129

©

Reference: Aluminum, Volume I. Properties, Physical Metallurgy and Phase Diagrams, American Society for Metals, Metals Park, Ohio (1967). Data for alloy 771.0 supplied by the U.S. Reduction Company, East Chicago, Indiana.

Note: These typical properties are not guaranteed, and should not be used for design purposes but only as a basis for general comparison of alloys and tempers with respect to any given characteristic.

© Assuming solid (void-free) metal. Since some porosity cannot be avoided in commercial castings, the actual values will be slightly less than those given.

© Cgs units equals calories per second per square centimeter per centimeter of thickness per degree centigrade. © Chill cast samples; all other samples cast in green sand mold. (5 Estimated value. (5 Exceeds operating temperature.

Reference: Aluminum, Volume I. Properties, Physical Metallurgy and Phase Diagrams, American Society for Metals, Metals Park, Ohio (1967). Data for alloy 771.0 supplied by the U.S. Reduction Company, East Chicago, Indiana.

Note: These typical properties are not guaranteed, and should not be used for design purposes but only as a basis for general comparison of alloys and tempers with respect to any given characteristic.

© Assuming solid (void-free) metal. Since some porosity cannot be avoided in commercial castings, the actual values will be slightly less than those given.

© Cgs units equals calories per second per square centimeter per centimeter of thickness per degree centigrade. © Chill cast samples; all other samples cast in green sand mold. (5 Estimated value. (5 Exceeds operating temperature.

9.2.2.1 Minimum and Typical Mechanical Properties

There are several bases for mechanical properties. A typical property is an average property. A minimum property is defined by the aluminum industry as the value that 99% of samples will equal or exceed with a probability of 95%. (The U.S. military calls such minimum values "A" values and also defines "B" values as those that 90% of samples will equal or exceed with a probability of 95%, a slightly less stringent criterion that yields higher values.) Typical mechanical properties are given in Table 9.14. Some minimum mechanical properties are given in ASTM and other specifications [17]; more are given in Table 9.15 for wrought alloys and Table 9.16 for cast alloys. Minimum mechanical properties are called "guaranteed" when product specifications require them to be met and are called "expected" when they are not required by-product specifications.

Structural design of aluminum components is usually based on minimum strengths. The rules for such design are given in the Aluminum Association's Specification for Aluminum Structures, part of the Aluminum Design Manual [2]. Safety factors given there, varying from 1.65 to 2.64 by type of structure, type of failure (yielding or fracture), and type of component (member or connection) are applied to the minimum strengths to determine the safe capacity of a component [25]. Typical strengths should be used to determine the capacity of fabrication equipment (e.g., the force required to shear a piece) or the strength of parts designed to fail at a given force to preclude failure of an entire structure. (Pressure-relieving panels are an example of this, called frangible design.) Maximum ultimate strengths are specified for some aluminum products (usually in softer tempers), but these materials are usually intended to be cold worked into final use products, changing their strength.

9.2.2.2 Strengths

While the stress-strain curve of aluminum is approximately linear in the elastic region, aluminum alloys do not exhibit a pronounced yield point like mild carbon

TABLE 9.12 Typical Physical Properties of Wrought Alloys
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