A comparative study on fatigue behavior of recycled Aluminum alloys and their welded joints A. Sarkar1,∗, L. M. Viespoli2, B. Nyhus2, N. Razavi1 1 Department of Mechanical and Industrial Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway 2 SINTEF Industry, 7491 Trondheim, Norway ∗ aritra.sarkar@ntnu.no Keywords: Recycling, HCF, Al-alloys Recycling of Al-alloys is crucial to avoid the high energy requirement for production of primary Al. However, one of the major concerns in using recycled Al in load bearing engineering components is how the fatigue properties get affected. This calls for a thorough and systematic investigation on fatigue behaviour of recycled Al-alloys. Towards this, different alloy variants are designed with enhanced impurity content (Fe, Si, Cu, Zn etc. systematically increased from variants GA1 to GA3) which is commensurate with that found in post-consumer scrap Al. High cycle fatigue (HCF) tests under stress-controlled mode are conducted both in base alloy as well as friction-stirwelded butt joints (FSW joints) for these alloy variants. The test results show that fatigue life is higher in the base metal compared to FSW joints for both the alloy variants GA1 and GA3, with a higher fatigue limit observed for the base material. This indicates better fatigue properties in the base material compared to the FSW joints. To understand this variation in fatigue properties between the base and weld, and among the alloy variants, detailed fractographic investigation on tested specimens are carried out. The investigation revealed that the failure primarily occurs through transgranular crack initiation from the surface in the case of base material and FSW joints. However, multiple crack initiation sites are observed in case of FSW joints, as opposed to one or two crack initiation sites for the base material. This accentuated the crack initiation process in FSW joint, thereby curtailing the fatigue life. This behavior is attributed to presence of defects (surface and sub-surface) in case of the FSW joint which prompted early crack initiation from several sites. Failure location in the FSW joints is found to change in some cases from the weld-toe to the base metal, especially in alloy GA3. This is caused due to the presence of large volumetric defects in GA3 wherein the impurity content (like Fe, Cu and Zn) is higher compared to GA1. 115
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