Sheet and Plate

When aluminum is passed between rolls under pressure, it becomes thinner and longer in the direction in which it is moving. This simple process is the basis for aluminum's most widely used forms: plate, sheet, and foil.

Aluminum can be rolled and re-rolled until it reaches the desired thickness or gage. When the rolling process is stopped largely determines whether the final product will be plate (0.250 inch thick or more), sheet (0.249 to 0.006 inch), or foil (0.0079 inch or less). (Note: There is an overlap (0.006-0.0079 inch) in the thickness ranges defined for foil and sheet. Foil products in this gage range are supplied to foil product specifications, and sheet products are supplied to sheet specifications.)

The Production Process
Rolling begins with huge sheet ingots weighing as much as 20 tons that have been preheated to make them easier to shape. As the size of rolling mills has increased, so has the size of these ingots, but a typical ingot is about 6 feet wide, 20 feet long, and more than 2 feet thick.

The ingot is first fed into a breakdown mill, where it is rolled back and forth, reversing between the rolls until the thickness has been reduced to just a few inches. At this point, some plate is removed and readied for shipment. The plate is heat-treated and quickly cooled, or quenched, for added strength and then stretched to straighten and relieve internal stress built up during rolling and heat-treating. Finally, the plate is trimmed and aged at the desired temperature to develop its final properties.

Plate that is slated to become sheet or foil is trimmed after leaving the breakdown mill and sent through a continuous mill to reduce thickness further. Sheet thicknesses are then coiled.

To continue its reducing process, the coiled sheet is heated in a furnace to soften it for cold rolling. Cold rolling is the last step for some sheet. But other types, known as heat-treatable, are subjected to further elevated-temperature processing to increase their strength.

Products and Applications
Plate is used in heavy-duty applications in the aerospace, machinery, and transportation markets.

Aluminum plate, machined to shape, forms the skins of jumbo jets and spacecraft fuel tanks. It is used for storage tanks and containers in many industries and, because many aluminum alloys actually gain strength at supercold temperatures, it is especially useful in holding cryogenic (very-low-temperature) materials.

Plate provides structural sections for rail cars and large ships, as well as armor protection for military vehicles and trucks that carry payroll.

Sheet, the most widely used form of aluminum, is found in all of the aluminum industry's major markets.

In packaging, sheet is used for cans and closures. In transportation, it provides panels for automobile bodies and for tractor trailer vehicles. Sheet is used in home appliances and cookware. In building and construction, it forms siding and gutters, downspouts and roofing, and awnings and carports.

License plates and light bulb bases, pleasure boats and printing plates, highway signs and high-flying planes are also frequently made from aluminum sheet.

Sheet can be color anodized to black, gold, red, blue, and hundreds of other colors. It can be etched to a "matte" finish or polished to a sparkling brightness, textured to resemble wood, or painted for lasting beauty.

Visual Quality Characteristics of Aluminum (Adobe PDF File)
Aluminum at Sea (Adobe PDF File)
Rolling Aluminum: From the Mine Through the Mill (Adobe PDF File)
LEED Fact Sheet (August 2008) (Adobe PDF File)
Aluminum Applications in the Rail Industry (Adobe PDF File)

Guidelines for Minimizing Water Staining of Aluminum, 2009