AZ91D is generally selected when higher strength, hardness and broad die-casting availability are important, while AM60B is often preferred when greater ductility and impact performance are required. AZ91D is widely used for electronic housings, industrial components and general die-cast parts. AM60B is commonly considered for automotive structural components and parts that must absorb impact. The final choice should also account for wall thickness, corrosion protection, joining, machining and applicable material standards.
For a rigid housing, cover, bracket, or general-purpose casting, AZ91D is usually where the discussion starts. It is a familiar high-pressure die-casting grade with a useful balance of strength, hardness, and established supply.
AM60B enters the picture when the part has to take an impact or has to deform without giving up too suddenly. That is why it appears so often in automotive structural conversations. A casting with a thick boss beside a thin wall, a tight gate location, and a machined sealing face will still need a real die review, whichever grade is chosen.
| Selection point | AZ91D | AM60B |
|---|---|---|
| Main reason engineers choose it | Strength, hardness, common use | Ductility and impact behavior |
| Common process | High-pressure die casting with finish machining where needed | High-pressure die casting with finish machining where needed |
| Typical part families | Housings, covers, brackets, industrial parts | Automotive structural and impact-loaded parts |
| Thin-wall die casting | Must be assessed from the actual geometry | Must be assessed from the actual geometry |
| CNC finish machining | Feasible with a magnesium-aware process | Feasible with a magnesium-aware process |
| Surface protection | Selected for the service environment | Selected for the service environment |
| Decision driver | Strength and supply practicality | Ductility and energy absorption |
AZ91D: the familiar die-casting workhorse
AZ91D is a magnesium-aluminum-zinc alloy. Its chemistry and established casting history make it a common starting point for housings, covers, brackets, tool bodies, and other parts that need a light, rigid casting with reasonable strength.
On a real program, AZ91D tends to come up early because many engineers, die casters, and buyers already know how to source and process it. That is useful, especially when the part has complex geometry and production volume needs to justify die casting. The AZ91D magnesium alloy product page is a useful starting point for reviewing supply form and specification details.
There is a tradeoff. Compared with AM60B, AZ91D is generally less ductile. If a design expects the casting to deform and absorb energy rather than stay stiff, the material discussion should not stop at AZ91D simply because it is familiar.
AM60B: when the part needs more room to deform
AM60B contains less aluminum than AZ91D and is commonly associated with better ductility and impact performance. That makes it a frequent candidate for automotive structures and components where the failure mode matters as much as the static load number.
That last point is easy to miss in a spreadsheet. Two materials can both look adequate under a basic tensile requirement, then behave quite differently under an impact event or in a part with a sharp local stress concentration. Geometry still matters. A poorly designed rib, abrupt wall change, or weak gate area will not be rescued by choosing AM60B.
For stock, chemistry, and application information, review the AM60B magnesium alloy page alongside the drawing and the end-use requirements.
Chemical differences: aluminum, zinc, and manganese
AZ91D is an aluminum-zinc magnesium alloy with more aluminum than AM60B. AM60B is primarily a magnesium-aluminum-manganese grade and typically runs lower in aluminum. That chemical shift sits behind much of the familiar strength-versus-ductility difference.
Manganese and impurity control are not background details. On a part exposed to moisture or salt, they belong in the material review with the coating plan and fastener stack-up. Final chemistry limits should come from the applicable standard and the material certificate—not from a generic web table.
Why the data sheet does not settle the argument
NADCA reference data for separately die-cast test specimens lists typical ultimate tensile strength around 230 MPa for AZ91D and 220 MPa for AM60B, with typical elongation around 3% and 8%, respectively. AZ91D also carries higher typical yield strength in that reference. The numbers are useful because they show why AM60B is brought into impact discussions.
In a die-casting review, nobody should sign off on a material choice from that tensile column alone. Section thickness, porosity, die temperature, gate location, local cooling, and the test method all affect what a finished casting does. When elongation or tensile performance is critical, define the test location, specimen method, acceptance criterion, and reporting requirement before the die is released.
Stiff housing or impact-loaded structure?
Imagine two different parts. One is an electronics housing that needs stiffness, clean die-cast geometry, threads or bosses after machining, and ordinary handling durability. The other is a vehicle component expected to see impact or deformation in service. The first conversation often starts with AZ91D. The second should include AM60B early.
