AMS 5878 Sheet vs AMS 6521 Sheet for Aerospace Fabrication

An aerospace component rarely fails because of bad design. It fails because the wrong material was used in the wrong operating condition. Choosing between AMS 5878 Sheet and AMS 6521 Sheet is one of those decisions where two alloys look similar on a specification sheet but behave nothing alike under heat or load.

Both are widely specified across aerospace programs, yet they come from entirely different alloy families. One holds its strength at 1,800°F. The other delivers 300 ksi tensile strength at room temperature. Getting this choice wrong adds rework and warranty risk to a program.

Understanding AMS 5878 Sheet and AMS 6521 Sheet

What is AMS 5878 Sheet?

AMS 5878 Sheet covers Haynes 230, a nickel-chromium-tungsten-molybdenum alloy. It contains roughly 57% nickel, 20-24% chromium, 13-15% tungsten, and 1-3% molybdenum, with carbon held at 0.05-0.15% to support weldability.

It’s the chemistry of this alloy that makes it special: It resists oxidation up to 2,100°F and retains strength up to 1,800°F. It’s also available in sheet form with 115 ksi tensile strength, 50 ksi yield strength and 40% elongation at room temperature, making it well suited to combustors, exhaust systems and furnace parts, where heat over time destroys standard stainless within months.

What is AMS 6521 Sheet?

AMS 6521 Sheet specifies Maraging 300, also called C300, an 18% nickel maraging steel built around 18.5% nickel, 9.0% cobalt, 4.9% molybdenum, 0.65% titanium, and 0.10% aluminum. Unlike carbon steels, it hardens through age precipitation: machined solution-annealed at 35 HRC max, then aged near 480°C to unlock full strength.

After aging, it delivers a minimum 270 ksi yield strength and tensile strength near 300 ksi, while still holding 11% elongation. Most steels trade strength for ductility. Maraging 300 keeps both, which puts it in landing gear, rocket motor cases, and structural parts carrying heavy loads with little weight margin.

Key Material Differences Between AMS 5878 Sheet and AMS 6521 Sheet

Chemical Composition Comparison

The two alloys share no major alloying element at a meaningful concentration. AMS 5878 Sheet leans on chromium and tungsten to resist oxidation at extreme heat. AMS 6521 Sheet leans on cobalt and molybdenum to drive precipitation hardening through intermetallic compounds, mainly Ni3Mo and Ni3Ti. Neither mechanism transfers to the other alloy.

Mechanical Properties Comparison

AMS 6521 Sheet wins decisively on raw strength. Its 300 ksi tensile and 270 ksi yield strength outweighs the 115 ksi tensile and 50 ksi yield strength of AMS 5878 Sheet. Hardness follows the same pattern: aged Maraging 300 exceeds 50 HRC, while Haynes 230 sheet stays near 25 HB max.

Toughness flips the comparison. AMS 5878 Sheet offers 40% elongation, nearly four times the 11% elongation of aged Maraging 300, though Maraging 300’s fatigue resistance still holds up well, aided by notch ductility down to -50°C.

Temperature Performance Characteristics

AMS 5878 Sheet is built for heat, holding useful strength to 1,800°F and resisting oxidation to 2,100°F under sustained exposure. AMS 6521 Sheet retains its strength only to 450°C, around 842°F. For elevated-temperature components, that gap rules out Maraging 300 immediately.

Corrosion and Oxidation Resistance

Chromium gives AMS 5878 Sheet a protective oxide layer that holds up under prolonged thermal cycling. AMS 6521 Sheet relies on dense, low-carbon martensite for corrosion resistance, which performs well in dry structural service but does not match a chromium-rich nickel alloy in high-heat conditions.

Fabrication Considerations for Aerospace Applications

Formability and Sheet Processing

AMS 5878 Sheet forms well annealed, using its high elongation to shape complex contours without cracking. AMS 6521 Sheet is formed before aging, while still soft at 35 HRC max, then hardened afterward to avoid post-aging cracking.

Weldability and Joining Performance

Haynes 230’s low carbon content supports clean welds without the carbide issues common in higher-carbon nickel alloys. Maraging 300 also welds well after aging, provided the heat-affected zone gets a re-aging treatment to restore local strength.

