We compare AZ91D vs. ADC12 across strength, corrosion, manufacturability, and total cost to guide your material selection.
In the engineering world, “Lightweighting” is the holy grail.
Whether you are designing a handheld gimbal that needs to be held for hours, or a drone where every gram equals 10 seconds of flight time, you eventually hit a wall with Aluminum.
That’s when the question arises: “Should we switch to Magnesium?”
At Sureton, we see this debate play out in our conference room weekly. The allure of Magnesium is obvious (it’s lighter), but the fears are real (it corrodes, it burns, it’s expensive).
As a manufacturer who casts both, we want to give you an honest, unvarnished comparison between Magnesium (AZ91D) and Aluminum (ADC12). No sales fluff—just the physics and the financials.
1. The Physics: The “33% Rule”
Let’s start with the undeniable advantage.
Aluminum Density: ~2.7 g/cm³
Magnesium Density: ~1.8 g/cm³
Magnesium is roughly 33% lighter than Aluminum.
If you have a 1kg aluminum housing, switching to magnesium (with the same geometry) instantly drops the weight to ~670g. For a soldier carrying gear or a surgeon holding a powered tool, this difference is massive.
But here is the nuance: Magnesium has a lower Modulus of Elasticity (Stiffness) than Aluminum (~45 GPa vs ~71 GPa).
The Engineering Reality:
If stiffness is critical, you can’t just swap the material 1:1. You might need to add ribs or slightly increase wall thickness to match the stiffness of the aluminum part. This can significantly offset the theoretical weight saving.
The Solution: The net benefit must be calculated through careful stiffness-driven redesign. This is where Sureton’s DFM analysis provides critical value, optimizing rib patterns and wall profiles to maximize weight reduction without sacrificing rigidity.
2. The Process: Hot Chamber vs. Cold Chamber
This is where the manufacturing economics get interesting.
Aluminum (ADC12) is cast in a Cold Chamber machine.
The molten metal is ladled into the sleeve.
High pressure is required.
Cycle times are slower because the metal cools in the sleeve.
Tool Life: ~80k – 100k shots (Aluminum attacks steel aggressively).
Magnesium (AZ91D) is typically cast in a Hot Chamber machine (similar to Zinc).
The injection mechanism is submerged in the molten bath.
Cycle Time: 20-30% faster than aluminum.
Tool Life: 200k – 300k shots. Magnesium doesn’t attack the H13 steel mold as aggressively as aluminum does.
Sureton’s Insight: If you have a high-volume project (e.g., 200,000 units/year), the savings on mold replacement and faster cycle times can sometimes offset the higher raw material cost of Magnesium.
3. The “Elephant in the Room”: Corrosion
“But won’t it rot?”
This is the #1 fear. Magnesium is highly reactive. If you leave a raw magnesium part in a salty environment, it will disappear.
However, modern metallurgy has changed the game. Crucially, a magnesium component is not a “finished” part until it receives a robust, continuous protective coating. This is a non-negotiable added cost and process step.
High Purity Alloys: We use High Purity AZ91D (Iron < 0.004%). Iron is the impurity that accelerates corrosion. By keeping it ultra-low, the corrosion resistance improves dramatically.
Surface Treatment is Mandatory: You cannot leave Magnesium raw.
Standard: Conversion Coating (chemical film) + Powder Coat.
Premium: Micro-Arc Oxidation (MAO) or E-Coating.
The Cost Reality: With proper E-coating, a magnesium part can pass 1,000 hours of salt spray testing, matching aluminum. However, achieving this level of protection often adds 15-30% to the part’s base cost compared to a standard aluminum finish.
Design Rule: The biggest risk isn’t the environment; it’s Galvanic Corrosion. Never bolt a stainless steel screw directly into magnesium. You must use a washer, a coating, or a compatible plating to break the electrical path.
4. The Safety Myth: “Will it Catch Fire?”
We often hear: “I don’t want my product to explode.”
Let’s debunk this. Solid Magnesium die castings do not burn. You can hold a blowtorch to a magnesium laptop case, and it will just melt.
The fire risk exists only in the manufacturing stage (machining chips and dust).
At Sureton: We have strict safety protocols for machining magnesium (wet machining, specialized fire suppression).
For You (The User): Once the part is cast and solid, it is completely safe. It is used in car steering wheels and aircraft seats every day.
5. Machinability & Thin Walls
Magnesium is the easiest structural metal to machine.
Power Consumption: It requires 55% less power to machine than aluminum.
Tool Wear: Cutters last significantly longer. This translates to lower per-part machining costs and higher throughput.
Thin Walls: Magnesium flows better than aluminum. We can cast walls down to 1.0mm – 1.5mm reliably, whereas aluminum often struggles below 2.0mm without vacuum assist.
Benefit: This superior fluidity can enable part consolidation (reducing assembly cost) or further weight savings that aluminum cannot achieve, amplifying the initial lightweight benefit.
The Verdict: When to Switch?
So, is the switch worth it? Here is our decision matrix:
Stick with Aluminum (ADC12) if:
Cost is King: Aluminum raw material is cheaper and more stable in price.
Extreme Environments: While protectable, securing long-term corrosion resistance in marine or chemical splash zones is more proven and cost-effective with aluminum.
Thermal Conductivity: Aluminum dissipates heat better (~96 W/m·K vs ~72 W/m·K for Mg).
Switch to Magnesium (AZ91D) if:
Weight is the Selling Point: Handheld tools, AR/VR headsets, Drones, Portable Medical Devices.
Vibration Damping: Magnesium absorbs vibration 100x better than aluminum. Great for optical mounts or chainsaw housings.
Complex, Thin-Wall Geometry: Where aluminum would require multiple parts or risk incomplete filling, magnesium’s flowability enables simpler, more reliable tooling.
Let’s Weigh Your Options (Literally)
Switching materials is a big engineering change. It affects your tolerancing, your finishing, and your assembly.
Don’t guess. Send your 3D model to Sureton.
Beyond a side-by-side quote, our engineers will provide a manufacturability and lifecycle analysis for both materials, highlighting trade-offs in tooling design, finishing processes, and assembly implications specific to your volume.