An AZ91D part can still pass an impact-related requirement, and an AM60B part can still be strong enough for a static structural job. The deciding work happens in the load path, allowable deformation, attachment method, wall transitions, and failure consequence. A tensile number does not show where a rib will crack or how a bolted joint will spread a load.
Die casting is decided at the gate, not in the alloy brochure
Both grades are used in high-pressure die casting. Both can make complex lightweight geometry when the die, runner system, venting, and thermal control are suited to the part.
The question that matters during a design review is usually more specific: Where will the last metal arrive? Where will gas go? Which boss is thick enough to become a local hot spot? Is the thin wall fed well enough to fill before it freezes? A casting that looks fine after trim can still reveal a problem when a sealing face is machined or a thread is loaded.
The magnesium die casting process should be selected with the part geometry and production volume in mind. Thixomolding, conventional die casting, and machining from wrought stock are not interchangeable routes, even if the finished part looks similar in CAD.
Once machining opens up the casting
AZ91D and AM60B can both be finish-machined for holes, datums, threads, sealing faces, and other controlled features. The machining discussion is less about declaring one grade “easy” and more about the condition of the casting.
A casting with variable wall thickness, a large unsupported face, or porosity near the surface may behave differently once material is removed. The drawing should identify machined datums, critical surface finish, permissible edge breaks, and any areas where porosity is unacceptable after machining. Shops also need an appropriate magnesium chip-control and housekeeping plan. Read more about magnesium CNC machining when post-cast features are a meaningful part of the design.
Corrosion is often an assembly problem
Neither alloy should be treated as maintenance-free in a corrosive environment. Coating selection, pretreatment, drainage, dissimilar-metal contact, fastener isolation, and exposure to salts or moisture can matter as much as the base alloy.
Ask early whether the part will live indoors, in a controlled enclosure, in a humid industrial setting, or near road salt. A coating system that works for an electronics cover may not be enough for an exposed automotive or outdoor component. The same goes for fasteners: a small contact area between unlike metals can become the problem spot.
Typical places these grades show up
AZ91D is often evaluated for electronics housings, covers, general brackets, gear or equipment housings, and industrial die-cast components. It is a practical place to start when strength, hardness, castability, and supply familiarity are high on the list.
AM60B is often evaluated for automotive structural castings, impact-loaded parts, portable equipment frames, and designs where higher ductility has a clear purpose. “Automotive” alone is not enough reason to pick it; the load case should justify the choice.
The alloy price is rarely the whole cost story
Material price is only one line in a die-casting program. Die complexity, expected scrap, cycle time, machining allowance, coating, inspection, and annual volume can have a larger effect on the final part cost.
For a mature high-volume program, a small difference in alloy price may matter less than a die design change that improves yield or removes a secondary operation. For a low-volume requirement, machining from a different magnesium product form may be more sensible than casting tooling at all. Put the casting route, secondary operations, and expected volume beside the alloy price when comparing quotes.
Reading the drawing before choosing the grade
Start with the failure mode. If the part must stay stiff, support a cover, hold geometry, and serve as a general-purpose casting, AZ91D is a reasonable candidate. If it needs to manage deformation or impact without becoming brittle, AM60B deserves serious consideration.
Then work through the rest of the drawing: minimum wall thickness, wall transitions, bosses, ribs, gate access, machined features, coating, joining method, service temperature, and corrosion exposure. A die caster needs those details before recommending a grade with any confidence.
What the die caster will need before quoting
Send the alloy grade and applicable material standard, a 2D drawing and 3D model, part dimensions, minimum wall thickness, critical tolerances, projected annual quantity, die-casting quantity, CNC machining requirements, surface treatment, corrosion environment, inspection report needs, material certification, and packaging requirements.
If you are still comparing the two grades, say so. A supplier can then quote the realistic route and point out whether a load case, a corrosion concern, a machined sealing face, or a lead-time constraint is likely to decide the choice.
Need help reviewing an AZ91D or AM60B part?
If you have a drawing that could go either way, request a magnesium manufacturing review. Send the material target, part function, expected volume, environment, and any mechanical or inspection requirement. The review can identify the questions that need answers before the die or production route is fixed.
