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Aluminum and Aluminum Alloys Types, Characteristics What is Temper What is Finishing Alloy Numbers
What is an alloy? An alloy is simply a mixture of metals melted together to form a new metal with characteristics distinct from those metals from which it is made. What is an Aluminum Alloy? An Aluminum alloy is an alloy primarily of pure aluminum, mixed with different alloying elements that give rise to an entire range of materials, each of which is designed to maximize a particular characteristic such as strength, ductility, formability, machine-ability, or electrical conductivity
Aluminum and Aluminum Alloys Commercially pure aluminum is a white, lustrous metal, light in weight and corrosion resistant. Aluminum alloys in which the principal alloying ingredients are: manganese, magnesium, chromium, magnesium and silicon, On the other hand, those alloys in which substantial percentages of copper are used are more susceptible to corrosive action. The total percentage of alloying elements is seldom more than 6 or 7 percent in the wrought aluminum alloys.
TYPES, CHARACTERISTICS, AND USES Aluminum is one of the most widely used metals in modern aircraft construction. It is vital to the aviation industry because of its high strength/weight ratio, its corrosion-resisting qualities, and its comparative ease of fabrication. The outstanding characteristic of aluminum is its light weight. Commercially pure aluminum melts at the comparatively low temperature of 1,216°F. It is nonmagnetic, and is an excellent conductor of electricity. Commercially pure aluminum has a tensile strength of about 13,000 psi, but by rolling or other cold-working processes, its strength may be approximately doubled. By alloying with other metals, together with the use of heat-treating processes, the tensile strength may be raised to as high as 96,000 psi, or to well within the strength range of structural steel.
advantage/disadvantage One disadvantage of aluminum alloy is the difficulty of making reliable soldered joints. Oxidation of the surface of the heated metal prevents soft solder from adhering to the material; therefore, to produce good joints of aluminum alloy, a riveting process is used. Some aluminum alloys are also successfully welded. The various types of aluminum maybe divided into two classes: a. Casing alloys (those suitable for casting in sand, permanent mold, and die castings) b. Wrought alloys (those that may be shaped by rolling, drawing, or forging).
This is the quality of metal that describes it’s ability to spring back after it is flexed. It doesn’t have anything to do with how hard the metal is. Soft temper means that when it is bent, it stays bent, and it doesn’t take much force to do it. Hard temper means that when it is bent, it springs back flat, and it takes a lot of force to put a kink into it.
The temper designation follows the alloy designation and shows the actual condition of the metal. alloy designation by a letter and dash. The letter F following the alloy designation indicates the "as fabricated condition, in which no effort has been made to control the mechanical properties of the metal, The letter O indicates dead soft, or annealed, condition. The letter W indicates solution heat treated. Solution heat treatment consists of heating the metal to a high temperature followed by a rapid quench in cold water , This in an unstable temper, applicable only to those alloys that spontaneously age at room temperature.
The letter H indicates: strain hardened, cold-worked, hand-drawn, or rolled. Additional digits are added to the H to indicate the degree of strain hardening. This letter designates a process of stretching or compressing in order to impart a particular temper. H_1 1/8 hard H_2 1/4 hard H_3 3/8 hard H_4 1/2 hard H_5 5/8 hard H_6 3/4 hard H_7 7/8 hard H_8 Full hard
The letter T tempers (thermally treated tempers) These tempers are imparted by heating, quenching, or cooling in a controlled way. Greater strength is obtainable in the heat- treatable alloys T1 Cooled after being shaped to its final dimensions during a process involving a lot of heat (such as extrusion), then naturally aged to a stable condition. T2 Cooled after being shaped to its final dimensions during a process involving a lot of heat (such as extrusion), then cold worked. T3 Solution heat treated, cold worked and naturally aged to a stable condition. T4 Solution heat treated and naturally aged to a stable condition T5 Cooled after being shaped to its final dimensions during a process involving a lot of heat (such as extrusion), then artificially aged. T5 is T1 that has been artificially aged. T6 Solution heat treated and artificially aged to a stable condition. T6 is T4 that has been artificially aged. T7 Solution heat treated and naturally aged past the point of a stable condition. This process provides control of some special characteristics. T8 Solution heat treated, cold worked and artificially aged. T8 is T3 that has been artificially aged. T9 Solution heat treated, artificially aged and cold worked A stable temper T9 is T6 that has been cold worked. T10 Cooled after being shaped to its final dimensions during a process involving a lot of heat (such as extrusion), then cold worked and artificially aged. T10 is T2 that has been artificially aged.
