824 A Study of Small Crack Growth in 1050 and 7075 Aluminum Alloys

Abstract

Small fatigue-crack growth in annealed 1050 and 7075 aluminum alloys have been investigated by rotating bending test. In 1050 alloy, larger grain size reduces the fatigue strength and a fatigue limit almost equal to the yield strength is obtained in 1050 alloy with grain size of 200μm. This fatigue limit is apparently determined by the critical cyclic stress for the small crack propagating through the grain boundary. Though the same trend was observed in 7075,i.e. fatigue strength tends to reduce with a coarser microstructure; small crack growth in 7075 is strongly influenced by the size and particularly the spacing between insoluble particles rather than its grain boundary.