A357 aluminum is a high-strength aluminum-silicon-magnesium casting alloy with about 7% silicon and 0.4 to 0.7% magnesium, plus a small beryllium addition. The extra magnesium lets A357 reach higher strength than A356 after T6 heat treatment, which makes it a common choice for aerospace, defense, and other premium structural castings. E357 and F357 are beryllium-free members of the same family that deliver similar performance without beryllium’s handling requirements.
A357 aluminum is what engineers reach for when A356 doesn’t quite meet the strength requirement. The tradeoff is somewhat lower elongation and a tighter process window in the foundry. This guide is for design engineers, materials specialists, and buyers sourcing high-strength aluminum castings. It covers A357 composition, the role of beryllium, how E357 and F357 differ, mechanical properties and heat treatment, how A357 compares with A356, and what to look for in a supplier.
What Is A357 Aluminum?
A357 is a heat-treatable casting alloy in the Aluminum Association’s 3xx.x series. It shares the same silicon range as A356 but roughly doubles the magnesium, which produces more strengthening precipitates during aging.
- A357.0: The casting designation.
- UNS A13570: The Unified Numbering System designation.
- 357 family: Includes 357, A357, E357, and F357, all built on the same Al-Si-Mg base with different limits on magnesium, beryllium, and impurities.
A357 is usually poured in sand molds, permanent molds, or investment molds. Like A356, it is not a good fit for conventional high-pressure die casting.
What Is the Composition of A357, and Why Does It Contain Beryllium?
A357 contains 6.5 to 7.5 percent silicon, 0.40 to 0.70 percent magnesium, 0.20 percent maximum copper, and 0.04 to 0.07 percent beryllium. Iron is held low to protect ductility.
- Silicon (Si), 6.5 to 7.5%: Provides fluidity and feeding during casting.
- Magnesium (Mg), 0.40 to 0.70%: The main strengthening element after heat treatment.
- Beryllium (Be), 0.04 to 0.07%: Reduces magnesium oxidation in the melt and changes iron-bearing phases into a less harmful form, which helps ductility.
- Copper (Cu), 0.20% max: Limited to protect corrosion resistance.
- Titanium (Ti): Added in controlled amounts as a grain refiner.
Beryllium is the reason the E357 and F357 variants exist. Beryllium dust and fumes are a recognized occupational health hazard, so melting, grinding, and machining beryllium-bearing alloys requires extra controls. Many foundries, machine shops, and end users now prefer beryllium-free alternatives.
What Are E357 and F357 Aluminum?
E357 and F357 are beryllium-free versions of the 357 family, each holding beryllium to 0.002 percent maximum while keeping the higher magnesium content that gives A357 its strength.
[VISUAL: leclaire-357-alloy-family.png | Alt text: Comparison cards for A356, A357, E357, and F357 aluminum casting alloys showing magnesium range, beryllium content, and typical uses]
E357 Aluminum
E357 is a beryllium-free 357-family alloy registered with the Aluminum Association for sand, permanent mold, and investment castings. Its defining feature is a very narrow magnesium window of 0.55 to 0.60 percent, along with iron held to 0.10 percent maximum, titanium at 0.10 to 0.20 percent, and beryllium at 0.002 percent maximum. That tight chemistry gives a consistent heat treatment response from heat to heat.
E357 is one of the most widely used Al-Si7-Mg alloys for premium structural castings, and newer high-strength casting alloys are often benchmarked against it. Premium E357-T6 castings are commonly expected to deliver around 45 ksi tensile strength and 37 to 38 ksi yield strength with 5 percent or greater elongation.
F357 Aluminum
F357 is the beryllium-free version most often specified as a direct replacement for A357, with beryllium held to 0.002 percent maximum and low iron. The “F” is often described as standing for “free” of beryllium. F357 keeps a magnesium range closer to A357’s broader window. It is used in aerospace and defense castings and has also become a leading aluminum alloy for additive manufacturing (3D printing) of aerospace parts.
357 Aluminum
Plain 357 is the original alloy in the family. It has similar silicon and magnesium but looser impurity limits than the lettered variants, so it is used less often for premium structural work.
Quick comparison:
- A356: Magnesium 0.25 to 0.45%, no beryllium. The general-purpose baseline with the best ductility.
- A357: Magnesium 0.40 to 0.70%, beryllium 0.04 to 0.07%. High strength, with beryllium handling requirements.
- E357: Magnesium 0.55 to 0.60%, beryllium 0.002% max, iron 0.10% max. Tight chemistry for consistent premium castings.
- F357: A357-level magnesium, beryllium 0.002% max. The common beryllium-free replacement for A357 in aerospace and defense.
What Are the Mechanical Properties of A357-T6?
A357-T6 typically reaches tensile strength of about 45 to 52 ksi and yield strength of about 36 to 42 ksi, with elongation in the range of roughly 3 to 8 percent. That is noticeably stronger than A356-T6, with somewhat lower elongation. E357 and F357 reach comparable strength in the same tempers.
