Magnesium Machining and Fabrication in Kokomo, IN: AZ31B, AZ91D, and WE43 for Powertrain and EV Applications

Transmission assemblies built in the Kokomo region must hit precise mass targets set by OEM fuel-economy and range calculations. A single automatic transmission housing machined from AZ91D die-cast magnesium instead of aluminum can reduce component mass by 25 to 30 percent, directly improving vehicle efficiency across millions of production units. At the volumes Stellantis-linked programs demand — often tens of thousands of housings per month — that weight reduction translates into measurable fleet CO2 compliance gains. The Samsung SDI battery gigafactory supplying EV cells to the regional assembly network creates a parallel demand stream. Battery module end-plates, structural brackets, and cooling-channel frames benefit from AZ31B sheet-formed or AZ91D cast components that combine low mass with adequate thermal conductivity. Engineers specifying these parts must balance the material's 45 W/(m·K) thermal conductivity — roughly 60 percent of aluminum's — against its superior stiffness-to-weight ratio, making wall-thickness and rib geometry critical design variables. Kokomo's existing CNC machining infrastructure, built to hold ±0.001 inch tolerances on aluminum and steel powertrain parts, adapts well to magnesium. Cutting speeds for AZ31B wrought plate typically run 3,000 to 5,000 surface feet per minute with sharp uncoated carbide tooling, allowing shops to maintain cycle times comparable to aluminum while using the same multi-axis machining centers already on the floor.

AZ31B is the workhorse wrought alloy — available as rolled sheet, plate, and extruded bar — and it dominates applications requiring formed or machined structural panels, brackets, and covers. Its tensile strength of approximately 260 MPa with 15 percent elongation makes it formable enough for press-brake bending at elevated temperatures while still delivering the rigidity needed for enclosure structures. In Kokomo's EV supply chain context, AZ31B sheet cut to precise blanks and formed into battery module side walls or upper covers is a common procurement need. AZ91D is the dominant die-casting alloy, accounting for the majority of magnesium castings produced globally. Its aluminum content (approximately 9 percent) and zinc addition yield a castable alloy with 230 MPa tensile strength, good corrosion resistance relative to other magnesium alloys, and excellent fluidity for thin-wall complex geometries. Transmission valve bodies, shifter housings, and instrument-panel cross-car beam brackets are all AZ91D territory. Die-cast AZ91D parts require careful attention to porosity — X-ray or CT inspection to ASTM E505 standards is standard practice on safety-critical powertrain components. WE43 serves the elevated-temperature niche. With rare-earth additions (yttrium and zirconium), WE43 retains useful strength to 250°C and offers superior creep resistance versus AZ-series alloys. Electric motor housings that see sustained heat soak, or gearbox components adjacent to high-efficiency inverters, are natural WE43 applications. The alloy's yield strength of approximately 200 MPa at 150°C makes it the preferred choice when operating temperatures exceed the 120°C ceiling where AZ91D begins to lose dimensional stability.

Machining magnesium in a production environment requires specific protocols that go beyond standard aluminum practice. Fine magnesium chips and powder are combustible; shops must use dedicated dry vacuum systems, segregate magnesium swarf from other metals, and store chips in sealed steel containers with dry sand nearby. OSHA 29 CFR 1910.94 and NFPA 480 govern magnesium storage and handling, and any supplier running magnesium on a production basis in Kokomo should hold documented fire-safety procedures as part of their quality management system. With those precautions in place, magnesium is one of the most machinable metals available. Tool life is excellent, surface finishes of Ra 32 microinch or better are routinely achieved with single-point turning, and the low cutting forces reduce fixturing demands on thin-wall castings. Five-axis machining centers commonly used for aluminum transmission components in the Kokomo corridor handle magnesium without significant reprogramming — the primary change is flood coolant selection, where water-based coolants must be carefully managed to prevent hydrogen generation from chip-coolant contact. Corrosion protection is the other critical finishing requirement. Bare magnesium corrodes rapidly in humid environments; chromate conversion coatings (per MIL-DTL-45204), micro-arc oxidation, or epoxy powder coat are the standard treatments for automotive magnesium parts. EV enclosure applications often specify a two-stage system: conversion coat followed by e-coat or powder coat, matching the protection level applied to adjacent aluminum and steel structures.

Raw material sourcing for magnesium in central Indiana runs primarily through regional metal service centers that stock AZ31B plate and sheet in thicknesses from 0.040 inch to 2.0 inch, and through die casting specialists concentrated in the Indianapolis-to-Fort Wayne corridor that produce AZ91D blanks to near-net shape. Lead times for standard AZ31B plate in 0.125 to 0.500 inch thickness typically run two to four weeks from domestic warehouse stock; WE43 bar and plate requires longer lead times — often eight to twelve weeks — due to limited domestic production capacity. For Kokomo buyers on EV platform programs with firm launch timelines, the most practical sourcing approach combines a domestic service center for AZ31B sheet with a qualified die caster for AZ91D structural castings, supplemented by an ITAR-aware importer for WE43 when aerospace crossover requirements apply. ManufacturingBase connects Kokomo procurement teams with verified suppliers across all three tiers, with traceability documentation — mill certs, heat numbers, and chemical analysis reports — included as a standard deliverable.