How To Choose The Correct Aluminum Alloy
Aluminum is a common metal that combines robust mechanical properties with relatively low weight and low cost. It is almost three times lighter than steel, making it the one of the go-to material choices in aerospace, automotive, and other applications requiring low weight. Aluminum alloys are most often extruded, rolled (cold formed), or cast – each of which can have profound impacts on material behavior. Other factors such as alloy composition and heat treatment can further modify the performance of an alloy.
Types of Aluminum Alloys
There are 7 main types, or series, of wrought aluminum alloys. Each series can contain hundreds of unique alloys, each of which can be defined by a simple code.
1000 Series
1000 series alloys are chemically pure (99%+ aluminum) and are commonly available in wire and thin sheets. This series has excellent corrosion resistance, workability, and high thermal and electrical conductivity. 1350, for example, is the go-to choice for high voltage transmission lines and other large-scale electrical products.
2000 Series
2000 series alloys are alloyed with copper, which allows the material to be precipitation hardened to strengths near those of steel. This is, however, at the expense of corrosion resistance. 2024 was once one of the most common high-strength aerospace alloys, but has been increasingly replaced by 7000 series materials which aren’t as susceptible to stress-corrosion cracking.
3000 Series
Manganese is the alloying element in 3000 series aluminums. This alloy has good corrosion resistance and strength, and also performs notably well in stamping applications. This makes it the material of choice for beverage cans, grating, and many types of tubing.
4000 Series
Silicon is used as the main alloying element in 4000 series alloys. Silicon improves the fluidity of the material in its molten state which is helpful in products like welding wire and brazing rod.
5000 Series
5000 series aluminum is alloyed mainly with magnesium and silicon, giving it superb corrosion resistance. This is helpful in marine applications where the material is subjected to constant harsh conditions. 5052 aluminum is widely known for being one of the easiest alloys to weld. Combine that with the alloy’s excellent corrosion resistance and you have a perfect material for pressure vessels and ship hulls.
6000 Series
The 6000 series materials are alloyed with magnesium and silicon. They are easily machined, weldable, and heat treatable (though not to the same strengths as 2000 and 7000 series). 6000 series alloys like 6061 and 6063 are extremely common in machining and architectural applications. 6061, for example, is available in almost any shape and size you could imagine including bar, plate, sheet, tube, channel and more.
7000 Series
Zinc is the primary alloying element in 7000 series alloys, but magnesium and copper are usually present as well. These materials possess the highest strengths of any of the aluminum alloys. 7075 is commonly used in aircraft landing gears and other parts requiring high strength to weight ratios. 7050 is another common 7000 series alloy and is also heavily used in aerospace applications requiring stress-corrosion resistance.
Temper and Age Conditions
Temper designations tell the material producer and consumer how an alloy has been mechanically and/or thermally modified to achieve certain properties. The first letter designates the class of treatment, while the succeeding number(s) designate specific processes that have been applied to an alloy.
F – as fabricated. These are semi-finished products that have not yet been thermally modified.
O – annealed. Materials with the O designations have been annealed, usually to maximize workability.
H – strain hardened. This is for non-heat-treatable alloys that have had their strength increased by stain hardening. This process, of course, usually does not involve heat as is performed at room temperature.
T – thermally treated. This designation represents products that have gone through the entire tempering process. These materials have been given a solution heat treatment followed by quenching and artificial aging.
W – solution heat treated. This designation usually represents an unfinished product. Solution heat treating is the process by which a material is heated up and held at a certain temperature for a specified amount of time, and then rapidly cooled to “lock in” the properties of the heated material. This process is usually followed by tempering and quenching.
Key Takeaways
For an engineer or part designer, series numbers are the most important topic to understand. Temper and age conditions are somewhat set-in stone, and engineers typically don’t specify these in the design stage, except in very specific circumstances. For example, if you would like a part to made from 6061 aluminum, it is likely going to be of the 6061-T6511 designation. Engineers should also understand the shapes and sizes alloys are available in. McMaster Carr is a good source for this information.
Choosing the correct alloy can have major impacts not only on the performance of your parts, but also on the cost. If you need help selecting the right material for your parts, contact us or get a quote!