Evaluation of Size Effect on the Fatigue Properties of Aluminum Alloys 7075, 7079 and X7080

The first phase of an evaluation to determine the size effect on the fatigue properties of 7075-T651, 7079-T651 aluminum alloy stretcher leveled plates and an X7080 aluminum alloy hand forging has been completed. Evaluation of the large section specimens 4 square inches test section showed that the fatigue strength of the X7080 aluminum alloy hand forging, 40,000 p.s.i. at 1, 000,000 cycles, was approximately 48 and 60 higher than the fatigue strengths of 27,000 p.s.i. and 25,000 p.s.i. for the 7075 and 7079 alloy stretcher leveled plates, respectively. The notched fatigue strength of the X7080 alloy, 14,000 p. s.i. at 1,000,000 cycles, was approximately 17 higher than the notched fatigue strength of 12,000 p.s.i. for the 7075 and 7079 alloys.