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Why are aluminum-zinc-magnesium 7XXX alloys used in aircraft?

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aluminum processing Rolls of processed aluminum.

Aluminum-zinc-magnesium 7XXX alloys are utilized in the aircraft industry primarily because they offer the highest strength among aluminum alloys and possess a superior ratio of strength to density.1

These alloys achieve their exceptional strength through heat treatment, which promotes the precipitation of major alloying elements. While the highest-strength variants contain copper and are not weldable, this is not a disadvantage in aircraft construction, as joints are typically riveted rather than welded.1

Specific 7XXX alloys have been engineered to meet rigorous aerospace demands:
* Alloy 7050: Developed to provide high strength along with high resistance to stress and corrosion cracking for use in bulkheads and other components machined from thick products for military aircraft.1
* Alloy 7150: A higher-strength variant developed for use on the upper wing skin of commercial aircraft, with tempers designed to provide high resistance to corrosion at maximum strength levels.1