Die Casting Aluminum Alloy Selection A356 vs A380 Performance Trade-Offs for Your Application

Content Menu

● Introduction

● Composition and Microstructure Breakdown

● Mechanical Properties Face-Off

● Corrosion Resistance and Environmental Durability

● Thermal and Casting Performance

● Application-Specific Trade-Offs

● Conclusion

 

Introduction

If you’re working in die casting, picking between A356 and A380 usually comes down to what your part actually needs to do versus how easily it can be made. Both alloys are staples in aluminum die casting, but they pull in different directions. A356 gives you better mechanical properties and corrosion resistance, especially after heat treatment, while A380 excels at filling complex molds quickly and cheaply in high-volume runs.

Engineers often face this choice when designing components for automotive, electronics, or industrial equipment. A356 tends to show up in structural parts that see stress or need to last outdoors. A380 is more common in housings and brackets where production speed and low cost matter more than top-end strength.

The differences start with their chemistry. A356 has lower silicon and copper but enough magnesium to respond well to T6 heat treatment. A380 carries more silicon and copper, which makes it flow better and harden without extra steps. Those changes affect everything: how the metal fills the die, how strong the finished part is, how it holds up to corrosion, and even how much heat it conducts.

This article looks at the key differences in detail—composition, microstructure, mechanical behavior, corrosion performance, thermal properties, and real-world applications. The goal is to help you decide which alloy fits your project better, based on actual performance data rather than just typical industry preferences.

Composition and Microstructure Breakdown

A356 is an Al-Si-Mg alloy with roughly 6.5–7.5% silicon, 0.25–0.45% magnesium, and very low copper (usually under 0.2%). The silicon improves fluidity and reduces shrinkage, while magnesium allows strengthening through heat treatment by forming Mg₂Si precipitates. Iron is kept low to avoid brittle phases.

A380, by contrast, has 7.5–9.5% silicon, 3.0–4.0% copper, and up to 1.3% iron. The extra copper boosts hardness and strength as-cast, but it also lowers corrosion resistance. Higher silicon makes the alloy more fluid and helps prevent hot cracking.

Microstructurally, A356 is hypoeutectic: you see primary aluminum dendrites surrounded by Al-Si eutectic. Heat treatment (T6) rounds the silicon particles and disperses precipitates, greatly improving ductility. A380 is closer to eutectic, with finer silicon and copper-rich intermetallics like Al₂Cu scattered throughout.

In practice, these differences show up in casting behavior. A356 often needs careful gating and sometimes grain refinement to control shrinkage porosity. A380 fills thin sections more reliably and tolerates wider process variations.

Mechanical Properties Face-Off

Mechanical performance is where the two alloys diverge most clearly.

As-cast, A356 typically shows tensile strength around 170–200 MPa, yield strength 80–100 MPa, and elongation 3–5%. After T6 heat treatment (solution at ~540°C, quench, age at ~155–175°C), those numbers jump to 280–310 MPa tensile, 200–240 MPa yield, and 6–10% elongation.

A380 as-cast delivers higher tensile strength (320–350 MPa) and yield (150–180 MPa), but elongation stays low at 3–4%. Its Brinell hardness is usually 80–90, compared to A356′s 60–70 as-cast or 80–95 after T6.

Fatigue behavior also favors A356 in high-cycle applications. Properly treated A356 can endure millions of cycles at stresses where A380 might crack earlier due to its lower ductility.

In real parts, A356 is chosen for suspension components, wheels, and structural brackets that need to absorb impacts without sudden failure. A380 is more common in motor housings, valve covers, and transmission cases where stiffness and wear resistance matter more than toughness.

Corrosion Resistance and Environmental Durability

Corrosion resistance is a clear win for A356. Its low copper content means fewer galvanic cells in the microstructure. In neutral salt spray or immersion tests, A356 shows corrosion rates roughly half those of A380.

A380′s copper forms Al₂Cu phases that act as cathodes, accelerating pitting and general corrosion, especially in chloride environments. Many A380 parts used outdoors or in marine settings need anodizing, powder coating, or e-coating to protect them.

For example, battery housings for electric vehicles often use A356 because they must survive road salt and humidity over long service life. A380 might be used for internal electronics enclosures that stay dry and avoid aggressive atmospheres.

Thermal and Casting Performance

Thermal conductivity is noticeably higher in A356—around 150–170 W/m·K versus A380′s 90–110 W/m·K. That makes A356 better for heat sinks, LED housings, or any part that needs to dissipate heat quickly.

Casting performance leans toward A380. Its higher silicon and copper give it excellent fluidity, allowing thinner walls (down to 0.8–1.0 mm) with fewer misruns or cold shuts. Cycle times are often shorter, and scrap rates lower in complex geometries.

A356 can be cast successfully but usually requires hotter dies, higher injection pressures, and tighter process control to avoid shrinkage porosity. It also benefits from vacuum-assisted die casting to reduce gas entrapment.

Application-Specific Trade-Offs

In automotive, A356 is preferred for wheels, control arms, and steering knuckles where ductility and fatigue life are critical. A380 dominates in transmission cases, engine brackets, and pump housings where cost and production volume are priorities.

Aerospace and defense often stick with A356 for its reliability under cyclic loading and good fracture toughness. Electronics housings frequently use A380 because parts are complex, thin-walled, and produced in large quantities.

Cost-wise, A380 is usually cheaper. No heat treatment is needed, and the alloy itself is slightly less expensive due to higher iron tolerance. A356 parts carry the added expense of T6 processing, but that cost can be offset by longer service life or reduced warranty claims.

Sustainability is similar for both—aluminum is highly recyclable—but A356′s better durability can mean fewer replacements over time.

Conclusion

Deciding between A356 and A380 comes down to balancing what the part must do against how it will be made. A356 offers superior ductility, corrosion resistance, and heat-treatable strength, making it the better choice for structural, fatigue-critical, or outdoor applications. A380 provides excellent castability, higher as-cast hardness, and lower production costs, which makes it ideal for high-volume, intricate parts that don’t face extreme mechanical or environmental demands.

Look at your specific requirements: Does the part need to bend without breaking? Will it see salt, humidity, or thermal cycling? Is thin-wall capability more important than maximum strength? Those answers usually point clearly to one alloy or the other.

In many cases, prototyping with both or running a cost-benefit analysis on the full lifecycle (including machining, finishing, and service life) helps confirm the choice. Either way, understanding these trade-offs lets you pick the alloy that delivers the best performance for your actual application.