What is Finishing? Finishing aluminum is a little more complex than it seems at first. Aluminum is an extremely reactive metal. It combines instantly on contact with air to form a thin film of aluminum oxide. This film is not really visible, but it if the metal is touched, it comes off on your hands as a black smudge Polishing It can be polished, with an abrasive finish, or even a high polish, but the metal itself is comparatively soft. Lacquering The best way for a fabricator keep the silvery look of the parent metal is to abrade the surface with the abrasive finish you require, then lacquer the piece with a clear organic finish that is specifically designed for use with aluminum conventional finishes will either react with the metal, or will not adhere correctly.
Anodizing It is a process of dipping the aluminum into a liquid solution that contains chemicals that clear the metal surface of its coating of aluminum oxide where a dye is introduced into the solution which can now penetrate the surface of the metal to some depth. The process requires a high current to pass through the metal during the process in order to fix the dye and seal the aluminum with a hard surface.
These numbers refer to a specific chemical composition of the aluminum alloy - the "recipe" of the metal. Pure aluminum is not a very useful product in any structural work - aluminum products almost without exception are produced from batches of pure aluminum mixed with a number of alloying elements that have been carefully specified to maximize particular characteristics of the finished metal. For example, an aluminum alloy that is easily extruded, May be difficult to machine, An alloy that machines well, may be difficult to weld,.
Aluminum products are identified by a universally used designation system. Under this arrangement, wrought aluminum and wrought aluminum alloys are designated by a four-digit index system. The first digit of the designation indicates the major alloying element or alloy group The lxxx indicates aluminum of percent or greater; The 2xxx indicates an aluminum alloy in which copper is the major alloying element; The 3xxx indicates an aluminum alloy with manganese as the major alloying element; etc..
In the 1xxx group, the second digit in the designation indicates modifications in impurity limits. If the second digit is zero, it indicates that there is no special control on individual impurities. The last two of the four digits indicate the minimum aluminum percentage. Thus, alloy 1030 indicates percent aluminum without special control on impurities. Alloys 1130, 1230, 1330, etc., indicate the same aluminum purity with special control on one or more impurities. Likewise, 1075, 1175,1275, etc., indicate percent aluminum.
In the 2xxx through 8xxx groups the second digit indicates alloy modifications. If the second digit in the designation is zero, It indicates the original alloy, while numbers 1 through 9, assigned consecutively, indicate alloy modifications. The last two of the four digits have no special significance, but serve only to identify the different alloys in the group
Aluminum percent minimum and greater ………………………………………1xxx Aluminum alloy, grouped by major alloying element: Copper………………………2xxx Manganese………....……...3xxx Silicon………………….……4xxx Magnesium………………….5xxx Magnesium and silicon …...6xxx Zinc……………………….….7xxx
Alloy 1100 A low strength but very workable alloy with excellent corrosion resistance. It is not heat treatable. It is easily welded, however it is soft, and spalls when machined O: Annealed (or "soft", bendable condition) 1100-H14: Strain hardened Alloy 2011 A free machining, heat treatable alloy, with fair corrosion resistance, but not very easily welded T3: Heat treated, cold worked and naturally aged Alloy 2024 Heat treatable with high strength, good machinability and fair corrosion resistance. It welds very poorly O: Annealed (or "soft", bendable condition) 2024-T3: Heat treated, cold worked and naturally aged 2024-T351: Heat treated, cold worked and naturally aged Alloy 3003 This alloy is not heat treatable but welds very well and has very good workability. Like alloy 1100 it is somewhat soft and difficult to machine H14: Strain hardened 3003-H22: Strain hardened, partially annealed Alloy 5005 Poor machinability, good workability and welds very well. It finishes very well, and offers excellent corrosion resistance H34: Strain-hardened and stabilized
