Heat treatment studies of aluminium alloy type 7050 forgings. Interim report no. 3: Corroded-specimen fatigue tests and SCC propagation tests

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The influence of previous corrosion on the fatigue life was investigated. It was foimd that a slight corrosive attack could drastically reduce the fatigue life. The damaging effect of corrosion was greater for the alloy AA 7050 than for AZ 74.61. It could be established that fatigue cracks initiated from various corrosion pits. A second series of stress corrosion crack propagation tests on AA 7050 was performed. Quenching in boiling water was found to lead to high crack growth rates and a low threshold stress intensity value KISCC in spite of the low yield stress obtained. Other heat treatments led to a monotonie increase in KISCC with decreasing strength.