Influence of Friction Stir Processing on Microstructure and Mechanical Properties of As-Cast Magnesium Alloy Nanocomposites

In this work, the results of a recent study aimed at the synthesis of magnesium alloy nanocomposites [AZ91–xAl2O3 (x = 1, 1.5, and 2 wt%)] that were prepared using the stir casting method followed by friction stir processing (FSP) with the primary intent of minimizing casting-related defects will be presented and appropriated discussed. Microstructural observations revealed a significant refinement in the grain size along with a dense distribution of the reinforcing alumina (Al2O3) particles on both the retreating side and advancing side of the stir zone. Due to severe plastic deformation, the FSP composites revealed the β-Mg17A12 precipitates to be fragmented into fine particles that were distributed near-uniformly in the stir zone. Microhardness of the friction stir processed AZ91–xAl2O3 nanocomposites revealed an increase on the retreating side of the stir zone and a decrease on the advancing side of the stir zone. The tensile strength of the friction stir processed AZ91 nanocomposites increased with an increase in reinforcement content, i.e., Al2O3, in the metal matrix. Maximum tensile strength of 225 MPa was achieved for the nanocomposite containing 2—wt% Al2O3 when compared to the unreinforced friction stir processed AZ91 alloy [110 MPa].