Alloy 5052 Strong, not heat treatable, easily welded, with excellent corrosion characteristics O: Annealed (or "soft", bendable condition) 5052-H32: Strain-hardened and stabilized Alloy 5086 Very strong, not heat treatable, with excellent corrosion resistance and good weldability H116: Strain-hardened only 5086-H32: Strain-hardened and stabilized 5086-H34: Strain-hardened and stabilized Alloy 6061 Heat treatable, easily welded, with very good corrosion resistance and finishing characteristics. Very commonly used for architectural products 6061-O: Annealed (or "soft", bendable condition) 6061-T4: Heat treated and naturally aged 6061-T6: Heat treated and artificially aged 6061-T65: Heat treated and artificially aged 6061-T6511: Heat treated and artificially aged Alloy 6063 This heat treatable is specifically designed for extrusions, very popular for architectural shapes T52: Cooled from an elevated temperature shaping process and artificially aged Alloy 7050 High strength, excellent corrosion resistence, heat treatable, and weldable, but has poor workability T7451: Heat treated, overaged and strengthened Alloy 7075 Heat treatable, this alloy is the strongest and hardest aluminum alloy. It has good machining characteristics but is not very easliy welded nor is it very workable O: Annealed (or "soft", bendable condition) 7075-T6: Heat treated and artificially aged 7075-T651: Heat treated and artificially aged
Heat Treatment for Aluminum -2 Solution Heat Treatments Improve mechanical properties by developing maximum practical concentration of the hardening constituents in solid solution; involves heating to above the critical temperature, holding, and abrupt quenching. Quenching Cooling alloy fast enough to retain a supersaturated solid solution of alloying constituents without introducing adverse metallurgical or mechanical conditions; Most common quenching media are water, air blast, soap solutions and hot oil
Heat Treatment for Aluminum - 3 Precipitation Hardening : Some times called age hardening, used on aluminum, copper, nickel, magnesium and some stainless alloys Ageing: The ageing process can be divided into two main categories after the ageing temperature Natural Ageing : The Heat treatable alloys changes properties when stored at room temperature after solution heat treatment and quenching. Artificial Ageing: By heating the solution heat treated material to a temperature above room temperature and holding it there the precipitation accelerates and the strength is farther increased compare to natural ageing
Heat Treatment for Aluminum Preheating or Homogenizing Typically a preliminary to other treatments to reduce chemical segregation of cast structures and improve their workability; reduce brittleness in cast structure Annealing Aids in workability by softening aluminum and heat treated alloy structures to relive stresses and stabilize properties and dimensions of product
Figure 1: Al-Cu phase diagram (Al rich, partial), showing three steps in precipitation hardening and the
The first step in the process of aging is the formation of Guinier – Preston Zones (GP zones). GP Zones are solute atoms that have diffused into coherent clusters. Coherent clusters are clusters of the solute atoms that distort the crystal structure, but are still connected to the rest of the crystal structure. The GP Zones contain these solute clusters that stop the procession of dislocations, thus strengthening the material.
GP I Zones, which are very thin precipitates form first, right after the supersaturated solid solution has been heated below the solvus temperature (solution-treatment). Then the GP I Zones thicken into thin disks called GP II Zones. If diffusion continues, the GP II Zones will grow into coherent equiaxed theta prime precipitates. Finally, incoherent stable theta precipitates
Under aging occurs when the alloy is heated for too short of time. This will provide a relatively weak alloy due to the undeveloped GP zones. Over aged, which indicates that the alloy had been heated for too long of time, the final product will be a relatively weak alloy. Maximum strength is obtained when the alloy is critically aged. Dimensional changes can occur in the specimen during age hardening. The change depends on the type of alloy, size and shape of the specimen, quenching process, aging temperature an time.
Before Solution Heat Treatment After Solution Heat Treatment