Swiss Machining Magnesium: AZ31B, AZ91D and WE43

Magnesium's defining machining issue is not how it cuts but how it burns. Fine chips, turnings, and especially the dust generated by light finishing cuts are flammable, and a magnesium fire burns extremely hot and cannot be extinguished with water or standard extinguishers; water reacts with burning magnesium to release hydrogen and intensify the fire. Class D dry-powder extinguishers and dry sand are the only correct response, and they must be on hand. The controls follow directly: many shops run magnesium with dry or minimum-quantity machining rather than water-based coolant (because water reacts), or use specially formulated mineral-oil coolants and accept the fire-management discipline. Sharp tooling and adequate feed keep chips coarse rather than producing fine flammable dust, since coarse chips ignite far less readily than dust. Chip accumulation is never allowed; swarf is cleared frequently and stored in covered metal containers away from other materials. Good ventilation and dust collection rated for combustible metal are part of the setup. The bottom line for a buyer is that magnesium Swiss machining is done only by shops equipped and trained for it, which narrows the supplier pool and is the first thing to confirm when sourcing.

AZ31B is a wrought magnesium-aluminum-zinc alloy, the common general-purpose grade, with good strength-to-weight and excellent machinability; it is used for lightweight structural and electronic housing parts. AZ91D is primarily a die-casting alloy, higher in aluminum, with good corrosion resistance for a magnesium alloy and used where cast components are then machined; it machines cleanly when cut from cast or bar stock. WE43 is the specialist: a magnesium-yttrium-rare-earth alloy with high strength and good elevated-temperature performance, used in aerospace and, notably, in bioresorbable medical implants because magnesium can be safely metabolized by the body as it corrodes away in service. That resorbable behavior is the rare case where magnesium's reactivity is the feature, not the bug, letting an implant dissolve as bone heals rather than requiring removal surgery. All three alloys cut fast and clean; the choice is driven by the application (general lightweighting, castability, or high-performance/resorbable medical use) rather than by machining difficulty, since all magnesium machines easily once the fire-safety question is solved.

Magnesium is about two-thirds the density of aluminum and a quarter that of steel, the lightest structural metal available, which is the entire reason it is specified: every gram matters in aerospace, portable electronics, and some automotive applications, and magnesium delivers stiffness and strength at a weight nothing else matches. When a small turned part must be as light as physically possible, magnesium is the answer despite the handling demands. The machining itself is a pleasure when done safely: surface speeds can run very high, cutting forces are low so parts deflect little, tool life is excellent, and finishes come off the tool bright and smooth with minimal effort, often better than aluminum. Tolerances comparable to aluminum, in the +/-0.0005 inch range or tighter, are readily held, with the caveat that magnesium has a high thermal expansion coefficient so thermal control matters for the tightest work. Corrosion is the downside in service: bare magnesium corrodes readily, so parts are typically given a protective conversion coating, anodize-type treatment, or paint, and the finish must be specified. For buyers, magnesium is a deliberate weight-driven choice, and the cost premium comes more from the limited supplier base and safety overhead than from the cutting itself.