Aluminum (Al) is the third most common element in the earth’s crust, but was not discovered as an atomic element until the discovery of bauxite in 1821 in Les Baux, 1. than to exist in nature in its pure form it is found as aluminum oxide Al2O3 in different minerals with the reddish stone Bauxite as the most common. It was first produced in its pure form in the late 1820?s & remained an exclusive metal far more expensive than gold until the late 1800?s. A known story is that the Emperor of Germany, Napoleon III, one time invited to a banquet where the emperor’s relatives & the most honored guests where given the privilege of eating from aluminum plates while the guests of lower ranks had to manage with gold. The age when pure aluminum was a precious metal ended in 1886 with the discovery that pure aluminum could be produced industrially from Al2O3 by electrolysis. Although the methods from then are slightly changed, electrolysis still remains the principal process for producing pure aluminum. Today, however they have the possibilities of producing far more waste amounts of it.
Aluminum in its pure form is normally very soft and has none or few practical applications. Adding small amounts of other elements to the liquid metal, in order to make an alloy where its strength strongly increased. The principle alloying additions to aluminum are copper, manganese, silicon, magnesium, and zinc; other alloying elements are also added in smaller amount for grain refinement and to develop special properties. So there is a wide variety of aluminum alloy. Nowadays the hardness of a typical aluminum alloy actually scales like ?10 compared to the hardness of pure aluminum, and make it to one of the most common materials utilized in daily life.
Aluminum is what’s called a lightweight metal with a density of 2700 kg/m3 in comparison with steel which has a density of 7800 kg/m3 2. Although it doesn’t have the same strength as steel it has a higher strength-to-weight ratio which makes it appropriate for several lightweight applications in i.e. Cars, airplanes construction of machines, appliances, and structures, as cooking utensils, as shields for electronic equipment, and as pressure vessels for cryogenic applications, and in innumerable other areas.. In addition to the high strength to weight ratio aluminum in the form of Al-alloys has many other excellent properties, including high electrical and thermal conductivity, high resistance to corrosion, and no ductile to brittle transformation at low temperatures, easy shapeability and low energy amounts needed for recycling. Only 5% of the energy required making it, Al-alloys are greatly used in different articles such as packaging like in beverage cans 2.
However, despite of its benefits, Al-alloys possess weaknesses that confine their areas of application. Their low fatigue limit, low hardness compared with steel and a melting point of only ? 660oC make them unsuitable for several applications. For example certain parts of automotive need to be strong to withstand high forces, and therefore need strength higher than obtained by Al-alloys. Improving today’s Al-alloys to be able to overcome some of the mentioned weaknesses can be of excellent industrial importance. It allows Al-alloys to substitute steels in a higher number of applications that means great environmental advantages could be achieved.
1.2 Aluminum wrought alloys
The term of wrought alloys is applied to alloys which produced in the form of billet or ingot and consequently worked by any processes such as, extruding, forging, rolling and drawing, or other metalworking process in order to produce semi-finished products. At the end of this products, final product parts are subsequently made.
When dealing with alloys general one refers to all possible mixings of aluminum with different elements. According to that there are many different alloys so a system for classifying them is needed. Aluminum alloys can most roughly be divided into the two groups wrought and casting alloys, dependent on the way they are fabricated. According to the two groups, the alloys have their own designation system that sorts them into different subcategories. They are organized by using the category yxxx for wrought alloys and yxx.x for casting alloys. Designed for wrought alloys y denotes the main group of alloying elements and the remaining numbers xxx denoted the modifications and amount of alloying elements.
In addition to the numbering system, all aluminum alloys also can be divided into to two groups influenced by whether they are heat treatable or non-heat treatable. Heat treatable one means that the alloy can be exposed to elevated temperatures for various times to alter their particular atomic structure as shown in Fig 1.
Aluminum Association Wrought Alloy Designation System involves four digits, in some cases it may have an alphabetic prefixes or suffixes, but in general there are just four numbers:
The first digit is noted to the basis of the main alloying element.
The second is defined the purity of alloy or alloy modification: that digit may be a zero (0) for the original composition, a one (1) for the first variation, a two (2) for the second variation, and so on.
The third and fourth digits are substantial in the 1xxx series which refer to the minimum purity of Aluminum, there is no special indications to the values of those digits in all other series only used in sequence.
X is an alphabetic prefix which is used to denote that an alloy is at an experimental stage of its development.
1xxx: Unalloyed (pure) composition, usually used in electrical and chemical industries
2xxx: A series of alloys in which copper is the major alloying element. Due to their high strength alloys are widely used in aircraft applications.
3xxx: Alloys in which manganese is the principal alloying element, generally used for architectural applications and several products.
4xxx: Silicon is the major alloying element of this group, widely used in welding rods and brazing sheet.
5xxx: Magnesium is the main alloying element, used in boat hulls, gangplanks, and applications for marine environments.
6xxx: Magnesium and silicon are the main alloying elements, commonly used for automotive components and architectural extrusions.
7xxx: A series of alloys in which zinc is the major alloying element (although other alloying elements may be added, such as Cu, Mg, Cr, and Zr), used in aircraft structural components and other high-strength applications.
8xxx: Alloys characterizing miscellaneous compositions. 8xxx series alloys may contain appreciable amounts of tin, lithium, and/or iron.
9xxx: Reserved for future use.