Magnesium Alloy and Aluminium Alloy

Stress Corrosion Cracking of Magnesium Alloys:Mechanism, Influencing Factors, and Prevention Technology Article

SONG Yulai, FU Hongde, WANG Zhen, YANG Pengcong

Materials Reports 2019,33(5 ):834 -840. DOI:10.11896/cldb.201905016

Abstract （1091）

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Save With the increasing requirements for energy saving and environmental protection, the development and application of environmentally friendly structural materials have attracted enormous attention. Thanks to their low environmental pollution and high recycling efficiency. Magnesium alloys have become the most promising commercial lightweight materials in the 21st century, with widespread application in aerospace, computer, communications and other industrial fields.
Unfortunately, many problems have also been exposed duringthe application of magnesium alloys. Suffering from the active chemical nature of magnesium, magnesium alloys are highly susceptible to corrosion in the service environment. For example, pitting corrosion, galvanic corrosion, and intergranular corrosion are likely to occur in magnesium alloys in humid atmospheres, marine atmospheres, and sulfur-containing atmospheres, leading to the whole or partial failure of structural parts of the magnesium alloy. Particularly, stress corrosion cracking of magnesium alloys may take place under the combined effects of corrosion and external force, resulting in brittle fracture of structural components. In recent years, there is a continuous increase in structural failure cases caused by stress corrosion cracking of magnesium alloys, which bring about huge economic losses. Therefore, great efforts have been put in the research work on stress corrosion cracking of magnesium alloys, focusing on their mechanism, influencing factors, and protective technologies.According to relevant studies by scholars at home and abroad, the stress corrosion cracking mechanism of magnesium alloyscan be generally explained by two major theories, namely, anodic dissolution and hydrogen embrittlement. Specifically, slipping dissolution theory and localized plasticization of hydrogen are recognized as the main viewpoints of the above mentioned two theories, respectively. However, owing to the diversity of magnesium alloy materials, service environment, and the complexity of mechanical and electrochemical corrosion behaviors, the existing theoretical mechanisms lack universal applicability and direct experimental verification. Consequently, further systematic research is urgently needed. The stress corrosion resistance of magnesium alloys is affected by multiple factors such as the service environments, the processing parameters, and the alloy elements in the magnesium alloy. Therefore, according to the stress corrosion mechanism, and taking the influencing factors into consideration, stress corrosion cracking sensitivity of the magnesium alloy can be effectively reduce by reasonable addition of alloying elements to develop new magnesium alloy, surface laser shock modification or surface coating, heat treatment, modification treatment of magnesium alloy. Especially, the addition of rare earth elements like erbium and cerium contri-bute to optimizing the microstructure of the magnesium alloy and forming new rare earth phases, which exert favorable effect on reducing the stress corrosion cracking susceptibility.
In this article, the research progress of stress corrosion cracking of magnesium alloys is systematically summarized, and the stress corrosion cracking mechanism, influencing factors, and protective measures of magnesium alloys are discussed. The relevant research results at home and abroad in the past ten years are emphatically introduced. Meanwhile, future research directions and urgent issues in the field of stress corrosion cracking of magnesium alloys are also proposed.

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Ultrafine Grained Magnesium Alloys Research:Status Quo and Future Directions Article

