Most aluminium castings are made from a small handful of alloys, and in the majority of cases the alloy is chosen for how well it casts rather than for exotic mechanical properties.
Aluminium casting alloys are essentially aluminium with silicon, plus smaller additions of copper, magnesium and other elements. Silicon improves fluidity and reduces shrinkage, which is why nearly every casting alloy contains a significant amount of it. Copper adds strength and machinability but reduces corrosion resistance. Magnesium enables heat treatment response.
The alloys we run
High pressure die casting
| Alloy | Character | Typical use |
|---|---|---|
| ADC12 | The workhorse. Excellent castability, good strength, good machinability | General purpose housings, covers, brackets |
| ADC10 | Similar to ADC12, slightly different copper range | Thin-wall castings, general components |
| LM2 | Good fluidity, general purpose pressure die casting | Covers, housings, non-critical parts |
| LM24 | Good machinability and strength, tolerant of impurities | Industrial housings, gearbox parts |
| LM6 | Near-eutectic, excellent fluidity and corrosion resistance | Thin or intricate parts, marine and electrical |
| LM9 | LM6 with magnesium, higher strength, heat treatable | Stressed parts needing corrosion resistance |
| LM13 | Low expansion, good wear resistance | Pistons and high-temperature components |
| LM20 | Good fluidity and pressure tightness | Thin-section and pressure-tight parts |
| AlSi-132 | High silicon, low expansion, wear resistant | Pistons, wear surfaces |
Gravity die casting
| Alloy | Character | Typical use |
|---|---|---|
| LM25 | Excellent mechanical properties, heat treatable to T6, good corrosion resistance | Structural and safety-critical parts, wheels, housings |
| LM4 | Good general purpose, moderate strength, good castability | General engineering castings |
| LM6 | Outstanding fluidity, excellent corrosion resistance, not heat treatable | Intricate shapes, marine, water-contact parts |
| LM9 | LM6 base with magnesium, heat treatable | Parts needing both corrosion resistance and strength |
| LM13 | Low thermal expansion, wear resistant | Pistons, high-temperature applications |
How to choose, in practice
Start with the process
The casting process narrows the field immediately. High pressure die casting needs alloys that flow fast and release cleanly from the die. ADC12 and LM24 dominate for good reason. Gravity casting can use alloys like LM25 that develop better properties through slower solidification and heat treatment.
Then the operating environment
- Outdoors, marine or wet environments → LM6 or LM9. Low copper content means far better corrosion resistance.
- Structural or safety-critical → LM25 in gravity casting, heat treated to T6.
- Hot running or wear surfaces → LM13 or AlSi-132, where low thermal expansion matters.
- General housings and covers → ADC12. It is the default for a reason.
Then machining and finishing
Copper-bearing alloys such as ADC12 and LM24 machine well and take a clean thread. If your part will be anodised, however, high-silicon alloys give a dark, uneven finish, powder coating is usually the better route for die cast aluminium that needs colour.
Specifying a high-strength heat-treatable alloy for a part that is not structurally loaded. It raises cost, restricts the process options and may not even be achievable in high pressure die casting. Specify the property you actually need, and let the foundry propose the alloy.
Silicon, copper, magnesium, what each does
Equivalents across standards
The same metal appears under different names depending on the standard. ADC12 (JIS) is broadly equivalent to A383/A380 (ASTM) and to LM24 (BS). If your drawing specifies a European or American grade, send it to us, in most cases we can match it from stock or arrange the exact specification.
See the full list of grades we hold on our capabilities page.
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