退火处理对Al/ZE42/Al复合板界面组织和腐蚀行为的影响

采用光学显微镜、扫描电镜、盐水浸泡等方法研究了退火热处理工艺对Al/ZE42/Al复合板界面微观组织和该复合板在5.0%Na Cl(质量分数)水溶液中腐蚀行为的影响。实验结果表明:Al/ZE42/Al复合板经退火处理后,界面区域发生Mg和Al等元素的互扩散,界面扩散层包含2个反应层,靠近ZE42镁合金一侧的反应层为Mg_(17)Al_(12)相,靠近Al板一侧的反应层为Al_3Mg_2相,随着退火温度的升高或者保温时间的延长,ZE42/Al界面扩散层的厚度增加,ZE42镁合金发生了再结晶组织转变;退火热处理没有明显改善Al/ZE42/Al复合板的耐腐蚀性能,提高了腐蚀速率,其腐蚀机制为复合板边部向内部扩散而导致的电偶腐蚀加剧。     

Effect of Silane on Galvanic Corrosion between EW75 Magnesium Alloy and TC4 Alloy

硅烷处理对镁合金具有良好的保护性。为了抑制 Mg-7Gd-5Y-Nd-Zr (EW75) 稀土镁合金和 Ti-6Al-4V (TC4) 钛合金的电偶腐蚀作用,以自腐蚀镁合金为对照组,对硅烷改性和未改性的镁合金与TC4钛合金的电偶腐蚀进行了研究。用数码照片和扫描电镜 (SEM) 观察分析了浸泡 48 h 后的镁合金表面形貌,样品的自腐蚀电流密度和电偶腐蚀电流密度分别用极化曲线和电偶腐蚀测量来表征获得。结果表明,硅烷膜可以减少失重比,使腐蚀形式由点腐蚀变为均匀腐蚀,因此硅烷改性的镁合金比未改性的镁合金具有更好的抗电偶腐蚀能力,其原因是硅烷膜可以提高镁合金的电位,并减小电偶腐蚀电流密度     

Vanadia-based coatings of self-repairing functionality for advanced magnesium Elektron ZE41 Mg–Zn–rare earth alloy

A smart vanadia protective coating of self-repairing functionality that has proven to provide superior corrosion resistance for several magnesium and aluminum alloys has successfully been designed by our group. A newly developed series of magnesium alloys, namely ZE41 alloy, has recently been proposed for automotive, electronics and aerospace applications. The advanced ZE41 alloy possesses very low density, high specific strength, and good castability and weldability characteristics compared to aluminum and steel based alloys. However, the corrosion resistance of ZE41 alloy in the presence of corrosive chloride environment is relatively low. The possibility of utilizing such coatings to add self-repairing functionalities to ZE41 alloy was discussed in this paper. The electrochemical corrosion behavior of the vanadia coatings over ZE41 alloy was investigated in 3.5% NaCl solution using EIS, linear polarization and cyclic voltammetry techniques. The optimum conditions for obtaining protective vanadia coatings of self-repairing abilities and improved localized corrosion resistance were determined. Surface examination of the coatings was investigated using SEM-EDS and macroscopic imaging.     

Cold Spray Al-5% Mg Coatings for the Corrosion Protection of Magnesium Alloys

Poor corrosion resistance is a significant limitation of magnesium alloys as structural materials. To address this problem, the objective of this study was to apply to a magnesium alloy a corrosion-resistant barrier coating that has galvanic compatibility with magnesium and a hardness value no less than that of magnesium. Aluminum coatings were applied to ZE41A-T5 Mg by the cold spray process. A custom-made high-purity Al-5 wt.% Mg powder was produced by spray metal forming for the coating evaluation. In addition, coatings of commercially pure Al (99.5 wt.%), high-purity Al (99.95 wt.%), AA5356, and AA4047 were used for comparison. Coating evaluation included mechanical testing (hardness and adhesion strength) and corrosion testing (salt spray, galvanic coupling, and crevice corrosion). The Al-5% Mg powder resulted in the best overall performance, including a high hardness, 125 H_v100, and an adhesion strength, over 60 MPa, when treated for over 1000 h in a salt spray chamber and with a low galvanic current.     

