Mg-15Li合金在碱性NaCl溶液中的腐蚀行为

    用电化学方法研究了Mg-15Li合金在碱性NaCl溶液中的腐蚀行为.结果表明：在强碱性pH=13及扫描电镜环境下,当Cl^-浓度低于0.4 mol/L时,合金表面形成稳定的钝化膜;随Cl^-浓度增加,点蚀电位逐渐降低.     

Effect of ageing treatment on microstructures,mechanical properties and corrosion behavior of Mg-Zn-RE-Zr alloy micro-alloyed with Ca and Sr

Effects of ageing treatment on the microstructures, mechanical properties and corrosion behavior of the Mg-4.2Zn-1.7RE-0.8Zr-xCa-ySr [x=0, 0.2 (wt.%), y=0, 0.1, 0.2, 0.4 (wt.%)] alloys were investigated. Results showed that Ca or/and Sr additions promoted the precipitation hardening behavior of Mg-4.2Zn-1.7RE-0.8Zr alloy and shortened the time to reaching peak hardness from 13 h to 12 h. The maximum hardness of 77.1±0.6 HV for the peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy was obtained. The microstructures of peak-aged alloys mainly consist of α-Mg phase, Mg₅₁Zn₂₀ phase and ternary T-phase. The Zn-Zr phase is formed within the α-Mg matrix, and the Mg₂Ca phase is formed near T-phase due to the enrichment of Ca in front of the solid-liquid interface. Furthermore, fine short rod-shaped β′₁ phase is precipitated within the α-Mg matrix in the peak-aged condition. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy exhibits optimal mechanical properties with an ultimate tensile strength of 208 MPa, yield strength of 150 MPa and elongation of 3.5%, which is mainly attributed to precipitation strengthening. In addition, corrosion properties of experimental alloys in the 3.5wt.% NaCl solution were studied by the electrochemical tests, weight loss, hydrogen evolution measurement and corrosion morphology observation. The results suggest that peak-aged alloys show reduced corrosion rates compared with the as-cast alloys, and minor additions of Ca and/or Sr improve the corrosion resistance of the Mg-4.2Zn-1.7RE-0.8Zr alloy. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy possesses the best corrosion resistance, which is mainly due to the continuous and compact barrier wall constructed by the homogeneous and continuous second phases.

     

Ni对Zr-Cu-Al系非晶合金在NaCl溶液中腐蚀性能的影响

利用动电位极化和电化学阻抗谱研究了Ni元素对Zr-Cu-Al系非晶合金在3.5wt.%NaCl中性溶液中的电化学腐蚀行为的影响规律。结果表明：含Ni元素的Zr₅₅Cu₃₀Ni₅Al₁₀比Zr₅₅Cu₃₅Al₁₀非晶合金在NaCl溶液中具有更优异的耐腐蚀性能。Zr-Cu-Al系非晶合金在NaCl溶液中发生点腐蚀,圆形腐蚀坑内布满泡沫状孔洞。通过腐蚀前后的元素分布对比,发现Zr-Cu-Al非晶合金在Cl^_-作用下合金元素选择性溶解。含Ni元素的非晶合金形成致密的钝化膜,抑制了金属元素的选择性溶解,从而提高了耐腐蚀性能。研究结果可为耐Cl^_-环境腐蚀非晶合金成分设计及其应用提供参考。     

Ca Addition Effects on the Microstructure,Tensile and Corrosion Properties of Mg Matrix Alloy Containing 8 wt.% Mg<Subscript>2</Subscript>Si

