What Aluminum Alloy Is Used for Casting? A Practical Buyer's Guide for Engineers

If your engineer has just asked you "what aluminum alloy is used for casting?" before you send the RFQ to a supplier, the direct answer is: A356 for sand and permanent mold casting, A380 for high-pressure die casting, and A383 when the casting has very thin walls or complex internal passages. Those three grades cover a large share of the custom aluminum parts we produce for automotive, motor, instrumentation, and fluid-control customers. The alloy choice, however, is never a standalone decision. It interacts with the casting process, the part geometry, the end-use environment, and your cost target.

This guide explains the alloy numbers from the perspective of a manufacturer that operates its own mold shop, die casting cells, machining lines, and surface treatment lines. Instead of repeating textbook definitions, it focuses on the trade-offs that actually affect your part: which alloy fills a thin wall cleanly, which one stays pressure-tight, which one machines well, and which one will survive a salty or humid environment for years. You will also find a comparison table, a property chart, and a set of questions to ask before you commit to a supplier.

What Aluminum Casting Alloys Are and Why the Answer Matters

Casting alloys are not the same as the aluminum grades you see in extrusion profiles or sheet metal. A wrought grade like 6061 is selected because it can be rolled, drawn, or extruded into a shape. A casting alloy must do something harder: it has to fill a mold cavity cleanly, solidify without internal tearing, and still produce a part with known mechanical properties. That is why casting alloys contain a deliberately balanced mix of silicon, copper, magnesium, iron, and other trace elements.

Silicon is the most important element in a casting alloy. It improves fluidity, which means the liquid metal can reach thin sections before it freezes. It also reduces shrinkage porosity because the solidification range narrows as silicon content increases. Most commercial aluminum casting alloys sit between 5% and 12% silicon, with a few special grades going above 16% for wear applications. Copper adds strength and hardness at room temperature and at elevated temperature, but it lowers corrosion resistance and can make the alloy more prone to hot tearing. Magnesium creates the precipitation-hardening effect behind the T6 temper; it is the element that allows A356 to reach its high-strength state. Iron is normally an impurity that forms brittle needles, but in die casting a controlled iron level of about 0.8% to 1.2% is intentionally kept in the alloy to reduce soldering between the casting and the steel die.

If you want a step-by-step explanation of how these alloys move through the mold-making, melting, casting, trimming, machining, and surface treatment stages, read our complete guide to aluminum casting before you start the sourcing conversation.

The Most Common Aluminum Alloys Used for Casting

Across foundries in North America, Europe, and Asia, the same alloy names appear in the majority of purchase orders. The table below lists the grades you will meet most often, with the elements that define them and the applications where they perform best.

The pattern in the table is simple: as silicon increases, the metal becomes easier to cast and more pressure tight, but harder to machine and less ductile. As copper increases, tensile strength and hardness climb while corrosion resistance drops. This is why the best alloy always depends on the priority of your application.

To compare the three die casting workhorses at a glance, the chart below provides a relative rating for five properties that matter in day-to-day engineering decisions. The scale is a comparative index, not an absolute material value.

A Closer Look at Each Common Grade

The alloy list below is arranged by family so you can compare similar candidates side by side. For each grade, the notes emphasize the real production consequences rather than the datasheet numbers.

A356 / 356 — the heat-treatable workhorse

A356 is the standard choice for sand casting and permanent mold casting when strength, ductility, and weldability are required. It contains about 7% silicon with small amounts of magnesium, which makes it responsive to T6 heat treatment. A T6 temper raises yield strength and hardness considerably while retaining useful elongation. It also has better corrosion resistance than copper-containing alloys, and it can be anodized to a uniform appearance. The main limitation is fluidity: A356 needs a heavier gate system and carefully controlled pouring temperature to fill thin sections. The non-heat-treated counterpart, 356, is specified when the part will be welded or when the cost of heat treatment is not justified.

319 — the elevated-temperature grade

319 adds copper to a leaner silicon level, which raises strength at temperatures of 150°C to 200°C. This makes it a traditional material for cylinder heads, intake manifolds, and engine-related castings. The trade-off is lower ductility and poorer corrosion resistance compared with A356. The alloy also does not have the same fluidity as high-silicon die casting grades, so it is rarely used for complex thin-wall geometry.

535 — the ductile and corrosion-resistant option

535 is a low-alloy grade containing about 4% magnesium and almost no silicon. Its as-cast ductility is among the highest of all aluminum casting alloys, and its corrosion resistance in marine environments is excellent. However, the absence of silicon makes it more difficult to cast: the wide freezing range requires careful feeding with risers, and the melt is prone to oxidation. This grade carries a higher cost and is selected when elongation or seawater performance is critical enough to justify the extra process care.

