Aerospace Materials: Selection, Specs and Paperwork

How to use this materials library

Each page in this section covers one material family the way a manufacturing engineer would brief a peer: the alloy or polymer designations that actually show up on aerospace drawings, the specifications that govern them, typical properties with the source of each number, the machining and processing problems that cause scrap, and the paperwork a buyer should require.

Two rules run through every page. First, a typical value is not a design value. Data sheets and handbooks publish typical or nominal numbers, while procurement specifications publish minimums, and design allowables come from statistically based sources such as MMPDS. Second, a property is only as good as the traceability behind it. If the certification does not tie the heat or lot to the specification and revision on your drawing, the number on the cert does not belong to your part.

The pages in this section are:

• Aluminum alloys: 2024, 6061, 7075, 7050, 2219 and cast A356, tempers, anodize response and stress corrosion.
• Titanium alloys: CP grades, Ti-6Al-4V and ELI, Ti-6-2-4-2, alpha case and machining.
• Nickel superalloys: Inconel 718 and 625, Hastelloy, Haynes 230, Monel K-500 and oxygen compatibility.
• Stainless and specialty steels: 304/316, 15-5PH, 17-4PH, A286, 4130/4340 and maraging steel.
• Engineering plastics: PEEK, PEI, PAI, polyimide, PTFE and PCTFE, outgassing and oxygen service.
• Controlled expansion and copper alloys: Invar 36, Kovar, beryllium copper and RF coppers.
• Material certs and traceability: mill certs, EN 10204 3.1, DFARS specialty metals, lot control and PMI.

Material families at a glance

The table below is a starting map, not a selection tool. It lists where each family usually earns its place on aerospace hardware, the specification families you will see on drawings, and the failure or process trap that most often bites.

Start with the environment: stress corrosion ratings

For hardware exposed to salt air, the most useful single screen is NASA MSFC-STD-3029, which sorts alloys and tempers into high, moderate and low resistance to stress corrosion cracking (SCC) in sodium chloride environments. Table I alloys can be used without approval; Table II and Table III alloys need NASA approval and a stress corrosion evaluation before use on NASA hardware.

The ratings are temper specific, which is why the temper on a drawing matters as much as the alloy. A few examples taken directly from the standard:

The standard also states that protective coatings do not change an alloy's rating. A painted or anodized 7075-T6 part is still a Table III part. Its rationale is simple: coatings get scratched, and sustained tensile stress in the short transverse direction, from interference fits, clamp-up or residual stress, does the rest.

Oxygen, propellants and flammability

If the part touches gaseous or liquid oxygen, flammability and ignition become selection criteria alongside strength. NASA-STD-6001B (currently with Change 3) defines the flammability, offgassing and compatibility tests NASA uses, including upward flammability in gaseous oxygen (Test 17), pneumatic impact for nonmetals (Test 14), and supplemental mechanical impact tests in liquid and gaseous oxygen (Tests 13A and 13B). It calls for oxygen compatibility assessments per NASA/TM-2007-213740 and points to the MAPTIS database for existing ratings.

In practice this means alloy choice for oxygen hardware leans toward nickel-copper and nickel-base alloys over aluminum and titanium for burn-prone geometries, and nonmetal choice leans toward fluoropolymers with test history. The nickel superalloys and engineering plastics pages go deeper, and cleaning to an oxygen-service level is covered under precision and oxygen cleaning.

Vacuum and outgassing

Spacecraft and vacuum chamber hardware add a third screen: what the material releases in vacuum. ASTM E595 measures total mass loss (TML) and collected volatile condensable materials (CVCM) after 24 hours at 125 C under a vacuum below 5 x 10^-5 torr, with condensables collected on a 25 C plate. The standard notes that TML of 1.00 percent and CVCM of 0.10 percent have historically been used as screening levels, but acceptance criteria belong to the user.

NASA Goddard maintains a searchable database of E595 results by material and cure condition. Check the exact grade and processing, because a different filler, cure or bake can change the result. Metals rarely outgas meaningfully, but their coatings, lubricants, adhesives and the plastics in the assembly often do.

