Page 176 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 6.2 Aluminum and Aluminum Alloys

Designation of Cast Aluminum Alloys. Designations for cast aluminum alloys
also consist of four digits. The first digit indicates the major alloy group, as follows:
1xx.x-Aluminum (99.00% minimum)
2xx.x-Aluminum-copper
3xx.x-Aluminum-silicon (with copper and/or magnesium)
4xx.x-Aluminum-silicon
5xx.x-Aluminum-magnesium
6xx.x-Unused series
7xx.x-Aluminum-zinc
8xx.x-Aluminum-tin
In the 1xx.x series, the second and third digits indicate the minimum aluminum
content, as do the third and fourth in wrought aluminum. For the other series, the
second and third digits have no numerical significance. The fourth digit (to the right
of the decimal point) indicates the product form.

Temper Designations. The temper designations for both wrought and cast alu-
minum are as follows:

° F-As fabricated (by cold or hot working or by casting)
° O-Annealed (from the cold-worked or the cast state)
° H-Strain hardened by cold working (for wrought products only)
° T-Heat treated
° W-Solution treated only (unstable temper)

Unified Numbering System. As is the case with steels, aluminum and other nonfer-
rous metals and alloys now are identified internationally by the Unified Numbering
System (UNS), consisting of a letter indicating the general class of the alloy, followed
by five digits indicating its chemical composition. For example, A is for aluminum, C
for copper, N for nickel alloys, P for precious metals, and Z for zinc. In the UNS des-
ignation, 2024 wrought aluminum alloy is A92024.
Production. Aluminum was first produced in 1 825. It is the most abundant metallic
element, making up about 8% of the earth’s crust, and is produced in a quantity sec-
ond only to that of iron. The principal ore for aluminum is bauxite, which is a
hydrous (water-containing) aluminum oxide and includes various other oxides. After
the clay and dirt are washed off, the ore is crushed into powder and treated with hot
caustic soda (sodium hydroxide) to remove impurities. Next, Alumina (aluminum
oxide) is extracted from this solution and then dissolved in a molten sodium-fluoride
and aluminum-fluoride bath at 940° to 980°C. This mixture is then subjected to di-
rect-current electrolysis. Aluminum metal forms at the cathode (negative pole), while
oxygen is released at the anode (positive pole). Commercially pure aluminum is up to
99.99% Al, also referred to in industry as “four nines” aluminum. The production
process consumes a great deal of electricity, which contributes significantly to the cost
of aluminum.

Porous Aluminum. Blocks of aluminum have been produced that are 37% lighter
than solid aluminum and have uniform permeability (microporosity). This charac-
teristic allows their use in applications where a vacuum or differential pressure has
to be maintained. Examples are the vacuum holding of fixtures for assembly and
automation, and the vacuum forming or thermoforming of plastics (Section 196).
These blocks are 70 to 90% aluminum powder; the rest is epoxy resin. They can be
machined with relative ease and can be joined together using adhesives.