A380 — the die casting standard

A380 is the most common aluminum die casting alloy worldwide. Its balance of roughly 8% silicon and 3.5% copper gives good fluidity, good strength, and acceptable machinability. Parts such as motor housings, electronic enclosures, and structural brackets are routinely produced in A380 because the alloy fills the die quickly and produces pressure-tight walls with an attractive finish. For most industrial products with no special corrosion demand, A380 is the default specification that keeps the die casting cost in the expected range.

A383 — the thin-wall specialist

A383 holds more silicon and less copper than A380. The higher silicon content lowers shrinkage and improves the filling of thin sections, making it the first choice when a die casting has walls below 2 mm or complex ribs. A383 is also easier to anodize than A380 because of the lower copper. It is widely used in telecommunication housings, computer enclosures, and automotive electronics covers. A useful rule of thumb: if the mold-filling simulation shows flow problems with A380 in a thin-wall part, switch to A383 before changing any geometry.

A360 — the dense and corrosion-resistant die alloy

A360 has around 9.5% silicon and a copper content below 0.6%. The result is a dense, relatively corrosion-resistant die casting alloy with high strength and good pressure tightness. It is often found in hydraulic couplings, valve housings, and pump bodies where leakage must be minimized. The lower copper content gives A360 better resistance to salt spray and mild chemicals than A380, which is why it appears in marine and outdoor equipment.

A413 — the maximum-fluidity alloy

A413 carries 12% silicon and almost no copper. It has the highest fluidity of the standard commercial casting alloys, so it fills extremely intricate cavities and produces pressure-tight parts in complex housings. The low copper also improves corrosion resistance. Compressor bodies, refrigeration fittings, and housings with deep fins are typical A413 applications. Its limits are reduced machinability and lower ductility, which are acceptable when the priority is a leak-free, highly detailed casting.

B390 — the wear-resistant hypereutectic alloy

B390 is a hypereutectic alloy with 16% to 18% silicon and around 4.5% copper. The primary silicon particles give exceptional wear resistance and a low coefficient of thermal expansion, which is why B390 is found in cylinder bores, engine blocks, and sliding components. The same hard silicon particles make machining difficult, and diamond tooling is often required. B390 is selected for performance rather than for economy, and it demands a foundry with experience in hypereutectic alloys.

How to Choose the Right Alloy: Seven Criteria That Decide the Grade

Instead of memorizing alloy datasheets, evaluate your part against the following seven criteria. Each one eliminates certain grades and narrows the list to two or three candidates. The order below follows the way most engineering reviews actually progress.

How the Casting Process Limits the Alloy List

The process you choose will eliminate more alloys than any other factor. A very complex part with internal passages is often die cast; a large structural component is sand cast; a series of 500 parts might be produced on a permanent mold machine. Each process has its own alloy preferences because the cooling rate and the feeding behavior are completely different.

High-pressure die casting relies on alloys with narrow solidification ranges, because the metal is injected into the die and must freeze quickly. A380 and A383 were developed for exactly this condition. Sand casting, in contrast, gives the metal time to feed; alloys with a wide freezing range such as 535 can be handled with carefully placed risers. If you try to substitute a die casting alloy into a sand casting pattern, you may lose ductility and corrosion resistance without gaining any cost benefit.

The volume forecast also matters. Die casting has a high initial tooling cost but the lowest unit cost at high volumes. Permanent mold and sand casting tooling is cheaper, but the cycle time is longer and the unit price is higher. The alloy choice follows that economic logic: a die casting grade such as A380 becomes attractive only when the tooling investment can be divided across enough parts.

Application-Driven Alloy Selection: Examples from Our Production Floor

The examples below mirror parts we have produced in our own plant. They show the reasoning steps that a die casting engineer goes through when converting a design into a manufacturable part. Use them as a reference when you brief your next supplier.

Automotive and in-vehicle electronics

Automotive components face vibration, wide temperature swings, and in some cases direct exposure to road salt. For structural or safety-related castings, we typically specify A356 with T6 heat treatment; it gives predictable yield strength, good elongation for crash energy absorption, and corrosion resistance that survives an unpainted underbody environment. For electronics enclosures such as wireless charging housings, A383 is preferred because the thin ribs and snap-fit features fill cleanly and the part can be anodized for a consistent look.

Motor housings

Motor housings need a combination of dimensional stability, thermal conductivity, and sealing at the joint faces. A380 is the standard grade because it casts quickly, holds tight flatness tolerances, and provides a stable bore for the stator. When the motor is exposed to water spray or high humidity, we move to A360 or add a waterproof coating; when the stator fits into a thin-walled can, A383 fills the wall more reliably. The product below is an example of a die-cast motor housing produced with these requirements in mind.

Instrument and control housings

Instrument housings protect sensitive electronics and often carry mounting bosses, viewing windows, and cable glands. The priority here is dimensional accuracy and surface quality. A356 in permanent mold gives the best combination of finish and strength for medium volumes, while A380 or A383 in die casting is chosen when the housing volume exceeds 10,000 pieces per year. For outdoor instrument enclosures, the alloy is selected together with the surface treatment; powder coating covers most alloy differences, but clear anodizing still favors A356 or low-copper die casting grades.

