Definition
A descriptive phrase for clad aluminum sheet (commonly known as Alclad), in which a strong but corrosion-prone aluminum alloy core is bonded between two thin outer layers of commercially pure aluminum. The pure aluminum surfaces resist corrosion, while the alloy core provides the structural strength needed for aircraft skin and structural components.
Plain English
It is a sheet of aluminum made in three layers: a strong middle layer that can corrode, with thin layers of pure, corrosion-resistant aluminum on each side to protect it. You get strength from the middle and corrosion protection from the outside.
Context Anchor
Seen in aircraft structures and maintenance discussions, especially when describing aluminum aircraft skin, sheet metal repairs, and corrosion protection.
Derivation
The phrase describes the construction itself. 'Sandwich' comes from food, where a filling sits between two slices of bread; here the strong alloy is the filling and the pure aluminum layers are the bread. Pure aluminum resists corrosion well but is too soft for structure, while alloyed aluminum is strong but corrodes more easily, so combining them gives both qualities in one sheet.
Why Pilots Care
Used for aircraft skins and structures because it combines the strength required for flight loads with built-in resistance to corrosion that would otherwise weaken the airframe.
Analogy
Think of a chocolate bar with a soft caramel coating over a harder nougat center. The coating protects the inside, but if you scratch through the coating, the inside is exposed. Aircraft skin works the same way: the thin pure aluminum is the coating, the strong alloy is the inside.
Grounding Statement
The strong inner metal carries the load, while the thin pure-aluminum outside helps protect the surface.
Intuition Check
“Sandwiched” does not mean the layers are loose or glued together like a food sandwich. Here it means the layers are permanently bonded into one sheet during manufacture.
Example Sentence 1
The aircraft's outer skin is made from aluminum alloy sandwiched between thin layers of pure aluminum, which is why deep scratches must be treated promptly to prevent corrosion.
Example Sentence 2
During inspection the mechanic noted that the control surfaces were made from aluminum alloy sandwiched between thin layers of pure aluminum.