Selected Metals - 6: Aluminum
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
In 1825 Hans Christian Oersted, a Danish chemist, had extracted tiny amounts of aluminum powder from alum (aluminum potassium sulfate mined from the earth). He was the first person to do so. However aluminum making was not an economical process until 1889 when American, Charles Martin Hall, patented an inexpensive method (below) for the production of aluminum, which brought the metal into wide commercial use.

Aluminum, is not useful in its pure state so it must be alloyed with magnesium and one or more of the following elements: copper, silicon, manganese, chromium.

Annealed aluminum is much too soft and gummy for machining so the machinist usually gets the material after it has been heat treated. This is quite the opposite of most machine shop steels which are usually machined before heat treating. The type of treatment (called temper) is appended to the alloy number as one of the following designator letters:

  1. F designates as fabricated
  2. O designates annealed
  3. W designates solution heat treated
  4. H designates strain hardened
  5. T designates thermally heat treated

The T temper has ten subdivisions numbered 1-10 that denote the specific process of the thermal heat treatment used. The T temper is the most common designator found in machine shop aluminum.

The following three alloyed aluminums are familiar to machinists: (the machinability characteristics are comparisons of aluminum to aluminum, not comparisons of aluminum to steel.). The American Standard for Metals (ASM) designation is in parenthesis.

A92024 (ASM 2024)

  • Primary alloy copper
  • Machinability fair, use oil based coolants
  • Temper T4 or T6 (i.e. 2024-T4 or 2024-T6)
  • Weldability not recommended
  • Applications truck wheels, aircraft structures
  • Comments a very common aluminum alloy which has a high strength to weight ratio

A96061 (ASM 6061)

  • Primary alloy silicon and magnesium
  • Machinability very good. The standard that all other aluminums are compared to.
  • Temper T4 or T6 (i.e. 2024-T4 or 2024-T6)
  • Weldability very good by all techniques
  • Applications commonly used in applications that require excellent corrosion resistance such as railroad cars, marine equipment, and other outside structures.
  • Comments The most common aluminum alloy available.

A97049 (ASM 7049)

  • Primary alloy zinc
  • Machinability good, use oil based coolants
  • Temper varies
  • Weldability not recommended
  • Applications aircraft structures
  • Comments the machinist nearly always gets this material in a forged condition. Very common for aircraft landing gear, engine mounts, and wing spars.

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