Tribological behaviors of AZ91D magnesium alloy under the lubrication of oil suspended synthetic magnesium silicate hydroxide nanotubes

Efficient lubrication of magnesium alloys is a highly challenging topic in the field of tribology. In this study, magnesium silicate hydroxide (MSH) nanotubes with serpentine structures were synthesized. The tribological behavior of AZ91D magnesium alloy rubbed against GCr15 steel was studied under lubricating oil with surface-modified MSH nanotubes as additives. The effects of the concentration, applied load, and reciprocating frequency on the friction and wear of the AZ91D alloy were studied using an SRV-4 sliding wear tester. Results show a decrease of 18.7–68.5% in friction coefficient, and a reduction of 19.4–54.3% in wear volume of magnesium alloy can be achieved by applying the synthetic serpentine additive under different conditions. A suspension containing 0.3 wt.% MSH was most efficient in reducing wear and friction. High frequency and medium load were more conducive to improving the tribological properties of magnesium alloys. A series of beneficial physical and chemical processes occurring at the AZ91D alloy/steel interface can be used to explain friction and wear reduction based on the characterization of the morphology, chemical composition, chemical state, microstructure, and nanomechanical properties of the worn surface. The synthetic MSH, with serpentine structure and nanotube morphology, possesses excellent adsorbability, high chemical activity, and good self-lubrication and catalytic activity. Therefore, physical polishing, tribochemical reactions, and physical-chemical depositions can occur easily on the sliding contacts. A dense tribolayer with a complex composition and composite structure was formed on the worn surface. Its high hardness, good toughness and plasticity, and prominent lubricity resulted in the improvement of friction and wear, making the synthetic MSH a promising efficient oil additive for magnesium alloys under boundary and mixed lubrication.