Magnesium alloys have attracted considerable interest in the field of orthopedic implants due to their elastic modulus being comparable to that of natural bone, their excellent biodegradability, and their ability to avoid secondary removal surgery. However, their high chemical reactivity leads to rapid corrosion in physiological environments. During service, simultaneous mechanical friction further accelerates the detachment of corrosion products and induces wear-corrosion coupling failures, ultimately causing premature loss of mechanical support and severely limiting their clinical applicability. Silane modification, as an environmentally friendly and cost-effective surface treatment method, can form an organic-inorganic hybrid coating through hydrolysis and condensation reactions of silane molecules on metal surfaces, providing both biocompatibility and protective functionality. Nevertheless, the coating density, crosslinking degree, and interfacial bonding quality are highly dependent on processing parameters, particularly the silane concentration. Therefore, this study investigates Mg-1.6Ca-2.0Zn medical magnesium alloys and systematically elucidates how silane concentration regulates the microstructure of the alkali-treated coating, the interfacial chemical bonding mechanism, and the resulting wear and corrosion resistance, so as to provide theoretical support and technological guidance for surface functionalization and clinical translation of magnesium-based implant materials. In this work, self-fabricated Mg-1.6Ca-2.0Zn alloys are wire-cut, mechanically polished, and subsequently alkali-treated using a NaOH solution to generate a porous Mg(OH)2-rich precursor layer. Samples are then immersed in hydrolyzed BTSPS silane solutions of different concentrations (0.5%, 1%, 3%, and 5%) to form surface coatings, and are labeled as AR, Si-0.5, Si-1.0, Si-3.0, and Si-5.0, respectively. Coating morphology and interfacial chemical composition are characterized by SEM, FTIR, and XPS. Reciprocating wear tests are conducted under dry and simulated body fluid (SBF) conditions, while the electrochemical behavior is evaluated through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results demonstrate that silane concentration exerts a significant influence on coating structure and interfacial bonding. FTIR spectra reveals characteristic Si—O—Si and Si—O—Mg peaks in the 1 000-1 150 cm-1 range, while XPS analysis at the Mg 1s region confirms the presence of Mg—O—Si covalent bonds, indicating that the silane layer is chemically grafted to the substrate. SEM observations show that the Si-0.5 coating is thin, porous, and locally delaminated; the Si-5.0 coating exhibits agglomeration and cracking due to excessive self-condensation; in contrast, the Si-3.0 coating presents uniform thickness, compact structure, and no visible defects, representing the best overall quality. Wear tests reveal that Si-3.0 exhibits superior performance in both dry and wet conditions: the dry wear rate is 0.55×10-5 mm/(N·m) (95% lower than AR), while the wet wear rate is 1.86×10-5 mm/(N·m) (94% lower than AR). The friction coefficient of Si-3.0 remains stable without sudden increases indicating coating failures. Electrochemical measurements further confirm its excellent corrosion resistance, with a corrosion current density of only 1.87×10-5 A/cm2 and a corrosion rate of 0.413 mm/year. EIS analysis reveals a charge-transfer resistance of 1 260.1 Ω·cm2 and a two-time-constant spectrum, indicating significantly enhanced barrier capability against corrosive ions compared with the single-time-constant response of the AR sample. In contrast, Si-0.5 suffers from easy wear-through due to its loose structure, while Si-5.0 degrades due to coating cracks, and both exhibit inferior performance compared with Si-3.0. Overall, a 3% silane concentration achieves the optimal balance among coating thickness, crosslinking density, and interfacial bonding strength. The dense silane layer, reinforced by Mg—O—Si bonding, effectively distributes frictional loads and prevents the permeation of SBF media, thereby fundamentally mitigating corrosion and wear of magnesium implants. This study proposes an efficient and controllable silane-based surface modification strategy and provides a reliable technological pathway for the clinical application of medical magnesium alloys.
Key words
magnesium alloy /
silane modification /
coating /
wear resistance /
corrosion resistance
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Funding
Natural Science Foundation of Shandong Province (ZR2023MC140,ZR2023ME077); The Disciplinary Interdisciplinary Convergence Construction Project of University of Jinan in 2024 (XKJC-202406)
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