Properties ... Top Of Page

The properties of aluminum that contribute to its widespread use are:

• Aluminum is light;its density is only one third that of steel.
• Aluminum is resistant to weather, common atmospheric gases, and a wide range of liquids.
• Aluminum can be used in contact with a wide range of foodstuffs.
• Aluminum has a high refelctivity, and,therefore, finds more decoarative uses.
• Aluminum alloys can equal or even exceed the strength of normal construction steel.
• Aluminum has high elasticity, which is an advantage in structures under shock loads.
• Aluminum keeps its toughness down to very low temperatures, without becoming brittlelike carbon steels.
• Aluminum is easilyworked and formed;it can be rolled to very thin foil.
• Aluminum conducts electricity and heat nearly as well as copper.

Products - Alumina ... Top Of Page

Aluminum originates as an oxide called alumina, and because aluminum itself does not occur in nature as a metal, the prcessing of aluminum took a giant leap forward with the advent of electricity.

Deposits of bauxite ore are mined and refined into alumina—one of the feedstocks for aluminum metal. Then alumina and electricity are combined in a cell with molten electrolyte called cryolite. Direct current electricity is passed from a consumable carbon anode into the cryolite, splitting the aluminum oxide into molten aluminum metal and carbon dioxide.

The molten aluminum collects at the bottom of the cell and is periodically “tapped” into a crucible and cast into ingots. While continual progress has been made over the more than 110-year history of aluminum processing to reduce the amount of electricity used, there are currently no viable alternatives to the electrometallurgical process.

However, between materials recovery and ongoing innovative research and development efforts, the industry is constantly searching for areas in which costs can be reduced.

The worldwide alumina industry produces more than 70 million dry metric tons of bauxite residue annually. Australia is the largest alumina refiner in the world, processing nearly one-third of the total alumina.

Products - Alloys ... Top Of Page

An alloy is a material made up of two or more metals. Alloys are designed and produced have certain specific, desirable characteristics, including strength, formability, and corrosion resistance.

Some of the common elements alloyed with aluminum include copper, manganese, silicon, magnesium and zinc. Typical applications and uses of aluminum alloys include building products (siding and structural), rigid and flexible packaging (foil, food and beverage cans) and transportation (automobiles, aircraft, and railcars).

Chemical composition limits for commercialized alloys are registered with The Aluminum Association, Inc., which reviews and assigns appropriate alloy designations to the set of composition limits. The association maintains “registration records” listing domestic and internationally registered composition limits and their corresponding alloy designations.

These registration records include:

• International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys, commonly referred to as the Teal Sheets, reflecting the color of the paper on which they are printed;
• Designations and Chemical Composition Limits for Aluminum Alloys in the Form of Castings and Ingots, Pink Sheets, can be ordered from the association’s Bookstore.

It should be noted that The Aluminum Association is the only entity recognized by the American National Standards Institute (ANSI) aluminum standards for the registration of aluminum alloy compositions and assignment of alloy designations.

Products - Castings ... Top Of Page

Casting is a simple, inexpensive, and versatile way of forming aluminum, so it is not surprising that it was also the first method used.

Such historical items as the baby rattle for the French’s emperor’s son, the cap atop the Washington Monument and the tea kettle were all produced by casting.

The Production Process

Today, casting continues to be the most widely used method of forming. Technical advances, of course, have been made, but the principle remains the same: molten aluminum is poured into a mold to duplicate a desired pattern.

The three most important methods are die casting, permanent mold casting, and sand casting.

Die casting, in which molten metal is forced into a steel die, or mold, under pressure is normally used for high-volume production. Accurate parts, requiring a minimum of machinery can be produced.

Permanent mold casting involves molds and cores of steel or other metal. Molten aluminum is generally poured into the mold, although vacuum is sometimes applied.

Permanent mold castings can be made stronger than either die or sand castings. Semi-permanent mold casting, which uses expendable cores of sand or other material, is used when permanent cores would be impossible to remove from the finished part.

The most versatile method is sand casting. Virtually any pattern can be pressed into a fine sand mixture to form a mold into which the aluminum is poured. This is a slow process, but usually more economical for small quantities, intricate designs, or when a very large casting is needed.

Casting Products

The automotive industry is the largest market for aluminum castings and cast products make up more than half of the aluminum used in cars. Cast aluminum transmission housing and pistons have been virtually universal in cars and trucks throughout the world for years. Many other engine parts are cast aluminum and the applications grow as automakers seek new ways to save weight and gain fuel efficiency and performance.

Cast aluminum is also widely used in other forms of transportation, including aircraft and marine engines and structures.

Parts of small appliances, hand tools, lawnmowers and other machinery use thousands of different aluminum castings, but the cast product most often seen by consumers is cookware – the product that marked the beginning of low-cost everyday aluminum use.

Products - Extrusions ... Top Of Page

Extruding aluminum is the most innovative forming process for this versatile metal, allowing designers almost unlimited creativity and imagination to specify profiles to meet their exact, specialized needs.

The process begins with creation of a metal die, which precisely matches the profile of the shape specified by the designer. Aluminum billets or logs, produced from ingots, are heated and forced under pressure through the die. The process is quite similar to squeezing toothpaste from a tube. The variety of shapes is virtually endless, and profiles are produced to exact specifications, with very close tolerances.

