발간논문

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Vol.19, No.4, 310 ~ 318, 1981
Title
Effect of Two Step Ageing on the Fatigue and Stress Corrosion Resistance in 7075 Aluminium Alloy
류재석Jae Seok Ryu, 김인섭In Sup Kim
Abstract
The effect of two step ageing (TAA) on the microstructure, fatigue and stress corrosion resistance was investigated on the 7075 aluminium alloy. The width of precipitate free zone (PFZ) and the size of precipitates along grain boundries were decreased with the TAA treatment without substantial loss of mechanical strength. Specimens which were failed by fatigue, showed various fracture modes depending on applied stress and heat treatment. The variation of fatigue fracture modes was caused by the initiation conditions of the fatigue cracks. The propagation of the stress corrosion cracks was controlled by the microstructure near the grain boundaries and by the deformation characteristics of the matrix. The fatigue limit at 10^7 cycles was improved up to 10% due to the possible introduction of matrix precipitate incoherency. The narrow PFZ and the small size of grain boundary precipitates have reduced the depth of stress corrosion cracks from 170㎛ to 110㎛.
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