AZ31B Magnesium vs 6061-T6
AZ31B magnesium and 6061-T6 aluminum are both lightweight structural metals, but magnesium pushes weight savings to the extreme. AZ31 is about a third lighter than aluminum at ~1.77 g/cm3 versus ~2.7, yet it gives up strength, stiffness, corrosion stability, and cost. 6061-T6 is the all-round default: stronger, cheaper, corrosion-stable, and easy to work. The decision hinges on whether ultralight weight justifies magnesium's penalties.
The verdict
Choose AZ31B magnesium only when ultralight weight is the dominant requirement and you can manage its corrosion, galvanic, and flammable-swarf risks. Choose 6061-T6 aluminum for nearly everything else — it is stronger, cheaper, more corrosion-stable, and far easier to source and process. Aluminum is the safe default; magnesium is a weight-critical specialty.
Side-by-side data
| Property | AZ31B Magnesium | 6061-T6 |
|---|---|---|
| Category | Magnesium | Aluminum |
| Density (g/cm³) | 1.77 | 2.7 |
| Tensile strength (MPa) | 260 | 310 |
| Yield strength (MPa) | 200 | 276 |
| Elongation (%) | 15 | 12 |
| Hardness | 49 HB | 95 HB |
| Max service temp (°C) | 120 | 170 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 96 | 167 |
| Typically used for | Lightweight wrought structures | All-round structural & machined parts — the default aluminum |
Which should you choose?
Choose AZ31B Magnesium when…
- Minimum weight is the overriding priority — magnesium is ~35% lighter than aluminum (~1.77 vs ~2.7 g/cm3)
- Excellent damping and lightweight stiffness-per-volume matter for housings or handheld devices
- Machinability is a plus — AZ31 rates 5/5, the best in the dataset (but swarf is flammable)
- The design can tolerate or protect against poor corrosion resistance (2.0/5)
- You can manage galvanic isolation where magnesium contacts dissimilar metals
- Wrought structures, extrusions, or forgings in lightweight applications are the target
Choose 6061-T6 Aluminum when…
- You want a stronger, stiffer part — tensile ~310 MPa vs AZ31's ~260 MPa, with higher modulus
- Cost matters — 6061 is ~2.0/5 versus magnesium at ~3.0/5
- Corrosion stability is needed; aluminum rates 3.5/5 and forms a protective oxide (vs 2.0/5)
- You need a forgiving, well-understood material for structural and machined parts
- Galvanic and flammability hazards must be avoided in fabrication and service
- Broad availability across CNC, sheet metal, and extrusion is required
Key differences that matter
- Magnesium is dramatically lighter (~1.77 vs ~2.7 g/cm3), the core reason to choose it
- Aluminum is stronger (~310 vs ~260 MPa tensile) and notably stiffer per part
- 6061 is cheaper (~2.0/5 vs ~3.0/5) — magnesium carries a cost premium despite lower density
- Aluminum resists corrosion better (3.5/5 vs 2.0/5); magnesium often needs coatings or sealing
- Magnesium swarf and fine chips are flammable, requiring special machining precautions
- Magnesium poses galvanic-corrosion risk when coupled to steel, aluminum, or fasteners
- Both list ~120-170 C max service; aluminum's 170 C edges out magnesium's 120 C here
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Open the Material SelectorGet a Quote →Frequently asked questions
When does magnesium actually beat aluminum?
When weight is the dominant constraint and the design can absorb magnesium's downsides. At ~35% lower density, AZ31 saves significant mass in aerospace, portable electronics, and handheld tools. But you pay with lower strength and stiffness, weaker corrosion resistance, higher cost, and fabrication hazards. If shaving grams is not mission-critical, aluminum almost always wins.
Is magnesium really flammable?
Bulk magnesium is hard to ignite, but fine chips, dust, and swarf from machining are genuinely flammable and burn intensely. Shops machining magnesium use dry-cutting precautions, avoid water-based coolant on fines, and keep Class D extinguishers nearby. This is a real handling cost that aluminum, which machines safely, does not impose.
Why is the lighter metal more expensive?
Magnesium's higher cost (~3.0/5 vs aluminum's ~2.0/5) reflects more involved extraction, smaller supply chains, and added handling and corrosion-protection steps. So you pay more per part for a material that is also weaker — which is why magnesium only makes sense when its weight advantage is decisive.
How do they compare on corrosion?
Aluminum is clearly better, rating 3.5/5 versus magnesium's 2.0/5. 6061 forms a stable protective oxide and tolerates many environments bare. Magnesium corrodes readily, especially in salt or humid conditions, and usually requires conversion coatings, anodizing, or paint plus careful galvanic isolation from other metals.
Do I need to worry about galvanic corrosion with magnesium?
Yes. Magnesium is very anodic, so when it contacts steel, aluminum, or stainless fasteners in the presence of moisture it corrodes sacrificially and quickly. Designs must isolate magnesium with coatings, gaskets, or compatible fasteners. Aluminum is far more galvanically forgiving, another reason it is the default for mixed-metal assemblies.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.