While elemental aluminium is a versatile substance with many useful properties, 100% pure aluminium is rarely used for commercial applications. Most aluminium used commercially is mixed with some other substance, forming an alloy. Alloys may contain up to fifteen percent by weight of another element, such as iron, silicon, copper, magnesium, manganese and zinc. Literally hundreds of different combinations are used in manufacturing today.
Wrought aluminium alloys are differentiated from each other by giving each one a four- or five-digit number with a decimal point. The metals alloyed with the aluminium is designated by the digit in the hundreds place, and the digit after the decimal point specifies whether it is to be cast in a shape or made into an ingot.
Temper is indicated by a dash and a letter or series of digits after the dash. The industry recognizes five major temper categories: “F” means it is tempered as fabricated (no temper), “H” refers to strain hardening either with or without thermal treatment, “O” is annealed, or cooled naturally, “T” means the alloy has been heat treated to produce a stable temper, and “W” means the metal was solution heat treated only. Categories “H” and “T” have several sub-categories relevant to different processes for strain hardening and heat treatment, respectively.
Although other systems exist, the International Alloy Designation System is the most widespread and widely recognized for wrought aluminium alloys. Adopted in the United States in 1954 and internationally in 1970, the system is administered by the Aluminum Association’s Technical Committee on Product Standards (TCPS). The IADS began with 75 alloys and has expanded to recognizing over five hundred unique mixtures at the present time.
The system divides alloys into eight major categories: 1000’s are basically pure aluminium, 2000’s, previously known as “duralumin,” are alloyed with copper and are capable of being hardened to a strength to that of steel, 3000’s are alloyed with manganese, 4000’s are alloyed with silicon and are sometimes known as “silumin,” 5000’s are alloyed with magnesium, 6000’s are alloyed with magnesium and silicon, 7000’s are alloyed with zinc and form some of the hardest aluminium alloys, and 8000’s are alloyed with any other material.
Cast aluminium alloys are categorized by a system developed by the Aluminum Association, and they follow closely with the categories for wrought aluminium with a few exceptions. Cast aluminium is divided into eight categories as well: 100.0’s are pure aluminium, 200.0’s are alloyed with copper, 300.0’s are alloyed with silicon, copper and/or magnesium, 400.0’s are alloyed with silicon, 500.0’s are alloyed with magnesium, 700.0’s are alloyed with zinc, 800.0’s are alloyed with tin, and 900.0’s are alloyed with anything else. The 600.0 designation is not used. In this designation, the digits in the tens and ones places indicate the minimum percentage of aluminium in the alloy, and the digit after the decimal point refers to whether the material is cast or made into an ingot, represented by the digits “0” and “1,” respectively.
A few alloys are known to the industry by name in addition to by a numeral designation. Birmabright is the trade name for 5251 aluminium, and was developed by a British firm in 1929 for use in making boats and, more famously, the body of the original Land Rover in 1948.
As mentioned above Duralumin is a trade name for 2000-level aluminium alloys. It is one of the earliest age-hardened alloys, as it was developed by German metallurgist Alfred Wilm at Dürener Metallwerke Aktien Gesellschaft in 1903. Despite being published in German scientific journals beforehand, the composition and method of production was a secret in Imperial Germany during the Great War. The alloy’s initial use was in German airships, including the ill-fated Hindenburg. Present-day applications include aircraft fittings, space booster tanks, truck frames and suspension, auto body paneling, and aerospace structural components.
Avional is 2017 aluminium, which is composed of aluminium alloyed with copper and approximately 1% silicon. It was also known in France as AU4G, and saw use between the Wars in aircraft parts in France and Italy. It was also used in certain auto racing applications in the 1960’s.
Magnalium is an alloy of aluminium with magnesium, plus small amounts of tin and nickel. Some mixes may contain up to 50% magnesium. Magnalium with lower amounts of magnesium are useful in automotive and aircraft applications due to their high strength, greater corrosion resistance, and lower density. However, as the percentage of magnesium increases, the substance becomes more brittle and susceptible to corrosion. The higher-magnesium mixes are used in pyrotechnics, as it provides both aluminium’s stability and magnesium’s reactivity.
Magnox, which is short for “magnesium non-oxidizing” is an alloy of magnesium with small amounts of aluminium. Its primary use is in containing unenriched uranium and containing fission products from being released by the uranium into nuclear reactors.
Perhaps the most common aluminium alloy is 6061. This alloy, developed in 1935, is an alloy of 95% aluminium, plus less than one percent each of silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium, and a very small amount of other elements. This alloy, which is easily weldable, is used in aluminium extrusions. It is highly versatile, being used for such applications as aircraft, yachts, SCUBA tanks, bicycle frames, firearms, and, most often, aluminium beverage cans.