Applications of Aluminum Alloys

Terms of Use

The data contained in the Technical Manual section has been compiled by United Aluminum. The data should be thoroughly evaluated and tested by technically skilled personnel before any use is made thereof. United Aluminum assumes no responsibility or liability for any use of this data and no warranties are given or implied by United Aluminum.

SELECTION GUIDE FOR ALUMINUM ALLOYS AND TEMPERS

SELECTION GUIDE FOR ALUMINUM ALLOYS AND TEMPERS

Corrosion ratings A through E are relative ratings in decreasing order of merit, based on exposures to sodium chloride solution by intermittent spraying or immersion. Alloys with A and B ratings can be used in industrial and seacoast atmospheres without protection. Alloys with C, D and E ratings generally should be protected at least on faying surfaces.

Stress-corrosion cracking ratings are based on service experience and on laboratory tests of specimens exposed to the 3.5% sodium chloride alternate immersion test.

A = No known instance of failure in service or in laboratory tests.

B = No known instance of failure in service; limited failures in laboratory tests of short transverse specimens.

C = Service failures with sustained tension stress acting in short transverse direction relative to grain structure; limited failures in laboratory tests of long transverse specimens.

D = Limited service failures with sustained longitudinal or long transverse stress.

Ratings A through D for Workability (cold), and A through E for Machinability, are relative ratings in decreasing order of merit.

Ratings A through D for Weldability and Brazeability are relative ratings defined as follows: A = Generally weldable by all commercial procedures and methods.

B = Weldable with special techniques or for specific applications which justify preliminary trials or testing to develop welding procedure and weld performance.

C = Limited Weldability because of crack sensitivity or loss in resistance to corrosion and mechanical properties. D = No commonly used welding methods have been developed.

RECOMMENDED MINIMUM BEND RADII FOR 90-DEGREE COLD FORMING OF SHEET

The radii listed are the minimum recommended for bending sheets and plates without fracturing in a standard press brake with air bend dies. Other types of bending operations may require larger radii or permit smaller radii. The minimum permissible radii will also vary with the design and condition of the tooling.

WATERSTAIN AND ITS PREVENTION

What is Waterstain?

Sometimes, when a coil of aluminum is unwound, some patches of white, chalky stains can be seen on the surface — this is a sure indication that the coil has been exposed to moisture at some time. Although usually white, the colors of the stains can also be brown, black or even show iridescent colors.

How does the staining occur?

Aluminum reacts with oxygen in the air to form a very tenacious oxide coating. It is this coating that gives aluminum its excellent corrosion resistance.

Under most conditions aluminum will not react with water at all, but aluminum is very prone to waterstaining when water is trapped between mating surfaces, such as when it is in the form of a tightly wound coil or in a stack of flat sheet.

Because oxygen from the air is prevented from reaching much of the aluminum surface, a chemical reaction occurs between the entrapped water and the aluminum, which results in a white hydroxide film forming instead of the usual transparent oxide film. The stains have no significant affect on the mechanical strength, but they can be unsightly and are often objectionable for esthetic reasons. They may cause processing problems where additional surface finishing or fabrication is to be performed.

Where does the water come from?

Obviously aluminum coils should not be stored in an area where they would be exposed to rain, or to water from a leaking roof or a leaking water pipe, or be exposed to any water splashes from nearby processing equipment. However, waterstain can still occur in an apparently dry storage area. This is because the most common source of water is condensation.

Air contains water in the form of water vapor. Warm air can hold more moisture than cold and so, if the air is chilled, it releases its moisture in the form of dew. A familiar example is the condensation of water that forms on the outside of a glass of cold liquid.