Aluminum Casting Alloy Comparison Chart: A356 vs 380 vs 413

Why comparing aluminum casting alloys matters

Selecting the right aluminum alloy is one of the most critical decisions in any casting project. A wrong choice can result in parts with excessive porosity, insufficient mechanical properties, mold filling problems, or unnecessarily high production costs. In the automotive, aerospace, and general manufacturing industries, the difference between an A356 and a 380 alloy is not simply a matter of chemical composition: it implies fundamental differences in the required casting process, applicable heat treatments, resulting mechanical properties, and final part cost.

This comparison guide is designed for foundry engineers, procurement managers, and product designers who need to make informed decisions about aluminum alloys. We present real technical data, verified against ASTM B108, ASTM B85, and EN 1706 standards, for the seven most widely used aluminum casting alloys worldwide.

Chemical composition and properties comparison table

The following table summarizes the nominal chemical composition, typical mechanical properties, and primary application of each alloy. Strength values correspond to the most common condition for each alloy: T6 for heat-treatable alloys (A356, A357) and F condition (as-cast) for die casting alloys (380, A383, 413).

Radar visualization of key properties

A numerical table comparison is useful for exact values, but a radar chart allows you to quickly visualize the profile of each alloy across multiple dimensions simultaneously. The following diagram compares the seven alloys on five axes: mechanical strength, elongation, castability, weldability, and corrosión resistance.

Individual property bar comparison

To analyze a specific property in isolation, comparative bars offer a more direct reading. Select the property of interest to see how each alloy ranks.

Casting process compatibility

Not all alloys are suitable for all casting processes. The compatibility between alloy and process is critical: an alloy optimized for high-pressure die casting may give mediocre results in gravity casting, and vice versa. The determining factors include the solidification range, melt fluidity, shrinkage tendency, and susceptibility to hot tearing.

Gravity casting (permanent mold and sand)

Gravity casting is characterized by moderate fill speeds and longer solidification times than die casting. This requires alloys with good feeding characteristics and low tendency for shrinkage microporosity. Al-Si-Mg system alloys are preferred.

• A356.0: The reference alloy for gravity casting. Its short solidification range (approximately 60 degrees C between liquidus and solidus) minimizes porosity. The 7% silicon content provides good fluidity without embrittling the part. Responds excellently to T6 heat treatment.
• A357.0: Higher-strength version of A356, with higher magnesium content (0.45-0.70% vs 0.25-0.45%). Requires tighter control of degassing and solidification rate. Justified in applications requiring tensile strength above 290 MPa.
• 319.0: Al-Si-Cu alloy with good castability and excellent machinability. Copper improves strength but reduces corrosion resistance. Ideal for engine blocks and transmission components where machinability is a priority.

High-pressure die casting (HPDC)

High-pressure die casting injects metal at gate velocities of 30-60 m/s and pressures of 50-120 MPa. These extreme conditions require alloys with excellent fluidity, low tendency for die soldering, and tolerance to higher iron contents. Iron, which is detrimental in gravity casting, is deliberately added in die casting alloys (up to 1.3%) to prevent aluminum from soldering to the die steel.

• 380.0: The most widely used die casting alloy in the world. It represents approximately 85% of die casting production in North America. The combination of Si (8.5%) and Cu (3.5%) provides excellent fluidity and good strength. Its permitted iron content (1.3%) makes it process-tolerant.
• A383.0: Similar to 380 but with higher silicon content (10.5%) and lower copper (2.5%). Offers better hot cracking resistance and superior fluidity, making it preferred for thin-wall parts and complex geometries.
• 413.0: Eutectic alloy (12% Si) with the best fluidity of all commercial alloys. Its singular solidification point (vs. a range) minimizes shrinkage porosity. Ideal for pressure-tight parts and hydraulic applications.

Squeeze casting and mega casting

Squeeze casting combines die casting pressure with slow fill speeds, producing parts with near-100% density and mechanical properties superior to any other casting process. Mega die casting cells (6,000-9,000 tons of clamping force) use a new generation of alloys designed specifically for large-scale automotive structures.

• AlSi10MnMg (Silafont-36, Castasil-37, Aural-2): Family of alloys developed for structural die casting. Their ultra-low iron content (max 0.15%) eliminates brittle beta phases; absence of copper improves corrosion resistance and weldability; and a balanced Si-Mg content provides high elongation (8-15%) in F condition (as-cast) without T6 heat treatment. This last point is critical for mega casting: parts 1-1.5 meters long would suffer unacceptable dimensional distortion during T6 quenching. Tesla popularized this approach with rear underbody parts for the Model Y cast in 6,000-ton cells.
• A356 / A357 in squeeze casting: These classic alloys achieve 15-25% higher mechanical properties when processed by squeeze casting compared to gravity, thanks to near-total elimination of porosity.

