Aluminum casting alloys are grouped by their main alloying element: 2xx alloys use copper for the highest strength, 3xx alloys use silicon for the best castability and pressure tightness, and 5xx alloys use magnesium for corrosion resistance. LeClaire Manufacturing pours nine alloys across those three families: A201 and A206; A356, B356, A357, E357, F357, and C355; and 535. The right choice depends on the strength, corrosion resistance, and part complexity your application needs.
Alloy selection is one of the first engineering decisions on any casting program, and it shapes tooling, heat treatment, cost, and lead time. Picking the wrong family usually means either paying for strength the part doesn’t need or fighting castability problems the part didn’t need to have.
This page is for engineers and procurement managers comparing aluminum casting alloys for sand and permanent mold parts. Use it to narrow the field, then follow the links to the full guide for each alloy. Every alloy listed here is one LeClaire pours today.
How are aluminum casting alloys designated?
Aluminum casting alloys use a three-digit number with a decimal, registered with the Aluminum Association. The first digit tells you the alloy family, and a letter prefix tells you the alloy is a variation of the base chemistry.
- First digit (family): 2xx is aluminum-copper, 3xx is aluminum-silicon with copper and/or magnesium, and 5xx is aluminum-magnesium. Other families exist, including 4xx (silicon) and 7xx (zinc).
- Decimal: “.0” means a casting. “.1” and “.2” refer to ingot, which is why you’ll see A356.0 on a casting drawing and A356.2 on a foundry ingot spec.
- Letter prefix: A, B, C, E, or F marks a variation of the base alloy, usually tighter impurity limits. A356 is a higher-purity version of 356, and C355 is a higher-purity version of 355.
- Temper: The suffix after the alloy number shows its condition. F is as cast, T4 is solution treated and naturally aged, T6 and T61 are solution treated and artificially aged, and T7 is overaged for stability. Our heat treatment process guide explains each one.
Which aluminum casting alloys does LeClaire pour?
LeClaire pours nine alloys across the 2xx, 3xx, and 5xx families in both sand casting and permanent mold casting. Each alloy below links to its full guide.
2xx aluminum-copper alloys: highest strength
- A201: A silver-bearing aluminum-copper alloy and the strongest aluminum alloy commonly sand or permanent mold cast. Used for weight-critical defense and aerospace parts.
- A206: A high-strength, high-toughness aluminum-copper alloy that can replace ductile iron in many structural parts at well under half the weight. Lower cost than A201.
3xx aluminum-silicon alloys: best castability
- A356: The most widely used aluminum casting alloy, combining excellent castability, pressure tightness, good corrosion resistance, and solid strength after T6 heat treatment.
- B356: A higher-purity version of A356 with tighter iron limits, used when a part needs more ductility than A356 provides.
- A357: A higher-magnesium relative of A356 that reaches higher strength after heat treatment. Common in premium, high-integrity castings.
- E357 and F357: Beryllium-free variants of A357 that deliver similar performance without beryllium in the melt.
- C355: An aluminum-silicon-copper-magnesium alloy with more strength than A356 and better performance at moderately elevated temperatures, while staying pressure tight.
5xx aluminum-magnesium alloys: corrosion resistance
- 535 (Almag 35): An aluminum-magnesium alloy with excellent saltwater corrosion resistance and high elongation that reaches full properties as cast, with no heat treatment.
How do you choose the right aluminum casting alloy?
Start with the property your part can’t do without, then check castability and cost. Every family trades one strength for another, so the best alloy is the one that meets the requirement with the fewest compromises.
- Maximum strength-to-weight: A201 or A206. Expect higher cost and more demanding foundry practice.
- Strength, pressure tightness, and castability together: A356, A357, or C355.
- High-integrity, premium castings: A357, E357, or F357.
- Strength near heat sources: C355, thanks to its copper content.
- Saltwater corrosion resistance without heat treatment: 535.
- Thin walls, complex cores, and intricate geometry: The 3xx aluminum-silicon alloys, which flow best into detailed molds.
- Lowest overall cost for general-purpose parts: A356, the most common and widely understood casting alloy.
The general tradeoff runs in one direction: as strength rises from 3xx to 2xx, castability and corrosion resistance fall. 5xx alloys sit apart, with moderate strength, top corrosion resistance, and more difficult pouring than 3xx alloys.
Which aluminum casting alloys fit which industries?
Each industry LeClaire serves leans toward the alloys that match its usual demands. These are common fits, and the final choice always depends on the specific part.
- Heavy truck: C355 and A356 for housings and brackets, and A206 for structural parts converted from iron.
- Military and defense: A201 and A206 for high-strength structural castings, and A357 for premium high-integrity parts.
- Marine: 535 for saltwater-exposed hardware, and A356 for complex or pressure-tight housings.
- Engine components: C355 and A356 for parts that run at operating temperature.
- Valves and pumps: A356 and C355 for pressure-tight bodies and housings.
- Agriculture and recreational vehicles: A356 for general-purpose structural and housing castings.
Does sand casting or permanent mold casting change the alloy choice?
The process doesn’t change which alloy family fits your part, but it does change the properties you’ll get. Permanent mold castings cool faster in a metal mold, which produces a finer grain structure and mechanical properties roughly 15% higher than sand castings in the same alloy.
- Sand casting: Suits larger parts, complex core assemblies, prototypes, and lower volumes, with lower tooling cost.
- Permanent mold casting: Suits higher volumes, tighter tolerances, and smoother as-cast finishes.
- Demanding alloys: The 2xx copper alloys and 535 need tighter process control in either method, so foundry experience matters more than usual.
LeClaire builds tooling in-house, runs solidification simulation before metal is poured, and handles heat treating and CNC machining under the same roof.
Frequently asked questions
What is the most common aluminum casting alloy?
A356 and its parent alloy 356 are the most widely used aluminum casting alloys. A356 combines excellent castability, pressure tightness, and good strength after T6 heat treatment, which makes it the default starting point for many parts.
What is the strongest aluminum casting alloy?
A201 is the strongest aluminum alloy commonly produced in sand and permanent mold, with typical T6 tensile strength around 70 ksi. A206 is close behind and costs less because it contains no silver.
Which aluminum casting alloy is best for corrosion resistance?
535 is the best choice among LeClaire’s alloys for saltwater and other corrosive environments. Its magnesium-based chemistry with almost no copper gives it excellent resistance in marine service.
What does the letter in front of an aluminum alloy number mean?
A letter prefix such as A, B, C, E, or F marks a registered variation of the base alloy. Most often it means tighter impurity limits, such as lower iron, which improves ductility and strength.
Can LeClaire help select an aluminum casting alloy?
Yes. Alloy selection is part of the upfront engineering review on every new part. LeClaire’s engineers look at your loads, environment, geometry, and volume and recommend the alloy and process that fit.
Get help choosing the right aluminum casting alloy
The right aluminum casting alloy comes down to the property your part needs most: copper alloys for strength, silicon alloys for castability and pressure tightness, or magnesium alloys for corrosion resistance. LeClaire Manufacturing pours nine aluminum casting alloys in sand and permanent mold and reviews every new part before tooling is built. Request a quote and our engineers will recommend the alloy that fits.