Nanometer-Thick Base Oil Tribofilms with Acrylamide Additive as Lubricants for AZ91 Mg Alloy

Herein, an in situ atomic force microscopy (AFM) study of tribological properties of the AZ91 Mg alloy under lubricant containing acrylamide additive is reported. The in situ nanoscale study unravels the significance of microstructure (matrix vs second phase), stress, and temperature on the friction, wear, and tribofilm growth within the localized regions of an AZ91 Mg alloy. The results suggest that at elevated temperature (110 °C), the nanometer thick tribofilm forms on precipitate and matrix surfaces; however, there was no evidence of its formation at ambient temperature. The tribofilm growth in both regions was strongly dependent on the contact stress. Moreover, there exists an apparent stress value at which the thickness of the tribofilm is maximum. The friction force with sliding time shows similar variation over precipitate and matrix during the tribofilm growth. However, the magnitude of the friction force is strongly dependent on the thickness of the tribofilm. Finally, the results suggest acrylamide as a potential alternative to zinc dialkyldithiophosphate (ZDDP) for effective lubrication of Mg based alloys.