Magnesium Alloy AZ91D · temper
Magnesium Alloy AZ91D-T4
Properties of the T4 condition, compared with the other AZ91D tempers.
Used on gravity/sand/permanent-mould AZ91 castings when maximum ductility and impact toughness are needed (not applicable to porous HPDC parts, which blister).
What is AZ91D-T4?
AZ91D-T4 is AZ91D in the T4 temper — used on gravity/sand/permanent-mould AZ91 castings when maximum ductility and impact toughness are needed (not applicable to porous HPDC parts, which blister). AZ91D-T4 has a yield strength of 90 MPa (13.1 ksi) and a tensile strength of 275 MPa (39.9 ksi) — weaker than 96% of magnesium alloy grades. Elongation at break is 14% and the elastic modulus is 45 GPa (6.53 Msi). AZ91D-T4 has a density of 1.81 g/cm³ (0.0654 lb/in³), heavier than 58% of magnesium alloy grades. It melts at 470°C (878 °F). As Cast is the default condition FabDigit quotes; T4 is available on request or by drawing note.
Advantages
- Good corrosion resistance — 33/100, better than 99% of magnesium alloy grades
- Tough — resists crack growth — 16 MPa·√m (14.6 ksi·√in), better than 85% of magnesium alloy grades
- Ductile — tolerates forming and impact — 14%, better than 83% of magnesium alloy grades
- Forms and bends easily — 30/100, better than 81% of magnesium alloy grades
Limitations
- Low electrical conductivity — 11 % IACS, worse than 98% of magnesium alloy grades
- Low strength — 90 MPa (13.1 ksi), worse than 96% of magnesium alloy grades
- Limited service temperature — 120°C (248 °F), worse than 78% of magnesium alloy grades
AZ91D-T4 properties
Typical room-temperature values for AZ91D-T4 — 22 properties are specific to this condition; the rest are grade-level values shared by every AZ91D temper. Each bar shows where the value sits among the magnesium alloy grades in FabDigit's library — further right is higher.
Physical3
AZ91D-T4 has a density of 1.81 g/cm³ (0.0654 lb/in³), heavier than 58% of magnesium alloy grades. It melts at 470°C (878 °F).
Mechanical14
AZ91D-T4 has a yield strength of 90 MPa (13.1 ksi) and a tensile strength of 275 MPa (39.9 ksi) — weaker than 96% of magnesium alloy grades. Elongation at break is 14% and the elastic modulus is 45 GPa (6.53 Msi).
Thermal6
AZ91D-T4 is rated for continuous service to 120°C (248 °F). It conducts heat at 72 W/m·K (41.6 BTU/hr·ft·°F), worse than 70% of magnesium alloy grades. Thermal expansion is 26 µm/m·K (14.4 µin/in·°F).
Electrical3
AZ91D-T4 conducts electricity at 11 % IACS, worse than 98% of magnesium alloy grades.
Chemical & Environmental3
Corrosion resistance is poor (33/100), better than 99% of magnesium alloy grades.
Sustainability4
Producing a kilogram of AZ91D-T4 takes about 320 MJ of energy and emits 32 kg of CO₂ — less than 74% of magnesium alloy grades. Typical recycled content is 35%.
Manufacturability8
AZ91D-T4's machinability is excellent (95/100, better than 54% of magnesium alloy grades); weldability good (60/100); formability poor (30/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other AZ91D tempers and conditions
AZ91D is also supplied in 6 other conditions. The full side-by-side table is on the AZ91D overview.
- As CastDefaultStandard high-pressure die cast condition — the way essentially all AZ91D is supplied and used.160 MPa yield · 63 HB
- As PrintedRapid-solidified AM condition: fine grain gives higher strength and hardness than die casting, but very low elongation and anisotropy — use with stress relief or HIP for load-bearing parts.240 MPa yield · 88 HB
- FHigh-purity AZ91D (EN-MC21120, MgAl9Zn1(A)) in the as-fabricated F condition, typically high-pressure die cast — good strength, excellent castability, best-in-class salt-spray corrosion resistance among AZ91 variants.160 MPa yield · 63 HB
- T6Highest yield strength/hardness combination for gravity-cast or HIPed AZ91 parts; ductility lower than T4.145 MPa yield · 70 HB
- T4Used on gravity/sand/permanent-mould AZ91 castings when maximum ductility and impact toughness are needed (not applicable to porous HPDC parts, which blister).90 MPa yield · 55 HB
Working with AZ91D-T4
Is AZ91D easy to machine?
Machines faster and with lower cutting forces than any other structural metal — use sharp, high-rake, polished-flute tools, high speed and generous chip clearance; never let fine chips accumulate, keep dry or use mineral-oil coolant (no water-based) and have Class D extinguishing media at hand.
