Wear of magnesium composites reinforced with nano-sized alumina particulates

Magnesium (Mg)-based metal-matrix composites (MMCs) reinforced with only 1.11 vol.% of nano-sized alumina particulates had earlier exhibited mechanical properties comparable or even superior to similar composites containing much higher levels of micron-sized reinforcements. More surprisingly, the ductility of these composites exceeded even that of pure Mg. Studies have previously demonstrated that a smaller particulate size reduced wear in MMCs caused by delamination, a mechanism that has been shown to limit the advantages of the increased hardness and strength of the composites during sliding wear tests. This paper explores the wear characteristics of Mg composites containing various amounts (up to 1.11 vol.%) of nano-sized alumina particulates in pin-on-disc dry sliding tests against hardened tool steel, using a range of sliding speeds from 1 to 10 m/s, under a constant load of 10 N. The wear resistance of the composites improved with increasing amounts of reinforcement, which were particularly effective under the higher sliding speeds. Field-emission scanning electron microscopy (FESEM) identified the dominant wear mechanisms as abrasion, adhesion and thermal softening. Wear by delamination, which had been common in earlier work on Mg and Al MMCs with micron-sized reinforcements, was not evident.