Corrosion behavior of 3C magnesium alloys in simulated sweat solution

AZ series Mg alloys AZ31, AZ61, and AZ80 are widely applied in 3C (computer, communication, and consumer electronic) industry. Their corrosion characters in simulated sweat solution have been investigated by electrochemical technology, surface analysis, and pH measurements. Electrochemical test results showed that the three magnesium alloys revealed different corrosion resistance (R_t) in simulated sweat solution, R_t(AZ31) < R_t(AZ61) < R_t(AZ80). Three major components of simulated sweat solution played different roles during corrosion processes. Lactic acid was a kind of strong erosive medium for the magnesium alloys, and NaCl can induce pitting corrosion on alloys surface, while urea acted as a corrosion inhibitor. The corroded surface morphology of the three magnesium alloys was observed using scanning electron microscopy (SEM) and corrosion products were analyzed by X‐ray diffraction (XRD). Result of pH measurement tests showed that there were differences in climbing speed and final values of pH for the three magnesium alloys in simulated sweat solution.     

Corrosion and electrochemical behavior ofAZ31D magnesium alloys in sodium chloride

The corrosion and electrochemical behavior of extruded AZ31D magnesium alloys in NaCl solution were investigated using SEM, XRD and electrochemical method. It is found that AZ31D is susceptive to Cl^- ion, and the open circuit potential shifts to more negative values with increasing chloride concentration. Pitting occurs at corrosion potential and corrosion area enlarges with enhanced polarization. Tafel slopes of the cathode branches in different testing solution are almost the same. Cl^- concentration affects cathode course slightly. High frequency capacitive loops shrink with the increase of Cl^- concentration. Corrosion initiates from the grain boundary and spreads to entire surface with time.     

Mg合金的腐蚀与防护

介绍了Mg合金的腐蚀原理、腐蚀类型以及合金元素在镁合金中的作用。综述了Mg合金的化学转化膜、阳极氧化、微弧氧化、化学镀等经典的表面处理方法 ,以及快速凝固工艺和表面改性技术对Mg合金表面耐蚀性能的影响。Mg合金易发生全面腐蚀、电偶腐蚀、点蚀、应力腐蚀和高温氧化。解决Mg合金腐蚀的方法有 :一是研究新合金 ,提高Mg合金自身的热力学稳定性 ,稀土Mg合金是最有前途的耐蚀合金 ;二是通过表面处理使Mg合金表面富SiO2 和Al2 O3 、含SiC和F-等物质或获得的非晶态的涂层结构能有效地提高Mg合金的耐蚀耐磨性能 ;三是改进加工工艺 ,快速凝固和激光退火不仅能获得力学性能优秀的Mg合金产品 ,还能获得纳米结构的表面涂层防护膜 ,提高Mg合金的耐蚀耐磨性能。使镁合金表面涂层结构纳米化、玻璃化是表面处理工艺的发展趋势。     

Corrosion performance of magnesium alloys MEZ and AZ91

The corrosion performance of sand cast MEZ_S, zirconium-grain-refined MEZ_R, sand cast AZ91_S, and high pressure diecast AZ91_D magnesium alloys were evaluated by means of salt spray testing, optical metallography, hydrogen evolution, polarisation curve measurement and AC impedance spectroscopy. The results show that the corrosion resistance of the four alloys can be ranked in decreasing order as AZ91_D > AZ91_S ≈ MEZ_R > MEZ_S and that the intergranular phases and chemical composition of the matrix phase have a significant influence on the corrosion performance. Alloys with a finer grain size and higher aluminum or zirconium contents exhibit better corrosion resistance.     

General and localized corrosion of magnesium alloys: A critical review

Magnesium (Mg) alloys as well as experimental alloys are emerging as light structural materials for current, new, and innovative applications. This paper describes the influence of the alloying elements and the different casting processes on the microstructure and performance of these alloys and corrosion. It gives a comprehensible approach for the resistance of these alloys to general, localized and metallurgically influenced corrosion, which are the main challenges for their use. Exposure to humid air with ∼65% relative humidity during 4 days gives 100–150 nm thickness. The film is amorphous and has an oxidation rate less than 0.01 μm/y. The pH values between 8.5 and 11.5 correspond to a relatively protective oxide or hydroxide film; however above 11.5 a passive stable layer is observed. The poor corrosion resistance of many Mg alloys can be due to the internal galvanic corrosion caused by second phases or impurities. Agitation or any other means of destroying or preventing the formation of a protective film leads to increasing corrosion kinetics. The pH changes during pitting corrosion can come from two different reduction reactions: reduction of dissolved oxygen (O) and that of hydrogen (H) ions. Filiform corrosion was observed in the uncoated AZ31, while general corrosion mainly occurred in some deposition coated alloys. Crevice corrosion can probably be initiated due to the hydrolysis reaction. Exfoliation can be considered as a type of intergranular attack, and this is observed in unalloyed Mg above a critical chloride concentration.     

