In-situ Construction of Functionalized Modified Layers on Zn-0.5wt.%Li Alloy via Friction Stir Processing and Their Degradation Mechanism in Artificial Urine

ZHONG Li; DAI Zhenhai; HE Donglei; ZHOU Mengran; ZHANG Ziyue; DONG Xinze; CHEN Gaoqiang; ZHA Yuru; HAN Yuxiang; ZHU Yixing; KANG Jun; LIU Fan; LIU Yake; YE Fan; SHI Qingyu; ZHAO Weikang

doi:10.16490/j.cnki.issn.1001-3660.2026.18.004

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Surface Technology ›› 2026, Vol. 55 ›› Issue (18) : 38-47. DOI: 10.16490/j.cnki.issn.1001-3660.2026.18.004

In-situ Construction of Functionalized Modified Layers on Zn-0.5wt.%Li Alloy via Friction Stir Processing and Their Degradation Mechanism in Artificial Urine

ZHONG Li¹, DAI Zhenhai¹, HE Donglei^2a,2b, ZHOU Mengran^2a,2b,*, ZHANG Ziyue^2a,2b, DONG Xinze^2a,2b, CHEN Gaoqiang^2a,2b, ZHA Yuru^2a,2b, HAN Yuxiang^2a,2b, ZHU Yixing³, KANG Jun^4,5, LIU Fan⁶, LIU Yake⁶, YE Fan⁷, SHI Qingyu^2a,2b, ZHAO Weikang⁸

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Abstract

As-cast Zn-0.5wt%Li alloy encounters severe localized corrosion and excessive encrustation in urinary implant applications, which greatly restrict its clinical use. The coarse and continuously distributed primary β-LiZn₄ dendrites lead to intense electrochemical heterogeneity in the microstructure. These intermetallic phases act as effective cathodes and form micro-galvanic cells with the α-Zn matrix, which significantly accelerates localized degradation and causes a rapid increase in local pH value at the alloy surface. This pH variation promotes the continuous deposition of phosphate substances and further leads to the blockage of urinary implants during clinical service.
In this work, friction stir processing (FSP) was employed to in-situ fabricate a homogeneous functionalized modified layer on the surface of Zn-0.5wt.%Li alloy to overcome these drawbacks. As a solid-state surface modification technique, FSP avoided melting and solidification defects, and achieved controllable microstructure regulation at the surface region. Single-pass FSP was performed with optimized processing parameters, including a rotation speed of 800 rpm, a traveling speed of 100 mm/min, a tool tilt angle of 2.5° and a plunge depth of 0.3 mm. The microstructural evolution of the modified layer was characterized by X-ray diffraction and scanning electron microscopy. The corrosion resistance and anti-encrustation properties were evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy and 28-day in vitro immersion tests in artificial urine at 37 ℃. The composition and morphology of corrosion products were analyzed by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.
Microstructural results confirmed that FSP effectively eliminated the microstructure inhomogeneity of the as-cast alloy. The coarse primary β-LiZn₄ dendrites and lamellar Zn/β-LiZn₄ eutectic structures were thoroughly broken and refined. Dynamic recrystallization induced by FSP promoted the formation of uniform equiaxed fine grains. The high-density dislocations introduced by severe plastic deformation accelerated the dissolution of β-LiZn₄ phase, reducing its volume fraction from 30.8% to 25.4%. Meanwhile, a strong (0002) basal plane texture was formed in the α-Zn matrix, which was the most densely packed crystal plane in hexagonal close-packed Zn.
Benefiting from the optimized microstructure, the FSP-modified alloy presented significantly enhanced corrosion resistance and anti-encrustation performance. The corrosion current density was reduced by 54.7%, from 59.2 μA/cm² to 26.8 μA/cm². The charge transfer resistance increased from 59 Ω·cm² to 156 Ω·cm², and the film resistance rose from 80 Ω·cm² to 172 Ω·cm². After 28-day immersion, the stable degradation rate of the FSP sample was 0.05 mm/a, which was much lower than 0.12 mm/y of the as-cast sample. The surface encrustation weight was reduced by 54%, from 8.2 mg/cm² to 3.8 mg/cm², and the corrosion products presented a thinner and more compact layered structure on the modified surface.
The enhancement mechanism revealed that phase homogenization and β-LiZn₄ dissolution suppressed micro-galvanic corrosion by reducing potential differences. The (0002) basal texture acted as a physical barrier to inhibit ion dissolution. The uniform degradation process avoided sharp local pH increase, thus restraining the precipitation of Zn₃(PO₄)₂ and the formation of CaZn₂(PO₄)₂·2H₂O. This work provides a feasible surface modification method for the development of anti-encrustation biodegradable Zn-Li alloys for urinary implants, and also offers a reliable design strategy for high-performance biodegradable metallic implants.

Key words

Zn-Li alloy / friction stir processing / artificial urine / biodegradable / corrosion behavior

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ZHONG Li, DAI Zhenhai, HE Donglei, ZHOU Mengran, ZHANG Ziyue, DONG Xinze, CHEN Gaoqiang, ZHA Yuru, HAN Yuxiang, ZHU Yixing, KANG Jun, LIU Fan, LIU Yake, YE Fan, SHI Qingyu, ZHAO Weikang. In-situ Construction of Functionalized Modified Layers on Zn-0.5wt.%Li Alloy via Friction Stir Processing and Their Degradation Mechanism in Artificial Urine[J]. Surface Technology. 2026, 55(18): 38-47

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