A guide for the skeptical consumer.
I probably see more camping and overlanding content than most, but lately I’ve noticed more products advertised with aerospace and military (aka “MIL spec”) grade materials. Is it false advertising? Not really, but it doesn’t automatically mean a higher quality product. Let’s dive into some (simplified) metallurgical nerdery.
A metal’s properties are controlled by its ingredients (alloy) and its heat treatment (temper). One example is 7075-T6 (alloy + temper), which follows the numbering convention set by Aerospace Material Specification 4045 (AMS-4045). FWIW, that spec is maintained by the Society of Automotive Engineers (SAE). So, 7075-T6 is used in airplanes and is in the AMS spec, so I’d call it “aerospace grade.”
But, there’s also a 7075 alloy in the American Society for Materials and Testing’s more general ASTM-B209 spec. Take a look at the table below—it’s the same stuff. Over the years, the acronym soup of organizations have mostly converged in their requirements. This helps metal manufacturers streamline their catalogs and minimize near-duplicate inventories. There are some discrepancies between US, European, and Asian specifications, but metals are a global commodity and many of the specifications overlap.
7075 Alloy composition
The Aerospace Material Specification and the American Society of Testing and Materials specification agree—this is 7075.
The same table comparison could be made for alloys 2024, 6061, or 6063. It’s more common for aircraft structural parts to be made from 2024 or 7075, but there’s literal tons of 6063 flying over our heads every day. And, you can find 6063 in thousands of things at Home Depot, but they aren’t labeled as “aerospace grade.” This is where shrewd marketing takes over. Shoppers might think they’re overpaying for a $20 door threshold if it’s “aircraft quality” but they might be enticed to buy a $300 camping stove if it shares materials with an actual rocket.
Some aerospace grade aluminum…
…hiding in your local hardware store. It’s not labelled as such (the sticker doesn’t even note the alloy!) but a quick search on the manufacturer’s website confirms: it’s 6063.
The same can be said of many “military” or “marine” stainless steels. The 316 alloy is more corrosion resistant than 304, because it has more molybedum and nickel, and it’s often called “marine grade,” but the US Navy doesn’t have a special 316. The same steel mill could be supplying a defense contractor and a frying pan factory.
Tempering your expectations
Now for the temper grades, which describe how the metal is heat treated to achieve a certain hardness and microscopic grain structure. Two common tempers for aluminum are “O” and “T6.” As shown in the table, a “high strength” alloy like 7075 can actually be weaker than 6061 or 6063, depending on its temper. Manufacturers often purchase the softer “O” grades to make forming easier, and then heat treat the formed parts to achieve the stronger “T6.” It’s unusual to see a finished product in O temper.
Aluminum alloy and temper comparison
Each alloy and temper is a good choice for a specific application.
You can now imagine how selection of the right alloy and temper is key for a product designer. For an inexpensive bicycle pedal crank, I’d pick 6061-T6. For a high performance crank, I could design the part thinner, but specify the more-expensive 7075-T6 to achieve the same part strength. For a heat sink with no structural requirements, I’d pick 6063 for its superior heat conduction. It might be formed as O, then treated to T6.
When is it more than advertising?
There are materials with specialized, high-performance purposes. Military spec MIL-A-46100 defines a ballistic grade steel that can be up to 12” thick, undergoes X ray inspection, and is heat treated to specifically withstand munitions impact. You won’t find that at Home Depot, and if you need bomb-proof parts for your overland truck, you should probably camp somewhere safer.
Specifications regarding the form of a component can indicate specialization (but not always higher strength!) MIL-spec and SAE washers are smaller in diameter, but can be made from ordinary carbon steel. Bolts made to AN standards will have stronger, rolled threads, which matters in aircraft and race cars, but is less important for every day use. And, the shape of many standard, extruded aluminum parts follow AMS standards, with different corner radii than structural aluminum.
As a consumer, there are other indicators of quality beyond metal grades, but if you do want to embrace the metallurgy (I’ve only scratched the soft, O-tempered surface here), research the actual alloys and tempers of the products you’re buying, to see if the advertised material actually offers a benefit. And if you’re a manufacturer, you may already be using a using an “aerospace” metal—let your marketing department know!