The microstructure, tensile properties and corrosion behavior of the Mg-8 wt.% Mg₂Si-x%Ca alloy have been studied by the use of optical microscopy, scanning electron microscopy equipped with energy-dispersive spectroscopy, x-ray diffraction, standard tensile testing, polarization test and electrochemical impedance spectroscopy (EIS) measurements. Microstructural studies indicated that Ca modifies both primary and eutectic Mg₂Si phase. It was found that the average size of primary Mg₂Si particles is about 60 μm, which is dropped by about 82% in the alloy containing 0.05 wt.% Ca. By the addition of different Ca contents, Ca-rich intermetallics (i.e., CaSi₂ and CaMgSi) were formed. The modification mechanism of adding Ca during solidification was found to be due to the strong effect of CaMgSi phase as a heterogonous nucleation site, apart from CaSi₂ which was reported before, for Mg₂Si intermetallics. Tensile testing results ascertained that Ca addition enhances both ultimate tensile strength (UTS) and elongation values. The optimum amount of Ca was found to be 0.1 wt.%, which improved UTS and elongation values from about 130 MPa and 2% to 165 MPa and 5.5%, whereas more Ca addition (i.e., 3 wt.%) reduced the tensile properties of the alloy to about 105 MPa and 1.8%, which can be due to the formation of CaMgSi intermetallics with deteriorating needle-like morphology. Polarization and EIS tests also showed that the Mg-3%Si-0.5%Ca alloy pronounces as the best anti-corrosion alloy. Nevertheless, further added Ca (up to 3 wt.%) deteriorated the corrosion resistance due to predominance of worse galvanic coupling effect stemmed from the presence of stronger CaMgSi cathode in comparison with Mg₂Si. With higher Ca additions, an adverse effect was seen on corrosion resistance of the Mg-3%Si alloy, as a result of forming a weak film on the alloy specimen surface.     

Characteristics of plasma electrolytic oxide coatings on Mg-Al-Zn alloy prepared by powder metallurgy

Mg-6 wt.%Al-1 wt.%Zn alloy powders were produced by gas atomization, and subsequently compacted and sintered under various conditions of temperature, time, and pressure. The bulk Mg-6 wt.%Al-1 wt.%Zn alloy was coated by the plasma electrolytic oxidation (PEO) method. The optimum condition of compaction and sintering for PEO coatings was established based on the investigation of microstructure, microhardness, and corrosion properties of coatings which were compared to those of cast Mg-6 wt.%Al alloy. The coatings on Mg-6 wt.%Al and Mg-6 wt.%Al-1 wt.%Zn alloys consisted of MgO, MgAl₂O₄, and Mg₂SiO₄. The Mg-6 wt.%Al-1 wt.%Zn alloy compacted at room temperature for 10 min and sintered at 893 K for 3 h showed the most porous and nonuniform coating layer because the coatings had grown through grain boundaries that resulted from poor bonding between powder particles in the substrate. However, the coated Mg-6 wt.%Al-1 wt.%Zn alloy hot-compacted at 593 K for 10 min had the thickest coating layer and the highest microhardness. In addition, it demonstrated the best corrosion resistance as verified by polarization curves in 3.5% NaCl solution.     

纯Mg和Mg-15Li合金在弱碱性NaCl溶液中的腐蚀行为

    采用开路电极电位与时间的关系曲线、极化曲线、电化学阻抗谱、扫描电子显微镜及失重法等手段研究了纯Mg和Mg-15Li合金在pH=10.5的3.5%NaCl溶液中的腐蚀行为.结果表明：在弱碱性的环境下,纯Mg和Mg-15Li合金均不耐腐蚀,腐蚀初期,纯Mg比Mg-15Li合金的耐蚀性高一些,经过24h腐蚀后,纯Mg表现为特异活性点的腐蚀,腐蚀坑大而深,Mg-15Li合金则表现为全面点腐蚀.     

硝酸根离子对U-0.79Ti合金腐蚀行为的抑制作用

采用电化学方法研究了硝酸根离子(NO3-)对U-0.79Ti合金在0.01mol/LNa Cl溶液中腐蚀的抑制作用。实验证明,NO3-对U-0.79Ti合金在含氯离子(Cl-)溶液中的腐蚀具有抑制作用,且与NO3-浓度密切相关。当NO3-与Cl-浓度比大于0.1时,NO3-能够有效抑制U-0.79Ti合金点蚀的发生;而低于这个比例时,NO3-对U-0.79Ti合金的腐蚀行为几乎无影响。从电化学过程来看,加入NO3-能够降低浓差极化并增大极限扩散电流密度。同时,NO3-能够降低氧化膜的阳极活性溶解速度,提高U-0.79Ti合金的点蚀电位。表面划痕实验则表明,NO3-的抑制作用很可能缘于其优先于Cl-在表面缺陷处吸附,阻碍了Cl-的点蚀成核。     

Effect of Ca addition on the as-cast microstructure and creep properties of Mg-5Zn-5Sn magnesium alloy

