The surface, microstructure and corrosion of magnesium alloy AZ31 sheet

This study investigates the effect of some industrial pre-treatments, including heat-treatment, surface grinding and polishing, acid cleaning and sandblasting, on the corrosion performance of Mg alloy AZ31 sheet. It is found that tempering accelerates the corrosion of AZ31. Surface grinding and acid cleaning dramatically improve its corrosion resistance, while sandblasting severely deteriorates its corrosion performance. Surface analysis indicates that the change in corrosion behavior of AZ31 by these pre-treatments can be associated with the alteration of its impurity contamination, surface state, grain size and intermetallic particles. A corrosion model concerning the dissolution and precipitation of tiny Al-Mn-(Fe) particles in grains and grain boundaries is proposed to explain the effect of mechanical deformation and heat-treatment on the corrosion performance of AZ31.     

A two-step surface treatment,combining anodisation and silanisation,for improved corrosion protection of the Mg alloy WE54

The present work reports an innovative approach for surface functionalisation of magnesium alloys (WE54) containing yttrium and rare-earth (RE) elements. A two-step surface modification consisting on the formation of an anodic film followed by the deposition of a hybrid silane layer obtained by dipping in a bis-[triethoxysilylpropyl]tetrasulfide silane (BTESPT) solution was performed on the WE54 alloy.     

Fabrication of hydrophobic surface with hierarchical structure on Mg alloy and its corrosion resistance

A hydrotalcite/hydromagnesite conversion coating with hierarchical structure has been fabricated on a Mg alloy substrate by in situ hydrothermal crystallization method. A MgO layer existing between the hydrotalcite/hydromagnesite film and the substrate was formed prior to the hydrotalcite/hydromagnesite film during the crystallization process. After surface treatment with silane coupling agent, the surface of conversion coating changes from hydrophilic to hydrophobic. Scanning electron microscopy (SEM) revealed that the silylated conversion coating with hierarchical structure maintains the original rough surface of which was composed of numerous micro-scale flakes and beautiful flower-like protrusions. Polarization measurements have shown that the hydrophobic conversion coating exhibited a low corrosion current density value of 0.432 μA/cm², which means that the hydrophobic conversion coating can effectively protect Mg alloy from corrosion. Electrochemical impedance spectroscopy (EIS) showed that the impedance of the hydrophobic conversion coating was 9000 Ω. It means that the coating served as a passive layer with high charge transfer resistance.     

Synthesis of a novel nanostructured zinc oxide/baghdadite coating on Mg alloy for biomedical application: In-vitro degradation behavior and antibacterial activities

In this research, zinc oxide (ZnO) and zinc oxide/baghdadite (ZnO/Ca₃ZrSi₂O₉) were prepared on the surface of Mg alloy using physical vapor deposition (PVD) coupled with electrophoretic deposition (EPD). For this purpose, the nanostructured ZnO was prepared with a thickness of 900 nm and crystallite sizes of 64 nm as under layer while nanostructured baghdadite with a thickness of 10 µm was deposited on the Mg alloy substrate as an over-layer. Electrochemical measurement exhibited that the ZnO/Ca₃ZrSi₂O₉-coated specimen has a higher corrosion resistance and superior stability in simulated body fluid (SBF) solution in comparison with the ZnO-coated and bare Mg alloy samples. Antibacterial activities of the uncoated and coated specimens were evaluated against various pathogenic species (Escherichia coli, Klebsiella pneumoniae, and Shigella dysenteriae) via disc diffusion method. The obtained results showed that ZnO and ZnO/Ca₃ZrSi₂O₉ coatings have great zones of inhibition (ZOI) against E. coli, Klebsiella, and Shigella. However, less ZOI was found around the bare Mg alloy. Therefore, ZnO/Ca₃ZrSi₂O₉ is a promising coating for orthopedic applications of biodegradable Mg alloys considering its excellent antibacterial activities and high corrosion resistance.     