Can AZ91D be welded?
GTAW/GMAW with AZ92A or AZ61A filler works on low-porosity gravity castings and AM parts, but standard high-pressure die castings blister and crack from trapped gas — mechanical joining, adhesive bonding or friction stir spot welding are preferred.
Can AZ91D be formed, bent or molded?
A benchmark hot-chamber die casting alloy: excellent fluidity for 0.6–1.5 mm walls, low hot-tear tendency, long die life; essentially no cold formability (HCP), so any bending/forming must be done above ~230 °C.
What surface finishes work on AZ91D?
No sulfuric anodizing; specify chromate-free conversion coating or micro-arc/plasma electrolytic oxidation plus E-coat/powder coat, and isolate steel fasteners with washers or coatings to avoid galvanic attack; electroless Ni over a zinc-immersion pretreat is used where wear or EMI plating is required.
AZ91D chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Al | 8.3 – 9.7 | 9 |
| Zn | 0.35 – 1 | 0.7 |
| MnMn min tied to Fe/Mn ratio limit | 0.15 – 0.5 | 0.25 |
| Si | ≤ 0.1 | 0.03 |
| Cu | ≤ 0.03 | 0.01 |
| Nihigh-purity limit for salt-spray performance | ≤ 0 | 0 |
| FeFe/Mn ratio ≤ 0.032 | ≤ 0.01 | 0 |
| Others (each) | ≤ 0.02 | — |
| Mg | balance | — |
AZ91D-T4 — frequently asked
What is AZ91D-T4 used for?
AZ91D-T4 is typically used for laptop and display enclosures, automotive interior and instrument-panel supports, steering column and seat frame castings, powertrain and transmission covers, handheld power tool housings and camera and projector bodies. In short: workhorse die-cast magnesium.
What is the yield strength of AZ91D-T4?
AZ91D-T4 has a typical yield strength of 90 MPa (13.1 ksi) and a tensile strength of 275 MPa (39.9 ksi) — weaker than 96% of magnesium alloy grades. Strength varies by condition: see the 7 listed tempers.
Is AZ91D-T4 easy to machine?
Yes — machinability is rated excellent (95/100, better than 54% of magnesium alloy grades). Machines faster and with lower cutting forces than any other structural metal — use sharp, high-rake, polished-flute tools, high speed and generous chip clearance; never let fine chips accumulate, keep dry or use mineral-oil coolant (no water-based) and have Class D extinguishing media at hand.
Can AZ91D-T4 be welded?
Yes — weldability is rated good (60/100). GTAW/GMAW with AZ92A or AZ61A filler works on low-porosity gravity castings and AM parts, but standard high-pressure die castings blister and crack from trapped gas — mechanical joining, adhesive bonding or friction stir spot welding are preferred.
What surface finishes work on AZ91D-T4?
No sulfuric anodizing; specify chromate-free conversion coating or micro-arc/plasma electrolytic oxidation plus E-coat/powder coat, and isolate steel fasteners with washers or coatings to avoid galvanic attack; electroless Ni over a zinc-immersion pretreat is used where wear or EMI plating is required.
Can AZ91D-T4 be formed, bent or molded?
A benchmark hot-chamber die casting alloy: excellent fluidity for 0.6–1.5 mm walls, low hot-tear tendency, long die life; essentially no cold formability (HCP), so any bending/forming must be done above ~230 °C.
What is the maximum service temperature of AZ91D-T4?
AZ91D-T4 is rated for continuous use to about 120°C (248 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between AZ91D As Cast and AZ91D-T4?
As Cast is the default condition — standard high-pressure die cast condition — the way essentially all AZ91D is supplied and used. T4: used on gravity/sand/permanent-mould AZ91 castings when maximum ductility and impact toughness are needed (not applicable to porous HPDC parts, which blister). Yield strength is 160 MPa in As Cast versus 90 MPa in T4.
Can FabDigit make parts in AZ91D-T4?
Yes — AZ91D-T4 is available for CNC machining and casting & forging with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM B94 — Standard Specification for Magnesium-Alloy Die Castings — ASTM International (2018)
- ASTM B93/B93M — Magnesium Alloys in Ingot Form for Sand, Permanent Mold and Die Castings — ASTM International (2020)
- ASM Specialty Handbook: Magnesium and Magnesium Alloys — ASM International (1999)
- ASM Handbook Vol.2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials — ASM International (1990)
- ASTM D1732 — Preparation of Magnesium Alloy Surfaces for Painting — ASTM International (2019)
- Published L-PBF AZ91D process/property studies (as-built and HIP) — peer-reviewed AM literature (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.