A356 aluminum is an aluminum-silicon-magnesium casting alloy containing about 7% silicon and 0.3% magnesium, with tight limits on iron and copper. It combines excellent castability with good strength, ductility, corrosion resistance, and pressure tightness, and it responds well to heat treatment. In the T6 temper, A356 is one of the most commonly specified alloys for sand and permanent mold castings in aerospace, automotive, agriculture, marine, and defense.
A356 aluminum is a higher-purity version of alloy 356. Lower iron is what gives A356 its better elongation and fatigue performance, which is why engineers choose it for structural and safety-related parts. This guide is for design engineers, quality managers, and buyers who specify or source aluminum castings. It covers A356 composition, mechanical and physical properties, heat treatment, sand versus permanent mold casting, how A356 compares with related alloys, typical applications, and what to include on a drawing or RFQ for A356 parts.
What Is A356 Aluminum?
A356 is a hypoeutectic aluminum casting alloy in the Aluminum Association’s 3xx.x series, the aluminum-silicon alloys with copper and/or magnesium. The silicon gives it fluidity and low shrinkage during casting. The magnesium makes it heat treatable, forming fine magnesium silicide precipitates during aging that raise strength.
You will see A356 written several ways:
- A356.0: The casting designation. The “.0” indicates a casting rather than ingot.
- A356.2: The foundry ingot form, with tighter limits on some impurities.
- UNS A13560: The Unified Numbering System designation.
- AlSi7Mg0.3 / EN AC-42100: The closest European designation.
A356 is typically poured in sand molds or permanent molds, including semi-permanent molds that use sand cores. It is less suited to high-pressure die casting, where alloys with higher iron content are used to prevent die soldering.
What Is the Chemical Composition of A356 Aluminum?
A356 contains 6.5 to 7.5 percent silicon and 0.25 to 0.45 percent magnesium, with iron and copper each limited to 0.20 percent maximum. Aluminum makes up the balance.
- Silicon (Si), 6.5 to 7.5%: Improves fluidity and feeding, reduces shrinkage, and lowers the melting range.
- Magnesium (Mg), 0.25 to 0.45%: Combines with silicon to form the precipitates that strengthen the alloy during aging.
- Iron (Fe), 0.20% max: Kept low because iron forms brittle needle-shaped phases that reduce ductility.
- Copper (Cu), 0.20% max: Kept low to protect corrosion resistance.
- Titanium (Ti), 0.20% max: Often added in controlled amounts as a grain refiner.
- Manganese (Mn) and Zinc (Zn), 0.10% max each: Limited as impurities.
[VISUAL: leclaire-a356-composition.png | Alt text: Bar chart of A356 aluminum chemical composition showing silicon 6.5 to 7.5 percent, magnesium 0.25 to 0.45 percent, and maximum limits for iron, copper, titanium, manganese, and zinc]
Foundries also treat the melt to get the most from the alloy. Strontium or sodium modifies the silicon into a finer, fibrous form that improves ductility. Titanium-boron grain refiners produce a finer grain structure. Degassing removes dissolved hydrogen, the main cause of gas porosity in aluminum castings.
What Are the Mechanical and Physical Properties of A356?
A356-T6 typically delivers tensile strength in the range of about 33 to 45 ksi, yield strength of about 24 to 32 ksi, and elongation of roughly 3 to 12 percent. Where a part falls in those ranges depends mostly on the casting process, section thickness, and the quality of melt treatment.
Typical Mechanical Properties by Temper
- A356-F (as-cast): Lowest strength. Used where loads are light and cost matters most.
- A356-T51: Artificially aged without solution treatment. Modest strength gain with good dimensional stability.
- A356-T6: Solution treated, quenched, and artificially aged. The most common temper, with roughly double the yield strength of as-cast material.
- A356-T61: A variation with different aging, used to reach higher minimum properties, especially in permanent mold castings.
- A356-T7: Overaged or stabilized. Trades some strength for dimensional stability and steadier properties at elevated temperature.
Spec minimums depend on how the part is cast and how test bars are taken. ASTM B26 covers sand castings, ASTM B108 covers permanent mold castings, and ASTM B686 and AMS-A-21180 cover high-strength and premium castings with higher minimums.
Typical Physical Properties
- Density: About 0.097 lb/in³ (2.68 g/cm³), roughly one-third the weight of steel.
- Melting range: About 1,035 to 1,135°F (557 to 613°C).
- Thermal conductivity: About 150 W/m·K in the T6 temper, useful for housings that need to shed heat.
- Corrosion resistance: Good, thanks to low copper. Suitable for marine and outdoor service with appropriate finishing.
- Weldability: Good. Weld repair is common, though welding locally reduces heat-treated strength.
- Machinability: Fair to good, and better in the T6 temper than as-cast.
How Is A356 Aluminum Heat Treated?
A356 reaches its best properties through a T6 precipitation hardening cycle: solution treatment near 1,000°F, a rapid quench, and artificial aging at roughly 310 to 340°F. Exact times and temperatures depend on section thickness and the specification being met.
- Solution treatment: Castings are held for several hours to dissolve magnesium and silicon into the aluminum and round off the eutectic silicon particles.
- Quench: Parts are rapidly cooled in water or a polymer quench. Quench delay is measured in seconds because slow transfer lowers final strength.
- Artificial aging: Parts are held at a lower temperature for several hours to form the strengthening precipitates.
- Verification: Tensile test bars from the same batch and hardness checks confirm properties.
Distortion is the main risk during quenching, especially in thin or uneven sections. Fixturing, controlled quench media, and straightening after heat treat keep parts within tolerance. LeClaire runs all heat treating in-house with a drop-bottom quench system and tensile tests bars from every batch.
