Ductile Iron vs. Aluminium

Aluminium's low density is its defining advantage — approximately one third that of iron — which directly reduces inertia, handling effort, shipping mass and energy consumption in moving assemblies.

Ductile iron's elastic modulus is far higher, so for the same shape it deflects much less under load. A stiffness-critical aluminium redesign therefore has to add section, ribs or depth, which claws back part of the weight saving and consumes package space.

Aluminium conducts heat several times better than cast iron, which is why heat sinks, coolers and many housings that must shed heat are aluminium. Its higher coefficient of thermal expansion, however, must be accounted for in fits, clearances and mixed-material assemblies.

Aluminium forms a self-repairing oxide film that gives good atmospheric corrosion resistance and can be enhanced by anodising. Ductile iron requires paint, coating or plating in humid or wet service.

Cast irons resist sliding wear better than most aluminium alloys and damp vibration more effectively. Where an aluminium housing has to carry a sliding or rotating interface, the design usually needs a steel or bronze insert, an iron liner, or a hard surface treatment.

Ductile iron also tolerates local overload and point loading at bolted joints better, which simplifies mounting arrangements and reduces the need for load-spreading hardware.

Aluminium machines quickly, at high cutting speeds and with low tool wear, and it is available as extrusions, plate, bar and castings. That combination supports fast prototyping and light, complex profiles.

Ductile iron is cheaper per kilogram and casts complex shapes economically at volume. Comparing costs only makes sense on the finished part, taking into account material, machining time, surface protection, inserts and assembly.