MG · magnesium
Magnesium Alloy AZ31B
Magnesium machines faster than aluminium with a sharper finish, provided the chip is kept moving and the swarf rules are respected. The fire risk is real and the housekeeping is not optional.
Quoting this material
- Typical lead time
- 12–20 working days
- Condition
- Annealed (extruded or rolled product)
- Achievable finish
- Ra 1.6 µm typical · Ra 0.4 µm best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
Magnesium machines faster than aluminium with a sharper finish, provided the chip is kept moving and the swarf rules are respected. The fire risk is real and the housekeeping is not optional.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength | 260 | MPa |
| Yield strength (0.2%) | 200 | MPa |
| Elongation | 15 | % |
| Hardness | 50–60 | HB |
| Thermal conductivity | 96 | W/m·K |
| Modulus of elasticity | 45 | GPa |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Annealed (extruded or rolled product)
Heat treatment
Not hardenable by heat treatment. Annealing after forming relieves stress; the strength comes from the alloy and the product form, not from a thermal cycle.
Achievable surface finish
Ra 1.6 µm
Ra 0.4 µm
Takes an excellent finish - among the best of any metal. Corrosion protection is then mandatory: chromate conversion or anodising, plus coated fasteners.
Tooling and cutting parameters
Cutting speed
- 300–700 m/min (sharp uncoated carbide, high rake, high clearance)
Feed
- 0.10–0.40 mm/rev turning · 0.10–0.30 mm/tooth milling
Tooling
- Sharp uncoated carbide with a polished face and large clearance; no coatings that increase friction
Coolant
- Mineral-oil mist or dry. Never water-based coolant on the swarf
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Aerospace and defence housings
- Portable equipment frames
- Automotive and motorsport brackets
- Camera and optical hardware
- Electronic device enclosures
DFM notes for this grade
- Stiffness is the design limit, not strength: the modulus is 45 GPa, roughly 45% of aluminium, so a magnesium part deflects more than twice as much for the same load
- Corrosion protection is part of the part: bare machined magnesium will corrode in a normal atmosphere, and contact with steel or stainless fasteners needs isolation to stop galvanic attack
- Fine chips can ignite - no water-based coolant on the swarf, no accumulation of fines, sharp tooling and a class D extinguisher within reach
Questions buyers ask
- Is machining magnesium actually dangerous?
- It is manageable with the right process. The risk is fine chips and dust, which can ignite; solid magnesium and coarse chips are far less reactive. The rules are simple: no water-based coolant on the swarf, do not let fines accumulate, keep the tool sharp and handle the chips the same day they are produced.
- Why is magnesium not used more if it is the lightest structural metal?
- Corrosion and stiffness. Bare magnesium needs a coating system and isolation from other metals, and its low modulus means a magnesium part is more flexible than the aluminium one it replaces. Where weight is the leading constraint, neither matters; where it is not, aluminium is easier to live with.
Grades we would quote instead
AZ91D
8/10The most common die-casting magnesium: high aluminium content gives good castability and decent strength, and it machines fast with excellent finishes.
AZ61A
8/10A wrought magnesium alloy sitting between AZ31 and AZ80: more strength than AZ31, easier to extrude and form than AZ80, and it machines cleanly.
6061-T6
9/10The alloy most of our cycle times are quoted against.