The patented chemical composition and strengthening heat treatment ensure a high corrosion resistance and thermal stability of 1424 alloy sheets. 1424 alloy is as good as 2024 alloy on fatigue crack propagation rate at testing in air both before and under LLTE at 85 degreesC up to 3000 hrs. But tests in 3.5% sodium chloride solution result in a considerable increase of FCPR especially under decreasing of load frequency down to 0.03 Hz, that is not influenced by the heating at 85 degreesC. One of the reasons of FCPR increase is electrochemical behavior of 1424 alloy in pH3-pH4 environment, formed in the crack tip during the testing. The change of the alloy phase condition as a result of heat treatment correction ensures decreasing of FCPR by 2 times at testing in 3.5% NaCl.