镁合金阳极氧化的研究进展与展望

回顾镁合金阳极氧化历史，介绍制备工艺、电解液组成及作用，同时对镁合金阳极氧化机理进行探讨。随着人类环保意识的增强，世界能源的紧缺和氧化设备的不断更新，认为电参数如频率、占空比、电压和电流密度对氧化膜性能的影响、阳极氧化电流效率的测定、氧化膜扩散规律的研究和环保型电解液的开发为未来镁合金阳极氧化研究的重点。     

基于专利文献的镁合金腐蚀与防护技术的最新进展(英文)

对镁合金腐蚀与防护的国内外相关专利文献进行分析,总结最新的表面防护技术,包括转化膜、电镀、表面涂层和多种复合处理技术,此外还介绍一些新的处理技术。发现转化膜技术在所有专利文献中占有极大的比例,说明在实际的工业应用中转化膜技术非常重要,且占主导地位。由于镁合金零部件形状和使用特性的多样性,单一的表面技术难以满足性能所需,越来越多的复合表面处理技术、环保型的新技术被发明用来进行镁合金的防护处理。此外,专利技术的投资成本、操作的难易程度、涂层的性能等因素极大地影响该专利技术的工业应用。     

Corrosion behavior of WE54 magnesium alloy in 3.5%NaCl solution

The corrosion behavior of WE54 magnesium alloy was investigated in 3.5%NaCl aqueous solution. The electrochemical study shows that the value of corrosion potential of WE54 magnesium was -1.8V（vs SCE）. In the initial stage of immersion, a kind of visible thin film, which has the appearance of artificial conversion coating by microscopy observation, formed on the surface of WE54 alloy. Through the comparison of corrosion behavior between WE54 and AZ91D, it is shown that the value of corrosion potential of WE54 is approximately 200 mV lower than that of AZ91D, and the corrosion rate of WE54 was one order smaller than that of AZ91D. After 72 h constant immersion and corrosion products removal, deeper grooves along grain boundaries was revealed but lighter corrosion was apparent on the matrix of WE54 alloy. As far as AZ91D alloy was concerned, severe localized corrosion was dominant and network-bone-like structure was remained.     

Corrosion of magnesium alloys in commercial engine coolants

A number of magnesium alloys show promise as engine block materials. However, a critical issue for the automotive industry is corrosion of the engine block by the coolant and this could limit the use of magnesium engine blocks. This work assesses the corrosion performance of conventional magnesium alloy AZ91D and a recently developed engine block magnesium alloy AM‐SC1 in several commercial coolants. Immersion testing, hydrogen evolution measurement, galvanic current monitoring and the standard ASTM D1384 test were employed to reveal the corrosion performance of the magnesium alloys subjected to the coolants. The results show that the tested commercial coolants are corrosive to the magnesium alloys in terms of general and galvanic corrosion. The two magnesium alloys exhibited slightly different corrosion resistance to the coolants with AZ91D being more corrosion resistant than AM‐SC1. The corrosivity varied from coolant to coolant. Generally speaking, an organic‐acid based long life coolant was less corrosive to the magnesium alloys than a traditional coolant. Among the studied commercial coolants, Toyota long life coolant appeared to be the most promising one. In addition, it was found that potassium fluoride effectively inhibited corrosion of the magnesium alloys in the studied commercial coolants. Both general and galvanic corrosion rates were significantly decreased by addition of KF, and there were no evident side effects on the other engine block materials, such as copper, solder, brass, steel and aluminium alloys, in terms of their corrosion performance. The ASTM D 1384 test further confirmed these results and suggested that Toyota long life coolant with 1%wt KF addition is a promising coolant for magnesium engine blocks.     