How to read the comparison table

Understanding what each column in the table means is essential for making correct decisions. Below we explain each property and its practical relevance.

Silicon (Si %)

Silicon is the primary alloying element in all aluminum casting alloys. It improves melt fluidity, reduces solidification shrinkage, and increases wear resistance. The eutectic point of the Al-Si system is at approximately 12.6% Si (alloy 413 is near this point). Hypoeutectic alloys (< 12.6% Si, such as A356 at 7% and 380 at 8.5%) solidify with a structure of primary aluminum dendrites surrounded by Al-Si eutectic. Near-eutectic alloys (413, A383) solidify with a narrower range, which improves feeding and reduces porosity.

Copper (Cu %)

Copper significantly increases mechanical strength and hardness, especially after heat treatment. It also improves machinability by producing shorter, more brittle chips. However, copper drastically reduces corrosión resistance: alloys with Cu > 1% (380, 319) are not suitable for marine environments or prolonged outdoor exposure without protective coating. Copper-free alloys (A356, AlSi10MnMg) offer much better corrosión resistance and are preferred for automotive structural body parts.

Magnesium (Mg %)

Magnesium is the element that enables precipitation hardening (T6 heat treatment) in Al-Si alloys. During heat treatment, Mg forms Mg2Si precipitates that block dislocation movement, increasing tensile strength and yield strength. A content of 0.30-0.45% Mg (as in A356) is optimal for a good balance between strength and ductility. Higher contents (A357 at 0.45-0.70%) yield greater strength but lower elongation. In die casting alloys (380, 413), Mg is kept low (< 0.10%) because T6 treatment is not feasible on conventional die cast parts due to blister formation from entrapped gas.

Tensile strength and elongation

Ultimate tensile strength (UTS) indicates the maximum load the material can withstand before fracture. Elongation indicates the capacity for plastic deformation before failure. For structural safety parts (engine mounts, suspensión components, body nodes), elongation is as important as or more important than strength: a part with high strength but low elongation will fracture in a brittle, catastrophic manner. Modern automotive specifications typically require a minimum of 7% elongation for structural components, which rules out high-copper alloys (380, 319) in favor of A356-T6 or AlSi10MnMg.

Castability

Castability is a qualitative measure of how easily the alloy fills the mold completely without defects. It depends on fluidity (the ability of molten metal to flow through narrow channels), the solidification range (difference between liquidus and solidus), and shrinkage tendency. Near-eutectic alloys (413, A383) have the best castability. A356 has good castability but requires more generous feeding systems than die casting alloys.

Frequently asked questions

Can I use 380 alloy for structural safety parts?

Generally not recommended. The 380 alloy has good tensile strength (317 MPa), but its elongation is limited (3.5%) and its high iron content generates brittle phases that act as crack initiation points under cyclic loading. Additionally, its copper content makes it susceptible to intergranular corrosión. For structural safety parts (brackets, nodes, impact bars), automotive OEMs specify alloys such as AlSi10MnMg or A356/A357, which offer elongation above 5% and better fatigue resistance.

What is the practical difference between A356 and A357?

Both alloys share the same base composition (Al-7Si) and are heat-treatable to T6. The main difference is magnesium content: A357 has 0.45-0.70% Mg vs. 0.25-0.45% for A356. This gives A357 approximately 15-20% higher tensile and yield strength after T6, but with a reduction in elongation (3% vs. 5%). A357 is also more sensitive to solidification rate and requires tighter degassing control (hydrogen levels must be below 0.10 mL/100g). It is justified only when mechanical specifications cannot be met with A356-T6.

What is AlSi10MnMg and why is it used in mega casting?

AlSi10MnMg is a family of alloys (trade names: Silafont-36 by Rheinfelden, Castasil-37, Aural-2 by Rio Tinto) designed specifically for structural die casting. Their key characteristics are: ultra-low iron content (< 0.15%) that eliminates brittle beta phases; absence of copper that improves corrosión resistance and weldability; and a balanced Si-Mg content that provides high elongation (8-15%) in F condition (as-cast) without T6 heat treatment. This last point is critical for mega casting: parts 1-1.5 meters long would suffer unacceptable dimensional distortion during T6 quenching. Tesla popularized this approach with rear underbody castings for the Model Y produced in 6,000-ton cells.

Which alloy has the best machinability?

Alloy 319 has the best machinability among casting alloys, thanks to its copper content (3-4%) which produces short, brittle chips. 380 also offers good machinability for the same reason. In contrast, copper-free alloys (A356, AlSi10MnMg) produce longer, continuous chips that can wrap around the tool. To improve A356 machinability, some foundries add small amounts of tin (0.05-0.10%) or bismuth. Polycrystalline diamond (PCD) cutting tools are standard for all aluminum casting alloys.