Rare-Earth Magnesium Alloys
Rare-earth magnesium alloys replace aluminum with yttrium, neodymium, gadolinium or mixed rare earths, grain-refined by zirconium, and gain their strength from precipitates that do not coarsen until well above 200 °C. WE43-T6 holds about 170–195 MPa yield at room temperature and keeps most of it at 250 °C, where AZ91D has lost half; EZ33A creeps less at 250 °C than any other common magnesium alloy; and the yttrium grades corrode at rates approaching aluminum castings rather than AZ magnesium. They are sand, investment and permanent-mold casting alloys (plus extruded and additively manufactured WE43), specified for helicopter gearboxes, race engines and, in the case of WE43, bioabsorbable implants.
Popular rare-earth magnesium grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| WE43 | 175 | 260 | 1.84 | Excellent | Very good | Gearbox housings to 250 °C; extrusions, AM, implants |
| EV31A | 110 | 195 | 1.82 | Excellent | Very good | Elektron 21: castable, 200 °C sand and investment castings |
| WE54 | 200 | 270 | 1.85 | Excellent | Very good | Higher strength, 300 °C short-term |
| EZ33A | 110 | 160 | 1.8 | Excellent | Very good | Lowest creep, pressure-tight casings to 250 °C |
| ZE41A | 140 | 205 | 1.84 | Excellent | Very good | General aerospace castings to 150 °C |
| QE22A | 195 | 260 | 1.82 | Excellent | Good | Silver-bearing high-strength castings to 200 °C |
| EQ21A | 195 | 260 | 1.81 | Excellent | Very good | Lower-silver alternative to QE22A |
Choose rare-earth magnesium for
Helicopter and turboprop gearbox housings, generator and accessory cases, race-car gearbox and engine castings, aircraft canopy frames and actuator bodies, motorsport and aerospace extrusions, additively built brackets, and bioabsorbable orthopaedic fixation — anywhere a magnesium part must hold load at 150–300 °C, resist creep in bolted joints, or corrode slowly enough to be trusted for decades.
Look elsewhere when
The part runs below 120 °C indoors in volume (AZ91D die casting), it is machined from plate (AZ31B, which the rare-earth grades are not sold as), the temperature or load exceeds what 300 °C magnesium can do (A201 or 2618 aluminum, then Grade 5 titanium), the casting is small and cheap where rare-earth melt cost dominates, or the environment is truly wet and salty — even WE43 needs its coating and insulated fasteners.
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Rare-earth magnesium by application
- Gearbox and generator housings
- WE43-T6 or EV31A-T6 sand and investment castings for helicopter transmissions, accessory gearboxes and generator frames at 150–250 °C; EZ33A-T5 where creep in the bolted flange matters more than strength.
- Motorsport castings and extrusions
- WE43 and WE54 for race engine covers, gearbox cases, wheels and extruded suspension components that run hot and are inspected every event; QE22A where an airframe-grade casting must reach about 195 MPa yield.
- Additive and machined structure
- WE43 powder is the qualified laser-powder-bed magnesium alloy for brackets and lattice structures; extruded WE43 bar is machined for prototypes that will later be cast in the same alloy.
- Resorbable implants
- WE43 in its medical-purity form for bioabsorbable bone screws, pins and plates that dissolve over one to two years — a use no other structural alloy offers.
Working with rare-earth magnesium
- Casting and heat treatment
- Sand, investment, permanent-mold and low-pressure casting with zirconium grain refinement under protective cover gas; EV31A and EZ33A feed best, WE43 and WE54 need careful gating and chills. T6 for WE43: solution-treat about 8 h at 525 °C, hot-water or air quench, age 16 h at 250 °C; EZ33A and ZE41A are aged directly to T5 at 175–215 °C. Die casting of these grades is not standard practice.
- Machining
- As fast and clean as any magnesium — dry or mineral-oil cutting at high speed, coarse chips, sharp tools — and the T6 castings hold tolerance well because the precipitates are stable at shop temperatures. Cast skin and the zirconium-rich grain boundaries wear tools slightly faster than AZ91D. Same fire discipline as all magnesium: no fine dust accumulation, Class D extinguishers on hand.
