| Summary: | During the last decade, FSP of magnesium alloys has become more popular due to the potential microstructure refinement of their eutectic phases, and interest has increased around the AZ1 that is one of the most commercially used magnesium alloys. In this work, high pressure die cast AZ91 plates were tensile tested at high temperatures after friction stir processing (FSP), with the stirred region in the middle of the gauge length. Samples deformed at 350 °C revealed an increment of ductility that was doubled as compared to those deformed at 300 °C and a strengthening of the nugget was measured by Vickers microhardness (HV). The correlation of HV average values to local grain size confirmed the validity of the Hall–Petch type equation where stress is replaced by hardness. X-rays diffraction and electrical conductivity highlighted the potential increment of solute atoms in solid solution during FSP. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) investigations performed on as-FSPed and hot deformed samples determined MgAlZn and AlMn particles type evolution through statistical analysis that supported mechanical properties and the strengthening mechanisms. Keywords: AZ91, Friction stir processing, Mechanical properties, Microstructure, SEM, TEM
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