Materials Monday: The Allure of Aluminum

In the recent blog post Materials Monday: The Big Picture, we noted that aluminum is the “darling of aircraft manufacturers and cookware producers alike.” The reason is clear. Aluminum alloys in all their many forms are strong, lightweight, and corrosion resistant, attributes that make it the perfect metal for a huge variety of applications.

You already know that soda cans are made of aluminum, but so are many skyscraper parts, high-tension electrical wires, various car and truck components, as well as the hulls of an increasing number of seagoing vessels. In addition, aluminum is used in many electronic components, both at the board level, such as for the heat sink pictured at the top of this page, and for the housing enclosures that contain such components. In fact, aluminum is the world’s second-most used metal, after iron (primarily used in making steel). Approximately 63 million tons of aluminum are mined each year and combined with other industrial metals to produce a variety of alloys.

Mixing it up

But there’s that word again: alloys. What we didn’t delve into in that earlier article is that pure, elemental aluminum—number 13 on the periodic table—is actually pretty darned wimpy. As in Clark Kent wimpy. It’s not until you introduce tiny amounts of magnesium, silicon, and other alloying elements—some of which are also found in steel, stainless steel, and superalloys—and then cook the resultant blend in a furnace for a while that aluminum acquires its Superman properties.

Aluminum is not so easy to extract, despite the fact that it’s the most abundant metallic element on Earth. First discovered in 1825, it wasn’t produced at industrial levels until the invention of the Hall Héroult process in 1886, which converts the aluminum oxide found in bauxite ore into pure aluminum. So important was this discovery that co-inventor Charles Hall later went on to form the Pittsburgh Reduction Company, known today as Alcoa. Today most aluminum is mined in China, Russia, and Canada, followed by the US, Australia, India and Brazil.

What’s in a name?

As with steel alloys, aluminum has its own unique and often confusing numbering system. We won’t get into all the nuances here except to say that two broad classes of aluminum alloy exist—those that are heat-treatable, and those that are strengthened through rolling and other cold working methods. In either case, wrought alloys fall into one of eight families—1xxx through 8xxx—with the first digit indicating the primary alloying element(s), followed by a temper designation (ex. -T651). Cast alloys also use a four-digit nomenclature, but with a decimal number at the end specifying the raw form. Oh, and by the way, anyone in the UK, Germany, or France who might be reading this is already very much aware that you have your own DIN and British Standards that must be cross-referenced to the ones just listed.

Manufacturing geeks and those wishing for some late-night reading can find all the mind-numbing details by cruising over to the websites of The Aluminum Association, ASTM International (formerly known as American Society for Testing and Materials), and SAE International (formerly known as the Society of Automotive Engineers). There’s also ESAB, a manufacturer of welding and cutting systems, which has some excellent educational information available in the ESAB Knowledge Center.

The aforementioned organizations are great for reference materials and research, however, there may be some costs associated with certain resources. So, unless you’re a metallurgist, the chances are excellent that your favorite sheet metal fabricator, machine shop, or die casting house (quick self-serving plug: Prismier offers all three of these services) can provide the information needed to guide you to the correct material for your current project.

Choices, choices

Here are some examples of the more common aluminum alloys in use today, along with some typical applications:

• 2024 aluminum alloy is one of the darlings of the commercial aircraft industry mentioned earlier. It contains between 3.8 to 4.9 percent copper, is very soft and formable in its -O state, but can be strengthened significantly (2024-T3, for example) via heat-treating. Although it is widely used for airplane fuselage components, its corrosion resistance is fairly low, so it is often anodized or clad with a thin layer of high-purity aluminum (known as Alclad).
• 3003 is said to be the most widely used of all aluminum alloys. Its principal alloying element is manganese, the stuff of strong bones and healthy brains, along with a smidge of copper. The siding on your house is probably made of 3003, as are your kitchen appliances, garage door, and lawn furniture. Though not heat-treatable, it is very corrosion resistant, and can be made quite strong through cold-working, or deep drawn and welded to make parts such as pressure vessels and chemical tanks.
• 5052 aluminum, though not heat-treatable, boasts one of the highest fatigue strengths of all aluminum grades. It’s also weldable and very resistant to saltwater and marine environments, which is why the seagoing vessels cited at the top of this article are probably made of 5052. So are architectural facades (think skyscrapers), fuel tanks, and heat exchangers. The 5xxx family contains 2.5 percent or of magnesium along with a little chromium.
• 6061 is one of the most well-known of all aluminums, especially to machine shops. It is available in the annealed state (-0), although -T6 and -T651 (heat-treated) grades are more common. Alloyed with roughly 1.0 percent magnesium and about half that amount of silicon, 6061 is the workhorse of aluminums. It is strong, resistant to stress, cracks, and corrosion, weldable, and formable. You’ll find 6061 in structural applications, bike and car parts, and a broad range of general engineering uses.
• 7075 ranks among the highest strength aluminums of all, containing up to 6.1 percent zinc and 2.5 percent magnesium along with copper, chromium, titanium, and a few other elements. The landing gear on many planes contains 7075 components, as do all-terrain vehicles, mountain climbing gear, and many aerospace or military-grade parts. For many applications, 7075 is considered the lightweight alternative to steel.

That’s but a small sampling of the 500 or so recognized aluminum alloys, with more being developed each year. Nor does it discuss the various die casting alloys that are available, although the ones just listed—along with their different tempers and shapes—comprise the lion’s share of all commercial and industrial uses. As mentioned, Prismier machines, bends, forms, stamps, laser cuts, and die-casts all types of aluminum components, and stands ready to help out on your next prototyping or large-scale production project. So, if you want to talk aluminum (or any other metal), give us a shout.