铝上一次浸锌工艺的研究

研制出一种新型的不含氰化物,氟化物以及有毒重金属离子的HG铝合金浸锌液。研究了浸渍温度,时间,搅拌和铝合金材料对镀层结合力的影响。该浸锌液的工作温度为0－40度,较佳温度范围为20－30度,当温度低于20度时,浸锌时间应在30S以上;当温度高于30℃时,浸锌时间应小于30S。在静止,机械或超声搅拌的情况下均能获得结合力优异的镀镍层,可用于硬铝、锻铝、铸铝及粉末冶金铝件的镀镍前处理。此外,热震试验能提高镀层与基体的结合力,因此,不能用于评价铝上镀镍的结合力。     

Zn-Mg系中温磷化工艺研究

通过对Ｚｎ－Ｍｇ系中温磷化工艺研究,优选了磷化液组成及工艺条件,并测定了磷化面积与游离酸度、总酸度间的相应关系,以及磷化时间与磷化膜厚度和耐蚀性的关系,表明该磷化工艺性能优异。     

Biopolymeric coatings for delivery of antibiotic and controlled degradation of bioresorbable Mg AZ31 alloys

Magnesium and magnesium alloys are attracting considerable interest as biodegradable materials with high potential for application as temporary implants. The high corrosion rate of Mg-based implants is considered a serious drawback, and it is crucial to design novel surface protection strategies that minimize the detrimental effects of corrosion, while contributing for introducing additional functionalities on the material surface. In this work, a layer-by-layer coating architecture composed of an inner poly(lactic-co-glycolic) acid layer, working as adhesion promoter, and additional polycaprolactone (PCL) layers working as reservoirs for antibiotic (levofloxacin) and for nanohydroxyapatite (nanoHA) particles was applied on the Mg alloy AZ31. The results demonstrate that the composition and number of PCL layers can tailor the biodegradation of the bare magnesium alloy, surface wettability, and the kinetics of release of antibiotic (levofloxacin). The distribution of nanoHA in the coating architecture plays a crucial role on tailoring the desired biocompatible functionalities and corrosion protection of the bare alloy.     

“Electroless” deposition of a pre-film of electrophoresis coating and its corrosion resistance on a Mg alloy

Magnesium has unique electrochemical performance, which can be utilized in its coating or surface treatment. In this study, a new self-deposited coating process is explored for magnesium alloys. It is found that a thin film can be rapidly formed on a Mg alloy AZ91D through simply dipping the alloy coupon in an E-coating bath solution without applying a current or potential that is essentially required in a normal E-coating process. The “electroless” deposition mechanism and the film growth kinetics are investigated and the formed pre-film of E-coating is evaluated for its stability and corrosion protection performance in a phosphating acidic electrolyte and a NaCl corrosive solution. It is believed that the surface alkalization effect of magnesium is responsible for the “electroless” deposition of the pre-film. The diffusion of hydroxyls in the porous film is controlling the growth of the pre-film. The rapidly formed pre-film can offer sufficient corrosion protection for the magnesium alloy in a chloride-containing environment and it is also stable enough to enable a magnesium alloy part to go through a phosphating bath in a paint line.     

Antibacterial activity and corrosion resistance of Ta2O5 thin film and electrospun PCL/MgO-Ag nanofiber coatings on biodegradable Mg alloy implants

Biodegradable magnesium (Mg) alloys have drawn considerable attention for use in orthopedic implants, but their antibacterial activity and corrosion resistance still require improvement. In the present work, functional Ta₂O₅ (tantalum pentoxide) compact layers and PCL/MgO-Ag (poly (ε-caprolactone)/magnesium oxide-silver) nanofiber porous layers were subsequently deposited on Mg alloys via reactive magnetron sputtering and electrospinning, respectively, to improve anticorrosion and antibacterial performance. Sputter coating of the Ta₂O₅ resulted in a thick layer (～1?μm) with an amorphous structure and high adhesive strength. The nanostructure exhibited bubble-like patterns with no obvious nano-cracks, nano-porosities, or pinholes. The electrospun PCL/MgO-Ag nanofiber coating was porous, smooth, and plain with no obvious beads. In vitro corrosion tests demonstrated the PCL/MgO-Ag nanofiber-coated alloy had greater corrosion resistance than a Ta₂O₅ sputter-coated alloy or uncoated Mg alloy. The additional electrospun PCL/MgO-Ag nanofiber coating also had greater antibacterial behavior toward Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria than the Ta₂O₅-coated or uncoated alloy specimens. Increasing the MgO-Ag concentration of the nanofibers from 1 to 3?wt% increased antibacterial activity. The combination of Ta₂O₅ and PCL/MgO-Ag nanofiber coatings on Mg alloys may therefore have potential applications for reducing bone infection as related to orthopedic implants for bone repair.     