- Welding and repair
- WE43, EZ33A, ZE41A and QE22A TIG-weld well with matching filler under argon, which is how aerospace foundries repair casting defects; re-heat-treat to T6 or T5 after welding to restore the aged properties. EV31A welds acceptably. Stress-relieve after any weld on a finished casting.
- Finishing and corrosion control
- Corrosion is far better than AZ91D but still magnesium: a chromate or chrome-free conversion coat plus epoxy primer indoors, an anodic ceramic layer (HAE, Tagnite, Keronite) under paint for airframe and engine exposure, and every steel bolt isolated. Bioabsorbable WE43 implants are the deliberate exception — they are designed to corrode away in body fluid.
Other magnesium alloy series
Rare-Earth Magnesium Alloys — frequently asked
What is rare-earth magnesium?
Rare-earth magnesium alloys replace aluminum with yttrium, neodymium, gadolinium or mixed rare earths, grain-refined by zirconium, and gain their strength from precipitates that do not coarsen until well above 200 °C. WE43-T6 holds about 170–195 MPa yield at room temperature and keeps most of it at 250 °C, where AZ91D has lost half; EZ33A creeps less at 250 °C than any other common magnesium alloy; and the yttrium grades corrode at rates approaching aluminum castings rather than AZ magnesium. They are sand, investment and permanent-mold casting alloys (plus extruded and additively manufactured WE43), specified for helicopter gearboxes, race engines and, in the case of WE43, bioabsorbable implants.
Which grade of rare-earth magnesium should I use?
WE43 (Mg-4Y-3Nd-Zr) for the demanding cases: gearbox and generator housings at 200–250 °C, motorsport castings, extruded and 3D-printed structure, and resorbable bone screws — the best combination of strength, creep and corrosion in the family. EV31A (Elektron 21, Mg-Nd-Gd-Zn-Zr) when the part is a complex sand or investment casting: it fills and feeds better than WE43, is cheaper to melt, and holds about 145–170 MPa yield in T6 to 200 °C. WE54 for a little more strength (about 185 MPa yield) and 300 °C short-term service, accepting that long exposure at 150 °C embrittles it. EZ33A-T5 is the classic creep-resistant, pressure-tight casing alloy — only about 110 MPa yield but stable to 250 °C and the easiest to cast. ZE41A-T5 is the general-purpose aerospace casting alloy to 150 °C at about 140 MPa yield, and QE22A-T6 the silver-bearing high-strength grade (about 195 MPa) for airframe castings to 200 °C.
Which grade of rare-earth magnesium is the strongest?
QE22 has the highest yield strength in the series at 200 MPa; WE54 follows at 200 MPa. Values are for each grade's default condition.
Which grade of rare-earth magnesium is easiest to machine?
ZE41 (machinability excellent, 96/100), then EZ33 (95/100).
Is rare-earth magnesium heat-treatable?
Yes. These grades gain their strength from heat treatment; the conditions and their properties are listed on each grade page.
WE43 or EV31A (Elektron 21)?
WE43 is the stronger, hotter alloy — about 170–195 MPa yield in T6, 250 °C continuous with the best creep and corrosion resistance in the family — and it is also available as extrusion, plate stock and AM powder. EV31A gives up 10–20 % of that strength and about 50 °C of service temperature in exchange for much better castability: it fills thin sections, feeds without hot tearing and machines the same. For a complex sand or investment casting at 150–200 °C specify EV31A; for a housing that runs at 250 °C, a wrought or printed part, or a resorbable implant, specify WE43.
How much better is WE43 corrosion resistance than AZ91D?
In salt-spray testing high-purity WE43 corrodes several times slower than high-purity AZ91D, and it is far less sensitive to the iron, nickel and copper pickups that wreck AZ alloys — the yttrium and rare earths form a more protective film and fewer cathodic second phases. It is still not aluminum: bare WE43 in seawater loses metal at a rate an A356 casting would not, so the coating system and insulated fasteners stay in the drawing. Where WE43 truly changes the design is that a coated part in a warm, humid engine bay survives for the life of the aircraft rather than the life of the paint.