Sand Casting vs. Permanent Mold Casting for A356
A356 casts well in both sand and permanent molds. Permanent mold castings usually reach higher properties because faster solidification produces a finer microstructure, while sand casting offers more design flexibility and lower tooling cost.
- Sand casting: Lower tooling cost, larger part sizes, and complex cored geometry. Best for prototypes, low to medium volumes, and large or intricate parts.
- Permanent mold casting: Higher strength and elongation, tighter dimensions, and better surface finish. Best for medium to high volumes where tooling cost can be spread across more parts.
- Semi-permanent mold: A metal mold with sand cores. Combines permanent mold properties with internal passages a metal core can’t produce.
For a broader process comparison, see die casting vs. sand casting.
How Does A356 Compare With 356, B356, A357, and 319?
A356 sits in the middle of its alloy family. It offers better ductility than 356, costs less than higher-purity B356 or higher-strength A357, and resists corrosion better than copper-bearing 319.
- A356 vs. 356: Same silicon and similar magnesium, but A356 allows far less iron (0.20% versus 0.6% max). That lower iron gives A356 better elongation and fatigue strength. 356 is a lower-cost choice for parts where ductility is less important.
- A356 vs. B356: B356 tightens the iron and copper limits even further. It is chosen when maximum ductility and fatigue resistance are required, often in aerospace.
- A356 vs. A357: A357 roughly doubles the magnesium content, reaching higher strength after heat treatment with somewhat lower elongation. See our A357 aluminum guide, including beryllium-free E357 and F357.
- A356 vs. 319: 319 contains copper, which improves machinability and elevated-temperature strength but reduces corrosion resistance and ductility.
Where Is A356 Aluminum Used?
A356 is used wherever a cast part needs to be light, strong, pressure tight, and corrosion resistant. Its balance of properties makes it a default choice across many industries.
- Aerospace and defense: Brackets, housings, and structural fittings, often in premium-quality grades.
- Automotive and heavy truck: Wheels, suspension components, brake parts, and housings. See aluminum casting for heavy trucks.
- Agriculture: Gearbox housings, valve bodies, and equipment components exposed to weather. See our agricultural casting guide.
- Marine: Outboard components, fittings, and housings that need corrosion resistance. See marine aluminum casting.
- Valves and pumps: Pressure-tight bodies and housings where leak testing is required.
- Recreational vehicles: Frame, drivetrain, and suspension components where weight matters.
How to Specify A356 Castings
A clear drawing and RFQ prevent most disputes over A356 castings. List the alloy, temper, governing spec, and acceptance criteria so every supplier quotes the same part.
- Alloy and temper: Write the full designation, such as A356.0-T6 or A356.0-T61.
- Governing specification: Reference ASTM B26, ASTM B108, ASTM B686, or AMS-A-21180 as appropriate.
- Test bar method: Note whether properties come from separately cast bars or bars cut from the casting. Cut-from-casting values are usually lower.
- Radiographic grade: Define x-ray acceptance levels for critical zones instead of the whole part, where possible.
- Pressure tightness: Specify leak test method and pressure, and whether impregnation is allowed.
- Critical dimensions and datums: Identify machined surfaces and datum targets so the foundry can plan stock and fixturing.
The most common quality issue in A356 is porosity, from either dissolved hydrogen or shrinkage. Good degassing, filtration, gating design, and simulation keep it under control. Our article on what causes porosity in sand casting covers the details.
A356 Aluminum Castings at LeClaire
A356 is one of the core alloys LeClaire pours in both green sand and permanent mold. Because tooling, core making, casting, heat treating, and CNC machining are all done under one roof in Bettendorf, Iowa, one team owns your part from first design review to finished, machined casting.
- Engineering: Simulation software and in-house tool and die design engineer defects out before production.
- Heat treat: In-house drop-bottom heat treating with tensile test bars from every batch for T5, T6, and T7 tempers.
- Inspection: Digital real-time x-ray, CMM and FARO laser scanning, and leak testing. See our quality capabilities.
- Track record: ISO 9001:2015 certified with a 98 percent on-time delivery record.
LeClaire also pours A357, E357, F357, B356, C355, A201, A206, and 535 for applications that call for different strength, ductility, or corrosion performance. Alloy specifications are maintained by the Aluminum Association.
Frequently Asked Questions About A356 Aluminum
What is A356 aluminum used for?
A356 is used for cast parts that need good strength, ductility, corrosion resistance, and pressure tightness. Common examples include wheels, suspension and brake components, pump and valve housings, aerospace brackets, and marine hardware.
What is the difference between A356 and 356 aluminum?
A356 has much lower iron and slightly lower copper limits than 356. The lower iron gives A356 better elongation and fatigue resistance, so it is preferred for structural and safety-related castings.
What does T6 mean in A356-T6?
T6 means the casting was solution heat treated, quenched, and artificially aged to near peak strength. It is the most commonly specified temper for A356.
Is A356 aluminum weldable?
Yes, A356 has good weldability and is commonly weld repaired. Welding reduces strength in the heat-affected zone, so critical parts may need re-heat-treatment after welding.
Can A356 be die cast?
A356 is rarely used in conventional high-pressure die casting because its low iron content causes die soldering. It is mainly cast in sand, permanent mold, and investment processes.
Source A356 Castings From One Supplier
A356 aluminum is the go-to casting alloy when a part needs strength, ductility, and pressure tightness in one package, and the T6 temper gets the most out of it. The results depend on melt quality, casting process, and heat treat control, which is why it pays to work with a foundry that manages all three. Request a quote from LeClaire Manufacturing and our engineers will review your A356 part.