Once the profile is extruded, it can be further fabricated—cut to length, machined, drilled, punched, notched, bent and assembled into a semi-finished product. An extruded tube even can be “stretched” to produce tubing of exact inside and outside dimensions. Profiles can be painted, anodized, brushed or polished, depending on the desired finish.

Products - Foil ... Top Of Page

Foil, like sheet and plate, is produced by passing aluminum between rolls under pressure. Foil is the thinnest of these three products and is less than 0.006 inch thick. Foil is produced from sheet coils that are heated and then passed through high-speed foil rolling mills.

Foil is considered to be the beauty of the flat-rolled family because of its shinny one-sided finish. Foil is shiny on only one side because as it passes through the final foil mill, two thicknesses of foil are rolled together. The sides facing each other emerge with the dull finish, while the sides in contact with the foil mills come out shinier – due to the burnishing effect of the rollers.

Flexible packaging and foil containers account for about three-fourths of all foil used, but the remainder goes into some exciting applications.

For instance, foil-backed building insulation reflects heat and provides a protective vapor barrier. Foil in electrical capacitors provides compact electrical storage and, if the surface is treated, foil’s oxide coating works as an insulator. Aluminum foil capacitors are found in virtually all electrical equipment, from television sets to computers.

Formed into fins, foil is the heat exchanger in some air-conditioning units and baseboard space heaters. Formed into honeycomb and sandwiched between sheets of aluminum, foil helps provide structural strength in aircraft and satellites where lightweight strength is so necessary.

Products - Forgings ... Top Of Page

Forging is a manufacturing process where metal is pressed, pounded or squeezed under great pressure into high strength parts known as forgings. This is usually done by heating the metal, but some forgings are produced without heating.

Generally, forged components are shaped by either a hammer or a press. Forging on the hammer is carried out in a succession of die impressions using repeated blows. In a press, the component is usually hit only once in each die impression.

The Forging Process

The three basic types of aluminum alloy forgings are: open-die forgings, closed-die forgings, and rolled rings.

In open die forging, the work component is not completely confined as it is being shaped by the dies. This process is commonly associated with large parts such as shafts, sleeves, and disks, but the part’s weight can range from 5 to 500,000 lbs.

Most open die forgings are produced on flat sides. Round swaging dies and V dies are also used in pairs or with a flat die.

As the forging workpiece is hammered or pressed, it is repeatedly manipulated between the dies until it reaches final forged dimensions. Because the process is inexact and requires a skilled forging operator, substantial workpiece stock allowances are retained to accommodate forging irregularities. The forged part is rough machined and then finished machined to final dimensions.

In open die forging, metals are worked above their recrystallization temperatures. Since the process requires repeated changes in workpiece positioning, the workpiece cools during open die forging below its hot-working or recrystallization temperature. It then must be reheated before forging can continue.

Impression die forging is the most basic example of impression die forging and accounts for the majority of forging production. In impression die forging, two dies are brought together and the workpiece undergoes plastic deformation until its enlarged sides touch the die side walls.

Some material flows outside the die impression, forming flash. The flash cools rapidly and presents increased resistance to deformation, effectively becoming part of the tool. This builds pressure inside the bulk of the workpiece, aiding material flow into unfilled impressions.

Ring rolling has evolved from an art into a strictly controlled engineering process. In the ring rolling process, a preform is heated to forging temperature and placed over the internal roll of the rolling machine. Pressure is applied to the wall by the main roll as the ring rotates. The cross-sectional area is reduced as the inner and outer diameters are expanded.

Rings can be rolled into numerous sizes, ranging from rollerbearing sleeves to rings of 25 ft in diameter with face heights of more than 80 in.

Forged Products

In automotive applications, forged components are commonly found at points of shock and stress. Forged automobile components include connecting rods, crankshafts, wheel spindles, axle beams, pistons, gears, and steering arms.

Forgings are also used in helicopters, piston-engine planes, commercial jets, and supersonic military aircraft. Many aircraft are "designed around" forgings and contain more than 450 structural forgings as well as hundreds of forged engine parts.

"Forged" is the mark of quality in hand tools and hardware. Pliers, hammers, sledgers, wrenches, garden implements, and surgical tools are almost always produced through forging.

Products - Impacts ... Top Of Page

An impact is a part formed in a confining die from a metal slug, usually cold, by rapid single stroke application of force through a punch, causing the metal to flow around the punch and/or through an opening in the punch or die. The four basis impacts are: reverse, forward, lateral and combination.

An impact implies a hammering action and can be differentiated from an aluminum extrusion whereby an ingot or billet is forced under applied pressure through a die opening to form an elongated shape or tube; and is, by a shade of meaning, different again from an impact extrusion, or back extrusion. The impact extrusion process combines extrusion and forging in a single press operation.

The first metal impact extrusion, a lead collapsible tube, is believed to have been produced in France around 1850. The first experimental work on aluminum impact extrusion was conducted in Switzerland in about 1914. In 1921, Aluminum Company of America produced the first aluminum impact extrusion in the United States.

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