The Many Types Of Aluminum Alloys

If there is one material that is widely used in a lot of different industries, it has to be aluminum. This is one material that has plenty of uses due to the fact that it is light and can suffer intense corrosion, which only leads to one of its greatest strengths. As the corrosion forms on the aluminum it forms a very well formed oxidant layer (Al203) which in turn prevents anymore corrosion from forming. So you can say that the fact that aluminum is easy prey for corrosion eventually makes it one of the best materials to use for protection against corrosion. There are many wonderful things about aluminum and no one can refute that it is indeed useful, but it has to be said that one of its greatest weaknesses is the fact that it lacks strength when in its pure form. This has made it necessary for people to look for other metals they can add to aluminum so they get a stronger end result.

Discovery of Alloys

What they wanted to do was to get around the lack of strength in the aluminum and yet still be able to preserve its low density factor as well as its light weight feature. What they did was look for other elements which were added to the aluminum so they can "pin" down its dislocations which mean they got reduced ductility but they increased the strength of the metal. It is by this method of creating allows for the creation of alloys which can be as strong as steel. There are many different elements that can be added to aluminum and each different element will produce different results but it is a given that the alloys are stronger than the pure aluminum.

If you were to add copper to aluminum this will increase its strengths and the added hardness will also make it heat treatable. Using a classification system that is currently being used, all aluminum alloys have a 4 digit number. The ones that have copper in them have a code that begins with a two and will look like this: 2---. However, copper is not all that you can add to aluminum because if you were to add magnesium to aluminum, you will get a metal that has increased tensile strength and a metal that also has increased resistance to marine corrosion. This end result will also be easier to weld. Alloys that have magnesium begin with a "5" as opposed to the "2" and are used for the ones with copper.

There other common elements added to aluminum that make for varied and very interesting alloys. One of these common elements happens to be Manganese, which also gives the metal increased strength and more resistance to corrosion. If you were to add silicon to aluminum however, you will get an end result that has a lower melting point and yet has improved casting ability. The aluminum alloys that have zinc however get to have increased strength and hardness. What makes aluminum alloys so special is they are able to keep all the lightweight properties of the aluminum and they gain extra properties which aluminum lacks.

Why are Alloys Stronger?

You may be wondering how the addition of such elements to the aluminum makes it stronger, and it really just concerns the structure of aluminum. You see, the structure of aluminum has dislocations that make it extremely ductile and very malleable. These properties are very useful but they are not much use when they do not have any strength which is usually more important. When you use different elements to make alloys they act as plugs to the dislocations and this is what makes the aluminum much harder. Most of the time, the aluminum you see being used in cars and planes or boats are alloys because aluminum in its pure form is simply not strong enough to be used for such things.

Types of Aluminum Alloys

Aluminum alloys can be classified into three types. The first type is comprised of wrought non-heat-treatable alloys which cannot be strengthened by the use of precipitation hardening and they are primarily hardened with cold working techniques. Under this category, you will find the commercial pure aluminum series which has the code 1---. You will also find the manganese-aluminum series (3---) plus the silicon-aluminum series (4---). The magnesium-aluminum series (5---) can also be found under this category. Do take note that some of the 4--- alloys can be toughened by heat treatment while most can only be hardened by through the cold working process.

There are also wrought alloys that are heat-treatable and are able to undergo precipitation hardening which makes the alloys develop maximum strength levels. The alloys that fall under this category are the 2--- series (Al-Cu-Mg and Al-Cu) and the (Al-Mg-Si) alloys or 6--- series alloys. The 7--- series alloys also fall here (Al-Zn-Mg-Cu, Al-Zn-Mg). Aluminum-lithium alloys that belong in the 8--- series also belong in this category. Do take note though that the 7--- and the 2--- alloys which are the ones that tend to develop the highest strength levels are the ones mainly used in metallic aircraft structures because they are the only ones that can withstand the stress and the pressure these structures demand.

Last but not the least are the casting alloys, which include heat treatable and non-heat-treatable alloys. In this category you will find the 2--.- Al-CU series, the 3--.- series Al-Si + CU or Al-Si +Mg. you will also find the 5--.- series Al-Mg and the 7--.- series Al-Zn. Most of the time, you can find the 8--.- Al-Sn alloys in this category as well. The 2--.-, 3--.- and the 8--.- aluminum alloys can be strengthened with the use of the precipitation hardening process, but the properties you will get may not be as good as the ones for wrought alloys which are heat-treatable.

Final Word on Aluminum

Aluminum in its pure form will have very limited uses but it will perform the tasks for which it is applied to exceptionally well. To truly get the most out of this material then alloys will have to be formed. Different alloys are created for many different uses in many different industries.