79

Source: Aluminum Association [12]. ® S = Sand cast, P = Permanent mold cast. © Unless otherwise noted, quench in water at 150-212F. ©Temperature range unless otherwise noted. (5 u se air blast quench.

© Casting process varies, sand, permanent mold, or composite to obtain desired mechanical properties.

© Solution heat treat as indicated then artificially age by heating uniformly for the time and temperature necessary to obtain the desired mechanical properties.

© Quench in water at 150-212 for 10-20 seconds only. © Cool in still air outside furnace to room temperature.

©Stress relieve for dimensional stability in following manner: (1) Hold at 775 ± 250F for 5 hrs. Then (2) furnace cool to 650°F for 2 or more hrs. Then (3) furnace cool to 450°F for not more than 1/2 hr. Then (4) furnace cool to 250°F for approximately 2 hr. Then (5) cool to room temperature in still air outside the furnace. © No quench required. Cool in still air outside furnace

Source: Aluminum Association [12]. ® S = Sand cast, P = Permanent mold cast. © Unless otherwise noted, quench in water at 150-212F. ©Temperature range unless otherwise noted. (5 u se air blast quench.

© Casting process varies, sand, permanent mold, or composite to obtain desired mechanical properties.

© Solution heat treat as indicated then artificially age by heating uniformly for the time and temperature necessary to obtain the desired mechanical properties.

© Quench in water at 150-212 for 10-20 seconds only. © Cool in still air outside furnace to room temperature.

©Stress relieve for dimensional stability in following manner: (1) Hold at 775 ± 250F for 5 hrs. Then (2) furnace cool to 650°F for 2 or more hrs. Then (3) furnace cool to 450°F for not more than 1/2 hr. Then (4) furnace cool to 250°F for approximately 2 hr. Then (5) cool to room temperature in still air outside the furnace. © No quench required. Cool in still air outside furnace

9.2 PROPERTIES 9.2.1 Physical Properties

Physical properties include all properties other than mechanical properties. The physical properties of most interest to material designers include density, melting point, electrical conductivity, thermal conductivity, and coefficient of thermal expansion. While these properties vary among alloys and tempers, average values can be useful to the designer.

Density doesn't vary much by alloy (since alloying elements make up such a small portion of the composition) ranging from 0.092 to 0.103 lb/in.3 and averaging around 0.1 lb/in.3 (2700 kg/m3). This compares to 0.065 for magnesium, 0.16 for titanium, and 0.283 lb/in.3 for steel. Density is calculated as the weighted average of the densities of the elements comprising the alloy; the 5xxx and 6xxx series alloys are the lightest of the common alloys since magnesium is the lightest of the main alloying elements. Densities for common wrought aluminum alloys are listed in Table 9.10. Densities for cast alloys are given in Table 9.11. The density of a casting is less than that of the cast alloy because some porosity cannot be avoided in producing castings. The density of castings is usually about 95-100% of the theoretical density of the cast alloy.

The melting point also varies by alloy. While pure aluminum melts at about 1220°F (660°C), the addition of alloying elements depresses the melting point to between about 900 and 1200°F (500 and 650°C) and produces a melting range since the different alloying elements melt at different temperatures. Most aluminum alloys' mechanical properties are significantly degraded well below their melting point. Few alloys are used above 400°F (200°C), although some, like 2219, have applications in engines up to about 600°F (300°C).

Thermal and electrical conductivity also vary widely by alloy. The purer grades of aluminum have the highest conductivities, up to a thermal conductivity of about

TABLE 9.10 Nominal Densities of Aluminum and

Aluminum Alloys

TABLE 9.10 Nominal Densities of Aluminum and

Aluminum Alloys

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