Surface nanoengineering of magnesium implants: From experimental characterization to multiscale and AI-assisted prediction

This study investigates the effects of Surface Mechanical Attrition Treatment (SMAT) on the structural and functional properties of AZ31 magnesium alloy. A key contribution of this work is the establishment of a correlation between SMAT duration and the resulting nanograin formation, deformed layer evolution, and improvements in mechanical, corrosion, and biocompatibility performance. In addition, an artificial intelligence (AI) model was developed to predict surface roughness, waviness, and isotropy, showing good agreement with the experimental data. Another novel aspect is the application of a multiscale Representative Volume Element (RVE) framework to map the von Mises stress distribution in nanocrystalline AZ31. In this study, SMAT was applied for durations ranging from 15 to 120 minutes, inducing the formation of a nanocrystalline surface layer. Increasing the treatment time resulted in a deformed layer thickness of up to 99 μm after 120 minutes, accompanied by significant grain refinement to the nanometer scale. A marked improvement in surface hardness was observed, with the 120-minute-treated samples exhibiting a 100% increase compared with the untreated samples. Wear testing revealed a notable reduction in the wear rate, with a 35% decrease after 120 minutes of SMAT. Surface topography parameters were quantitatively assessed using an artificial intelligence (AI) model based on the Gaussian Process Regression (GPR) algorithm. In addition, a multiscale RVE framework was employed under identical macroscopic strain conditions to model the von Mises stress distribution in SMAT-processed AZ31 samples with grain sizes ranging from 45 to 165 nm. The results showed that SMAT initially increased the friction coefficient because of surface roughening; however, prolonged treatment (120 minutes) reduced the coefficient by 25%, which was attributed to smoother and more refined surfaces. Wear volume loss decreased from approximately 0.32 × 10⁻³ mm³ for the untreated sample to 0.11 × 10⁻³ mm³ after 120 minutes of SMAT, corresponding to a 66% reduction. The corrosion current density (I corr ) initially increased with SMAT duration, reached a maximum at 60 minutes, and then decreased after 120 minutes of treatment. Biocompatibility was assessed through in vitro cell adhesion and proliferation assays using MG63 osteoblast-like cells. SMAT-treated surfaces significantly promoted cell attachment and proliferation, with the highest level of cell proliferation observed for the samples treated for 120 minutes.