PENG Peng, TANG Aitao, SHE Jia, ZHOU Shibo, PAN Fusheng

Materials Reports 2019,33(9 ):1526 -1534. DOI:10.11896/cldb.18010063

Abstract （1298）

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Save Magnesium and its alloys have become one of the most promising structural materials, thanks to their superiority in low density, high specific strength, high thermal conductivity, high damping and good electromagnetic shielding performance. As the rising environmental problems, there is a increasingly pressing need for light-weight products, energy conservation and emission reduction. Especially, it has become an urgent and widespread demand for structural materials with low density, high performance and recyclable remanufacturing properties, which provides a broad prospect for the development and application of magnesium alloys. Nevertheless, magnesium alloys especially the wrought magnesium alloys haven’t achieved a large-scale industrial application yet, and still remain some issues to be solved.
The key bottlenecks that affecting the application of wrought magnesium alloys lie in their low absolute strength and poor plasticity. In the four traditional reinforcement theories, precipitation strengthening, processing hardening can significantly enhance the absolute strength, yet accompanied by further deterioration of plasticity. Generally, solution strengthening is an effective approach to enhance strength, but also do harm to the ductility. Few solid solution elements are found to simultaneously contribute to strength and ductility, and the improvement of solid solution elements on strength and ductility is not satisfactory as well, hence further studied and exploration are still needed. Currently, grain refinement has been proved to be the most effective means for improving both strength and plasticity. The strength and ductility of materials will be significant boosted when the grain size is refined to several microns. In ultra-fine grained steel, it is generally believed that the goal of ultra-fine grained structure is to refine the grain size from dozens of microns to achieve the fine structure of 1—2 μm. In iron and steel materials, the properties of mate-rials can be doubled by using ultrafine grained structure. Accordingly, grain refinement is also one of the focuses of high-performance magnesium alloys. Recent studies have shown that ultrafine grained magnesium alloys also possess favorable strength, plasticity and even low temperature super plasticity. At present, two approaches commonly used for preparing ultrafine grained magnesium alloys are severe deformation and medium-low temperature deformation. The former primarily employs techniques like equal channel extrusion, high pressure torsion, cumulative rolling, multidirectional forging and powder metallurgy to achieve ultra-fine crystallization of grains, which holds a development history and a relatively deep research foundation. The latter is an emerging approach for preparing ultrafine grained magnesium alloys. The ultrafine magnesium alloys with an average grain size about 1 μm can also be successfully obtained, exhibiting a great potential for industrial application. Besides, there are significant difference in the properties of ultrafine grained magnesium alloys with diverse alloy components prepared by severe deformation and medium-low temperature deformation. Therefore, the composition design of alloys also plays a crucial role in preparation of ultrafine grained magnesium alloys in anyone of the approaches. Generally speaking, the leading direction of research on ultrafine magnesium alloys focus on designing various alloy components, optimizing the preparation process, regulating the recrystallization behavior during deformation, and preparing ultrafine magnesium alloys with satisfactory microstructure and excellent performance.
In this paper, we review the current status and the preparation approaches of ultrafine grained magnesium alloys with their merits and drawbacks, and analyze the effect of preparation approach and alloy design on microstructure and properties of ultrafine grained magnesium alloys. Finally, we point out the development direction of ultrafine grained magnesium alloys in the future.

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Research Progress of Edge Cracks During Rolling of Magnesium Alloy Sheets Article

LIU Jianglin, QI Yanyang, WANG Tao, WANG Yuelin, REN Zhongkai, HAN Jianchao

Materials Reports 2020,34(7 ):7138 -7145. DOI:10.11896/cldb.19020149

Abstract （807）

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Save Magnesium alloy is one of the most important metal structural materials in recent years. It has the advantages of light weight, high specific strength, large elastic modulus, good shock absorption, noise reduction and impact resistance. It has been widely used in many fields such as national economy and industrial production. In-depth research on key technologies of magnesium alloys is of great significance for solving the prominent problems of energy structure and industrial structure.
Rolling is one of the commonly used methods to produce magnesium alloy sheets, which can refine the microstructure, improve mechanical properties, and have the advantage of continuous mass production. However, a large number of edge cracks will occur in the rolling process of magnesium alloy sheets, and the resulting large amount of trimming waste seriously affects the yield and material utilization rate of magnesium alloy sheets, which limits and restricts the further development of this material.
To solve the problem of edge cracks during rolling of magnesium alloy sheets, researchers have studied the rolling process of magnesium alloy sheets by on-line heating, wrap rolling, hard-plate rolling, differential speed rolling, prefabricated crown, model prediction and other methods in recent years. The positive results have been achieved, which provides a possibility for the preparation of magnesium alloy sheets without edge cracks or with few edge cracks. Its industrialized production will bring enormous economic benefits in the future.
In this paper, the research progress of edge cracks during rolling of magnesium alloy sheets at home and abroad is reviewed. The macroscopic and microscopic causes of edge cracks during rolling of magnesium alloy sheets are briefly described. The mechanism and influence rule of edge cracks caused by macroscopic factors such as rolling temperature, reduction system, rolling speed and stress state are classified and summarized. The microscopic factors, including the crystal structure, texture, microstructure uniformity, twin and brittle phase are also discussed. The methods of reducing edge cracks are summarized based on the macro-microscopic mechanism and influence rule of edge cracks during rolling of magnesium alloy sheets. The edge cracks of magnesium alloy sheets are reduced by changing rolling mode, converting rolling path and improving composition design. Meanwhile, the shortcomings of current research are analyzed and the future research is prospected.

