Low Cycle Fatigue Behaviour of Extruded 7075 Aluminum Alloy Bar:Competition of Grain Sizes and Textures

Abstract

The low cycle fatigue behaviour of 7075 aluminum alloy bar with large size was investigated, and the results indicated that the microstructure at the center (0R) and surface section of the bar (R) were different in terms of grain sizes and textures. The microstructure of 0R specimen was featured by coarser elongated grain and higher <111> texture intensity as compared with that of the R specimen. The low cycle fatigue life of the 0R specimen was higher than that of the R specimen at strain amplitude range of 0.6%-0.9% showing the dominant effect of higher textures intensity. However, the 0R specimen sustained low fatigue life at low strain amplitude of 0.4% and 0.5% , indicating the predominant effect of grain refinement. The fracture analysis showed that there were wider striations for 0R specimen comparatively at strain amplitude of 0.4%. Interestingly, the yield strength, ultimate tensile strength and elongation of the 0R specimen were higher than that of the R specimen. The higher mechanical properties of the 0R specimen was in consistent with its longer low cycle fatigue life at strain amplitude range of 0.6%-0.9%. Moreover, features of fracture, including fracture initiation and fast fracture regions, were also elaborated. It can be rationalized that the competition of grain sizes and textures evolution determined the low cycle fatigue life of the alloy depending on strain amplitude range: the grain size effect gradually overshadowed that of the texture with decreasing strains in terms of fatigue life.

Keywords: Grain size, Texture, Low cycle fatigue, 7075 aluminum alloy, Fracture