Aluminium Alloy Selection:
ADC12, A380, and LM25 Compared

Alloy selection is not a procurement decision — it is a design decision. The choice of alloy affects the die design (fluidity determines gating and runner geometry), the machining strategy (hardness and chip formation differ between alloys), the surface treatment process, and the final mechanical performance of the component.

Changing alloy after tooling is committed is costly. If the gating system was designed for ADC12 fluidity and the alloy is switched to LM25 (which has lower fluidity), the die may need to be modified to ensure complete fill. Selecting the right alloy at the RFQ stage prevents expensive engineering changes downstream.

ADC12 (Japanese Industrial Standard designation, equivalent to ASTM A383 and EN AC-46000) is the most widely used aluminium die casting alloy globally. Its composition — approximately 9.6–12% silicon with copper additions — gives it excellent fluidity, allowing thin walls and complex geometries to be filled reliably.

Mechanical properties of ADC12 in the as-cast condition: tensile strength approximately 310 MPa, yield strength 160 MPa, elongation 2–3%, Brinell hardness 80–90 HB.

ADC12 is the default choice for consumer appliance components — ceiling fan covers, mixer grinder housings, fan motor bodies — where good surface finish, dimensional consistency, and cost efficiency are the primary requirements. It is also used for medium-complexity automotive ancillary components.

Limitations: ADC12 is not suitable for T6 heat treatment (porosity risk) and has limited weldability. Corrosion resistance is adequate for most indoor applications but inferior to LM25 in harsh environments.

A380 (ASTM designation, equivalent to ADC10 in JIS and EN AC-46100 in European standards) offers a slightly different balance of properties compared to ADC12. Silicon content of 7.5–9.5% with higher copper content gives A380 marginally better tensile strength and improved machinability.

Mechanical properties in the as-cast condition: tensile strength approximately 320 MPa, yield strength 160 MPa, elongation 3%, Brinell hardness 80 HB.

A380 is preferred for automotive components — pump housings, solenoid bodies, structural brackets — where both castability and mechanical performance are important. Its slightly better machinability compared to ADC12 reduces tool wear in high-volume CNC operations.

At SAPL, A380 is specified for tractor covers, mechanical pump housings, and solenoid housings where OEM drawing callouts specify this alloy or an equivalent.

LM25 (BS EN 1706 designation AC-42100, equivalent to A356) is fundamentally different from ADC12 and A380. It is a hypoeutectic alloy with 6.5–7.5% silicon and very low copper content, designed for gravity die casting (GDC) rather than high pressure die casting.

In the T6 heat-treated condition (solution treatment + artificial ageing), LM25 achieves tensile strength of 230–280 MPa with elongation of 5–8% — significantly better ductility than HPDC alloys. This makes it suitable for structural components subjected to impact loading.

LM25 is also biocompatible and approved for contact with food and pharmaceutical applications. At SAPL, LM25 is used for surgical bone cutter handles produced via gravity die casting, where dimensional accuracy, surface finish, and biocompatibility are critical.

The lower fluidity of LM25 compared to ADC12 means it cannot reliably fill the thin walls achievable with HPDC. Gravity die casting components typically have minimum wall thickness of 3–4 mm.

Use ADC12 when: volume is high (>10,000 per year), geometry is complex with thin walls, surface finish is important, and mechanical requirements are moderate. Typical applications: consumer appliance housings, covers, motor bodies.

Use A380 when: slightly higher mechanical performance is required alongside good castability, OEM drawings specify A380 or equivalent, or the component requires subsequent CNC machining of critical features. Typical applications: automotive ancillaries, pump housings, solenoid bodies.

Use LM25 when: heat treatment is required to achieve higher strength and ductility, the component is safety-critical or structural, biocompatibility is required, or the application involves elevated operating temperatures. Process: gravity die casting only. Typical applications: structural automotive components, medical device housings, pressure-critical pump bodies.