ALUMINUM - Materials for Civil and Construction Engineers - page 144

Figure 4.4 shows the two-phase diagram for aluminum and copper. This
diagram is typical of the phase diagrams of other two-phase aluminum al-
loys. The alloying elements have low solubility in aluminum, and the solu-
bility reduces as temperature drops.
As described previously, the properties of metals with this characteris-
tic are very sensitive to heat treatments, which affect the grain size of the
material and the distribution of the alloying element throughout the matrix
of the lattice structures. Heat treatments typically used on aluminum alloys
include annealing, hardening, aging, and stabilizing.

■ 4.2.1 Alloy Designation System

Aluminum classification starts by separating the product according to its pro-
duction method, either casting or wrought methods. Aluminum alloys de-
signed for casting are formulated to flow into the mold. Wrought aluminum
alloys are used for products fabricated by deforming the aluminum into its
final shape. The Aluminum Association has developed an aluminum alloy
classification system shown in Table 4.2.
The designation system for wrought alloys consists of a four-digit code.
The first digit indicates the alloy series. The second digit, if different from 0,
indicates a modification in the basic alloy. The third and forth digits identify
the specific alloy in the series; these digits are arbitrarily assigned, except for
the 1xxx series, in which the final two digits indicate the minimum alu-
minum content. For the 1xxx series, the aluminum content is 99% plus the

700

1200

L

600

a L

u L

a

1000

500

u
(CuAl 2 )

800

400

a u

600

300

200 400

0
(Al)

10 20 30 40 50

Composition, w t % Cu

FIGURE 4.4 Aluminum-copper phase diagram.