gas porosity blisters in a T4 solution treatment. Sand and permanent-mold castings in AZ91C, AZ91E, AZ92A and AM100A are solution-treated at about 415 °C and aged to T6 (or aged directly to T5) for 20–40 % more yield; a 200 °C stabilizing anneal on AZ91D castings improves dimensional stability before precision machining.
- Finishing and corrosion control
- A conversion coating is mandatory: chrome-free phosphate-permanganate or chromate for indoor parts, an anodic layer (HAE, Tagnite, Keronite plasma electrolytic oxide) under powder or e-coat for anything outdoors or automotive. Every steel fastener or insert is insulated with a coated washer, sleeve or adhesive; resin impregnation seals castings that must hold oil or pressure.
Other magnesium alloy series
Cast Magnesium Alloys — frequently asked
What is cast magnesium?
Cast magnesium alloys are Mg-Al based: 9 % aluminum with 1 % zinc in AZ91D for fluidity and strength, 5–6 % aluminum without zinc in AM50A and AM60B for ductility, and aluminum with silicon in AS41B for creep resistance. AZ91D die castings yield about 150 MPa with 3 % elongation, AM60B about 130 MPa with 8 %, and both fill walls of 1–1.5 mm in hot-chamber machines at faster cycles and longer die life than aluminum because magnesium does not solder to steel. The "D" and "B" suffixes mark the high-purity versions (iron, nickel and copper capped) that corrode an order of magnitude slower than the older grades — the only ones worth specifying today.
Which grade of cast magnesium should I use?
AZ91D for about 90 % of magnesium die castings — housings, brackets, frames, covers — because it casts best, is strongest as cast (about 230 MPa tensile) and is what every die caster runs daily. AM60B when the part must absorb impact without fracturing: steering-wheel armatures, seat frames, instrument-panel beams, at 8–10 % elongation against 3 %. AM50A pushes ductility further for thin crash structures; AM20 is the extreme case. AS41B (and AS21) for gearbox and engine covers that see 150 °C, where AZ91D creeps. For sand, investment or permanent-mold castings the grades change: AZ91E is the high-purity aerospace alloy for T6 sand castings, AZ92A and AM100A give about 150 MPa yield with pressure tightness in permanent molds, and AZ63A is the general sand-casting and anode alloy.
Which grade of cast magnesium is the strongest?
AZ91D Powder has the highest yield strength in the series at 245 MPa; MC3 follows at 165 MPa. Values are for each grade's default condition.
Which grade of cast magnesium is easiest to machine?
AZ91D (machinability excellent, 98/100), then ML5 (98/100).
Is cast magnesium heat-treatable?
Some grades are. Check the conditions listed on each grade page.
AZ91D or AM60B?
AZ91D when the part is a housing or bracket that is not crash-loaded: it fills thinner walls, is about 15 % stronger (150 versus 130 MPa yield) and is what the die caster runs by default. AM60B when the part must bend before it breaks — steering wheels, seat frames, anything that is impact-tested — because its 8–10 % elongation is three times that of AZ91D and it absorbs the energy without the brittle fracture that cost early magnesium seat frames their approvals. Castability and corrosion are similar in the high-purity grades; the choice is ductility against strength.
Magnesium AZ91D or aluminum A380 for a die casting?
AZ91D weighs 1.81 g/cm³ against 2.71 for A380 — a third lighter for the same wall — casts thinner (1 mm against 1.5–2 mm), machines faster and lasts two to three times longer in the die because it does not solder to steel. A380 is marginally stronger (about 160 versus 150 MPa yield, with similar 3–3.5 % elongation), far better in water, salt and dissimilar-metal contact, holds sustained load above 120 °C and needs no conversion coat indoors. Choose AZ91D when the design is sized by weight and stiffness and lives indoors or under paint; choose A380 for wet, hot or corrosion-critical parts.