Fatigue intergranular cracking in the weld joints of AA5086 in air

• Published in: International journal of fatigue Vol. 182; p. 108186
• Main Authors: Jaisawal, Rajneesh, Gaur, Vidit, Ahmed, Shahnawaz
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2024
• Subjects: Aluminum; Crack growth; Fatigue; Intergranular; Welding; Fatigue; Welding; Intergranular; Aluminum; Crack growth
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2024.108186

•Intergranular cracking in AA5086-H321 and its weld joints were studied.•Crack growth in the nugget zone (NZ) was mostly intergranular.•Area fraction of intergranular cracks followed inverse parabola trend with ΔK.•Nugget zone contained a significant number of high-angle grain boundaries.•Grain boundary precipitation in the NZ also favored the intergranular cracks. The intergranular cracking behavior and its root cause have been investigated in the friction stir weld joints of AA5086-H321 alloy. This study is in continuation to our previously published work that dealt with their high-cycle fatigue behavior, wherein the role of intergranular facets was anticipated in their enhanced fatigue properties. The same has been attempted to explore further in this study by performing fatigue crack growth tests in different zones of the weld joint. The cyclic loads were simulated using a 20 Hz sinusoidal type waveform at a load ratio of 0.1 in ambient conditions. Microscopic examinations of the fracture surfaces revealed a smooth intergranular-to-transgranular transition. A correlation between the estimated area fraction of intergranular cracks and the stress intensity factor range was observed i.e. first increasing proportionally followed by decreasing after attaining a particular maximum. The occurrence of these intergranular facets was attributed to the intense plastic deformation and high heat input, manifested during the friction stir welding process, that altered the grain size, characteristics of grain interfaces, misorientation angle, second-phase particles, etc. within the weld joint and are discussed in this study.