Corrosion behaviour of Mg/Al alloys in high humidity atmospheres

The influence of relative humidity (80–90–98% RH) and temperature (25 and 50 °C) on the corrosion behaviour of AZ31, AZ80 and AZ91D magnesium alloys was evaluated using gravimetric measurements. The results were compared with the data obtained for the same alloys immersed in Madrid tap water. The corrosion rates of AZ alloys increased with the RH and temperature and were influenced by the aluminium content and alloy microstructure for RH values above 90%. The initiation of corrosion was localised around the Al–Mn inclusions in the AZ31 alloy and at the centre of the α‐Mg phase in the AZ80 and AZ91D alloys. The β‐Mg₁₇Al₁₂ phase acted as a barrier against corrosion.     

汽车用AZ91镁合金的耐腐蚀性能

以AZ91镁合金为研究对象,研究了NaCl溶液的浓度、腐蚀时间、温度和搅拌速度对AZ91镁合金耐腐蚀性的影响。利用扫描电镜观察了腐蚀后的表面形貌和横截面形貌,定性分析了AZ91镁合金在NaCl溶液中的腐蚀行为。结果表明,随NaCl溶液浓度、腐蚀时间、温度和搅拌速度增加,AZ91镁合金腐蚀速率主要呈递增趋势,且腐蚀形式为沿晶腐蚀。     

Corrosion and mechanical properties of hot-extruded AZ31 magnesium alloys

AZ31 magnesium alloys were hot-extruded at 573 K and 623 K with extrusion ratio(λ) of 20,35 and 50.The corrosion and mechanical behavior of hot-extruded AZ31 were studied by galvanic tests and tensile tests.The microstructures of the studied AZ31 alloys were also investigated with optical microscope.The results show that,compared with the as-cast AZ31 alloy,the corrosion potentials of all hot-extruded AZ31 alloys are increased by 60 mV.Moreover,at the extrusion temperature of 623 K,the galvanic current o...     

镁合金表面化学转化膜研究进展

总结镁合金表面化学转化膜的研究现状,介绍铬酸盐转化膜、锡酸盐转化膜、磷酸盐/高锰酸盐转化膜、稀土转化膜、植酸转化膜和钼酸转化膜的处理工艺,讨论磷酸盐/高锰酸盐转化膜的成膜机理,分析各种化学转化膜的优缺点,展望今后镁合金表面化学转化膜的发展方向。     

Protection behavior of fluorine-containing cover gases on molten magnesium alloys

The sulphur hexa-fluoride gas（SF6）, which is commonly used as the cover gas of molten magnesium alloys in the magnesium industry today, has an extremely high global warming potential（GWP）. The protection mechanism of SF6 containing cover gases on molten magnesium alloys was presented. The cover gas protects the melt by reacting with the melt to form a coherent protective film on the melt surface. The film contains MgO and MgF2. Particles containing MgF2 form on the interface between the oxide film and the bulk magnesium alloy, which correspond to the concave areas from the surface observation. These particles increase the Pilling and Bedworth ratio of surface film and enhance the protective capability of the films. Based on the understanding of the mechanism of SF6, a melting technology in a sealed furnace was proposed, and the protection behavior of magnesium alloys in the sealed melting furnace was investigated under the protective atmosphere containing HFC-134a. The morphology and composition of the surface film were also studied. Experiments to evaluate the protective effect of two other fluorine containing gases with low GWPs on AZglD alloy in the sealed furnace were also carried out, and the results show that the new gases are potential substitutes for SF6.     

镁合金塑性成形技术研究进展

综述了镁合金塑性成形技术的研究现状,介绍了镁合金挤压、轧制、锻造、板料成形的成形特点及最新研究进展,探讨了关于镁合金塑性成形领域亟待解决的问题,展望了镁合金塑性成形技术的发展方向。     

Effects of electric parameters on corrosion resistance of anodic coatings formed on magnesium alloys

Anodic coatings were obtained by micro-arc oxidation on AZ91HP magnesium alloys in a solution containing 10 g/L NaOH and 8 g/L phytic acid. The effects of electric parameters including frequency, final voltage, duty cycle and current density on the corrosion resistance of anodic coatings formed on the magnesium alloys were investigated by using an orthogonal experiment of four factors with three levels. The results show that the final voltage plays a main role on the coating properties. The orders of affecting corrosion resistance and coating thickness are separately ranked from high to low as, final voltage>duty cycle>current density>frequency and final voltage>current density>frequency>duty cycle. The final voltage influences the corrosion resistance of the anodized samples mainly by changing the surface morphology and coating thickness.