FAA Aviation Mechanic Airframe (AMA)Airframe StructuresEasy
A technician needs to select an aluminum alloy sheet for a highly loaded wing spar cap where zinc is the principal alloying element, providing one of the highest strengths available in common aluminum alloys. Which alloy designation should be selected?
- A6061
- B7075
- C5052
- D2024
Show answer & explanationAnswer & explanation
Correct answer: B. 7075
In the aluminum alloy numbering system, the first digit identifies the principal alloying element: 7xxx series alloys (such as 7075) use zinc as the primary alloying element and provide very high strength, commonly used for highly loaded structural members like spar caps.
Why the other options are wrong
- A. 6061 is a 6xxx series alloy using magnesium and silicon as principal alloying elements.
- C. 5052 is a 5xxx series alloy using magnesium as the principal alloying element.
- D. 2024 is a 2xxx series alloy with copper as the principal alloying element.
Aluminum Alloy Numbering System
The first digit of a wrought aluminum alloy designation identifies the principal alloying element, allowing quick identification of an alloy's general properties.
- 1xxx = pure aluminum (99%+)
- 2xxx = copper (high strength, e.g., 2024)
- 6xxx = magnesium+silicon (good formability, e.g., 6061)
- 7xxx = zinc (highest strength, e.g., 7075)
Memory trick: Seven-Up has Zinc-y fizz — 7xxx means Zinc for max strength.