AZ91D magnesium
Selecting AZ91D by casting route, condition, test basis, corrosion protection and machining controls.
Tags: materials, magnesium, casting-alloys, specialty-metals
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Identity and purchase specification
The 2015 NADCA A-3-11 table gives 230 MPa tensile, 160 MPa 0.2%-offset yield and 3% elongation over 51 mm, all typical at 20°C for separately die-cast, as-cast AZ91D specimens. The table excludes specimens removed from production castings. Establish how the actual housing section will be accepted. NADCA 2015 alloy-data table
AZ91D is a magnesium-aluminum-zinc alloy designation commonly associated with die casting. The International Magnesium Society's ingot-designation table maps AZ91D to ISO-MgAl9Zn1(A) and ISO-MB21120. Such a cross-reference identifies an alloy family; it does not certify a casting, establish producer provenance or supply every composition and property requirement. IMS: magnesium ingot designations
Specify the governing material/product standard and edition, casting process, condition, drawing and required inspection documentation. For example, SAE AMS4490K, revised 30 May 2017, explicitly concerns die castings in AZ91D, Temper F, as cast. Its published scope illustrates why form and condition belong in the specification; it is not evidence that this historical revision is the current edition required by a project. SAE: AMS4490K
Do not substitute sand-cast AZ91 variants, wrought magnesium, powder or an additively manufactured part solely because a supplier uses “AZ91” in its description. Agree chemical limits, casting quality, mechanical requirements and any coating or repair restrictions for the actual ordered product.
Bounded mechanical data
The 2015 NADCA Product Specification Standards, Table A-3-11, presents these typical AZ91D values for as-cast, separately die-cast specimens, explicitly excluding specimens cut from production castings:
| Property | Typical value and stated basis |
|---|---|
| Ultimate tensile strength | 230 MPa at 20 °C |
| Yield strength | 160 MPa, 0.2% offset, at 20 °C |
| Elongation | 3% over 51 mm, at 20 °C |
| Young's modulus | 45 GPa at 20 °C |
Source: NADCA 2015, alloy-data section hosted by A&B Die Casting.
These typical data do not guarantee every location in a casting. Specify acceptance specimens, sampling location, orientation and section thickness; a test bar cannot rule out local defects in a housing.
Mass and stiffness need separate checks
Meridian's material chart lists AZ91D density as 1.81 g/cm³ and elastic modulus as 45 GPa. The accessible chart does not state a complete test/conditioning protocol, so treat it as selection guidance rather than a contractual acceptance table. Meridian: material-property comparison
Illustrative mass calculation: a nominal net material volume of 100 cm³ at 1.81 g/cm³ gives 181 g. This excludes coatings, fasteners and volume or density variation. It does not establish an interchangeable lightweight design: changing wall thickness, ribs, mounting points or material changes stiffness, buckling and stress distribution as well as mass. Reassess those requirements when redesigning an aluminum or steel part in magnesium.
Corrosion and assembly design
NADCA attributes AZ91D corrosion performance to strict control of iron, copper and nickel impurities. Preserve the applicable limits and delivered analysis; “high purity” does not establish environmental immunity. NADCA: magnesium-alloy selection
For the assembled component, specify humidity, salt or process-fluid exposure, dissimilar-metal contacts, crevices and cleaning chemicals. Review fasteners, inserts, electrical contacts and coating damage as an assembly, and obtain a qualified corrosion-protection system for the intended duty. Require tests representative of the contact geometry and exposure rather than extending a bare-alloy chart to a coated, bolted housing.
Record appearance criteria separately from loss of function or strength. Check coating continuity at edges and machined features, drainage and water-trapping details, and how the assembly will be inspected or repaired. A coating designation alone does not establish the life of a complete component.
Casting, heat exposure and alternative routes
Specify acceptance limits and inspection for porosity, cold shuts and other defects in critical features.
Room-temperature as-cast data do not establish elevated-temperature creep, long-term fastener retention or a permitted coating-bake cycle. Obtain condition-specific evidence for sustained heat exposure and confirm any post-casting thermal treatment with the foundry and applicable specification. This page supplies no general heat-treatment or remelting recipe.
Aconity3D's 09.20 AZ91D sheet illustrates the importance of route: it labels its mechanical data “as built” and says values depend on powder, process parameters and surrounding conditions. Those results are additive-process data, not replacements for die-cast specimen properties or proof of compliance with a casting specification. Aconity3D: AZ91D process datasheet
Machining and material handling
Luxfer MEL Technologies' Machining Magnesium, datasheet 254, treats tooling, machine/workpiece rigidity, chip extraction and heat generation together. Its guidance emphasizes sharp tools and adequate chip clearance; cutting recommendations depend on operation and equipment. Do not transfer a published maximum cutting speed directly to an unqualified machine, casting geometry or coolant system. Luxfer: machining magnesium
The International Magnesium Association's Safe Handling of Magnesium, February 2020, distinguishes solid material from molten metal and finely divided forms. It identifies chips, grinding residues and powder as readily ignitable, warns about airborne-dust explosion hazards, and calls for engineered collection and housekeeping. It also warns that water contact with molten magnesium is hazardous and that water must not be used on a magnesium fire. IMA: safe handling guidance
Use the exact supplier's current safety information and a facility procedure appropriate to the operation, including chip storage, coolant compatibility, dust collection and suitable fire response. A solid casting's normal handling behavior cannot establish the precautions for powder, accumulated swarf or melting. Avoid uncontrolled mixtures of chips, fluids and other shop waste.
Purchase and acceptance record
Retain:
- Full alloy designation, product specification/edition, casting route and condition.
- Producer/heat traceability and required chemical-analysis documentation.
- Sampling basis for properties and limits for casting defects or permitted rework.
- Dimensional, fastening, sealing and surface-finish requirements.
- Coating system and relevant thermal, corrosion and component tests.
- Machining, chip-handling and inspection procedures.
The cited NADCA section is explicitly 2015, SAE entry May 2017, IMA guide February 2020, and Aconity sheet 09.20. Meridian's chart and Luxfer's accessible machining sheet do not establish clear technical revision dates; a URL upload directory is not an edition. Confirm current controlled documents for procurement and process qualification.