CNC Machined Magnesium Parts & Suppliers

Karl Gillihan

🪶 MAGNESIUM

CNC Machining Magnesium: AZ31B, AZ91D and WE43 Lightweight Parts

Magnesium is the lightest structural metal, about a third lighter than aluminum, and one of the fastest-cutting materials a CNC ever sees, machinable at extreme speeds with almost no tool wear. The headline risk is the one everyone knows: fine magnesium chips and dust burn fiercely and burn hot. The reality is that experienced shops machine it safely every day, but the fire-management requirements shape who can do the work and what it costs.

AS9100ISO 9001ITAR

Fire safety: the real constraint, not a myth

Magnesium ignites as fine particles, chips, turnings, dust, and once burning it is hard to extinguish; water accelerates the reaction, releasing hydrogen, so Class D dry-powder extinguishers and dry sand are the tools, not a hose. This is the genuine constraint on magnesium machining, and it is why not every shop will quote it. Solid magnesium stock does not casually ignite, but the fine swarf does, especially when dry-cut and allowed to accumulate. The controls experienced shops use are specific: machine wet with mineral-oil-based coolant rather than water-based (water reacts with magnesium and promotes corrosion), or dry-machine with disciplined chip evacuation; keep cutters sharp to make chips rather than dust; never let fine swarf pile up; and have Class D extinguishing media on hand. Dull tools, light rubbing cuts and dust generation are the danger, not normal chip-forming cutting. For buyers, the practical implications are that magnesium parts should go to a shop with magnesium experience and proper fire procedures, that lead times can be slightly longer due to careful chip handling, and that the safety overhead is real but routine for qualified shops. It is not a reason to avoid magnesium when its weight savings are needed.

Cutting speed and the alloy lineup

When safety is handled, magnesium is a joy to cut: it has the lowest cutting forces and best machinability of any structural metal, allowing very high spindle speeds and feeds with minimal tool wear, often outpacing even aluminum. Power consumption is low and finishes come out clean. This makes magnesium attractive for high-feature parts where machining time would dominate, provided the weight advantage is worth the handling care. AZ31B is the wrought magnesium-aluminum-zinc alloy, available in sheet, plate and extrusion, with good strength and the easiest formability; it is common in aerospace and general lightweight machined parts. AZ91D is the high-aluminum die-casting alloy, often machined as cast components for automotive and consumer housings; it offers good castability and corrosion resistance for a magnesium alloy and machines well. WE43 is the high-performance grade, a magnesium-yttrium-rare-earth alloy with good strength retention at elevated temperature and, notably, a bioabsorbable variant used in resorbable medical implants such as bone screws that dissolve as bone heals. WE43 is the premium, specialty choice; AZ31B and AZ91D cover most structural and housing applications. The grade follows the role: wrought structure, cast housing, or high-temp/medical specialty.

Corrosion, finishing and applications

Magnesium's weakness is galvanic and general corrosion; bare magnesium corrodes readily, especially in contact with dissimilar metals or salt, so finishing is essentially mandatory for service parts. Chromate conversion coatings (chem-film), anodizing-type treatments such as the proprietary Tagnite and Keronite/plasma electrolytic oxidation processes, and primer-plus-paint or powder-coat systems are used to protect the surface. Fasteners and inserts in contact with magnesium must be isolated or chosen to avoid galvanic attack. Tolerances are readily held, +/-0.005 in standard and tighter on critical features, with good dimensional stability and low cutting forces aiding thin-wall work, though the soft metal can deflect and must be deburred carefully. Surface finish is good as-machined. Applications cluster where every gram matters: aerospace brackets, housings and gearbox cases; automotive and motorsport components; portable electronics and camera bodies; drone and UAV structure; and, for WE43, bioabsorbable orthopedic implants. The buyer logic is straightforward: magnesium is chosen when its roughly 35 percent weight saving over aluminum is genuinely valuable, and the finishing and fire-handling costs are accepted as part of that tradeoff. Where weight is not critical, aluminum is simpler and avoids the corrosion and safety overhead.

Frequently Asked Questions

Yes, qualified shops machine magnesium safely every day, but the fire risk is real and shapes how the work is done. The hazard is fine swarf: magnesium chips, turnings and especially dust can ignite, and once burning magnesium is hard to extinguish because water accelerates the reaction and releases hydrogen, so Class D dry-powder extinguishers and dry sand are required rather than water. Solid magnesium stock does not casually ignite; the danger is accumulated fine particles, particularly from dry cutting or dull tools that generate dust instead of chips. Experienced shops control this with sharp tooling to form chips rather than dust, disciplined and frequent chip evacuation so swarf never piles up, mineral-oil-based coolant rather than water-based, and Class D extinguishing media on hand. The practical takeaway for buyers is to source magnesium parts to a shop with genuine magnesium experience and proper fire procedures, expect the handling care to add modestly to cost and lead time, and understand that the safety overhead is routine for qualified shops, not a reason to avoid magnesium when you need its weight savings.

