Aluminum vs. Stainless Steel: Benefits of Both In Aviation & Aerospace

April 29, 2021 | Stainless Steel Baskets, Aerospace

aviation-blade-vane-basketOnce an indispensable material of the aerospace industry, aluminum now makes up only about 20% of aircraft parts in a jet today. Other materials have since taken its place, with factors such as superior capabilities and the desire for lighter aircraft serving as reasons for replacement.

While composite materials and carbon-reinforced polymers are light and help reduce an aircraft’s weight, the need for a corrosion-resistant and hardy metal is important. The result is a prominent increase in the use of stainless steel parts in the aerospace industry. Stainless steel parts are being used in aircraft and aerospace manufacturing now more than ever.


Aluminum vs. Stainless Steel: How Are They Different?

Though aluminum is a lighter material, stainless steel has higher tensile strength, melting point, and shear modulus than aluminum. Here’s a quick comparison table:

Mechanical Property Aluminum 304 Stainless Steel 316 Stainless Steel
Ultimate Tensile Strength 310 MPa (45,000 psi) 505 MPa (73,200 psi) 580 MPa (84,100 psi)
Weight 2.7 g/cm3 8 g/cm3 8 g/cm3
Shear Modulus 26 GPa (3770 ksi) 86 GPa (12,500 ksi) 82 GPa (11,893 ksi)
Melting Point 582-652˚C (1,080-1,205˚F) 1,400-1,455˚C (2,550-2,650˚F) 1,370-1,400˚C (2,500-2,550˚F)

Why Is Aluminum Used in Aircrafts and Aviation?

In 1903, the Wright brothers built their wood-framed biplane with an aluminum crankcase engine and set things into motion. By World War I, lightweight aluminum was essential in aircraft design and development, and during WWII, the production of aluminum soared. Between 1940 and 1945, an astounding 296,000 aircrafts were built and more than half were made primarily from aluminum.

While aluminum in aviation is less popular now, only making up about 20% of aircraft parts in the average jet, its usage continues due to its lightweight nature. It’s also easily machined and processed due to its high ductility, or stretchability. While pretty strong on its own, aluminum can be further strengthened by adding additional metals such as copper, and through a cold or heat treatment. Aluminum is also relatively cheap when compared to other metals due to its being an atomic element. 

Today, you’ll still find aluminum alloys in the fuselage, the wing panes, the rudder, the exhaust pipes, the door and floors, the seats, the engine turbines, and the cockpit instrumentation. Popular aluminum-based alloys include aluminum alloy 7075, 7475-02, and 6061 due to their lightweight and high electrical conductivity.  

Why Is Steel Used in Aircrafts and Aviation?

Stainless steels came into general commercial use around 1930 and were regarded by some as "wonder metals." That’s because, while stainless steels were much more expensive than plain carbon and alloy steels, they were far more effective in applications such as aircraft exhaust systems and turbo superchargers – turbine compressors driven by hot exhaust gases of an airplane engine.

Of course, stainless steel may seem a surprising choice for aviation. After all, it’s heavier than aluminum, and aircrafts generally try to be as lightweight as possible. Still, stainless steel has several advantages over aluminum. Stainless steel is highly resistant to corrosion, whether it's from atmospheric conditions or chemical solvents. Thanks to its protective oxide layer, stainless steel prohibits oxidation and corrosion. And while aluminum is strong, stainless steel has higher tensile strength and is able to resist impact damage better than aluminum. For instance, grade 304 stainless steel has a higher ultimate tensile strength than aluminum—505 MPa (73,200 psi) vs 310 MPa (45,000 psi). 

Besides a higher tensile strength, stainless steel has a greater shear modulus and a melting point than aluminum, properties that are essential for many aviation parts. Today, stainless steel is commonly used in airframes—the body of an aircraft—since the materials used here need to withstand extreme hot and cold temperatures as well as corrosives. Landing gear and jet engines also benefit from being made in stainless steel. Both need to be exceptionally strong to withstand continuous flight. 

Aluminum in Aerospace 

In his 1865 novel Journey to the Moon, Jules Verne provided a detailed description of an aluminum rocket. Almost a century later, in 1957, the Soviet Union launched Sputnik the Earth's first artificial satellite, which was made of aluminum alloy. After that, the United States began launching rockets made of aluminum alloys into orbit, turning Verne’s novel into reality. 

While aluminum use in aviation has declined, it remains the material of choice for aerospace structures because it’s lightweight and able to withstand the stresses that occur during launch and operation in space. It’s been used on the Apollo spacecraft, the Skylab, the space shuttles, and the International Space Station. Aluminum alloys consistently exceed other metals in such areas as mechanical stability, dampening, thermal management, and reduced weight.

Stainless Steel in Aerospace 

Despite the popularity of aluminum alloys for aerospace, stainless steel is making headway. Typically, the steels used in aerospace vehicles are stainless steel alloys (304, 304L, 316, and 316L are common aerospace grade stainless steel examples). SpaceX CEO Elon Musk recently raised eyebrows with Starship, a spacecraft featuring a Stainless Steel 301 skin and designed for interplanetary travel.

People wondered why he wouldn’t use some form of aerospace-grade aluminum alloy, which is lighter and cheaper to send into space. However, as a vehicle designed for interplanetary travel, Starship would be subjected to both freezing and scorching temperatures as it ascends from and descends into planetary atmospheres, making rugged stainless steel the best choice of material.

Stainless Steel Products for Aviation and Aerospace Manufacturing

Stainless steel isn’t just part of aircrafts and space vehicles; it’s also used to create more effective and efficient maintenance, repair, and operations (MRO) processes. Stainless steel custom wire baskets and carts protect expensive parts during harsh cleaning and assembly processes. Custom wire baskets made of stainless steel are also used to hold delicate, small parts through continuous chemical baths. 

Wire baskets with dividers and lids can protect parts from intermingling with each other and potentially escaping the basket during the cleaning process. Due to stainless steel’s excellent corrosion resistance, baskets made from stainless steel can also be subjected to continuous chemical processes without being corroded. 

Stainless steel carts also can be an efficient means of quickly transporting delicate and large aviation parts through MRO processes. Carts can prevent metal-on-metal contact, keeping aircraft parts safe from damage and reducing rejection rates from surface scratches. The durability of stainless steel ensures that carts can withstand years of continuous use. 

Marlin Steel’s Solutions for Aviation and Aerospace

Marlin Steel prides itself on designing and delivering custom stainless steel products for the aerospace industry. Whether as an aviation cleaning basket or a custom cart, stainless steel is vital for efficient aerospace manufacturing and aircraft MRO. 

Marlin Steel’s custom stainless steel carts are provided with neoprene liners (or other coatings) that prevent metal-on-metal contact—preventing parts from being damaged during movement. If you have a specific challenge for your aviation MRO, Marlin Steel’s engineers' design wire and stainless steel solutions customized to your needs. As a whole, stainless steel is essential for the 21st-century aerospace industry. 

Want to learn more about how to use stainless steel components in your aircraft? Do you need a custom aerospace parts cleaning basket? Start by reaching out to the Marlin Steel team today.