Friction stir welding (FSW) is an enabling technology for joining aluminum and magnesium alloys which are often classified as a difficult-to-weld type of materials using traditional fusion welding. Recent studies showed significant effects of welding speeds on the fatigue strength. A higher fatigue strength was observed at a lower welding speed. However, only limited studies on the fatigue properties of friction stir welded magnesium alloys have been reported in the literature. This study was aimed at evaluating fatigue strength of AZ31B-H_24 magnesium alloy after FSW at varying welding speeds. A lower welding speed resulted in a higher fatigue strength in the high cycle fatigue (HCF) region (N>105 cycles), but a lower strength in the low cycle fatigue (LCF) region. Fatigue failure was observed to occur either in the heat-affected zone or at the boundary between the stir zone and thermomechanically-affected zone. Fatigue crack initiation and defect-like features on the fracture surfaces were examined and discussed.
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