Heat exchangers corrosion protection by using organic coatings

Corrosion phenomena in aluminium heat exchangers represent a problem in terms of durability and efficiency of thermal exchange. This work evaluates the barrier properties of two coatings that represent the state of the art for the protection in the heat, ventilating, air conditioning/refrigerating field (HVAC/R): electrophoretic coating (E-coating) using epoxy resin and spraying of polyurethane coating with addition of metallic pigments. The ability of the coatings to cover the surface of heat exchanger has been evaluated by means of optical microscopy in order to highlight critical zones of the system for the application of the coatings. The electrochemical behaviour of coated heat exchangers has been studied by means of electrochemical impedance spectroscopy in 3.5% NaCl solution. The local electrochemical behaviour of coating defects has been investigated using the electrochemical micro-cell, which enables to perform potentiodynamic polarization measurements on single defects. E-coatings evidenced difficulties to provide uniform thickness of the coating at the extremities of the fins. Spraying of the polyurethane coating containing pigments require particular care in order to fully cover zones of the heat exchanger with difficult accessibility. The electrochemical behaviour of coated heat exchangers is affected by the existence of defects in the coatings.     

用于高硅铝合金的无氰沉锌液

采用无氰沉锌技术在高硅铝合金表面制备沉锌层.通过正交试验得到无氰沉锌的最佳工艺配方为:NiSO4·7H2O 4 g/L,CuSO4·5H2O 2 g/L,FeCl3 1 g/L,ZnO 8 g/L,NaOH 60 g/L,配位剂25 g/L,调整剂1g/L.对采用最佳配方制得的沉锌层进行了孔隙率、结合力、沉锌电位-时间...     

Electrochemical behavior of Mg and some Mg alloys in aqueous solutions of different pH

The electrochemical behavior of Mg, Mg-Al-Zn and Mg-Al-Zn-Mn alloys were investigated in aqueous acidic, neutral and basic solutions. Conventional electrochemical techniques such as open-circuit potential measurements, polarization methods and electrochemical impedance spectroscopy (EIS) were used. The results have shown that the rate of corrosion in acidic solution is relatively high compared to that in neutral or basic solutions. The presence of Al, Zn and Mn as alloying elements decreases the rate of corrosion of the alloy. The activation energy of the corrosion process occurring at the surface of Mg or Mg alloys in aqueous solutions is less than 40 kJ mol⁻¹. This value indicates a one electron transfer electrode as a rate controlling process. The impedance data were fitted to equivalent circuit models that explain the different electrochemical processes occurring at the electrode/electrolyte interface.     

LF2铝合金焊接气孔的控制

通过对铝合金气孔产生的原因及影响因素分析，并进行工艺实验，确定LF2焊接工艺，减少了LF2焊接气孔。     

镁合金黑色化学转化膜工艺研究

通过正交试验,优化得出镁合金黑色化学转化膜最佳工艺配方参数。分析了各成分对镁合金黑色化学转化膜耐腐蚀性、附着强度的影响。     

The effect of potential bias on the formation of ionic liquid generated surface films on Mg alloys

An electrochemical approach to the formation of a protective surface film on Mg alloys immersed in the ionic liquid (IL), trihexyl(tetradecyl)phosphonium-bis 2,4,4-trimethylpentylphosphinate, was investigated in this work. Initially, cyclic voltammetry was used with the Mg alloy being cycled from OCP to more anodic potentials. EIS data indicate that, under these circumstances, an optimum level of protection was achieved at intermediate potentials (e.g., 0 or 0.25 V versus Ag/AgCl). In the second part of this paper, a small constant bias was applied to the Mg alloy immersed in the IL for extended periods using a novel cell design. This electrochemical cell allowed us to monitor in situ surface film formation on the metal surface as well as the subsequent corrosion behaviour of the metal in a corrosive medium. This apparatus was used to investigate the evolution of the surface film on an AZ31 magnesium alloy under a potential bias (between ±100 mV versus open circuit) applied for over 24 h, and the film evolution was monitored using electrochemical impedance spectroscopy (EIS). A film resistance was determined from the EIS data and it was shown that this increased substantially during the first few hours (independent of the bias potential used) with a subsequent decrease upon longer exposure of the surface to the IL. Preliminary characterization of the film formed on the Mg alloy surface using ToF-SIMS indicates that a multilayer surface exists with a phosphorous rich outer layer and a native oxide/hydroxide film underlying this. The corrosion performance of a treated AZ31 specimen when exposed to 0.1 M NaCl aqueous solution showed considerable improvement, consistent with electrochemical data.     