The effect of Ca addition on the as-cast microstructure and creep properties of Mg-5Zn-5Sn magnesium alloy was investigated. The results indicate that adding 1.0 wt.% Ca to Mg-5Zn-5Sn alloy can effectively refine the as-cast microstructure of the alloy, and the CaMgSn phase with high thermal stability is formed in the alloy. In addition, adding 1.0 wt.% Ca to Mg-5Zn-5Sn alloy can also improve the creep properties of the alloy. After adding 1.0 wt.% Ca to Mg-5Zn-5Sn alloy, the second creep rate of the alloy at 150°C and 50 MPa for 100 h decreases from 4.67 × 10⁻⁸ to 1.43 × 10⁻⁸ s⁻¹. The strengthening mechanism is mainly attributed to the microstructural refinement and the formation of CaMgSn phase.     

Corrosion characterization of Mg-8Li alloy in NaCl solution

The corrosion mechanism of Mg-8Li alloy in NaCl solution was investigated by electrochemical testing and SEM observation. The electrochemical results indicated that the corrosion resistance of Mg-8Li alloy in 0.1 M NaCl solution gradually deteriorated with increasing of immersion time expect for 2 h immersion, which was consistent with the SEM observation of corrosion morphology. Mg-8Li alloy exhibited filiform type of attack under significant anodic control of magnesium solution reaction. The cathodic reaction was driven by hydrogen evolution reaction. The presence of filiform corrosion also proved a resistant oxide film naturally formed on the surface of Mg-8Li alloy.     

Mg-7Li合金微弧氧化过程放电规律及涂层耐蚀性分析

文中采用高速摄影机、原子力显微镜和电化学工作站研究了Mg-7Li合金表面微弧氧化过程的放电规律以及涂层的耐蚀性.结果表明,在硅酸钠溶液中,微弧氧化电源一个脉冲周期内同一位置的放电击穿持续到脉冲结束;不同脉冲周期内,放电击穿反复在同一位置进行,其断续时间达到160 ms以上.表面制备微弧氧化涂层合金的电极电位比基体提高了78.1 mV,腐蚀电流密度降低2个数量级,显著提高了镁锂合金的耐蚀性.     

Ca、Mn元素对Mg-Zn系合金在磷酸盐缓冲液中腐蚀行为的影响

采用XRD、SEM、EDS、三维轮廓仪和失重法等手段研究了Mg-6Zn、Mg-6Zn-1Ca和Mg-6Zn-1Mn合金在磷酸盐缓冲盐溶液(PBS)中的腐蚀行为,并探讨了3种合金的腐蚀机理。结果表明,添加相同含量的Ca和Mn均能使合金的失重率(W_r)降低,但添加Mn元素后(浸泡10d时W_r=3.91%)比添加Ca元素后(W_r=6.78%)合金的失重率更低,说明Mn元素更有抗PBS腐蚀能力,这与Mn的加入在合金表面形成致密的氧化膜有关;同时,Mg-6Zn-1Mn合金在浸泡过程中表面存在点蚀现象,经分析是由第二相与基体构成原电池导致。在420℃不同保温时间(2～20 h)固溶处理后,合金表面的点腐蚀现象随着保温时间的增加而减弱,表明长时间的固溶处理可以减少第二相与镁基体之间的微电偶腐蚀,增加了合金均匀腐蚀的倾向。     

Corrosion of anodically polarized Zn-Al alloys in saturated Ca(OH)2 containing Cl-

Cast Zn-Al alloys containing 0%, 20%, 40%, 55%, 80% and 100% aluminium have been anodically polarized in saturated Ca(OH)₂ containing Cl^- and the conditions for corrosion and for pitting with respect to alloy composition, chloride concentration and alloy microstructure broadly defined. Pure zinc has a large passivation range which shows an etch-pitting-passivation process above about 0.02 M Cl^-. Pure aluminium has a poorly defined passive region with a large passive current and the presence of Cl^- reduces the passive current substantially. All the alloys contain a large amount of a primary aluminium-rich phase which is preferentially corroded and the corrosion behaviour of the alloys reflects the behaviour of the aluminium-rich phase.     

