ALUMINUM - Materials for Civil and Construction Engineers - page 154

be either galvanized, aluminized, cadmium plated, or made of stainless steel
to prevent the development of galvanic corrosion. Rivet fasteners are made
of aluminum and are cold driven. Both bolt and rivet joints are designed
based on the shear strength of the fastener and the bearing strength of the
material being fastened.

4.5 Corrosion

Aluminum develops a thin oxidation layer immediately upon exposure to the
atmosphere. This tough oxide film protects the surface from further oxidation.
The alloying elements alter the corrosion resistance of the aluminum. The al-
loys used for airplanes are usually given extra protection by painting or
“cladding” with a thin coat of a corrosion-resistant alloy. Painting is generally
not needed for medium-strength alloys used for structural applications.
Galvanic corrosion occurs when aluminum is in contact with any of sev-
eral metals in the presence of an electrical conductor, such as water. The
best protection for this problem is to break the path of the galvanic cell by
painting, using an insulator, or keeping the dissimilar metals dry.

SUMMARY

Although aluminum has many desirable attributes, its use as a structural
material in civil engineering has been limited, primarily by economic con-
siderations and a lack of performance information. Aluminum alloys and
heat treatments provide products with a wide range of characteristics. The
advantages of aluminum relative to steel include lightweight, high strength-
to-weight ratio, and corrosion resistance.

QUESTIONS AND

PROBLEMS

4.1 Name the two primary factors that make aluminum an attractive

structural engineering material.

4.2 Compare the strength and modulus of elasticity of aluminum alloys

with those of steel.