535 aluminum, also known as Almag 35, is an aluminum-magnesium casting alloy with about 6.2 to 7.5% magnesium that reaches its full properties as cast, with no heat treatment. Sand castings must meet at least 35 ksi tensile strength, 18 ksi yield strength, and 9% elongation under ASTM B26, and the alloy’s resistance to saltwater corrosion makes it a standard choice for marine parts. It machines and finishes well, but it is harder to pour than aluminum-silicon alloys and is not the first choice for parts that must hold pressure.
535 combines three things marine engineers want in one alloy: strong corrosion resistance, good strength and shock resistance as cast, and a surface that machines, polishes, and anodizes cleanly. Skipping heat treatment also removes a production step, shortens lead time, and avoids the distortion that quenching can cause.
This guide is for engineers and procurement managers sourcing cast aluminum parts for boats, marine equipment, and other corrosive environments. It covers 535 composition, properties, corrosion behavior, how it compares with A356, common applications, and what to ask a foundry. For every alloy LeClaire pours, see our aluminum casting alloys guide.
What is 535 aluminum made of?
535 is a high-purity aluminum-magnesium alloy with almost no copper, which is the basis of its corrosion resistance.
- Magnesium (about 6.2 to 7.5%): The main alloying element. It strengthens the alloy in the as-cast condition and gives it its corrosion behavior.
- Manganese and titanium (about 0.10 to 0.25% each): Manganese controls iron-bearing phases, and titanium refines grain size.
- Beryllium (trace): A very small addition that limits oxidation of the magnesium-rich melt during pouring.
- Iron and silicon (0.15% max each) and copper (0.05% max): Held low. Keeping copper out is what protects 535 in saltwater.
A535 is a closely related variant with slightly different composition limits. Confirm which designation your drawing calls out before quoting.
Why doesn’t 535 aluminum need heat treatment?
535 develops its strength as the casting solidifies and stays stable afterward, so parts are used in the as-cast (F) condition. Most aluminum-silicon alloys, including A356, need solution heat treatment, quenching, and aging to reach comparable strength.
- Shorter lead time: Parts go from casting to machining without a heat treat cycle.
- Lower cost: No furnace time or heat treat handling is added to each part.
- Less distortion: Without a quench, there is less risk of warping thin or complex parts.
- Dimensional stability: 535 holds its dimensions well over time, which helps precision machined parts.
What are the mechanical properties of 535 aluminum?
535 offers strength comparable to heat-treated A356 with much higher elongation, plus good shock resistance.
- Tensile strength (ASTM B26 minimum, sand cast): 35 ksi (241 MPa).
- Yield strength (ASTM B26 minimum, sand cast): 18 ksi (124 MPa).
- Elongation (ASTM B26 minimum, sand cast): 9%, compared with 3.5% for A356-T6.
- Machinability: Excellent. 535 cuts faster and cleaner than common aluminum-silicon casting alloys.
- Surface finish: Polishes to a bright finish and responds well to anodizing.
- Density: Slightly lower than most aluminum-silicon casting alloys.
How does 535 aluminum resist saltwater corrosion?
535 is one of the most corrosion-resistant aluminum casting alloys in seawater because it is based on magnesium and contains almost no copper. Like all aluminum, it forms a protective oxide layer, and its chemistry keeps that layer stable in salt spray and immersion.
- Low copper: Copper is the element that most reduces aluminum’s corrosion resistance, and 535 keeps it at 0.05% or less.
- Elevated temperature caution: Long exposure to elevated service temperatures can cause magnesium-rich phases to form at grain boundaries, which makes the alloy susceptible to intergranular corrosion. 535 is best suited to parts that run near ambient temperature.
- Galvanic contact: As with any aluminum part, isolate 535 from stainless steel, bronze, and other dissimilar metals in saltwater using coatings, gaskets, or suitable fasteners.
- Coatings: 535 performs well bare, and anodizing or paint adds protection and appearance for exposed hardware.
For more on how aluminum holds up in marine environments, see our guide to marine aluminum casting and corrosion resistance.
535 vs A356: which alloy is better for marine parts?
Choose 535 for parts where corrosion resistance, shock resistance, and finish quality come first. Choose A356 for complex, thin-walled, or pressure-tight parts where castability matters more.
- Corrosion resistance: 535 is better in saltwater.
- Strength: Similar tensile minimums (35 ksi for 535-F, 34 ksi for A356-T6), with 535 offering far higher elongation.
- Heat treatment: 535 needs none. A356 needs a full T6 cycle to reach its rated strength.
- Castability: A356 is easier to pour and better for thin walls and complex cores. The magnesium in 535 oxidizes readily and needs careful melt handling.
- Pressure tightness: A356 is the better choice for housings that must hold fluid or air.
- Machining and finish: 535 machines faster and takes a brighter polished or anodized finish.
For A356 properties and tempers, see our A356 aluminum guide.
What marine parts use 535 aluminum?
535 is used across boats and marine equipment wherever a cast part faces salt exposure, impact, or a visible finish.
- Deck hardware and fittings: Cleats, brackets, and mounts that sit in salt spray and need a clean finish.
- Brackets and mounts: Structural castings that take shock and vibration from waves and engines.
- Covers and enclosures: Non-pressurized housings exposed to water.
- Other corrosive environments: Food handling, chemical, and outdoor equipment parts that benefit from the same corrosion resistance.
LeClaire casts and machines aluminum components for the marine industry, with engineering support for alloy selection on every new part.
What should you ask a foundry before sourcing 535 castings?
535 is less forgiving to pour than aluminum-silicon alloys, so look for a foundry with specific aluminum-magnesium experience.
- How do you control oxidation and dross? Magnesium-rich melts oxidize quickly, so melt handling and pouring practice directly affect casting quality.
- How is the gating designed? Gating that keeps metal flow calm reduces oxide inclusions and surface defects.
- Which process fits the part? Sand casting suits larger and lower-volume parts, while permanent mold casting suits repeatable higher volumes.
- Who machines and finishes the part? In-house machining keeps sealing surfaces and cosmetic features under one supplier’s control.
Frequently asked questions
Is Almag 35 the same as 535 aluminum?
Yes. Almag 35 is a long-standing trade name for 535 aluminum. Both refer to the same aluminum-magnesium casting alloy.
Does 535 aluminum need heat treatment?
No. 535 reaches its full properties in the as-cast condition, which saves a production step and avoids quench distortion. It is typically supplied in the F temper.
Is 535 aluminum good for saltwater?
Yes. 535 is one of the most saltwater-resistant aluminum casting alloys because it contains almost no copper. Isolate it from dissimilar metals to prevent galvanic corrosion.
Can 535 aluminum be anodized?
Yes. 535 responds well to anodizing and polishes to a bright finish, which is one reason it’s used for visible marine hardware.
Is 535 aluminum good for pressure-tight castings?
535 is generally not the first choice for parts that must hold pressure. Aluminum-silicon alloys such as A356 or C355 are better suited to pressure-tight housings.
Get a quote on your 535 castings
535 aluminum delivers saltwater corrosion resistance, high elongation, and good strength straight out of the mold, with no heat treatment required. LeClaire Manufacturing pours 535 for marine and other corrosive-environment parts and machines them in-house, so one supplier owns the casting from tooling to finished part. Request a quote to have your 535 part reviewed.