AZ91D Magnesium Alloy -The Industry Standard Magnesium Die Casting Alloy

AZ91D is the most widely produced magnesium die casting alloy globally, accounting for approximately 90% of magnesium die casting volume. The designation encodes its composition: A = aluminum (~9%), Z = zinc (~1%), 91 = nominal percentages, D = high-purity grade with strict limits on iron, nickel, and copper.

The "D" grade designation is critical. AZ91A and AZ91B are earlier grades with less stringent impurity limits. AZ91D was developed specifically for die casting with dramatically improved corrosion resistance through iron, nickel, and copper control at levels that reduce galvanic corrosion by orders of magnitude compared to earlier grades.

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Chemical Composition

Element	Nominal %	Allowable Range
Aluminum (Al)	9.0	8.3-8.7
Zinc (Zn)	0.7	0.35-1.0
Manganese (Mn)	0.2	0.15 min
Silicon (Si)	-	0.10 max
Copper (Cu)	-	0.030 max
Nickel (Ni)	-	0.002 max
Iron (Fe)	-	0.005 max
Magnesium (Mg)	Balance	-

Per ASTM B94; AZ91D high-purity grade

The tight limits on Fe, Ni, and Cu are the defining feature of AZ91D. These elements form galvanic couples with the magnesium matrix, dramatically accelerating corrosion. AZ91D's strict impurity control elevates corrosion resistance to a level usable in practical engineering applications.

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Mechanical Properties (As-Cast HPDC)

Property	Value
Tensile strength	230 MPa (33,400 psi)
Yield strength	160 MPa (23,200 psi)
Elongation	3%
Hardness	63 HRB
Compressive yield strength	160 MPa
Shear strength	140 MPa
Fatigue strength (5x10^8 cycles)	70 MPa

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Physical Properties

Property	Value
Density	1.81 g/cm³
Weight vs A380 aluminum	34% lighter
Melting range	470-495°C
Casting temperature	640-680°C (hot chamber)
Thermal conductivity	72 W/m·K
Electrical conductivity	12% IACS
Coefficient of thermal expansion	26 μm/m·°C
Modulus of elasticity	45 GPa
EMI attenuation	60-100 dB at 1 GHz

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Why AZ91D for Die Casting?

Lightest structural metal: At 1.81 g/cm³, AZ91D is 34% lighter than A380 aluminum and 73% lighter than Zamak 5 zinc. For automotive weight reduction and portable electronics, this density advantage is unmatched among die casting alloys.

Best corrosion resistance in the AZ family: Among AZ-series alloys, AZ91D has the highest aluminum content (9%), which promotes formation of a protective Mg17Al12 intermetallic phase at grain boundaries. Combined with the strict impurity limits of the D grade, AZ91D has significantly better corrosion resistance than AM60B or AM50A.

Highest strength in the AZ family: 230 MPa tensile strength is the highest of the common magnesium die casting alloys -making AZ91D the structural choice when strength per unit weight is the design driver.

Inherent EMI shielding: Magnesium alloys provide 60-100 dB attenuation across the 1 GHz frequency range without any conductive coating. This is inherent to the material and eliminates the need for separate EMI gaskets or coatings in electronics enclosures.

Good machinability: AZ91D machines approximately 4x faster than aluminum with lower cutting forces, better surface finish, and longer tool life. For programs with extensive post-cast machining, this significantly reduces secondary operation cost.

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AZ91D vs AM60B -When to Choose Each

Parameter	AZ91D	AM60B
Tensile strength	230 MPa	220 MPa
Elongation	3%	8%
Impact resistance	Lower	Higher
Corrosion resistance	Better	Good
Castability	Excellent	Excellent
Best application	Housings, covers, structural (non-impact)	Automotive safety structures, crash-relevant parts

AZ91D is chosen for housings, covers, electronic enclosures, and structural parts where maximum strength and corrosion resistance are required but crash performance is not the primary design driver.

AM60B is chosen for automotive safety-critical structural components -seat frames, instrument panel structures, steering wheel armatures -where elongation (ductility) under crash loading is required. Its 8% elongation vs AZ91D's 3% significantly improves energy absorption in impact.

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Applications

Automotive:

• Instrument panel cross-car beams and support structures
• Seat frames and back panels (non-safety zone)
• Transfer case and transmission covers
• Steering column brackets
• Door inner panel structures

Electronics and Telecommunications:

• Laptop and tablet computer chassis
• Camera bodies
• Mobile device frames and back covers
• 5G small cell housings and antenna enclosures
• Router and network equipment chassis

Power Tools and Industrial:

• Angle grinder and power drill housings
• Handheld scanner and test instrument housings
• Industrial robot components requiring weight reduction

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Surface Treatment Requirements

Bare AZ91D has limited corrosion resistance in humid or outdoor environments. Standard surface treatments:

Treatment	Purpose	Typical Specification
Chromate conversion (Alodine)	Corrosion protection, adhesion promotion	DOW 7 or similar
E-coating (cathodic epoxy)	Full coverage corrosion protection	15-25 μm
Powder coating	Color and outdoor protection	Over e-coat primer
Micro-arc oxidation (MAO)	Hard, ceramic-like surface, maximum corrosion resistance	Specialty applications

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Frequently Asked Questions

Is AZ91D safe to cast? What fire precautions are needed?

Magnesium in molten form ignites if exposed to water or CO2 KastMfg's magnesium casting cells use SF6/CO2gas cover over all open melt surfaces, dry sand fire suppression systems (not water or CO2extinguishers), and annually certified operators. Our safety protocols comply with international standards for magnesium die casting.

Can AZ91D be recycled?

Yes. Magnesium alloys are fully recyclable. KastMfg recycles all gates, runners, and scrap. Recycled AZ91D maintains its properties when properly processed -the impurity limits (especially Fe, Ni, Cu) must be maintained through selective remelting and verification.

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AZ91D magnesium inquiry: yaoqingpu1983@gmail.com | +86 138 1403 4409 | No.6, Rungu Road, Nanjing, China