Aluminium die casting alloys: ADC10, ADC12 and A380

Three grades, two standards

ADC10 and ADC12 are grades in JIS H 5302, the Japanese standard for aluminium die castings. A380 is a grade in ASTM B85, the American standard. They sit in the same family of Al-Si-Cu alloys, but the limits and the naming are not the same.

A drawing that says ADC12 and a supplier that casts A380 may produce a part that works, but the buyer has not specified the same material. The chemistry ranges overlap, and the mechanical properties depend on the casting process as much as on the grade. Treat a substitution as an engineering change, not a purchasing convenience.

The practical answer is to name the grade and the standard. If the supplier proposes an equivalent, ask for the chemistry, the mechanical properties and the process comparison before approval.

Composition and fluidity

Silicon is the main lever for fluidity. ADC12 has a higher silicon range than A380, which helps it fill thin walls and long flow paths. A380 has a lower silicon range and more copper, which supports strength and hardness but can reduce fluidity in a thin section.

Copper adds strength and hardness and reduces ductility. It also affects corrosion behaviour and can make the alloy more sensitive to certain finishes. Iron is present in all three, and its level and the cooling rate affect the formation of intermetallic phases.

The exact chemistry matters at the edges of the range. Two heats that both meet the same grade can machine differently if one sits at the top of the silicon range and the other at the bottom. Ask for the chemistry certificate, not only a statement of grade.

Strength and hardness

A380 is often chosen where strength and hardness matter, because its copper content supports those properties. ADC10 is close in copper and is used for similar general-purpose parts. ADC12 has a lower copper range in many specifications, so it is often chosen for thin-wall or large-area parts where fluidity matters more than peak strength.

The numbers on a certificate are not the numbers in the part. A die casting has a skin, a core and a gate region, and the local properties vary. A test bar cast separately may not represent a thin wall or a heavy boss.

If the part carries a structural load, say so and agree the test location and the acceptance. Do not assume that a grade name guarantees a strength in a complex casting.

Machinability and tool wear

Silicon is abrasive. A higher-silicon alloy such as ADC12 can increase tool wear, especially on a machined face with a long cycle. The effect depends on the cutting speed, the tool grade and the coolant. A shop that normally machines A380 may need to adjust the parameters for ADC12.

Porosity also affects machining. A pore near a machined face can open as a cavity, and a hard inclusion can chip a tool. The alloy choice interacts with the die design and the gate position, so the machining review should include the casting layout.

For a part with a critical machined bore or seal face, ask for a sample from the production die and check the cut surface. A test bar does not show the porosity that sits under the skin of the actual part.

Corrosion and finishing

Aluminium die castings are usually painted, powder coated or conversion coated. The copper content affects the corrosion behaviour and the response to some pretreatments. A high-copper alloy may need a different pretreatment from a low-copper grade.

Blistering during coating is a common failure. It can come from porosity that holds moisture or from a pretreatment that is not fully rinsed. The alloy and the casting quality both matter, so a finish problem should be reviewed with the die caster, not only the coater.

If the part is used outdoors or in a wet environment, specify the finish and the test. A salt spray result is comparative, not a guarantee for every site. State the hours and the acceptance criteria, and check the cut edges where the coating is thinnest.

Choosing by part function

For a thin-wall housing with a long flow path, fluidity is the first question. ADC12 is often a candidate. For a general-purpose part with moderate walls that needs strength and hardness, A380 or ADC10 may be a better fit. For a part with a critical machined face, the machining response and the porosity control may decide the grade.

Volume and tooling matter too. A die built for one alloy may not run another at the same cycle. The shrinkage, the thermal conductivity and the soldering tendency all change. If the grade is likely to change later, design the die and the process with that in mind.

Do not choose by price alone. The cost per kilogram is only one line. Tool life, scrap rate, cycle time, finish yield and machining time can move the total more than the metal price.

A trial on the production die is the best way to compare two grades. A test bar or a sample from a different tool does not show the fill pattern, the porosity or the cycle time that the real die will produce.

The three grades side by side

The table is a comparison guide, not a specification. Use the actual standard and the supplier's chemistry certificate for the limits that apply to your part.

What to put on the drawing

Name the grade and the standard, for example ADC12 to JIS H 5302. Add the condition or heat treatment if one is required. If the part is not heat treated, say so, because a supplier may assume a different route.

Add the critical requirements that the grade alone does not cover: porosity zones, pressure tightness, machined face condition, coating and the test method. A grade callout does not tell the supplier where a pore is acceptable or how the part will be leak tested.

Ask for the chemistry certificate, the lot or heat identity and the mechanical test result where applicable. If the supplier proposes a substitute, require a written comparison and a sample approval before the production die is cut.

For a production programme, agree a narrower chemistry range with the die caster rather than relying on the broad standard range. A narrow internal range can reduce variation in fluidity and machining, even when both heats meet the published grade. Record the agreed range on the purchase order and check each certificate against it. If the supplier cannot hold a narrow range, the part design or the process window has to absorb the variation.