The A380 has both composite and Al ribs, the composite ribs have Al caps made from 7449-T7651, and the Al ribs are machined from 7449-T7651 ingots.
The first digit in 7449-T7651 specifies the major alloying element. The 7XXX series aluminum alloys have Zinc as the major alloying element, 7449-T7651 is known as a Al-Zn (zinc) alloy, with over 8% Zn.
Al alloy series with their major alloying element.
1xxx Super- or commercial-purity aluminum
2xxx Aluminum-Copper-Magnesium Al-Cu(-Mg)
3xxx Aluminum-Manganese-Magnesium Al-Mn(-Mg)
4xxx Aluminum-Silicon Al-Si
5xxx Aluminum-Magnesium Al-Mg
6xxx Aluminum-Magnesium-Silicon Al-Mg-Si
7xxx Aluminum-Zinc-Magnesium-Copper Al-Zn-Mg(-Cu)
8xxx Aluminum-Lithium- Al-Li-
9xxx Unused Series
Most Al-Li alloys available to day are either 2XXX or 8XXX series alloys (e.g. 2090, 2091, 8090). Boeing has for years used 7XXX series alloys in their aircraft, they are used extensively by all manufacturers. On the 777 Boeing used 7XXX series alloys on the upper and lower wing skins, fuselage stringers, and various forgings. Airbus has previously used 7449 on the A330/A340 wing skins.
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