US Navy 5000-series aluminum superstructure cracking

Triggered by a Coast Guard / Navy student's report of severe corrosion and fatigue cracking on a 5456 cruiser superstructure. Tom traces the problem to residual stresses in heavy-thickness aluminum welds, plus pitting at 5456's higher alloy content acting as fatigue initiation sites. The Navy is now retreating to 5083 for LCS construction.

Student: I served on a ship with 5456 aluminum as the superstructure, and it was subject to severe corrosion cracking as well as some fatigue. Is that just because, with the 5000 series, you don't get the heat treatment on it to help prevent some of those?