The stress corrosion cracking behaviour of heat‐treated Al–Zn–Mg–Cu alloy in modified salt spray fog testing

The stress corrosion cracking behaviour of 7075 (Al–Zn–Mg–Cu) alloy have been studied in a salt spray fog chamber with two vapourised aqueous solutions (0 and 5% NaCl). The paper analyses the stress corrosion resistance of 7075 aluminium alloy with several precipitation‐ageing heat treatments. The results are compared with that obtained in 3.5% NaCl aqueous solution at 20 °C. The salt spray fog testing has permitted a good evaluation of SCC susceptibility in 7075 alloy. All temper conditions studied were susceptible to SCC in the different environments tested. 7075‐T6 temper was the most susceptible, while in all the cases studied 7075‐T73 temper was the least susceptible. Compared to 7075‐T6, 7075‐RRA temper improved the resistance against the SCC process, but the mechanical properties obtained were lower.     

Electrochemical investigation of the influence of laser surface melting on the microstructure and corrosion behaviour of ZE41 magnesium alloy – An EIS based study

Surface melting of a magnesium alloy, ZE41 (4%-Zn, 1%-RE) was performed to achieve electrochemical homogeneity at the surface by microstructure refinement. Large secondary precipitates are particularly known to cause severe pitting in magnesium alloys. The corrosion resistance of the laser treated and untreated alloy was investigated by potentiodynamic polarisation and electrochemical impedance spectroscopy. Contrary to the reported behaviour of other magnesium alloys (such as AZ series alloys), laser surface melting did not significantly improve the corrosion resistance of ZE41. This observation is attributed to the absence of beneficial alloying elements such as Al in ZE41 alloy.     

AZ91D镁合金电偶腐蚀的研究

在自来水和3.5%NaCl溶液中测试了铸造AZ91D镁合金与铝合金、锌合金、Q235碳钢和Cu偶合后的电偶腐蚀行为,研究了腐蚀环境、偶接材料和阴阳极面积比(CAAR)对铸造AZ91D镁合金电偶腐蚀行为的影响。在电偶腐蚀过程中测量溶液的pH值以及电偶腐蚀电流;用失重法计算了铸造AZ91D镁合金的电偶腐蚀速率,利用SEM观察了AZ91D镁合金的腐蚀形貌,并对腐蚀产物进行XRD分析。结果表明,AZ91D镁合金在电偶腐蚀过程中会使溶液的pH值升高,并伴有以Mg(OH)₂为主的腐蚀产物的生成;溶液中Cl^-的存在会加速AZ91D镁合金的电偶腐蚀速率;低氢过电位金属Q235碳钢和Cu对AZ91D镁合金的电偶腐蚀加速效果明显高于中氢过电位金属铝合金和锌合金,偶接材料的极化性能对AZ91D镁合金的电偶腐蚀速率有较大影响。同时,大的阴阳极面积比会加速AZ91D镁合金的电偶腐蚀速率,且AZ91D镁合金的电偶腐蚀电流随阴阳极面积比的增大而呈线性增长趋势。     

Stress corrosion cracking of a recent rare-earth containing magnesium alloy,EV31A,and a common Al-containing alloy,AZ91E

Stress corrosion cracking of the magnesium alloy Elektron 21 (ASTM–EV31A) and AZ91E was studied using constant load test in 0.1 M NaCl solution (saturated with Mg(OH)₂), and slow strain rate test using glycerol, distilled water and Mg(OH)₂ saturated, 0.01 M and 0.1 M NaCl solutions. Slow strain rate test indicated that EV31A was less susceptible to stress corrosion cracking than AZ91E. Under less intense loading of constant load, EV31A was found to be resistant to stress corrosion cracking. Fractography of EV31A specimens showed little evidence of hydrogen embrittlement. The superior resistance of EV31A is attributed to a more robust oxide/hydroxide layer.     

7075铝合金对AZ91镁合金组织和性能的影响

为了研究7075铝合金对AZ91镁合金组织与性能的影响,采用光学显微镜、扫描电镜、X 射线衍射仪、万能材料试验机研究了AZ91镁合金的显微组织与力学性能。结果表明：向AZ91镁合金中加入7075铝合金可使该合金的铸态组织明显细化,当7075铝合金含量超过4%（质量分数,下同）时,AZ91镁合金铸态组织中Mg17Al12相数量明显减少,并且组织中生成了Al6Mn新相。合金抗拉强度与延伸率随着7075铝合金加入量的增加而提高,当7075铝合金的加入达到4%,其抗拉强度与延伸率达到最大值,分别为186 MPa和8.2%     

