Effects of ultrasonic nanocrystalline surface modification on the tribological properties of AZ91D magnesium alloy

A nanocrystalline surface layer of about 100 μm thickness was generated on AZ91D Mg alloy using the ultrasonic nanocrystalline surface modification (UNSM) technique. Experiments were performed to study the effects of UNSM treatment on the tribological properties of AZ91D Mg alloy disk specimen and silicon nitride ceramic (Si3N4) ball combination. In the present study, UNSM-treated disk specimens with different nanocrystalline surface layer depths subjected to different impact loads were investigated. Electron backscatter diffraction (EBSD) observations revealed that the grain size at the top surface layer was decreased down to a few nanometers after UNSM treatment. The UNSM-treated specimens showed better tribological properties representing about 23% reduction in friction and about 30% in wear rate compared to that of the untreated specimens.

► Nanocrystalline surface layer of about 100 μm thickness was generated.
► EBSD observations revealed that the grain size was decreased to a few nanometers.
► UNSM-treated specimens showed better tribological properties.
► Surface analysis showed that abrasive wear was the major wear mechanism.