Machining and Production Efficiency

Maraging 300 machines efficiently in its annealed state, before aging locks in high hardness. Machining after aging slows production and wears tooling faster. AMS 5878 Sheet machines at a steady but slower rate throughout, since its nickel matrix work-hardens during cutting.

Aerospace Applications of AMS 5878 Sheet

High-Temperature Structural Components

Combustor liners, transition ducts, and afterburner components depend on AMS 5878 Sheet holding shape at 1,800°F without warping.

Engine and Exhaust System Components

Exhaust ducting and turbine casings benefit from oxidation resistance at 2,100°F, conditions that oxidize most stainless steel within a single flight cycle.

Aerospace Fabrication Requiring Corrosion Resistance

Parts exposed to combustion byproducts or aggressive atmospheric conditions hold up longer with Haynes 230’s chromium-driven oxide layer than with conventional heat-resistant steels.

Aerospace Applications of AMS 6521 Sheet

Structural Aerospace Components

Wing fittings and fuselage frames use AMS 6521 Sheet to cut weight while holding a 270 ksi minimum yield strength.

Landing Gear and Load-Bearing Parts

Landing gear sees repeated high-impact loading on every takeoff and landing cycle. Maraging 300’s strength-to-weight ratio supports this without the bulk a lower-strength alloy would need.

Aerospace Assemblies Requiring Wear Resistance

Actuator linkages and torsion members subjected to repeated stress cycles benefit from Maraging 300’s fatigue resistance and stable hardness after aging.

Factors to Consider When Selecting Between AMS 5878 Sheet and AMS 6521 Sheet

Operating Temperature Requirements

Match the alloy to the application’s thermal ceiling. Anything above 450°C pushes past Maraging 300’s limit and into AMS 5878 Sheet territory.

Mechanical Performance Requirements

Decide whether the part needs raw tensile strength, like AMS 6521 Sheet’s 300 ksi, or wide-temperature ductility, where AMS 5878 Sheet’s 40% elongation wins out.

Fabrication and Manufacturing Needs

Account for whether forming and welding happen before or after hardening. AMS 6521 Sheet’s two-stage process adds a planning step AMS 5878 Sheet does not require.

Service Environment Conditions

Weigh exposure to oxidizing atmospheres or chemical contact against each alloy’s corrosion mechanism, since chromium-based protection differs fundamentally from martensite-based protection.

Lifecycle Performance Expectations

Match expected service life to the right data set: fatigue data for AMS 6521 Sheet under cyclic load, oxidation life data for AMS 5878 Sheet under sustained heat.

Advantages of Choosing the Right Aerospace Sheet Material

Matching alloy to application improves component performance, since each material performs within the conditions it was developed for. Fabrication efficiency improves too, because forming and joining line up with the alloy’s actual behavior. Correct selection keeps a program compliant with aerospace specifications, reduces maintenance costs over the part’s service life, and raises operational safety by avoiding failure modes that mismatched materials invite.

Common Material Selection Mistakes in Aerospace Fabrication

Prioritizing Strength Without Considering Temperature Exposure

A 300 ksi tensile figure looks attractive on paper, but Maraging 300 loses that advantage past 450°C, risking strength loss exactly when a high-heat part needs it most.

Overlooking Fabrication Requirements

AMS 6521 Sheet should be formed after aging, not before. Forming of AMS 6521 after aging can result in cracking during forming, a mistake that is only evident when the part is in production.

Ignoring Corrosion and Oxidation Resistance Needs

The use of AMS 6521 Sheet for continuous oxidizing environments sacrifices long-term durability for short-term strength and shortens service life even before mechanical limits are reached.

Conclusion

AMS 5878 Sheet and AMS 6521 Sheet solve different problems. Haynes 230 holds strength and resists oxidation up to 2,100°F, making it the choice for combustors, exhaust paths, and other high-heat zones. Maraging 300 delivers 300 ksi tensile strength and 270 ksi yield strength at room and moderate temperatures, suiting landing gear and structural frames that never see extreme heat.

When you take into account all the factors like thermal performance, mechanical properties, fabrication sequence and service environment, rather than just one in isolation, the material choice will stand the test of the full service life of the part. Parag Metals offers both AMS 5878 Sheet and AMS 6521 Sheet to exact aerospace specifications, with quality checks at every stage. Contact Parag Metals to confirm specification, thickness and stock availability for your next aerospace fabrication order.