Aluminium is one of the newest metals for the modern world, despite being the most abundant metal in earth’s crust. It was first produced through Hall–Héroult process in 1886 simultaneously discovered by American Charles Martin Hall and Frenchman Paul Héroult. The Hall–Héroult invention brought aluminium into large-scale commercial production. That’s another story for another day!
Let’s talk about aluminium alloys, which revolutionized aluminium applications in the industrial sector. Unwrought or pure aluminium is usually a soft metal making it not suitable for end-use applications. Hence, alloying elements such as copper, zinc, magnesium and silicon are added to primary metal to create alloys characterized with strength, corrosion resistance, malleability and heat tolerance.
The origin of alloys
Duralumin, one of the first aluminium alloys, was a strong and lightweight alloy discovered in 1906 and patented in 1909 by Alfred Wilm, a German metallurgist. This alloy (containing 91-95% aluminium along with copper and magnesium) was flexible enough to be rolled, forged and extruded into various forms and products. The light weight and high strength of duralumin when compared to steel made it suitable for aircraft construction. The world’s first all-metal aircraft developed in 1915 by Hugo Junkers used Duralumin. Since then, aluminium has been at the forefront of aircraft manufacturing, all thanks to its strong, lightweight and heat tolerance properties.
Since then, several aluminium alloy compositions have been created using different materials depending on the usage. We now have over 500 registered alloy compositions being under use. Some of the alloy compositions are considered as milestones in the evolution of aluminium alloys, considering their key role in critical automotive and aerospace applications.
For example, Aluminium alloy 6061 is one of the most extruded alloys known for corrosion resistance and weldability. Originally called Alloy 61S, it is a medium to high strength heat-treatable alloy developed in 1935. It is highly suitable for a wide range of transport, building and electrical applications.
7075 aluminium alloy (AA7075) is another highly used aluminium alloy with zinc and copper as the alloying elements. The first 7075 was developed by Japan’s Sumitomo Metal secretly in 1935 but introduced commercially by Alcoa in 1943. The alloy was standardized for aerospace use in 1945 due to its excellent mechanical properties, good ductility and high strength
Classification of aluminum alloys
As we talk about aluminium alloy series 6061 and 7075, we also need to dive deeper to understand how these alloy classifications are made. The U.S. Aluminum Association originally developed designation systems to distinguish the various alloy compositions about 70 years ago. Later on, the International Organization for Standardization (ISO) adopted the designation system in 1970.
Aluminum alloys are primarily categorized into two groups – cast aluminum and wrought aluminum alloy depending on the processing technology used. Wrought aluminum alloys are processed through mechanical working of aluminium ingots and alloying elements into billets or slabs, further processing into extrusion, rolling, and forging. On the other hand, cast aluminum is formed by the pouring heated, molten aluminum into dies or shapes.
There are separate classification systems for wrought alloys and cast alloys, further categorized into heat-treatable and non-heat-treatable alloys. For example, wrought alloys can be categorized into Extrusions, Sheet and plate, Foil, Bar and Rod, Wire or Forgings. Cast alloys are basically shapes formed through sand or permanent moulds. Each alloy in these categories are allotted a number that identifies it as either wrought or cast. We will discuss the number system for aluminium alloys in our next blog post.
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Reference:
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