Impression Creep and Fatigue Crack Growth behaviour of Aluminium alloy Friction Stir Weldments
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2023
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Abstract
Joining Aluminium alloys by Friction stir welding (FSW) results in different weld zones viz, nugget zone (NZ), thermos-mechanically affected zone (TMAZ), heat affected zone (HAZ) and the base metal (BM). Each zone exhibits different microstructures and mechanical properties across the weld leading to poor mechanical attributes for the weldment. An insight in to the creep deformation and fatigue crack growth through these weld zones will enlighten the research community with the usage of these materials for elevated temperature applications as well as for conditions of dynamic loading. The present work was therefore taken up with the objective of joining defect free joints of Aluminium alloys by FSW and investigating the (i) creep behaviour of different weld zones at elevated temperatures by impression creep (IC) tests and (ii) fatigue crack growth (FCG) behaviour through different weld zones of the weldments. The materials chosen for the study are commercial Aluminium alloys viz, AA2014 and AA6061-T6. For obtaining the best quality joints of the two Aluminium alloys based on the mechanical properties the process parameters selected were low tool rotational speed, low welding speed, low plunge depth and moderate shoulder diameter of square pin (SQ) tool profile. The effect of process parameters on the mechanical properties viz, ultimate tensile strength (UTS), yield strength (YS), % elongation, Flexural strength (FS) and bend angles of the weldments were studied. The best AA6061-T6 weldments exhibited 97%, 98% and 98% of the UTS, YS and FS of the base metal respectively. In the case of AA2014 alloy the corresponding properties were 86%, 80% and 90% of the base metal. The results of the microstructure and fractography under field emission scanning electron microscope (FESEM) are studied and discussed.
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Supervisor: Robi, P S