Influence of Nd in extruded Mg10Gd base alloys on fatigue strength


Magnesium alloys containing Rare Earth elements have proven to be suitable candidates for uses at high temperatures due to their good creep resistance as well as for use in biodegradable implants due to their adequate corrosion rate and biocompatibility. This work investigates the fatigue strength and cyclic deformation behavior of an extruded Mg10Gd1Nd in comparison to Mg10Gd and possible benchmark alloys WE43 and AZ31. The influence of the alloying element Nd is remarkable. The finite life fatigue strengths of Mg10Gd1Nd in the SN-diagram (Wöhler curve) are strongly improved compared to Mg10Gd and almost reach the strength values of WE43. Fracture surface morphology and crack propagation are discussed with attention given to low and high cycle fatigue. The very fine grain size, as the result of dynamic recrystallization during extrusion, offers high elongation at fracture. Therefore the residual fracture surface, where rapid failure occurs, is rather small in the high cycle fatigue samples. The size of the slow crack growth area has been determined by the appearance of benchmark ridges and fatigue striations and is discussed in correlation to stress and number of cycles. Scatter behavior of fatigue life was investigated by optical microcopy. The microstructure consists of second phase alignments in the extrusion direction, which differs in length, precipitate size and distance. Crack branching appears depending on microstructure and the load applied.
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