Effect of the Soft Surface Layer on Fatigue Strength of LowTemperature Aged Al-2mass % Cu Alloy

Fatigue strength of Al-Cu alloy was examined by a repeated tensile mode when the specimens were aged and reversion annealed. The specimen quenched from 723K and aged fully around room temperature showed fatigue strength which depended on the existence of soft layer, while the specimen quenched from 723K and aged in the same way showed fatigue strength independent of the existence of the soft layer. Fatigue strength of the specimen, of which the soft surface layer was removed, was the same for either quenching temperature. Fatigue strength became higher when the soft surface layer was thickened with reversion annealing for 600s at 323K after aging. The soft surface layer was thought to increase fatigue strength of the aged Al-Cu alloy as well as Al-Zn alloy.