目的 探究镁合金表面316不锈钢涂层微观结构、耐腐蚀性及电偶腐蚀行为关联特性。方法 采用超音速火焰喷涂技术（HVOF）在AZ31B镁合金表面制备316不锈钢涂层,采用电化学工作站、扫描电子显微镜、能谱仪、X射线衍射仪和X射线光电子能谱仪等检测设备,通过镁合金基体和316不锈钢块体的腐蚀行为对比,研究AZ31B镁合金基体/316不锈钢涂层在3.5%（质量分数）NaCl溶液中的腐蚀及防护失效后的电偶腐蚀行为。结果 316不锈钢涂层可将AZ31B镁合金表面腐蚀电流密度降低2个数量级;涂层在沉积过程中造成的界面氧化和析出的少量σ相会消耗其周围Cr元素,所致的贫Cr区是形成点蚀的薄弱区域;涂层表面孔隙和片层界面等缺陷耦合作用所致的腐蚀聚集区易形成穿透性孔隙,腐蚀介质可经过穿透性孔隙与基体形成回路,零电阻安培计（ZRA）所测得电偶电流密度最高可达1.142×10-4 A/cm2,Ecorr负移至-1.218 V,接近AZ31B基体腐蚀电位（-1.521 V）。结论 316不锈钢涂层的表面孔隙和片层界面等缺陷相互作用,易形成贯穿性孔隙,引发电偶腐蚀,涂层-基体界面的电偶腐蚀产物会进一步迫使涂层开裂,进而加速镁合金基体的腐蚀损伤以及涂层的剥落失效。
Abstract
Surface protective coating systems constructed via thermal spraying technology can overcome the limitations of traditional coating processes in material selection and thickness control, effectively enhancing the mechanical properties and corrosion resistance of magnesium alloy surfaces. Among these coatings, 316 stainless steel coatings provide effective protection for magnesium alloys due to their superior mechanical performance and corrosion resistance. However, despite the significant improvements in wear resistance, corrosion resistance, and impact resistance imparted by metallic coatings, the extremely low standard electrode potential of magnesium alloys (-2.36 V) may induce galvanic corrosion between the coating and substrate. Therefore, investigating the correlation between the microstructure, corrosion resistance, and galvanic corrosion behavior of 316 stainless steel coatings on magnesium alloys is critical for expanding their application fields and service conditions.
The 316 stainless steel coating was fabricated on AZ31B magnesium alloy substrates through a two-pass HVOF process, achieving a coating thickness of approximately 200 μm. Prior to spraying, the substrate surfaces were meticulously prepared by cleaning with acetone and grit blasting to enhance the adhesion of the sprayed particles. The HVOF process parameters, such as propane flow rate of 68 m3/min, oxygen flow rate of 240 m3/min, compressed air flow rate of 375 m3/min, powder feed rate of 38 g/min, spray distance of 240 mm, and scanning velocity of 300 mm/s, were optimized to ensure coating quality. The microstructure and phase composition of the coating were characterized through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The corrosion behavior was evaluated through electrochemical testing, including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and zero-resistance ammetry (ZRA) measurements.
The 316 stainless steel coating significantly reduced the corrosion current density of the AZ31B magnesium alloy by two orders of magnitude, demonstrating its initial effectiveness as a physical barrier against uniform corrosion. However, interfacial oxidation during the HVOF deposition process and the precipitation of trace sigma (σ) phases led to localized chromium (Cr) depletion in adjacent regions, forming Cr-depleted zones that acted as preferential sites for pitting initiation. The synergistic interaction between surface pores and interlamellar interfaces within the coating promoted the formation of localized corrosion-aggregated zones, leading to the development of penetrative pores that allowed corrosive media to establish direct electrical contact with the substrate. Zero-resistance ammetry measurements revealed a galvanic current density of 1.142× 10-4 A/cm2, accompanied by a negative shift in corrosion potential (Ecorr) to -1.218 V, which approached the intrinsic corrosion potential of the AZ31B substrate (-1.521 V). This indicated that the coating failure led to accelerated corrosion of the magnesium alloy and promoted coating delamination. The accumulation of galvanic corrosion products at the coating-substrate interface generated mechanical stresses, leading to coating cracking and delamination, which further accelerated the failure of the protective system.
The 316 stainless steel coating initially enhances the corrosion resistance of AZ31B magnesium alloy by acting as a physical barrier. However, the coupling of surface pores and interlamellar interfaces facilitates the formation of penetrative pores, which establishes galvanic coupling pathways between the coating and substrate. This accelerates the corrosion rate of the magnesium alloy and promotes coating delamination. The degradation is driven by defect-mediated localized corrosion and sustained galvanic interactions. Furthermore, the accumulation of galvanic corrosion products at the coating-substrate interface generates mechanical stresses, leading to coating cracking and delamination, which accelerates the failure of the protective system. Optimizing HVOF parameters to suppress interfacial oxidation, minimize σ-phase formation, and reduce porosity is critical for improving the durability of magnesium alloy coatings in chloride-containing environments.
关键词
316不锈钢涂层 /
镁合金 /
HVOF /
电化学 /
腐蚀行为
Key words
316 stainless steel coating /
magnesium alloy /
HVOF /
electrochemistry /
corrosion mechanism
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基金
国家自然科学基金项目（W2412069）; 国家“111”计划项目（D21032）
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