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What is Aluminum Alloy Die-Casting?
The short answer
Aluminium alloy die casting injects molten aluminium into a hardened steel die under high pressure and holds it while it freezes, so one reusable die produces a near-net-shape part in seconds. Melt sits at 650 to 710 degrees, the cavity fills in 20 to 50 milliseconds, and as-cast tolerance lands near plus or minus 0.25 mm.
What the process actually is
Aluminium alloy die casting is a permanent-mould casting process in which molten aluminium is forced into a precision-machined steel die rather than poured into a mould that is used once. The die has two halves, a fixed cover die and a moving ejector die, clamped together by the machine at 400 to 4,000 tonnes of locking force. Molten metal is injected into the cavity under 10 to 175 megapascals, fills it in milliseconds, and is held under intensification pressure while it solidifies.
Three properties of the process follow from that description. The die is a master negative, so every part is geometrically identical to the first one. The fill is fast, so walls can be thin and detail fine. And because the metal freezes under pressure inside a cooled steel block, the part comes out close to final shape, which is what near-net means in practice.
The four stages, and the parameters that matter
- Die preparation. The two H13 tool-steel halves are preheated and coated with a release agent, then clamped at 400 to 4,000 tonnes. Die surface temperature is held between 180 and 250 degrees Celsius by cooling channels in the steel; too cold and the cavity will not fill, too hot and the die wears faster.
- Injection. Molten alloy at 650 to 710 degrees Celsius is driven into the cavity at a gate velocity of 30 to 100 metres per second, filling it in 20 to 50 milliseconds. The shot profile is split into a slow stage that pushes metal past the gate without splashing and a fast stage that fills the part.
- Solidification. Intensification pressure is held for 2 to 8 seconds to squeeze out shrinkage, and the casting cools in the water-cooled die for roughly 15 to 60 seconds depending on wall thickness. This is also where most porosity is decided, because air trapped by a turbulent fill has nowhere to go.
- Ejection and trimming. The die opens, ejector pins push the casting out, and the shot, runners, overflows and flash are trimmed. Parts then go to deburring, machining and surface treatment as required.
Typical cycle time for a complete shot is 30 to 120 seconds for automotive work, shorter for small parts and longer for thick sections. A pump or valve housing with a 3 millimetre wall commonly runs in the 25 to 38 second range.
Which alloy, and why it is nearly always A380 or ADC12
Die casting alloys are not chosen for maximum strength. They are chosen for fluidity, because the metal has to fill a thin cavity before it freezes. That is why the two workhorses, A380 in North America and ADC12 in Japan, both carry 8 to 12 percent silicon: silicon raises fluidity, reduces hot tearing and lowers the melting range. The two are close relatives with different national designations and slightly different balances of copper and silicon.
| Property | A380 (AA) | ADC12 (JIS) |
|---|---|---|
| Standard | North America, AA designation | Japan, JIS H 5302 |
| Density | 2.71 g/cm3 | 2.72 g/cm3 |
| Tensile strength | 310 to 345 MPa | 300 to 330 MPa |
| Yield strength | 160 to 180 MPa | 150 to 170 MPa |
| Elongation | 2 to 4 percent | 1 to 3 percent |
| Thermal conductivity | 96 to 105 W per m-K | 90 to 100 W per m-K |
| Heat treatable to T6 | No | No |
| Typical use | Automotive housings, covers | Thin-wall parts, electronics enclosures |
A third alloy, A356, is often mentioned alongside these two and belongs in a different conversation. It carries less silicon, holds higher strength and elongation after a T6 treatment, and is cast by gravity or low pressure rather than by high-pressure injection, because its lower fluidity does not suit a thin-wall fast fill. Where a programme needs T6 properties, the part leaves the die casting family rather than the alloy list.
What a die casting can and cannot hold
- Wall thickness: 1.2 millimetres is achievable in a local thin section; 1.5 millimetres is the usual structural minimum; a general wall of 1.5 to 3.5 millimetres is comfortable. Below about 1 millimetre the wall becomes a process variable rather than a design input.
