Page 224 - Materials Chemistry, Second Edition

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3.2. Metallic Structures and Properties

Figure 3.32. Unit cell representation of SnAuSc, where Sn ¼ white, Au ¼ gold, and Sc ¼ gray. The
gold atoms are situated within alternating tetrahedral vacancies within the unit cell, whereas Sn atoms are
within octahedral holes formed by a fcc array of Sc atoms.

Table 3.5. Types and Properties of Aluminum Alloys
Metal additive Resultant properties/applications
Cu (ca. 5%) Heat treatable, high strength to weight ratio, limited corrosion resistance and
weldability/autowheels and suspension components, aircraft fuselage, power lines
Mn (ca. 1.2%) Moderate strength without heat treating, high workability/beverage cans, cooking
utensils, heat exchangers, storage tanks, furniture, highway signs, roofing, side panels
Si (ca. 12%) Low thermal expansion and m.p., high wear resistance/forged engine pistons, welding
rod, brazing alloys, architectural products
Mg (ca. 0.3–5%) Good weldability and strength, good corrosion resistance/ornamental trim, cans,
household appliances, boats and ships, bridge railings, race cars
Zn (ca. 3–8%) Heat treatable, moderate-very high strength/airframe structures, high-strength forgings

Aluminum alloys
It is hard to imagine a world without aluminum-based materials. From the foil that
we wrap leftovers with, to the cans that house beverages and deodorant aerosols, our
world is inundated with applications for aluminum. The widespread use of this metal
is a direct result of its availability – 8.3 wt.% in the earth’s crust, making it the most
naturally abundant metal. The malleability of Al is second only to gold, and it
possesses other desirable characteristics such as non-sparking, high thermal/
electrical conductivity, corrosion resistance, and high ductility.
The strength of aluminum improves upon alloying, which extends its range of
applications (Table 3.5). One of the most popular alloys is the binary Mg/Al type,
which is sometimes referred to as magnalium. Only a maximum of 5 wt.% of Mg
may be dissolved in Al to provide solid-state strengthening. However, only 1.5 wt.%
of magnesium may be dissolved at room temperature, implying that supersaturation
will often occur, with precipitation of Mg species. This should be reminiscent of the