Correlation Between Microstructure and Corrosion Resistance of Magnesium Alloys Prepared by High Strain Rate Rolling

Microstructure and corrosion resistance in Hank’s solution of four magnesium alloys (pure Mg, ZK60, Mg-4Zn and Mg-4Zn-0.3Ca) prepared by high strain rate rolling (HSRR) and conventional rolling (CR) are comparatively investigated. The HSRR alloy exhibits better bio-corrosion resistance than the CR alloy. The HSRR ZK60 alloy has finer grains, higher dynamic recrystallization (DRX) extent, lower twin fraction, coarser residual second-phase particles, finer and denser nanometer β ₁ precipitates, lower residual compressive stress and stronger basal texture than the CR alloy. The average corrosion rate of the HSRR ZK60 sheet after 90-day immersion in Hank’s solution is 0.17 mg cm^?2 d^?1, about 19% lower than that of the CR sheet. Its corrosion current density is 30.9 μA/cm², about 45% lower than that of the CR sheet. Bio-corrosion resistance enhancement by HSRR can be mainly ascribe to the reduced grain size, the relatively adequate DRX, non-twinning, the coarser residual second-phase particles, the finer and denser nanometer precipitates and the slightly stronger (0001) texture.     

A novel phosphate conversion film on Mg-8.8Li alloy

The super light Mg-Li alloys exhibit excellent formability due to the addition of lithium, but the corrosion resistance is deteriorated. A novel conversion film is developed to improve the corrosion resistance. The surface morphology of conversion film was observed using scanning electron microscopy (SEM). The chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The corrosion behaviors of Mg-8.8Li alloy and conversion film were investigated with electrochemical and immersion tests. The experimental results indicated that the Mg-8.8Li alloys with and without the protection of conversion film can both be used in NaOH solution safely. But the Mg-8.8Li substrate was susceptible to corrode in NaCl and Na₂SO₄ solutions, and the conversion film can prevent them from corroding. Compared with the NaCl solution, the Na₂SO₄ solution was a strong corrosive medium to the conversion film.     

氟化处理对植入材料Mg-Ca二元合金腐蚀行为的影响(英文)

在室温下,将Mg-0.5Ca合金在不同浓度的氢氧化钠和HF溶液浸渍不同的时间,研究HF处理对合金腐蚀行为的影响。采用原子力显微镜、X射线衍射、场发射扫描电子显微镜表征样品的微观组织变化。通过动电位极化和Kokubo溶液浸泡试验测试样品的耐腐蚀性。结果表明,与35%HF处理的样品相比,经40%HF溶液处理的Mg-0.5Ca合金具有更均匀、更致密、更薄的涂层(12.6μm)。电化学测试表明,在Kokubo溶液中,经氟化物处理的Mg-0.5Ca合金样品的耐腐蚀性比未处理样品的高35倍;前者的体外降解速率远远低于后者的。在40%HF溶液处理过的样品表面只出现了一些腐蚀点,而未经处理的样品完全被腐蚀产物覆盖且出现了分层现象。40%HF处理的Mg-0.5Ca合金,具有低的降解速率和良好的生物相容性,是一种有潜力的植入材料。     

Mg-1lLi-3AI-O. 5RE合金在酸性NaCI溶液中腐蚀特性研究

为研究Mg-11Li-3Al-0.5RE合金在酸性NaCl溶液中的腐蚀特点,采用静态失重法和电化学方法对合金的腐蚀行为进行测试,并用SEM、XRD分别分析了腐蚀形貌和腐蚀产物.结果表明:在酸性NaCl溶液中,随着Cl-含量的升高,合金的平均腐蚀速率增大,腐蚀电位负移,体系中Rsol、Rt、Rf减小,腐蚀越严重; pH值减小时,合金的腐蚀电流增大,线性极化电阻减小,加快了腐蚀的进行.在酸性环境中,Mg-11Li-3Al-0.5RE合金腐蚀后形成较大、较深的蚀坑,腐蚀产物主要为Mg(OH)2和Al2O3.     