机械力表面改性对镁合金含铝涂层耐腐蚀性能影响的研究

在AZ91D镁合金表面涂覆含有铝粉的缩丁醛有机涂层，并对涂层表面进行机械力表面改性通过中性盐雾试验和W=5％的NaCl溶液浸泡试验研究了机械力表面改性和不同铝粉粒径对该涂层耐腐蚀性能的影响时涂层经机械力表面改性前后的微观形貌和NaCI溶液中的交流阻抗分踟进行了探讨结果表明，涂液中铝粉的粒径对涂层的耐蚀性有较大影响；该机械力表面改性处理可以增强有机涂层与基体的结合强度，提高涂层表面的致密程度．从而提高了涂层的耐腐蚀性能。     

High corrosion protection of a polyaniline/organophilic montmorillonite coating for magnesium alloys

Epoxy coatings containing polyaniline (PANI) and polyaniline/organophilic montmorillonite (PANI/OMMT) powders were prepared on the surface of AZ91D magnesium alloy. The corrosion performance of the coatings was evaluated by electrochemical impedance spectroscopy (EIS) and open-circuit potential analysis in 3.5% NaCl. The results indicate that the PANI/OMMT coating retained its high corrosion protection for AZ91D magnesium alloy after 6000 h of immersion. The protective mechanism conferred by the PANI/OMMT coating was also discussed. The effects of oxygen on the protective mechanism of PANI were evaluated by EIS measurements in a 3.5% deaerated NaCl solution.     

Influence of V-containing species on formation and corrosion resistance of PEO coatings developed on AZ31B Mg alloy

The defects, micropores, and microcracks on the plasma electrolytic oxidation (PEO) coating severely affect the long-term anti-corrosion feature. Inclusion of additives in the electrolyte is a feasible and effective strategy to attain the more intact PEO coating. The PEO coatings are fabricated on AZ31B Mg alloys in an silicon-based electrolyte with Na₃VO₄ (OPEO), NaVO₃ (MPEO), and V₂O₃ (VPEO), respectively, to explore the influence of additives on the corrosion resistance. MPEO sample has the smallest poriness and pore size unfolding the best anti-corrosion resistance, which is also consistent with the electrochemical analysis. Even after 336 h salt spray test, the MPEO coating exhibits the least corrosion. The excellent anti-corrosion performance of MPEO sample is the synergistic effect of inorganic salts and multiple metal oxides generated in the formation of PEO coating. Inclusion of inorganic salt with valence change metal is a feasible pathway to achieve the compact PEO coating since multiple metal oxides could be produced and deposited in the PEO coating during the fabrication.     

Smart self-healing anti-corrosion vanadia coating for magnesium alloys

Eco-friendly vanadia based chemical conversion coating was applied for improving the corrosion resistance of a newly developed magnesium AZ31 HP-O alloy. The effect of vanadia solution concentrations (10, 30 and 50 g/l) and pH (neutral pH 7 and pH 9) on the corrosion protection performance of a magnesium substrate were investigated. EIS and linear polarization techniques were used to evaluate the electrochemical behavior in 3.5% NaCl. The results showed a marked increase in the localized corrosion resistance after applying vanadia surface treatment of 50 g/l due to self-healing effect. The optimum conditions to obtain protective coatings for AZ31 HP-O with a self-healing ability were determined. Changes in surface morphology, composition and microstructure of the conversion coatings were followed by SEM-EDS and macroscopic imaging techniques.     

镁合金化学镀镍工艺研究进展

镁合金以其质量轻、比强度高、成型性好等优点备受人们关注.但是镁的电极电位比较低,容易被腐蚀,因此,使其应用受到限制.在镁合金表面进行化学镀镍,生成一层光滑、平整、致密的镍镀层,能有效地提高镁合金的耐蚀性能.