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Designation Systems for Wrought
Aluminium,
Wrought Aluminium Alloys, Casting Alloys and
Other Metallurgical Aspects: The Four-digit Designation System for the Identification of Wrought Aluminium And Wrought Aluminium Alloys This system is a four-digit numerical system in which the first digit indicates the alloy group as follows: Aluminium – 99 percent minimum and greater Aluminium Alloys – grouped by major alloying elements Copper 2XXX Manganese 3XXX Silicon 4XXX Magnesium 5XXX Magnesium and Silicone 6XXX Zinc, Magnesium, Copper 7XXX Other elements 8XXX Unused 9XXX In the 1XXX group, the last two of the four-digits indicate the minimum aluminium percentage. These digits are the same as the two digits to the right of the decimal comma in the minimum aluminium percentage when it is expressed to the nearest 0,01 percent. The second digit indicates modifications in impurity limits or alloying elements. If the second digit is zero, it indicates unalloyed aluminium having natural impurity limits; integers 1 to 9 indicate special control of one or more individual impurities or alloying elements. In the 2XXX to 8XXX groups, the last two digits have no special significance other then to identify different aluminium alloys in the group. The second digit indicates alloy modifications. If the second digit is zero it indicates the original alloy; integers 1 to 9 indicate consecutive alloy modifications. The designation system enjoys wide acceptance throughout the world and South Africa has adopted the system too. Designation System for Aluminium Alloy Castings And Foundry Ingot In South Africa, several conventions, mainly of foreign origin, have been used to describe casting alloys. It is quite likely that South Africa will adopt the CEN designations, which most closely match the local practices. Temper Designation System This system defines the sequence of basic treatments used to achieve the various tempers. The temper designation follows four-digit Aluminium Alloy Designation, the two being separated by a hyphen. The basic temper designation consists of a letter. Sub-divisions of the basic temper are indicated by one or more digits following the letter. Wrought Alloys Cold Worked Symbols: F As fabricated (i.e. rolled, extruded or forged) O Annealed, recrystallized H.. Strain hardened (H followed by two or more digits) H series – First digit represents the process H1. Strain hardened only H2. Strain hardened then partially annealed H3. Strain hardened and then stabilised* (*a low temperature annealing process plus minus 125oC) H4. Strain hardened and then stoved H series – Second digit represents the final degree of strain hardening H.9 Extra hard H.8 Full hard (result of approximately 75 percent reduction of area) H.6 Temper material is mid-way in tensile strength between 4 and 8 temper H.4 Temper material is about mid-way in tensile strength between full hard H.8 and fully annealed material O. H.2 Material is mid-way between H.4 and O material. Odd figures 1,3,5,7 designate intermediate strengths exactly between those for the adjacent even figures 0,2,4,6,8. Wrought and cast Alloys (Except Ingot) Heat Treatment Symbols: F As fabricated or cast* O Annealed, soft* T Thermally treated to produce stable tempers other than F, O and H T1 Controlled cooling from casting temperature and then naturally aged* T3 Solution heat-treated, cold worked and then naturally aged to a stable condition* T4 Solution heat-treated and then naturally aged to a stable condition* T5 Controlled cooling from an elevated temperature process (or casting process) and then artificially aged* T6 Solution heat-treated and then artificially aged* T64 Solution heat-treated and then artificially underaged* T7 Solution heat-treated and then artificially overaged (stabilised)* T8 Solution heat-treated, cold worked and then artificially aged T9 Solution heat-treated, artificially aged and then cold worked Note: Treatments marked * are applicable to casting alloys. Several other heat treatment symbols with more digits are also in use. (Details are available). Heat Treatment – Metallurgical Aspects In high-purity form aluminium is soft and ductile. To increase its strength various elements can be added to produce various alloys (see the four-digit numerical system). Non-heat-treatable alloys The non-heat-treatable alloys are those in which the mechanical properties are determined by the amount of cold work introduced (e.g. by rolling, drawing, etc.) after the last annealing operation. (See Cold Worked Symbols above). Usually the 1 000, 3 000, 4 000 and 5 000 alloys are non-heat-treatable. The properties obtained by cold work are destroyed by subsequent heating and cannot be restored except by additional cold work. Heat-treatable alloys The heat-treatable alloys are those in which the mechanical properties may be improved by heat-treatment. In contrast to the non-heat-treatable alloys the increased strength is obtained with little sacrifice of ductility. Heattreatable alloys have the further advantage that they can be re-heat-treated after annealing to restore their original properties. The various elements used in alloying, singly or in combination, show increasing solid solubility in aluminium with increasing temperatures. These alloys can therefore be subjected to thermal treatment to improve their strength. The first step, called solution heat treatment, is an elevated temperature process designed to put soluble elements into solid solution. This is followed by rapid quenching, usually in water, which momentarily “freezes” the structure for a short time and makes the material very workable. (This workable structure can be maintained by keeping the material at below freezing temperature.) The quenched alloys are not stable at room temperature and precipitation of the constituents from the super saturated solutions begins. This so-called “ageing process” which makes the alloy considerably stronger, can last for long periods of time. It can be speeded up by heating for a controlled period of time to an elevated temperature and this process is then called “artificially ageing” or “precipitation hardening”. This helps to achieve the highest strengths of the alloy. Some alloys will achieve their design strength by ageing at room temperature only, e.g. 2017A and 2024. Annealing This is a thermal treatment for the softening of alloys which have been hardened by cold work or by heat treatment and generally enables the metal to be cold worked. The metal should be heated to the annealing temperature and held at this temperature for a certain time. Slow cooling is required in most cases to prevent any possibility of partial solution heat treatment of the alloy. (For heat-treatable alloys only.) ▲ up The Use of Aluminium - Selection Guide Aluminium Alloys were developed separately across the world in various centres. Consequently different alloys with different naming systems have emerged. In 1982 it was agreed that the US four-digit system should become the international standard. This is the system South Africa has adopted for wrought alloys. For casting alloys the comments about the CEN designation system, as given in Chapter 2, apply. Because other literature may refer to other naming systems Tables 4 and 5 should enable conversion to the systems used in South Africa. Construction and General Engineering Industry The most common structural alloys readily available in South Africa and their common uses are listed:
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B. Covered and Insulated Wire and Cable
C. Bus Conductors
D. Magnet Conductors
E. Capacitor Foil
F. Cast Aluminium Rotors
For high torque rotors with a conductivity of 37 percent IACS alloy Al Si 5
can be used and for a 24
percent IACS conductivity alloy CEN 46500 is applicable.
H. Aluminium Lighting Poles and Transmission Towers
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