The effects of heat treatment and zirconium on the corrosion behaviour of Mg-3Nd-0.2Zn-0.4Zr (wt.%) alloy

The corrosion behaviours of Mg-3Nd-0.2Zn (wt.%) (NZ) and Mg-3Nd-0.2Zn-0.4Zr (wt.%) (NZK) alloys were investigated in as-cast (F), solution-treated (T4) and artificially-aged (T6) conditions in 5% NaCl solution using immersion test and electrochemical measurements. The immersion test indicates that both NZ and NZK alloys exhibit better corrosion resistances in T4 and T6 states than in the F condition due to the galvanic corrosion between the cathodic Mg₁₂Nd compound and the anodic α matrix in the F condition. The NZK alloy demonstrates lower corrosion rates than the NZ alloy in three conditions, which indicates that the addition of zirconium has a beneficial effect on the corrosion resistance. It was discovered by field emission scanning electron microscope (FE-SEM) that the corrosion products of NZK-T6 formed in salt solution are composed of sandwich shape compounds, while that of NZ-T6 is composed of fine needle-like compounds and small particles. The former are more uniform and compact than the latter and can play a more protective role for the alloy. Electrochemical measurements also confirmed that the more protective film formed on the NZK than on the NZ alloy.     

Effects of coolant chemistry on corrosion of 3003 aluminum alloy in automotive cooling system

In this work, effects of coolant chemistry, including concentrations of chloride ions and ethylene glycol and addition of various ions, on corrosion of 3003 Al alloy were investigated by electrochemical impedance spectroscopy measurements and scanning electron microscopy characterization. In chloride‐free, ethylene glycol–water solution, a layer of Al‐alcohol film is proposed to form on the electrode surface. With the increase of ethylene glycol concentration, more Al‐alcohol film is formed, resulting in the increase in film resistance and charge‐transfer resistance. In the presence of Cl^? ions, they would be involved in the film formation, decreasing the stability of the film. In 50% ethylene glycol–water solution, the threshold value of Cl^? concentration for pitting initiation is within the range of 100 ppm to 0.01 M. When the ethylene glycol concentration increases to 70%, the threshold Cl^? concentration for pitting is from 0.01 to 0.1 M. In 100% ethylene glycol, there is no pitting of 3003 Al alloy even at 0.1 M of Cl^?. Even a trace amount of impurity cation could affect significantly the corrosion behavior of 3003 Al alloy in ethylene glycol–water solution. Addition of Zn²⁺ is capable of increasing the corrosion resistance of Al alloy electrode, while Cu²⁺ ions containing in the solution would enhance corrosion, especially pitting corrosion, of Al alloy. The effect of Mg²⁺ on Al alloy corrosion is only slight.     

Zn对均匀化态Mg-3Sn-Ca镁合金腐蚀性能的影响

研究了Zn元素对均匀化态Mg-3Sn-Ca合金耐腐蚀性能的影响。通过XRD、金相、SEM、失重、析氢、电化学极化曲线和阻抗谱分析了Mg-3Sn-Ca(TX31)和Mg-3Sn-Ca-Zn(TXZ311)2种合金的耐蚀性能。结果表明,Mg-3Sn-Ca合金中主要由CaMgSn及Mg₂Sn相组成,加入Zn元素后晶粒得到显著细化,第二相体积分数增加并呈弥散分布,并有Mg₂Ca相析出。而Zn的添加可显著提高Mg-3Sn-Ca合金的耐蚀性能,这主要归因于TXZ311合金具有更细小的晶粒尺寸以及均匀密集分布的CaMgSn相,使合金在腐蚀过程中形成的钝化膜更加均匀。因此,TXZ311合金的耐蚀性远高于TX31合金。     

镁锂合金表面高锰酸盐转化膜的研究

采用化学转化法在镁锂合金表面制得了结构致密、耐蚀性能较好的高锰酸盐转化膜,研究了转化液中高锰酸盐溶液浓度对成膜效果的影响.实验采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和X射线光电子能谱(XPS)对所制得转化膜的表面形貌、结构和组成进行了测试.同时,使用动电位极化曲线、电化学交流阻抗谱和腐蚀失重3种方法对镁锂合金及其转化膜的耐腐蚀性能进行了深入研究.结果表明:高锰酸盐转化膜较均匀、平整,间隙较小,转化膜主要由锰的氧化物组成.提高了镁锂合金的耐腐蚀性能,当高锰酸盐溶液浓度为4.0 g/L时,转化膜的腐蚀电流密度小、容抗弧大、腐蚀速率低,耐腐蚀性能佳.