Magnesium is roughly 35 percent lighter than aluminum, with a density around 1.7-1.8 g/cm3 versus aluminum's 2.7 g/cm3, making it the lightest commonly used structural metal. That weight advantage is the entire reason to choose it, since on a strength-to-weight basis magnesium competes with aluminum for many parts while saving about a third of the mass. It is why magnesium appears in aerospace brackets and housings, automotive and motorsport components, portable electronics, camera bodies and drone structures, anywhere every gram counts. The tradeoffs are that magnesium has lower absolute strength and stiffness than the strongest aluminum alloys, corrodes more readily and so requires protective finishing, and demands fire-aware machining. For buyers, the decision is straightforward: if the roughly 35 percent weight saving over aluminum genuinely matters to the product, magnesium earns its place despite the finishing and handling overhead. If weight is not critical, aluminum is simpler, cheaper to protect, and avoids the corrosion and fire-safety considerations, so it remains the default for most lightweight parts where the extra weight reduction is not worth the added cost and care.

Match the alloy to the part's form and performance needs. AZ31B is the general-purpose wrought magnesium-aluminum-zinc alloy, supplied as sheet, plate and extrusion with good strength and the best formability of the three; it is the common choice for machined aerospace and general lightweight structural parts. AZ91D is the high-aluminum die-casting alloy, most often machined as cast housings and components for automotive, powertrain and consumer products; it offers good castability and relatively good corrosion resistance for magnesium and machines cleanly. WE43 is the premium specialty alloy, a magnesium-yttrium-rare-earth composition that retains strength at elevated temperatures better than the AZ alloys and is used in demanding aerospace and motorsport parts; a notable WE43 application is bioabsorbable medical implants such as resorbable bone screws that dissolve safely as bone heals. So choose AZ31B for wrought structural machined parts, AZ91D when starting from a die casting, and WE43 for high-temperature performance or bioabsorbable medical use. All three machine very fast with low tool wear, so the choice is driven by form, strength, temperature and application rather than machinability.

For almost all service parts, yes, because bare magnesium corrodes readily, especially in humid or salty environments and wherever it contacts dissimilar metals, which sets up galvanic corrosion. Finishing is therefore essentially mandatory rather than optional. Common protective systems include chromate conversion coatings (chem-film) for a basic corrosion barrier and paint adhesion, proprietary anodizing-type treatments such as Tagnite and plasma electrolytic oxidation processes like Keronite that build a hard, protective oxide layer, and primer-plus-paint or powder-coat topcoat systems for durable protection and appearance. Equally important is galvanic isolation: steel or aluminum fasteners, inserts and mating parts in contact with magnesium must be coated, isolated with barrier layers, or chosen carefully, because the dissimilar-metal junction is where corrosion concentrates. These finishing and isolation steps add cost and lead time, typically a few days for batched coating processes, and should be specified on the drawing along with masked areas. For prototypes that only need to function briefly indoors, a temporary protective film can suffice, but production magnesium parts should always carry a corrosion-protection callout to achieve acceptable service life.

Magnesium holds standard CNC tolerances comfortably, with +/-0.005 in (0.13 mm) routine on general dimensions and +/-0.001 in (0.025 mm) achievable on called-out critical features. Its very low cutting forces and excellent machinability actually help dimensional control and make thin-wall and lightweight features more achievable than in many metals, though the soft material can still deflect under load and needs careful deburring since burrs form readily. Dimensional stability during machining is good. As-machined surface finish is clean and smooth, typically in the 32-125 microinch Ra range depending on tooling and passes, and magnesium does not present the gumminess of copper or the work-hardening of stainless, so achieving a good finish is straightforward when tooling is sharp. The main planning consideration is not the machining tolerance but the finishing: protective coatings such as chem-film or plasma electrolytic oxidation add slight thickness and require masking of mating surfaces, so coordinate finish callouts with tight-tolerance features. Overall, between its fast cutting, low forces and good finish, magnesium is one of the more cooperative metals dimensionally once the fire-safety handling is in place.

Last updated: July 2026

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