Wrought Aluminum Products and their Designation
Nov/Dec 89
Aluminum is a base metal that can be manufactured to perform many different duties. This is accomplished by changing the various elements in the alloy and the way in which aluminum is fabricated, strain hardened, and/or heat treated. This article will discuss some of the various types of aluminum and how to interpret the numbering system for alloy designations.
ALLOY DESIGNATIONS
The numbering system for aluminum wrought products is grouped by the type of major element in the alloy.
Aluminum 99% - minimum purity
Major Alloying Element:
Copper
Manganese
Silicon
Magnesium
Magnesium and Silicon
Zinc
Other
Unused
1xxx Series
The aluminum in this group has a 99% purity. The best use for this series is in electrical, chemical, and other applications where good corrosion resistance, high electrical and thermal conductivity, and excellent workability are important.
2xxx Series
The principle alloy of this series is copper. These alloys require heat treating and their mechanical properties can exceed that of mild steel. The 2000 series does not have good corrosion resistance but can be clad with a metal from the 1000 or 6000 series to provide protection of the core material. Alloy 2024 is the most popular alloy and is commonly used in aircraft construction.
3xxx Series
Manganese is the principle alloy in this series and though there are few alloys in this series, some of these more popular sheet alloys provide good workability and moderate strength. A common example of a consumer products is soda cans.
4xxx Series
Silicon is the principle alloy in this series and since it has the ability to lower the melting point of aluminum and the alloys of this series can be used to make welding and brazing products. These alloys turn gray when anodized and are frequently used in architectural applications.
5xxx Series
Magnesium is the major alloy of this group. These alloys are non-heat treatable, provide good weldability, and good marine corrosion resistance. An alloy in this series is commonly used in the production of beverage can lids.
6xxx Series
The alloying elements in this group are magnesium and silicon in approximately equal proportions. Heat treating forms the hardening compound magnesium-silicide. The group provides alloys of moderate strength, good workability, and good corrosion resistance. Many extrusions are made from this series.
7xxx Series
Zinc is the major alloying element in this group. When small amounts of magnesium are treated, very high strengths can be achieved. 7075 is one of the highest strength aluminum alloys and is used in aircraft applications. The seven major groups, 1xxx through 7xxx, can be further broken down into two subdivisions based on the manner in which they are strengthened. The common alloys are those which are non-heat treatable and are hardened only by the amount of strain hardening, i.e., cold work. They cannot be strengthened by heat treatment. Heat treatment will only soften common alloys. The common alloys are in the 1xxx, 3xxx, 4xxx, and 5xxx series. The hard alloys are those which are hardened by heat treating. The heat treatment normally includes a high temperature heating, quenching, and re-heating at a lower temperature. The hard alloys are in the 2xxx, 6xxx, and 7xxx series. As an example, a typical percentage analysis for some common and hard alloys might be as shown on the chart below.
CHART KEY
Temperature Designations
The basic temper designations consist of a letter followed by one or more numbers. When the temper is written with the alloy designation the combination gives a complete description of the metal. For example, 3003-H16 is the alloy 3003 with temper H16.
The various temper designations are as follows:
F Temper
Fabricated with no control-employed properties.
O Temper
Applies to metal annealed to give the lowest possible strength.
H Temper
Applies to metal that has been strain hardened with maybe some additional annealing. The H is always followed by two or more numbers.
T Temper
Applies to metal that has been thermally treated with some additional strain hardening. The T is always followed by one or more numbers.
The H tempers are divided into 3 subdivisions: H1, H2, and H3
H1
Strain hardened only. Strain hardening means cold work.
H2
Strain hardened and partially annealed.
H3
Strain hardened and stabilized. This only applies to those alloys which would soften at room temperature unless stabilized with an additional heat treatment.
The H tempers are always followed by one or more numbers. The second digit represents a number scale designation ranging from 0 through 8, with 8 being the hardest and 0 being the fully annealed, or softest temper.
Therefore, the product 3003-H16 previously mentioned is a manganese-based alloy (3003) that has been strained hardened only (H1) to a three-quarter hard temper (6). The T designations are used to indicate stable tempers achieved by heat treating. The T is always followed by one or more digits, i.e., TXY. In this case, the X is a number from 2 through 10 and each represents a specific sequence of manufacturing operations. The second digit, Y, represents different end properties only and does not indicate any special set of conditions. Fabricators will not normally encounter T designations.
Anodizing
Anodizing is a method for accelerating the format of a hard oxide film on the aluminum surface by enveloping the metal in an electrolytic bath. The oxide film can be made clear and hard or colored with organic on inorganic colorings. In either finish, the natural metallic brilliance of the aluminum is retained.
Cladding
There are aluminum alloys that are susceptible to corrosion. The 2xxx series containing copper is especially sensitive to environment. The copper and aluminum have different galvanic potentials which create electrical corrosions within the metal. One method too avoid this corrosion is to clad the base material with a more pure alloy. This is done at the rolling mills where a layer of more pure aluminum is rolled onto the surface of the base metal, thus providing maximum surface protection with high core strength.
Welding
The hard heat treatable alloys, 2xxx, 6xxx, and 7xxx, can be welded by resistance welding. The common alloys, 1xxx, 3xxx, 4xxx, and 5xxx, are easily welded by fusion. TIG (tungsten inert gas) or MIG (metal inert gas) are good methods for fusion welding. There are several factors which must be considered when welding aluminum. One of the more important factors is the hard oxide film which must be removed before a good weld is possible. The film can be removed by cleaning with a stainless steel brush or chemical cleaning. Because aluminum melts at a low temperature, the temperature must be measured by physical conditions rather than appearances. There will be no color even at temperatures up to the melting point. The low strength of aluminum at high temperatures means that the part must be well supported to prevent distortions or collapse. This brief summary of aluminum alloys, their designations, tempers, and uses has been provided as an overview of a large amount of data. Your local metal supply house can provide you with data books on everyday types of aluminum alloys and shaped carried in stock. These books will also provide additional technical data and designations on weldability, resistance to corrosions, definitions, weights of shapes, and chemical composition.