🪶 MAGNESIUM
Sourcing Magnesium Alloys for Mobile's Aerospace and Marine Builders
Few cities pair an aircraft final assembly line with a working shipyard the way Mobile does, and both demand the lightest structural metals that will still hold tolerance. Magnesium, at roughly two-thirds the density of aluminum, earns its place in cast housings and machined brackets where mass is the enemy. This guide covers how Mobile buyers spec and source AZ31B, AZ91D, and WE43 without getting burned on corrosion or supply.
ISO 9001AS9100NADCAP
Why Magnesium Shows Up on Mobile Drawings
The single biggest pull for magnesium in Mobile is aerospace. With Airbus running A320, A220, and related final assembly at Brookley, the regional supply base has grown comfortable with the weight-down mandate that drives every aircraft program. Magnesium sits at about 1.74 g/cm3 against aluminum's 2.70, so a transmission housing or seat-frame bracket converted to magnesium can shed 25 to 30 percent mass before any topology work begins. That matters on parts that fly thousands of cycles.
The second pull is the marine and defense work along the Gulf. Austal's aluminum shipbuilding culture means local engineers already think in terms of corrosion management and dissimilar-metal isolation, which is exactly the discipline magnesium demands. Gearbox cases, electronics enclosures, and portable equipment housings are common candidates where a few pounds saved per unit compounds across a vessel.
The catch is always corrosion. Magnesium is anodic to nearly everything it touches, so Mobile buyers who succeed with it treat surface finish and fastener isolation as part of the spec, not an afterthought. Chromate-free conversion coatings, anodize per AMS standards, and nylon or coated fasteners are the norm rather than the exception.
Reading the Three Grades: AZ31B, AZ91D, WE43
AZ31B is the wrought workhorse, supplied as sheet, plate, and extrusion. With roughly 3% aluminum and 1% zinc, it formed and welds reasonably well and is the grade most Mobile sheet-metal and fabrication shops will reach for when a flat or bent magnesium part is needed. Expect tensile strength near 260 MPa and good machinability, though chip handling needs fire-aware housekeeping.
AZ91D is the die-casting standard. The higher aluminum content (around 9%) gives excellent castability and the controlled-impurity 'D' chemistry resists corrosion far better than older AZ91 variants. For housings, covers, and brackets produced in volume, AZ91D is what foundries quote. It is not a high-temperature alloy, so it stays clear of anything near an engine hot section.
WE43 is the premium aerospace and defense grade. Alloyed with yttrium and rare earths, it holds strength to roughly 250 C and is qualified on rotorcraft transmissions and missile components. It costs multiples of AZ91D and ships on longer lead times, so Mobile buyers reserve it for parts where elevated-temperature strength is non-negotiable. When a defense program calls it out, expect full traceability and likely NADCAP-accredited processing.
Frequently Asked Questions
Yes, but verify the paper trail before you commit. Aerospace magnesium parts almost always require AS9100 quality systems and, for special processes like heat treat, conversion coating, or nondestructive testing, NADCAP accreditation. Mobile's supply base has matured alongside the Airbus final assembly line at Brookley, so many shops already carry AS9100 and understand full material traceability from mill cert to finished part. For WE43 in particular, confirm the supplier can document chemistry, temper, and any post-processing because rare-earth magnesium alloys are tightly controlled on flight hardware. Ask to see a sample first-article inspection report and a recent certificate of conformance. If a shop cannot produce those quickly, they are likely not set up for flight work regardless of what their website claims. The safest path is to pre-qualify two suppliers so a single audit finding does not stall your program.
Treat corrosion control as part of the design, not a coating you add later. Mobile sits on a humid, salt-laden coastline, and magnesium is anodic to nearly every metal it contacts, so galvanic corrosion is the primary failure mode. Start with a controlled-impurity grade like AZ91D rather than legacy chemistries, since tight limits on iron, nickel, and copper dramatically slow corrosion. Then specify a conversion coating or anodize per the relevant AMS standard, and consider a sealing topcoat for exposed parts. Equally important is isolation at every interface: use coated or nylon fasteners, install insulating washers or gaskets where magnesium meets steel or aluminum, and avoid trapping moisture in blind pockets. Designers who drain water away and break electrical continuity between dissimilar metals get years of service; those who bolt bare magnesium to a steel bracket near salt air see white powder within weeks. Bring your finishing supplier into the conversation early.
Expect a large gap. AZ91D is a high-volume die-casting alloy with a mature supply chain, so raw material and casting costs are moderate and lead times are typically a few weeks for tooled parts. WE43 is a specialty aerospace and defense alloy containing yttrium and rare-earth elements, which makes the base material several times more expensive per pound and far less commonly stocked. Lead times for WE43 stock and especially for qualified, traceable WE43 processing can stretch significantly longer, particularly when a defense program requires NADCAP-accredited heat treatment and inspection. For Mobile buyers, the practical guidance is to use WE43 only where its elevated-temperature strength to roughly 250 C is genuinely required, such as rotorcraft gearbox housings, and default to AZ91D or wrought AZ31B everywhere else. Locking in material early and pre-positioning stock with your supplier is the most reliable way to protect a schedule on WE43 parts.
It can be, provided the shop is set up for it. Magnesium chips and dust are flammable and a magnesium fire cannot be extinguished with water, so the shop must have Class D extinguishers on hand, dedicated chip collection that does not let fines accumulate, and operators trained on the hazards. The good news is that magnesium machines easily and quickly, often at higher speeds and feeds than aluminum, which keeps cycle times attractive. Best practice is sharp carbide tooling, high spindle speed, ample chip clearance, and dry cutting or mineral-oil-based coolant rather than water-based fluid. The actual risk is not the solid part but a neglected pile of fine swarf, so good housekeeping is the real safety control. When you evaluate a Mobile machining partner for magnesium, ask directly how they store and dispose of chips and whether their staff has run magnesium before; the answer tells you whether they understand the material.
The clearest demand comes from aerospace and defense, driven by the Airbus final assembly presence and the broader Gulf Coast aerospace supply base. Aircraft programs constantly hunt for weight reduction, and magnesium brackets, housings, and gearbox components deliver that. Defense and marine work tied to the region's shipbuilding culture also generates magnesium demand for electronics enclosures and portable equipment where every pound matters. Beyond those, automotive and heavy-equipment makers in the wider region use AZ91D die castings for covers, brackets, and housings where mass reduction improves efficiency. The common thread is any application where shaving weight has real value and the operating environment can be managed for corrosion. If your part lives in a hot section, a high-wear interface, or an unprotected outdoor structural role, magnesium is usually the wrong call and aluminum or steel will serve better. Match the alloy to the duty cycle and the temperature, and magnesium pays off.
Last updated: July 2026
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