Formations of AZ91/Al2O3 nano-composite layer by friction stir processing

Composite layers containing ~0.8 %vol Al2O3 nanoparticles were produced on AZ91 magnesium alloy by friction stir processing (FSP). The treated layers were characterized using optical and scanning electron microscopes, as well as microhardness and wear testing units. It was noticed that, by reducing the rotational speed and increasing the travel speed, the grain size of the treated layer reduces and its hardness increases. In addition, the presence of nano Al2O3 reduces the grain sizes of the layers further and increases their hardness. Furthermore, FSP of AZ91 with Al2O3 particles improved the wear resistance significantly and changed the wear mechanism from oxidation and adhesive mode in the as-received AZ91 to oxidation and abrasive in the FSPed specimens. Finally, the rotational speed of 800 rpm and the travel speed of 40 mm/min were the optimum parameters for achieving a suitable composite layer with the highest hardness and wear resistance among the treated layers.