- Process effect: Permanent mold and well-chilled sand castings reach the higher end of the range because faster solidification creates a finer microstructure.
- Premium castings: ASTM B686 and AMS-A-21180 define high-strength and premium-quality classes, with minimum properties verified on test bars or specimens cut from the casting.
- Fatigue: Fatigue performance depends heavily on porosity and oxide control, so melt quality matters as much as alloy choice.
Heat Treatment for A357, E357, and F357
The 357 family is heat treated much like A356: solution treatment near 1,000°F, a fast quench, and artificial aging. Because of the higher magnesium, solution times are often longer to fully dissolve the alloying elements, and quench rate has a bigger effect on final strength. T6 and T61 are the most common tempers. LeClaire handles all heat treating in-house and tensile tests bars from every batch.
A357 vs. A356: Which Should You Specify?
Choose A357, E357, or F357 when the part needs more strength than A356-T6 can deliver. Stay with A356 when ductility, cost, and supplier availability matter more than peak strength.
- Strength: The 357 family is stronger in the T6 temper thanks to its higher magnesium.
- Ductility: A356 generally offers higher elongation and is more forgiving of impact.
- Process sensitivity: The 357 family has a tighter window for melt treatment, solidification, and heat treatment.
- Cost and availability: A356 is more common and usually costs less. Beryllium-free 357 variants cost more but avoid beryllium handling.
- Weight savings: Higher strength can allow thinner walls, which may offset alloy cost on weight-critical parts.
For a full look at the baseline alloy, see our A356 aluminum pillar guide.
Where Are A357, E357, and F357 Used?
The 357 family is used for cast parts where high strength-to-weight ratio is the top requirement and the part must also hold up to fatigue and corrosion.
- Aerospace: Airframe fittings, brackets, gearbox and actuator housings, and missile components.
- Military and defense: Structural housings, mounts, and defense components that must meet premium casting specs.
- Automotive and motorsport: High-performance suspension and chassis parts.
- Industrial: Pump and valve components and high-load housings where A356 falls short.
What to Look For in an A357, E357, or F357 Casting Supplier
Because the 357 family is less forgiving than A356, supplier process control has a direct effect on whether parts pass. Ask how the foundry handles each step.
- Melt quality: Degassing, filtration, and modification practice to control hydrogen porosity and oxides.
- Chemistry control: Spectrographic analysis to hold tight windows like E357’s 0.55 to 0.60 percent magnesium.
- Gating and solidification: Simulation and chill design to promote directional solidification in thick sections.
- Heat treat control: In-house furnaces, short quench delay, and test bars from every batch.
- Inspection: Real-time x-ray for internal soundness, plus dimensional inspection and leak testing where required.
- Beryllium handling: If A357 is specified, confirm the foundry is set up to melt and finish beryllium-bearing alloys, or discuss switching to E357 or F357.
A357, E357, and F357 Castings at LeClaire
LeClaire pours A357, E357, and F357 aluminum in sand and permanent mold processes, with tooling, core making, heat treating, and CNC machining under one roof. Simulation software and in-house tool and die design help get high-strength castings right before production, and digital real-time x-ray, CMM inspection, and leak testing verify them before they ship. LeClaire is ISO 9001:2015 certified with a 98 percent on-time delivery record.
Frequently Asked Questions About A357 Aluminum
What is the difference between A357 and A356?
A357 contains more magnesium (0.40 to 0.70% versus 0.25 to 0.45%) and a small beryllium addition. That gives A357 higher strength after T6 heat treatment, while A356 typically offers better elongation and lower cost.
What is the difference between A357 and F357?
F357 has essentially the same base chemistry as A357 but holds beryllium to 0.002 percent maximum instead of 0.04 to 0.07 percent. It is the common beryllium-free substitute for A357 in aerospace and defense.
What is the difference between E357 and F357?
Both are beryllium-free, with beryllium held to 0.002 percent maximum. E357 holds magnesium to a narrow 0.55 to 0.60 percent band and iron to 0.10 percent maximum for a very consistent heat treatment response. F357 follows a magnesium range closer to A357’s.
Why does A357 contain beryllium?
Beryllium reduces magnesium loss to oxidation in the melt and changes iron-bearing phases into a less harmful form, which helps ductility. Because beryllium is an occupational health hazard, many users now specify beryllium-free E357 or F357.
Is F357 as strong as A357?
F357 is designed to deliver comparable heat-treated strength to A357. Actual properties depend more on casting process, melt quality, and heat treatment than on the presence of beryllium alone.
Get High-Strength Aluminum Castings Right
A357 aluminum and its beryllium-free relatives E357 and F357 give engineers more strength than A356 in the same castable Al-Si-Mg family. Getting that strength in production depends on tight control of melt quality, chemistry, solidification, and heat treatment. Request a quote from LeClaire Manufacturing to review your A357, E357, or F357 part with our engineering team.