Aluminium, Zinc or Magnesium? Comparing Die Casting Materials
Aluminium, zinc and magnesium alloys account for the vast majority of die cast parts. Each material family brings its own combination of weight, strength, castability and surface quality, and each places different demands on the machine, the melt handling and the die. The choice of material therefore shapes the entire production setup, not only the part.
Which Die Casting Material Fits Which Application?
Aluminium is the most widely used choice for lightweight structural and housing parts and is processed on cold chamber machines. Zinc allows very thin walls, fine detail and high-quality surfaces for decorative or plated parts and is typically cast on hot chamber machines. Magnesium offers the lowest density of the three and is used where weight is critical; depending on part size it runs on hot or cold chamber machines.
The final decision depends on the required mechanical properties, operating temperature, corrosion environment, surface finish and production volume, which should be clarified with the customer specification and the alloy supplier.
The Three Material Families at a Glance
The table below gives qualitative orientation. Exact values for density, solidification range, strength and elongation differ from alloy to alloy and should always be taken from the relevant standard or the supplier's data sheet.
| Criterion | Aluminium Alloys | Zinc Alloys | Magnesium Alloys |
|---|---|---|---|
| Density (approx.) | approx. 2.7 g/cm³ | approx. 6.6–7 g/cm³ | approx. 1.8 g/cm³ |
| Typical machine type | Cold chamber | Hot chamber | Hot chamber for smaller parts, cold chamber for larger parts |
| Processing temperature | Comparatively high | Low | Comparable to aluminium |
| Thin walls and fine detail | Good | Very good | Very good flowability |
| Die life | Limited by thermal fatigue | Long, due to lower thermal load | Generally longer than with aluminium |
| Special attention | Melt cleanliness, hydrogen, heat checking | Creep at elevated temperatures, weight | Melt protection, fire safety, galvanic corrosion |
Aluminium: The Versatile Standard
Aluminium die casting alloys are mostly based on aluminium–silicon, often with copper or magnesium additions. Silicon improves fluidity and castability; copper raises strength but reduces corrosion resistance; low-iron variants alloyed with manganese and magnesium are used for structural parts that need higher ductility or heat treatment.
Because molten aluminium attacks iron-based components, it is not held in contact with the shot system for long periods. Instead, a measured quantity is ladled or dosed into the shot sleeve of a cold chamber die casting machine for every shot. The higher processing temperature increases thermal load on the die, which makes heat checking one of the main wear mechanisms.
Zinc: Precision, Detail and Surface
Zinc die casting alloys, commonly zinc–aluminium alloys with small copper and magnesium additions, melt at a much lower temperature than aluminium. This allows hot chamber processing with the shot system immersed in the melt, short cycles and very long die life.
Zinc parts are dimensionally precise and well suited to plating and decorative finishes, which is why they are common in fittings, hardware, locks and connectors. The trade-offs are the high density and a tendency to creep under sustained load at elevated temperatures, which limits use in warm, highly loaded applications.
Magnesium: Maximum Weight Saving
Magnesium is the lightest structural metal used in die casting. Common alloy groups contain aluminium and zinc for strength and castability, or aluminium and manganese for higher ductility. Magnesium fills thin sections well and, because it does not attack steel in the same way as aluminium, it can be processed in hot chamber machines for smaller parts and in cold chamber machines for larger ones.
Molten magnesium oxidises readily and must be protected by a cover gas. The gases permitted for this purpose are subject to environmental regulation, so the current rules should be checked for each site. Chips, fines and dust require dedicated fire-safety measures, and water must be kept away from the melt. In assemblies, contact with other metals must be designed to avoid galvanic corrosion.
What the Material Choice Means for Machines and Melt Shop
Cold or hot chamber, shot end size and plunger diameters follow from alloy and part.
Melting, holding and dosing must match alloy, temperature and throughput.
Die steel, temperature control and spraying depend strongly on the alloy.
Magnesium in particular needs melt protection and fire-safety concepts.
Changing material on an existing line is rarely a simple switch. A hot chamber zinc machine cannot be used for aluminium, and moving from aluminium to magnesium requires changes to melt handling and safety equipment. The differences between the two machine principles are covered in our article Cold Chamber or Hot Chamber?, and suitable melting and holding equipment can be found among our used furnaces.
Questions to Answer Before Choosing the Material
- Which mechanical properties are specified, and are they required in the as-cast or heat-treated condition?
- At what temperature and under what sustained load will the part operate?
- Which corrosion environment and which joining partners are involved?
- Which surface finish is required: machined, coated, plated or decorative?
- How critical is part weight compared to material and processing cost?
- What minimum wall thickness and level of detail does the design need?
- Which machine type and melt equipment are already available in-house?
- Are site permits and safety concepts in place for the chosen alloy?
Frequently Asked Questions
Why is aluminium not cast on hot chamber machines?
Molten aluminium attacks iron-based materials. Keeping the shot system permanently immersed in aluminium melt would lead to rapid wear, so aluminium is dosed into a cold chamber shot sleeve for each shot.
Is zinc always heavier than aluminium for the same part?
For the same volume, yes, since zinc alloys are roughly two and a half times as dense. Thinner walls can partly offset this, but zinc is rarely chosen when low weight is the main goal.
Can one machine process aluminium and magnesium?
A cold chamber machine can in principle be used for both, but melt handling, cover gas, dosing and safety equipment differ. A change must be planned as a process conversion, not simply a material swap.
FISS Helps Match Machine and Melt Shop to the Alloy.
Whether you are adding aluminium capacity or setting up a new process, FISS offers used cold chamber die casting machines and furnaces and can help assess which equipment suits your material and parts.
