About Aluminium 7075 – A popular engineering material
Aluminium alloys are known for their strength and lightness, which means they have a very wide range of uses. In the case of aluminium 7075 the properties of base aluminium are improved by the alloying element Zinc, which gives it new and exciting properties, plus tiny amounts of other metals.
The Aluminium Association defines alloys using a numbered scheme, based on the alloying elements used. Aluminium 7075 belongs in the 7xxx series of alloys, officially named 7075 aluminium alloy and possessing unusually high strength as an engineering material. It also comes with top class mechanical properties, good ductility, toughness, and great resistance to metal fatigue.
What is aluminium 7075?
Aluminium 7075 is an alloy of pure aluminium. It has a modulus of elasticity of 71.7 GPa or 10,400 ksi, and a shear modulus of 26.9 GPa or 3900 ksi. It’s known for its strength and ability to resist deformation, which means it’s widely used in applications where both toughness and lightness are vital.
The material’s yield strength – the maximum amount of stress or force it can take before being permanently deformed – is good and high with a tensile yield strength of 503 MPa or 83,000 psi, enabling an impressive 503 MPa of stress before it fails and can’t go back to its original shape. No wonder it’s so good for things like aluminium tubing.
It is also very strong, in other words it takes a lot of stress before it snaps at what’s called the fracture point. Before it snaps the material permanently deforms. 7075 aluminium alloy’s tensile strength of 572 MPa or 83000 psi is impressively high bearing in mind its low density.
The material also comes with a high shear strength of 331 MPa or 48000 psi, which is why it’s so useful to the aerospace industry. It matters because a material loaded with a high force enough times can suffer from micro fractures and eventual breakage. Because the fatigue strength of aluminium 7075 withstands cyclical loading, it’s great for applications involving repetitive loading cycles, things like planes and cars. Its fatigue strength is 159 MPa or 23,000 psi, calculated using an impressive 500,000,000 cycles of continuous loading.
How is aluminium 7075 made?
Aluminium 7075 is made using 90% Aluminium, 5.6% Zinc, 2.5% Manganese, 0.23% Chromium and 1.6% Copper, although these numbers can change a little depending on manufacturing factors. Its quite light for a metal, with a density of 2.81 g/cm3 or 0.102 lb/in³, but it’s also one of the strongest aluminium alloys available, perfect in high stress situations.
The copper in 7075 aluminium means it’s more at risk of corrosion than other alloys but the sheer strength and workability of the metal make a bit of corrosion worthwhile. To make it even stronger heat-treatment or ‘tempering’ is used, where the metal’s crystalline structure is broken down by 300-500 C heat to improve its overall mechanical properties. The tempering can be done in many ways, each delivering an alloy with its own distinct characteristics. T6 tempered 7075 aluminium alloy is one of the most commonly used, and the aerospace sector is the place where you’ll find it used most often.
Why was aluminium 7075 invented?
Like all alloys, this one was created with specific properties in mind. The first 7075 alloy was developed in secret by a Japanese company called Sumitomo Metal, way back in in 1935. It wasn’t introduced until 1943, by Alcoa, and was quickly standardised for use in the aerospace sector two years later in 1945. The first time the alloy was mass-produced it was used to build the Mitsubishi A6M Zero fighter, a plane famed for being extraordinary easy to manoeuvre.
What are the common uses of aluminium 7075?
This alloy is a big hit for transport applications requiring a high specific strength, sectors like marine, automotive and aviation. The same properties make it perfect for rock climbing equipment, cycle parts and hang glider frames as well as the chassis plates in hobby models.
Used to make M16 rifles for the US military, the alloy is also used by other nations to make military equipment, including Desert Tactical Arms, SIG Sauer, and PGM. It’s even used to make aluminium knives, forks and spoons for camping, and is widely harnessed for competition yo-yos!
7075 alloy played a vital part in the Space Shuttle SRB nozzles, and in the external tank SRB beam in the Inter-tank section, proving the extraordinary resilience of the metal.
What affects the price and supply of aluminium 7075?
The price and supply of aluminium itself affects the production of the 7075 alloy, as do the price and supply of the metals used to create the alloy. This means the relationships between producing countries have an impact, along with trade wars and price wars, political shenanigans, and of course Covid-19, which ultimately affects the mining of those metals as well as their transport around the globe.
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