- As-cast tolerance: ISO 8062 CT4 to CT6, roughly plus or minus 0.25 millimetres on a linear dimension, with wall thickness nearer plus or minus 0.10 millimetres.
- Machined tolerance: plus or minus 0.05 millimetres is routine on a fixtured secondary operation, which is why accurate features are cast oversize and cut afterwards.
- Surface finish: Ra 1.6 to 3.2 micrometres as cast from a good die, with a denser skin layer of roughly 0.5 to 1.0 millimetres that should not be machined through.
- Not heat treatable: A380 and ADC12 are not suitable for T6 solution treatment, so a part that needs it must be made by gravity or low-pressure casting instead.
- Porosity: conventional high-pressure die casting carries 1.2 to 2.5 percent gas porosity by volume. Pressure-tight or fatigue-critical parts need vacuum assistance or squeeze casting, and that decision is made before the die is cut.
- Volume: tooling runs from USD 15,000 to 80,000 with a lead time of six to ten weeks, so the process is economic above roughly 3,000 to 5,000 pieces a year and uncomfortable below it.
- Size: most machines work within about 600 millimetres and 20 kilograms, which puts large structural castings out of scope.
How to start an aluminium die casting project
Send a STEP model, a toleranced drawing, the annual volume, the alloy or the property that matters most, and the surfaces that have to be accurate. Those five items let an engineer confirm the wall sections, place the parting line and tell you which features must be machined rather than cast. See aluminium die casting for the service scope, surface finishing for the options after the shot and CNC machining for the secondary operations that hold the tight dimensions.
Scope and sources. Process stages, machine envelope, pressure, gate velocity, cycle time, wall thickness and the T6 limitation come from a 2026 high-pressure die casting specification (400 to 4,000 tonnes clamping, injection 10 to 175 MPa, melt 650 to 710 degrees Celsius, gate velocity 30 to 100 metres per second, cycle 15 to 90 seconds, minimum wall 1.5 mm, Ra 1.6 to 3.2 micrometres, ISO 8062 CT4 to CT6, A380 and ADC12 not heat treatable, tooling USD 15,000 to 80,000, economic above 5,000 pieces a year) and from a step-by-step OEM process guide (melt 660 to 700 degrees Celsius, injection 80 to 120 MPa, fill time 20 to 50 ms, holding pressure 10 to 30 ms, die temperature 180 to 220 degrees, cycle 30 to 60 seconds, as-cast tolerance plus or minus 0.05 to 0.2 mm after fixturing). Alloy properties come from an automotive alloy comparison (A380 against ADC12 on density 2.71 and 2.72 g/cm3, tensile 310 to 345 and 300 to 330 MPa, yield 160 to 180 and 150 to 170 MPa, elongation 2 to 4 and 1 to 3 percent, thermal conductivity 96 to 105 and 90 to 100 W per metre-kelvin, melting range 555 to 595 degrees, linear tolerance near plus or minus 0.25 mm, flatness 0.30 mm per 100 mm, wall thickness plus or minus 0.10 mm, injection 40 to 120 MPa with intensification 60 to 150 MPa, cycle 30 to 120 seconds). The A356 caveat and the tooling and die-life figures come from a die casting design and cost guideline (A356 at 310 MPa tensile and 5 to 10 percent elongation after T6, used in gravity and low-pressure casting rather than high-pressure injection, tooling USD 8,000 to 80,000, die life 100,000 to 500,000 shots). Porosity, machining stock and skin depth come from an OEM process benchmark (gate velocity near 42 metres per second giving 1.2 to 2.5 percent gas porosity, 1.0 to 1.5 mm machining stock, dense skin 0.5 to 1.0 mm). Figures are published planning ranges for 2026, not quotations, and the alloy and process for a specific part are confirmed against its own drawing.
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