Fatigue behavior of additive friction stir layer welding of Az31 magnesium alloy

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University of Alabama Libraries

This work examines the fatigue behavior of additive friction stir layer welding (AFSLW) of AZ31 Mg Alloy. The AFSLW process was used to fabricate a seven-layer build using 5 mm thick plates of AZ31 Mg alloy. Optical microscopy of the cross-section of the AFSLW build revealed an asymmetric grain size distribution through the layers of the build. In particular, the middle layers of the build exhibited more refined grain structure compared to the initial and final weld layers. Experimental tensile tests results of AFSLW specimens showed a 33% reduction in ultimate tensile strength (UTS) compared to the base material. In addition, experimental fatigue results of the AFSLW build demonstrated a reduction in the stress-life behavior compared to the base material. The reduction in fatigue performance is likely due to reheating the material caused by the multiple pass build method used to fabricate the build. The fatigue results of the AZ31 Mg alloy processed with AFSLW are not unexpected considering the loss of heat treatment due to the AFSLW process. Post-mortem analysis via scanning electron microscopy (SEM) showed that the AFSLW specimens exhibited similar fatigue crack initiation and crack growth mechanics compared to the base material. The results of this study suggest that structurally sound builds with generally acceptable mechanical properties for as-built structures can be achieved using the AFSLW process.

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Mechanical engineering