Pressure-reducing valves and hydraulic bodies

Valve bodies must hold pressure, seal against gaskets, and resist internal corrosion from the media. Die-cast A360 and A413 produce the densest structure for hydraulic applications. When the valve body is sand cast or permanent mold cast, A356 in the T6 temper offers verified pressure tightness together with ductility that allows the body to withstand tightening loads at the ports. Every valve part we ship receives a pressure test; the alloy choice is one of the first things we check if a casting ever fails the test.

General equipment and non-standard components

Equipment parts such as brackets, covers, connectors, and fixings rarely face extreme thermal or corrosive conditions. A380 is the default grade because it balances cost, strength, and castability. If the part has a complex shape with multiple undercuts, we review the option of A383 before changing the tool design. For parts that are welded into a larger assembly, we step down to A356 so the weld region remains sound and the final structure does not crack under vibration.

Common Casting Defects That Are Influenced by Alloy Choice

When a defect appears during development, the alloy choice is often the root cause. Understanding the link between the defect and the chemistry of the melt helps you read a supplier's corrective action report with better judgment.

• Shrinkage porosity: Alloys with low silicon such as 319 and 535 have a wide freezing range. They need additional risers and feeders. If the supplier reports internal shrinkage in a thin-wall section, the correct response may be a switch to A383 or a revision of the feeding system.
• Hot tearing: This crack-like discontinuity happens when the solidifying metal is too weak to withstand contraction stress. A356 is less prone to hot tearing than high-copper grades; when a die casting shows hot cracks near inserts, check whether the copper content is at the high end of the A380 range.
• Die soldering: When liquid aluminum welds itself to the steel die surface, the part sticks and the surface tears. A controlled iron content between 0.8% and 1.2% is the standard defense. If soldering recurs, the supplier should verify the iron level in the melt rather than simply changing the die coating.
• Gas porosity: Hydrogen is the main source of gas pores. The alloy itself does not create hydrogen, but high-silicon melts absorb gas when the furnace atmosphere is wet. A vacuum degassing step and dry handling of returned scrap will eliminate most of this defect.
• Tool wear and poor machinability: High-silicon grades such as B390 and A413 wear standard carbide tools quickly. If your unit cost is dominated by machining, compare the total cost of a high-fluidity alloy plus expensive tooling against a slightly thicker wall in A356 that allows lower-cost cutting.

Working with a Custom Aluminum Die Casting Manufacturer

Once you have narrowed the alloy to one or two candidates, the conversation with a supplier should focus on capability and verification. A serious manufacturer will be able to explain the alloy recommendation in writing, provide a composition certificate, and show you the process steps that ensure the casting matches the approved sample.

When requesting a quotation, include the following information: a 3D model in STEP or IGES format, a 2D drawing with GD&T symbols, the material standard you expect the supplier to follow, the annual volume and tooling budget, the surface finish requirement, the pressure or vacuum tightness requirement, the exposure temperature range, and any industry certification that your customer requires. The more complete the inquiry, the more accurate the alloy recommendation will be.

You should also ask direct verification questions: Which alloy and temper is quoted? Which standard covers it? Will the supplier perform a chemical analysis of the first production batch? Can they deliver a material certificate with each shipment? Do they keep the composition window inside the alloy specification or at the edge of it? These questions separate manufacturers that rely on a documented quality system from those that merely pour aluminum.

At our plant, the internal supply chain covers the full sequence: mold workshop, die casting workshop, polishing workshop, machining workshop, cleaning workshop, and warehouse. That one-stop arrangement means the alloy selection is reviewed by the same team that later machines the part, so we catch machinability or corrosion problems before the parts reach your line. We are certified to ISO 9001:2015 and IATF 16949:2016, and our quality records are available for every batch. You can also walk through the workshops remotely and evaluate the equipment and process control before you place an order.

For parts that have demanding tolerance and finish requirements, precision cast components are a typical starting point in our product range.

If you would like to see the actual equipment, take a virtual tour of our workshops before the RFQ discussion. The visual evidence of a clean melt area and a well-maintained machine park is worth more than any brochure claim.

Frequently Asked Questions About Aluminum Casting Alloys

After reviewing the alloy families, the selection criteria, and the production realities, you may still ask the same question: what aluminum alloy is used for casting? The honest answer is that it depends on your process, your geometry, and the environment the part will live in. But the decision process is now manageable. Start with the process, apply the seven criteria, and ask the supplier to justify the recommendation in writing with a composition certificate.

A foundry that can explain the why behind its alloy choice is usually the foundry that will deliver a consistent casting. The alloy is not a footnote in the quotation; it is the foundation of the dimensional stability, mechanical performance, and durability of every part you receive.

If you are preparing an inquiry and want a practical review of the grade and temper for your application, send us the drawing and the operating conditions. Our engineering team will give you an alloy recommendation with the reasoning included, and the supporting quality records to back it up.