strong, hard, lightweight alloy of aluminum, widely used in aircraft construction, discovered and patented in 1910 by Alfred Wilm, a German metallurgist; it was originally made only at Düren in Germany. The original composition has been varied for particular applications; it may contain about 3 or 4 percent copper, ¹/₂ to 1 percent manganese, ¹/₂ to 1 ¹/₂ percent magnesium, and, in some formulations, some silicon. After heat treatment and aging, these alloys are comparable to soft steel in strength.

Duralumin alloys are relatively soft, ductile, and workable in the normal state; they may be rolled, forged, extruded, or drawn into a variety of shapes and products. Their light weight and consequent high strength per unit weight compared to steel suit them for aircraft construction. Because duralumin loses strength in welding, a special laminated sheet form called alclad is used for aircraft construction; it has thin surface layers of pure aluminum or a corrosion-resistant aluminum alloy covering the strong duralumin core.