Magnesium Alloy AZ91C-T4
Temper
ASTM AZ91C · UNS M11914
T4 = solution heat treated and naturally aged
Choose for maximum ductility and impact toughness in cast magnesium parts, at the cost of low yield strength.
Values for the T4 condition
Other AZ91C tempers and conditions
AZ91C is listed in 4 conditions; see the grade overview at AZ91C.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
T4This page Solution heat treated and naturally aged | Choose for maximum ductility and impact toughness in cast magnesium parts, at the cost of low yield strength. | 90 | 275 | 14 | 55 HB | 68 W/m·K |
FDefault As fabricated | Default foundry condition: lowest cost, adequate for lightly loaded housings and covers where no heat treatment is justified. | 97 | 165 | 2.5 | 60 HB | 72 W/m·K |
Cooled from hot working and artificially aged | Low-cost stabilizing age used to raise yield strength and dimensional stability slightly without a full solution cycle. | 110 | 165 | 2 | 65 HB | — |
Solution heat treated and artificially aged | Highest-strength condition for structural sand/permanent-mold castings where yield strength and hardness matter more than ductility. | 145 | 275 | 6 | 70 HB | 72 W/m·K |
What is AZ91C-T4?
AZ91C-T4 is AZ91C in the T4 temper — choose for maximum ductility and impact toughness in cast magnesium parts, at the cost of low yield strength. AZ91C-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). AZ91C-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). F is the default condition FabDigit quotes; T4 is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 17 MPa·√m (15.5 ksi·√in), better than 94% of magnesium alloy grades
- Ductile — tolerates forming and impact — 14%, better than 83% of magnesium alloy grades
Limitations
- Limited service temperature — 110°C (230 °F), worse than 99% of magnesium alloy grades
- Low strength — 90 MPa (13.1 ksi), worse than 96% of magnesium alloy grades
- Poor heat conductor — 68 W/m·K (39.3 BTU/hr·ft·°F), worse than 81% of magnesium alloy grades
- Low electrical conductivity — 12 % IACS, worse than 78% of magnesium alloy grades
AZ91C-T4 properties
Typical room-temperature values for AZ91C-T4; 12 are specific to this condition. Other listed values are AZ91C reference data and may not represent this condition. Bars are the position among magnesium alloy grades.
Physical3
AZ91C-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).
Mechanical13
AZ91C-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
AZ91C-T4 is rated for continuous service to 110°C (230 °F). It conducts heat at 68 W/m·K (39.3 BTU/hr·ft·°F), worse than 81% of magnesium alloy grades. Thermal expansion is 26 µm/m·K (14.4 µin/in·°F).
Electrical3
AZ91C-T4 conducts electricity at 12 % IACS, worse than 78% of magnesium alloy grades.
Chemical & Environmental3
Corrosion resistance is poor (20/100), worse than 77% of magnesium alloy grades.
Sustainability4
Producing a kilogram of AZ91C-T4 takes about 355 MJ of energy and emits 28 kg of CO₂ — more than 85% of magnesium alloy grades. Typical recycled content is 35%.
Manufacturability8
AZ91C-T4's machinability is excellent (94/100, worse than 75% of magnesium alloy grades); weldability very good (70/100); formability not recommended (12/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with AZ91C-T4
Is AZ91C easy to machine?
Outstanding machinability — high speeds, low cutting forces, sharp positive-rake tools and dry or oil (never water-based) coolant; collect and control fine chips/dust because of fire risk.
Can AZ91C be welded?
Readily GTAW/GMAW welded in inert gas with AZ92A or AZ101A filler; preheat thin sections, avoid Zn-rich fillers on thick joints and stress relieve (~260 °C) to prevent SCC.
Can AZ91C be formed, bent or molded?
Casting alloy only — excellent sand and permanent-mold castability with SF6-free cover gas or flux; needs generous fillets and controlled solidification to avoid microporosity, and no cold forming.
What surface finishes work on AZ91C?
Not sulfuric-anodizable: apply chromate/fluoride or fluoride-free conversion coating, Dow 17/HAE or PEO, then epoxy primer and topcoat; insulate all steel/brass fasteners to avoid galvanic attack.
AZ91C 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 | 8.1 – 9.3 | 8.7 |
| Zn | 0.4 – 1 | 0.7 |
| Mn0.13 % min per ASTM B80 | ≥ 0.13 | 0.2 |
| Si | ≤ 0.3 | — |
| Cu | ≤ 0.1 | — |
| Ni | ≤ 0.01 | — |
| Others (total) | ≤ 0.3 | — |
| Mg | balance | — |
AZ91C-T4 — frequently asked
What is AZ91C-T4 used for?
AZ91C-T4 is typically used for sand-cast gearbox and machinery housings, permanent-mold pump bodies, instrument and avionics housings, prototype castings ahead of die-cast tooling, equipment brackets and covers and low-volume structural castings. In short: weldable AZ91 casting grade; sand and permanent-mold route; heat-treatable to T6.
What is the yield strength of AZ91C-T4?
AZ91C-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 4 listed tempers.
Is AZ91C-T4 easy to machine?
Yes — machinability is rated excellent (94/100, worse than 75% of magnesium alloy grades). Outstanding machinability — high speeds, low cutting forces, sharp positive-rake tools and dry or oil (never water-based) coolant; collect and control fine chips/dust because of fire risk.
Can AZ91C-T4 be welded?
Yes — weldability is rated very good (70/100). Readily GTAW/GMAW welded in inert gas with AZ92A or AZ101A filler; preheat thin sections, avoid Zn-rich fillers on thick joints and stress relieve (~260 °C) to prevent SCC.
What surface finishes work on AZ91C-T4?
Not sulfuric-anodizable: apply chromate/fluoride or fluoride-free conversion coating, Dow 17/HAE or PEO, then epoxy primer and topcoat; insulate all steel/brass fasteners to avoid galvanic attack.
Can AZ91C-T4 be formed, bent or molded?
Casting alloy only — excellent sand and permanent-mold castability with SF6-free cover gas or flux; needs generous fillets and controlled solidification to avoid microporosity, and no cold forming.
What is the maximum service temperature of AZ91C-T4?
AZ91C-T4 is rated for continuous use to about 110°C (230 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between AZ91C-F and AZ91C-T6?
F is the default condition — default foundry condition: lowest cost, adequate for lightly loaded housings and covers where no heat treatment is justified. T6: highest-strength condition for structural sand/permanent-mold castings where yield strength and hardness matter more than ductility. Yield strength is 97 MPa in F versus 145 MPa in T6.
Sources
- ASTM B80 — Magnesium-Alloy Sand Castings — ASTM International (2015)
- ASTM B199 — Magnesium-Alloy Permanent Mold Castings — ASTM International (2019)
- ASTM B661 — Heat Treatment of Magnesium Alloys — ASTM International (2019)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys (Magnesium) — ASM International (1990)
- ASM Handbook Vol. 15 — Casting (Magnesium Foundry Practice) — ASM International (2008)
- ASM Specialty Handbook: Magnesium and Magnesium Alloys — ASM International (1999)
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.