0Cr13Ni8Mo2Al钢与铝合金和钛台金接触腐蚀与防护研究

通过测定0Cr13Ni8Mo2Al钢与铝合金（LY12）和钛合金（TC4）组成的电偶对的电偶电流的方法,研究了0Cr13Ni8Mo2Al钢在使用中与铝合金和钛合金接触时发生电偶腐蚀的敏感性。研究结果表明:0Cr13Ni8Mo2Al钢与铝合金接触时会产生严重的电偶腐蚀,必须进行防护处理方可使用;与钛合金接触时产生的电偶腐蚀很轻微,可以不进行防护。0Cr13Ni8Mo2Al钢表面进行镀镉钛防护后,与铝合金接触时的电偶电流密度大为减小,相差近10倍;采用环氧锌黄底漆、XM-33-4双组分密封胶防护可以有效地防止0Cr13Ni8Mo2Al钢与铝合金和钛合金接触产生的电偶腐蚀。     

Corrosion behaviour of thermally sprayed Al and Al/SiCp composite coatings on ZE41 magnesium alloy in chloride medium

Thermally sprayed Al and Al/SiCp composite coatings have been deposited on ZE41 magnesium alloy and mechanical compaction at room temperature was applied to the Al and Al/SiCp coatings to reduce their porosity. Corrosion behaviour of coated samples was evaluated and compared to that of uncoated substrate in 3.5 wt.% NaCl solution using electrochemical measurements. Al and Al/SiCp composite coatings reduced the corrosion current density of Mg-Zn alloys by three and two orders of magnitude, respectively, and reductions up to four orders of magnitude were obtained after mechanical compaction.     

Improving corrosion resistance of Al‐11mass%Si alloy through a large number of ECAP passes

Ultrafine‐grained (UFG) Al‐11mass%Si alloy, processed by multi‐pass equal‐channel angular pressing (ECAP) at 573 K, was investigated on corrosion behavior in 0.6 M NaCl solution. Potentiodynamic polarization tests and scanning electron microscopy observation showed that a large number of ECAP passes resulted in lower corrosion current density, more positive corrosion potential, and rather smooth corroded surface with shallow corrosion pits. The uniform distribution of fine secondary‐phase particles on UFG Al matrix weakened the susceptibility to pitting corrosion while inhibited general microgalvanic reactions. The present results indicate that grain refinement of aluminum matrix to the UFG state and uniform redistribution of broken particles (including eutectic silicon and secondary phases), via severe plastic deformation at elevated temperature undergoing dynamic recrystallization, can significantly improve the corrosion resistance of Al alloys, besides the known exceptional mechanical advantages. The simple and effective ECAP procedure makes UFG Al alloys more attractive for high strength structural application in corrosive environment.     

ECAP变形后超硬铝合金的电化学腐蚀行为

采用电化学测量技术,研究了等径转角挤压方法(ECAP)变形后的AA7075-T651铝合金在NaCl溶液中的电化学腐蚀行为。结果表明:同道次ECAP状态下,随着Cl-浓度增加,AA7075-T651的自腐蚀电位和点蚀电位负移,耐腐蚀性能降低;而在同浓度NaCl溶液中,随着ECAP挤压道次增加,AA7075-T651的自腐蚀电位和点蚀电位正移,耐腐蚀性能提高。本次试验也表明了Cl-浓度对于该铝合金耐腐蚀性能的影响程度要远超过ECAP技术。     

The corrosion performance of anodised magnesium alloys

The corrosion performance of anodised magnesium and its alloys, such as commercial purity magnesium (CP-Mg) and high-purity magnesium (HP-Mg) ingots, magnesium alloy ingots of MEZ, ZE41, AM60 and AZ91D and diecast AM60 (AM60-DC) and AZ91D (AZ91D-DC) plates, was evaluated by salt spray and salt immersion testing. The corrosion resistance was in the sequential order: AZ91D ≈ AM60 ≈ MEZ ? AZ91D-DC ? AM60-DC > HP-Mg > ZE41 > CP-Mg. It was concluded the corrosion resistance of an anodised magnesium alloy was determined by the corrosion performance of the substrate alloy due to the porous coating formed on the substrate alloy acting as a simple corrosion barrier.     

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.     

