Engineering · Machining guide
How to machine magnesium AZ31.
Magnesium is the lightest structural metal in common use — 1.78 g/cc, two-thirds the density of aluminum. Machinability is excellent — magnesium cuts more freely than any other structural metal and rates far above B1112 free-machining steel on the steel scale (the 100 / 100 below is simply the top of our capped scale, not a reference value). The catch is fire safety: magnesium chips and fines burn aggressively and cannot be extinguished with water. The machining strategy is built around fire prevention as much as cutting parameters.
01 · Fire safety
Read this before cutting a chip.
Magnesium chips ignite at ~650 °C and burn at over 3,000 °C with a violent white flame. Water makes a magnesium fire dramatically worse — it reacts with the metal to liberate hydrogen, accelerating combustion. So does a CO₂ extinguisher (CO₂ reduces to carbon, oxidizing the magnesium). The right extinguishing agent is dry sodium chloride (Class D) or dry sand smothering.
Risk scales with chip size: large chips and bulk magnesium are very hard to ignite; fine swarf, dust, and grinding debris ignite easily. The strategy is therefore: keep chips coarse, evacuate them continuously, and never allow accumulation of fines.
- Class D fire extinguisher within reach
- Dedicated chip cart, kept dry, emptied frequently
- No water-based coolant — see coolant section below
- Never grind magnesium dry near other operations — vacuum collection mandatory
- If a fire starts: smother with dry sand or Class D agent. Evacuate the area; magnesium fires emit blinding light.
02 · Coolant
Never water. Mineral oil or dry.
- Mineral oil flood: the standard production coolant. Light cutting oil or kerosene-based fluid. Cools the chip and tool, suppresses fire, leaves clean parts.
- Dry machining: works for short cycles and large chip sizes. Mandatory chip evacuation; ventilation to prevent fines accumulation.
- Never water-soluble emulsion: water-based coolants react with magnesium to form hydroxide and hydrogen. Tool friction can ignite the hydrogen at the cutting edge.
- MQL (minimum quantity lubrication): works with mineral-oil-based MQL fluid. A practical compromise for shops without dedicated oil flood.
03 · Cutting parameters
Fast — magnesium loves to cut.
| Operation | Tool | SFM | IPT / IPR |
|---|---|---|---|
| Roughing turn | Uncoated carbide / HSS | 1500–3000 | 0.012–0.025 IPR |
| Finishing turn | Uncoated carbide | 2500–4000 | 0.005–0.012 IPR |
| End mill (rough) | Solid carbide 2-3FL | 1000–2000 | 0.005–0.012 IPT |
| End mill (finish) | Solid carbide 3FL | 1500–2500 | 0.003–0.008 IPT |
| Drilling | HSS or carbide | 300–600 | 0.005–0.015 IPR |
| Tapping | HSS | 100–200 | — |
IPT (chip-load) values assume roughly ½–1″ end mills; scale down for smaller tools — see the chip-load chart.
Heavy chip load is your friend: coarse chips dissipate heat better and are far less prone to ignition than fine swarf. Don’t reduce feed below the recommended chip load — it produces fines and increases fire risk.
04 · Applications
Where magnesium pays back the safety cost.
- Aerospace structural housings: drone airframes, missile housings, satellite bus components — when 35% weight savings vs aluminum justifies the process
- Defense electronics housings: handheld and portable systems where weight is a soldier-load issue
- Automotive: steering columns, transmission housings, seat frames in performance vehicles
- Sporting goods: camera housings, archery components, premium bicycle parts
Keep exploring
Related tools & references
Lightest structural metal — properties and tempers.
Push the high SFM magnesium loves — keep chips coarse.
Heavy chip loads reduce fines and fire risk.
1.78 g/cc — quantify the weight savings vs aluminum.
Weigh AZ31 against aluminum for lightweight work.
Need magnesium AZ31 parts machined?
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