The element aluminum (Al) has a specific gravity of 2.7, placing
it among the light-weight structural metals. It is used as a base
for die casting alloys with three primary constituents: silicon,
copper and magnesium. Eight available aluminum die casting alloys
give the designer the widest choice among the four primary alloy
groups, and they account for the majority of die castings in terms
of tons of components produced.
Seven of the eight alloys are based on the aluminum-silicon
system. The eutectic (system) composition, 11.7% silicon, is a
convenient reference point for grouping them. The seven alloys are
further grouped as either controlled copper content or restricted
copper content. Other major alloying elements in the
aluminum-silicon system are magnesium and iron. Some constituents
are considered impurities, and maximum limits, expressed as a
single number, are imposed. Alloy 518, with a very low silicon
content, is based on the aluminum-magnesium system. All eight
aluminum alloys are grouped according to silicon and copper
contents in Table 4.2 Aluminum Alloys by Silicon and Copper Content.
The comparative die casting and product characteristics of these
alloys are shown in Table 4.3 Comparative Characteristics of Aluminum Die Casting Alloys. The designation 1 indicates most
desirable; 5 indicates least desirable.
Table 4.3 is based on ASTM B85 except for 390, which is based on
judgment from experience. The ratings make comparisons among
aluminum die castings only and do not reflect relative
characteristics of other metal alloys.