Sourcing rules that limit your choices

For Department of Defense contracts, DFARS 252.225-7009 restricts where specialty metals are melted or produced. The clause covers steel with more than 0.25 percent of elements such as chromium, nickel, molybdenum, cobalt, niobium, titanium, tungsten or vanadium (or above set limits for manganese, silicon and copper), nickel and iron-nickel alloys and cobalt alloys with more than 10 percent other alloying metals, plus all titanium and zirconium alloys. Those metals must be melted or produced in the United States, its outlying areas or a qualifying country, with listed exceptions such as a 2 percent minimal content allowance and certain commercial off-the-shelf items.

Almost every alloy in this library other than aluminum and copper falls inside that definition. If the contract carries the clause, the certification needs a melt country, and the buyer needs to know before the PO is placed, not at receiving. Details are on the certs and traceability page.

Typical properties, minimums and allowables

Engineers lose time when a supplier, a data sheet and a stress report quote three different numbers for the same alloy. They are usually all correct, because they measure different things.

An example from 6061-T6: published figures show a specification minimum of about 42 ksi ultimate and 35 ksi yield against typical values near 45 and 39 ksi. Design to the first set, not the second. Thick plate and large forgings typically carry lower minimums than thin sheet, so always read the thickness band.

What to put on the drawing

Most material problems we see in purchasing trace back to an incomplete material callout. A complete callout lets any qualified supplier buy the right stock without a phone call.

• Alloy and temper or condition, for example 7075-T7351 rather than 7075.
• The procurement specification and product form, for example the AMS or ASTM spec for plate versus bar, and whether a specific revision is required.
• Grain direction requirements when the part is sensitive to short transverse loading.
• Heat treatment and the spec it is performed to, if the shop or a processor will heat treat after machining.
• Finish and its spec (anodize type and class, chem film class, passivation method, plating) and any hydrogen embrittlement relief bake.
• Special requirements: oxygen-clean level, outgassing limits, DFARS specialty metals, ultrasonic inspection of plate, or PMI.

If the drawing says only "aluminum" or "stainless," expect quotes based on whatever is cheapest to machine, and expect a cert that does not prove much.

Paperwork and controlled data

For any material that goes into flight or ground support hardware, require a certificate that names the specification, the heat or lot, chemistry and mechanical test results, and the producer. Keep the chain from mill to distributor to shop intact, with each step referencing the same heat. Our team checks that chain on every job before shipment and delivers the certs with the part.

Drawings and specifications for defense articles may be export controlled. Controlled data does not go through our website; it moves only by a secure method to authorized U.S. persons and authorized suppliers. See controlled programs for how that works.

Request parts or certified material

If you have a drawing with a full material callout, or a material question that is holding up a buy, send it through a hardware quote request. A person replies within 1 business day, we sign a mutual NDA before files are shared, and we flow your material, finish and certification requirements down to qualified suppliers, then check the cert package before the part ships.

In this section

• Aerospace Aluminum Alloys and Tempers
• Controlled Expansion Alloys and Copper Alloys for RF
• Engineering Plastics for Flight and Ground Hardware
• Material Certs, Specialty Metals and Lot Traceability
• Nickel Superalloys and Nickel-Copper Alloys
• Stainless and Specialty Steels for Aerospace Parts
• Titanium Alloys for Aerospace Hardware

Questions

Related

• Aerospace Aluminum Alloys and Tempers
• Titanium Alloys for Aerospace Hardware
• Nickel Superalloys and Nickel-Copper Alloys
• Material Certs, Specialty Metals and Lot Traceability

Sources

• NASA MSFC-STD-3029A, Guidelines for the Selection of Metallic Materials for Stress Corrosion Cracking Resistance in Sodium Chloride Environments
• NASA-STD-6001B, Flammability, Offgassing, and Compatibility Requirements and Test Procedures
• ASTM E595, Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment
• NASA Goddard outgassing database
• DFARS 252.225-7009, Restriction on Acquisition of Certain Articles Containing Specialty Metals
• 6061 aluminium alloy, minimum and typical properties