Material Matters: Aluminum
The thirteenth element on the periodic table, aluminum, is the most abundant metal on earth, the third most common element in the earth’s crust by weight, and its production is greater than all other nonferrous metals combined. This incredibly useful metal was once more expensive than gold. How could that be when it’s so abundant? Aluminum bonds easily to other elements, so it’s incredibly rare in its native form. Let’s learn more about this versatile metal.
HISTORY
Danish physicist Hans Christian Ørsted is credited for discovering aluminum in 1825, but because it’s rarely found in nature in its pure metal form and there was no affordable way to produce it, aluminum was very expensive. As a show of its worth, the Washington Monument was capped with a large aluminum casting in 1884 — no cheap undertaking.
Perhaps they should’ve waited a couple of years, when the price plummeted thanks to two intrepid engineers, American Charles Martin Hall and Frenchman Paul Héroult, who simultaneously developed an affordable method of aluminum production in 1886. Oceans apart, Hall and Héroult, both incidentally 22 years old at the time, came to the same conclusion, which is now commonly known as the Hall–Héroult process. They found that dissolving aluminum oxide in molten cryolite (an aluminum silicate) and then running electricity through it caused the aluminum to separate. The aluminum game was changed forever.
PROPERTIES
- Infinitely recyclable
- Abundant
- Low density
- Non-toxic
- High thermal conductivity
- Corrosion resistant
- Easily cast, machined, formed
- Non-magnetic
- Non-sparking
- Second most malleable metal and the sixth most ductile
SPECIFICATIONS
- Density: 2.7 g/cm³ at 20 °C
- Brinell Hardness: 245 [-] at 20°C/68°F
- Tensile strength: 90 MPa at 20°C/68°F
- Melting point: 660°C/221°F
- Specific heat capacity: 900 J/(kg·K) at 20°C/68°F
- Electrical resistivity: 2.6E-8 Ω·m at 20°C/68°F
ALUMINUM ALLOYS
Aluminum comes in a vast number of different alloys, each with different physical and thermal properties. An alloy is a mixture of chemical elements, one of which must be a metal. An aluminum alloy is an alloy where aluminum is predominant. Some of these alloys are easily cast, wrought, machined, or extruded. Other alloys are extremely strong, ductile, or resistant to stress cracking.
Aluminum alloys come in series from the 1000 series to the 7000 series. Here’s a basic breakdown:
- 1000 series: essentially pure aluminum, at least 99% aluminum by weight
- 2000 series: alloyed with copper, strong, but not as corrosion resistant as other alloys, can be precipitation-hardened to be nearly as strong as steel
- 3000 series: alloyed with manganese, workable, moderately strong, used for cooking utensils and cans
- 4000 series: alloyed with silicon, lower melting point without being brittle, used for welding wire
- 5000 series: alloyed with magnesium, strong, weldable, superior corrosion resistance, used for pressure vessels, tanks, marine applications
- 6000 series: alloyed with magnesium and silicon (making magnesium silicide), formable, weldable, corrosion resistant, moderate strength, easy to machine, most common general-purpose alloy, used for truck and boat frames, architectural applications
- 7000 series: alloyed with zinc, magnesium, and copper, heat-treatable, highest strength among alloys, can reach strengths in excess of 72,000 pounds per square inch, used in aircraft
One of the most popular all-purpose alloys is 6061 and we mill a lot of it using the Bantam Tools Desktop CNC Milling Machine and Bantam Tools Explorer™ CNC Milling Machine.
USES
At this point, it’s safe to say that almost everyone on the planet uses some product that contains aluminum. It’s just that ubiquitous. Let’s look at a few of them.
- Cans: Before 1959, the container of choice for most beverages was either steel cans or glass bottles. Needless to say, at that time, steel cans tended to affect the flavor of the liquids within. The aluminum beverage can was introduced in 1959 by none other than beer maker Coors, and the rest is history. The aluminum can is the most recyclable and sustainable material a drink can be housed in. Recycling aluminum takes less energy than creating it from scratch, and the largest producer of sheet aluminum for cans, Atlanta-based Novelis, states that more than 60% of the aluminum it produces is recycled, most of that from cans.
- Aircraft/Spacecraft: What was the magic material that enabled the Wright brothers to take their first flight? You guessed it! They were looking for ideas on how to lighten the weight of their four-cylinder gasoline engine, and their “mechanician” Charles Taylor suggested an alloy of aluminum and copper, which lightened their engine by 20 lbs, letting the Wright Flyer finally take flight. Many years later, NASA also started employing aluminum alloys for Apollo because of their light weight coupled with strength. The Orion space capsule is predominantly being made of an aluminum-lithium alloy.
- Architecture: The modern skyscraper owes its existence to aluminum. If you consider its innate qualities of being corrosion-resistant, lightweight, versatile, malleable, durable, and infinitely recyclable, it’s no wonder that aluminum is widely used in architecture. The Empire State Building, constructed in 1931, was the first building to make significant use of aluminum, from aluminum-framed doors and windows to horizontal aluminum spandrels between each floor to an aluminum relief of the building housed in the lobby. The building employed an estimated 650 tons of aluminum and stainless steel.
- Sustainable Energy: Aluminum is also central to sustainable building because of its recyclability and energy efficiency. It’s not only used extensively in solar panel platforms and wind turbines, but properly coated aluminum roofs can reflect up to 95% of the solar energy that strikes them.
UNCOMMON USES
While these uses of aluminum aren’t the most common, we found them fascinating and wanted to share.
- Shark tanks: Though the average person may not think much about shark tanks, divers and researchers certainly do. Aluminum is the most popular choice because it’s strong, buoyant, and doesn’t corrode in salt water.
- Rocket fuel: For the Space Launch System (SLS) rocket boosters, like the ones on the Space Shuttle, aluminum powder serves as the fuel and a mineral salt, ammonium perchlorate, is the oxidizer.
- Additive manufacturing: Market research firm SmarTech projected that the market for aluminum powder to use in additive manufacturing (like 3D printers) could grow to be a $300 million industry over the next 10 years.
CNC MACHINING SPOTLIGHT
We don’t normally like to play favorites, but with aluminum, it’s hard not to. It’s lightweight, durable, corrosion-resistant, and electrically conductive, making it ideal for a wide range of projects and excellent for prototyping. Our Bantam Tools Desktop CNC Milling Machine is not only optimized specifically for aluminum, but the milling machine bed, Z-carriage, and more are actually all made of aluminum.
Best bits: Use the biggest tool you possibly can to allow for the fastest material removal and least chance of tool breakage. When working with our Bantam Tools Milling Machines, the easiest tools to use are 1/4”, 1/8", and 1/16" flat or ball end mills. Aluminum is one of the less forgiving materials, and it’s easy to break small tools with too high of a feed rate or inadequate fixturing. That being said, any tool can be used to mill aluminum as long as the speeds and feeds settings are dialed in.
Hot tips: When dialing in a speeds and feeds recipe on a Bantam Tools Milling Machine, pay attention to the chip load and/or feed per tooth. While larger chips are better at distributing heat, making too large of a chip could lead to poor surface finish or even damage your end mill. On the flip side, smaller chips won’t be able to distribute heat as well and could cause chip welding.
COOL ALUMINUM PROJECTS
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