微弧氧化技术在铝、镁及其合金海洋环境防腐蚀中的应用

分析了海洋腐蚀的特点,对比了微弧氧化膜与几种常用防护膜层的形貌和耐蚀性,研究了微弧氧化膜的绝缘性能及其经喷漆、电泳后的耐蚀性能。结果表明:通过微弧氧化在铝、镁及其合金表面生成具有陶瓷组织的氧化膜,然后进行喷涂或电泳处理,可有效防止点蚀、缝隙腐蚀及电偶腐蚀的发生,是海洋环境中铝、镁合金防腐蚀的一条新途径。     

Corrosion behaviour of Mg–Al alloys with Al–11Si thermal spray coatings

The corrosion resistance of AZ31, AZ80 and AZ91D Mg–Al alloys with Al–11Si thermal spray coatings was evaluated by electrochemical and gravimetric measurements in 3.5 wt% NaCl solution. The changes in the morphology and corrosion behaviour of the Al–11Si coatings induced by a cold‐pressing post‐treatment under 32 MPa were also examined. The as‐sprayed Al–11Si coatings revealed high degree of porosity and poor corrosion protection, which resulted in galvanic acceleration of the corrosion of the magnesium substrates. The application of a cold‐pressing post‐treatment produced more compact Al–11Si coatings with better bonding at the substrate/coating interface and slightly higher corrosion resistance. However, interconnected pores remained in the cold‐pressed coatings due to the low plasticity of the Al–11Si powder and galvanic corrosion of the substrate was observed after immersion in 3.5 wt% NaCl for 10 days.     

Plasma anodized ZE41 magnesium alloy sealed with hybrid epoxy-silane coating

Anodic coatings on magnesium ZE41 alloy were formed by DC plasma electrolytic oxidation (PEO) in spark regime in solution composed of NaOH, Na₂SiO₃ and KF. The positive effect of poly(ethylene oxide) addition into the anodizing electrolyte on PEO process, anodic film porosity and its protective performance was described. Anodic films were sealed with hybrid epoxy-silane formulation. The corrosion behavior of the coated ZE41 was studied through electrochemical impedance spectroscopy (EIS) in 0.6 M NaCl solution. Resulting duplex PEO/epoxy-silane coating provides good protective performance without significant signs of corrosion during 1 month of immersion test.     

Galvanic compatibility of corrosion protective coatings with AA7075 aluminum alloy

The galvanic compatibility of aerospace aluminum alloy AA7075 with cadmium (Cd), zinc (Zn), and zinc–cobalt–iron (Zn–Co–Fe, 32–37%Co and 1%Fe) alloys was investigated. A comparison of open circuit potential [OCP vs. saturated calomel electrode (SCE)] measurements in 0.6 mM NaCl showed that all coatings would act anodically to AA7075 with an exception of Zn–Co–Fe (37%Co + 1%Fe) alloy which was electropositive to AA7075. During the zero resistance ammetry (ZRA) measurement in 0.6 M NaCl electrolyte the coupled OCP and current density were measured during 7 days of immersion and both Zn and Cd acted anodic and thus sacrificial to AA7075. Galvanic coupling of AA7075 with (37%Co + 1%Fe) Zn–Co–Fe alloy resulted in the consequent dissolution of the AA7075 aluminum alloy. In contrast, Zn–Co–Fe (32%Co + 1%Fe) alloy was found to be anodic to AA7075 during the first 26 h of immersion but after dezincification and cobalt enrichment at the surface became cathodic to the AA7075 aluminum alloy. During coupling with Zn, some pitting was also observed on AA7075.     

Anodic behaviour of a model second phase: Al-20at.%Mg-20at.%Cu

The anodic behaviour of sputtering-deposited Al-20at.%Mg-20at.%Cu alloy is investigated during anodizing and potentiodynamic polarization treatments using transmission electron microscopy, X-ray photoelectron spectroscopy and medium energy ion scattering. The composition of the alloy is close to that of the S-phase in 2024 aluminium alloy. The anodizing behaviour in both 0.1 M ammonium pentaborate and 0.1 M sodium hydroxide electrolytes follows the behaviour of more dilute, solid-solution, aluminium alloys, with enrichment of copper developing in the alloy during the growth of an alumina-based initial oxide containing incorporated magnesium species. Oxygen gas is generated following sufficient enrichment of copper for its oxidation to proceed and hence, for copper species to enter the oxide film. The generation of oxygen gas causes extensive damage to the film, which limits the voltage to relatively low values. Potentiodynamic polarization in 0.1 M sodium hydroxide electrolyte revealed mainly passive behaviour following an initial period of corrosion during which the passive film is developed. In this initial period, copper enriches in the alloy, beneath an oxide film containing aluminium and magnesium species. The magnesium species migrate faster through the film than the aluminium species and form a surface layer of MgO/Mg(OH)₂, which protects against losses of aluminium species to solution and permits the establishment of the passive film. The steady open-circuit potential of the passivated alloy in the hydroxide solution is about −550 mV (SCE), compared with about −1940 mV (SCE) for aluminium.