MG · magnesium
Magnesium Alloy AZ91D (die casting)
The most common die-casting magnesium: high aluminium content gives good castability and decent strength, and it machines fast with excellent finishes.
Quoting this material
- Typical lead time
- 12–20 working days
- Condition
- As die cast (high-purity D grade for corrosion resistance)
- 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.
The most common die-casting magnesium: high aluminium content gives good castability and decent strength, and it machines fast with excellent finishes.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength | 230–250 | MPa |
| Yield strength (0.2%) | 150–160 | MPa |
| Elongation | 3 | % |
| Hardness | 65–75 | HB |
| Thermal conductivity | 51 | 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
As die cast (high-purity D grade for corrosion resistance)
Heat treatment
Not hardenable by heat treatment in a useful way for a casting. The D grade is the high-purity version with low iron, nickel and copper, which is what gives it usable corrosion resistance.
Achievable surface finish
Ra 1.6 µm
Ra 0.4 µm
Machines to a bright finish; the as-cast skin is usually removed where a fit or a seal is needed.
Tooling and cutting parameters
Cutting speed
- 300–700 m/min (sharp uncoated carbide)
Feed
- 0.10–0.35 mm/rev turning · 0.10–0.30 mm/tooth milling
Tooling
- Sharp uncoated carbide with large clearance, polished
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
- Automotive instrument panels and housings
- Laptop and camera bodies
- Power tool housings
- Aerospace instrument casings
- Telecom and RF enclosures
DFM notes for this grade
- Casting porosity is normal in a die casting: a machined bore that has to be pressure tight needs a sealed insert or a different process
- Low elongation (3%) means a die cast AZ91D part does not like impact or a sharp corner - design radii into the casting
- The high-purity D grade is the one to specify for corrosion resistance; the standard grade with higher iron and copper corrodes noticeably faster
Questions buyers ask
- What does the D in AZ91D mean?
- High purity: tight limits on iron, nickel and copper, the three elements that drive galvanic corrosion in magnesium. The D grade corrodes far more slowly than the older standard grade, and it is the grade that made die-cast magnesium acceptable in volume applications.
- Can a die-cast AZ91 part be welded?
- It can be welded, but the porosity in a casting makes the joint unpredictable and it is rarely done in production. Where a joint is needed in a magnesium assembly, the casting is designed to be bolted or riveted with isolation from other metals.
Grades we would quote instead
AZ91E
8/10The sand-casting version of AZ91 with a high-purity specification: lower strength than the die-cast grade but a far lower casting cost for low volumes, and it machines the same way.
AM60B
8/10The ductile die-casting magnesium: less aluminium than AZ91, so lower strength but far better elongation.
AZ31B
9/10Magnesium machines faster than aluminium with a sharper finish, provided the chip is kept moving and the swarf rules are respected.