Structural components made from aluminum and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials. Aluminum and its alloys are today considered one of the most practical of metals for a variety of reasons. Aluminum is popular in the aerospace industry because of its ease of fabrication, non-toxicity, strength, and resistance to the corrosive atmospheres of industry and marine environments.
Aluminum alloys are widely used in engineering structures and components where lightweight or corrosion resistance is required. The strength and durability of aluminum alloys vary widely, not only as a result of the components of the specific alloy, but also as a result of heat treatments and manufacturing processes. Alloys composed mostly of the two lightweight metals aluminum and magnesium have been very important in aerospace manufacturing.
Major Alloying Element and Its Effect on Aluminum
● 1000's - Aluminum 99% min. - excellent corrosion resistance, high thermal and electrical conductivity, low mechanical properties
● 2000's - Copper - high mechanical properties, increased yield strength, best known and most widely used aircraft alloy
● 3000's - Manganese - good workability and weldability, high corrosion resistance, moderate strength
● 4000's - Silicon - low melting point, widely used in welding wire and as a brazing alloy
● 5000's - Magnesium - moderate to high strength, good welding characteristics, good resistance to corrosion, especially in marine environments
● 6000's - Magnesium/Silicon - good formability and corrosion resistance, moderate strength
● 7000's - Zinc - highest strength alloy available, used in air-frame structures and for highly stressed parts 8000's - Other element
Aluminum Association Alloy Designation System
● 1st digit - Identifies alloy types.
● 2nd digit - Identifies alloy modifications. Digit replaces letters formerly used.
● 3rd and 4th digits - Identifies the aluminum purity of the specific aluminum alloy.
● The digits are the same as the numbers in the old designations for alloys in use prior to the adoption of the four-digit system.
Temper Designations H-Tempers: Strain-Hardened
● H1 - strain-hardened only.
● H2 - strain-hardened and partially annealed.
● H3 - strain-hardened and stabilized by low-temperature thermal treatment.
The digit following H1, H2, or H3 indicates the temper:
● 2 1/4Hard
● 4 1/2 Hard
● 6 3/4 Hard
● 8 Full Hard
● 9 Extra Hard
● T1 - cooled from an elevated temperature shaping process and naturally aged to a substantially stable condition
● T2 - annealed (cast products only)
● T3 - solution heat-treated and then cold worked
● T4 - solution heat-treated and naturally aged to a substantially stable condition
● T5 - cooled from an elevated temperature shaping process and then artificially aged
Additional digits for T tempers include the following:
- T51- stress relieved by stretching
- T510- receives no further straightening after stretching
- T511- receives minor straightening after stretching to comply with standard tolerances
- T52 - stress relieved by compressing
- T54 - stress relieved by combined stretching and compressing
● T6 - solution heat-treated and then artificially aged
● T7 - solution heat-treated and then stabilized
● T8 - solution heat-treated, cold worked, and then artificially aged
● T9 - solution heat-treated, artificially aged, and then cold worked
● T10 - cooled from an elevated temperature shaping process, artificially aged and then cold worked