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A Review on Surface Self-nanocrystallization of Magnesium Alloys Article

WANG Chunming, YANG Munan, HUANG Jianhui, LIU Weijiang, LIANG Tongxiang

Materials Reports 2019,33(13 ):2260 -2265. DOI:10.11896/cldb.18040187

Abstract （799）

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Save Magnesium (Mg) alloys are the lightest engineering structure materials widely used in aerospace, transportation and electronic communications, etc. The poor wear resistance and corrosion resistance of Mg alloys restrict directly its wide application. Therefore, it is of great significance to improve the wear resistance and corrosion resistance of Mg alloy. Surface treatment is one of the effective methods to improve the wear resistance and corrosion resistance of Mg alloys. Thereinto, surface nanocrystallization has great potential for development and application due to its two advantages: (1) the microstructures present a gradient change along the thickness direction, no peeling and separation are occurred, no interfaces are considered; (2) traditional surface mechanical treatment or simple improvement can be achieved. At present, surface nanocrystallization of Mg alloys used commonly includes surface mechanical attrition treatment (SMAT), laser shot peening (LSP), ultrasonic shot peening (UST), high energy shot peening (HESP), supersonic particle bombardment, etc.
The basic principles of SMAT, HESP, UST are similar, the only difference is the vibration frequency. According to the vibration frequency from big to small, that is, UST, HESP, SMAT. Mg alloys with different composition after surface treatment obtain nanometer grain size as low as 20 nm. In addition, surface mechanical rolling technology (SMRT) is developed by refitting the SMA equipment. The thickness of nanolayer reaches 100 μm by SMRT. For LSP technology, the thickness of nanolayer is about 20 μm, the nanometer grain size reaches 20 nm. Furthermore, LSP has a better advantage in corrosion resistance due to the low surface roughness. The nanoscale grain of Mg alloys can reach up to 10 nm by supersonic particle bombardment technology. Meanwhile, the thickness of nanolayer is higher than that of LSP.
No matter what surface nanocrystallization technology is used, the surface structure layer of Mg alloys can be divided into four layers from the surface to interior: surface nanocrystallization layer, surface fine grain layer, coarse-grained strain layer and α-Mg matrix. The strain energy is the main factor affecting the nanograin size and nanolayer. Meanwhile, the microhardness of Mg alloys increases obviously after surface nanocrystallization, which can improve the friction and wear properties. The corrosion resistance of Mg alloys is mainly affected by the grain size and the particle size and volume fraction of second phases. The corrosion resistance increases with the grain size refinement in a certain grain size range. Except for the effect of surface roughness of Mg alloys, the corrosion mechanism is not clear in Mg alloys after surface nanocrystallization. In particular, the effect of the nanograin size and the particle size and volume fraction of second phases on the corrosion mechanism of Mg alloys should be further improved and optimized.
This paper reviewed the preparation process and characteristics of the surface nanocrystallization technology (surface mechanical attrition treatment, ultrasonic peening treatment, high-energy shot peening, laser shock processing and high velocity oxygen fuel) of Mg alloys. It mainly introduced the research status of the surface nanocrystallization of Mg alloys. Meanwhile, the influence of surface nanocrystallization on the Microstructure, mechanical properties and corrosion behavior of Mg alloys is analyzed. And the application prospect and existing problems to be solved are discussed.

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Progress in the Application of Molecular Dynamics in Microscopic Plastic Deformation of Magnesium and Its Alloys Article

WANG Yuye, TANG Aitao, PAN Rongjian, PAN Fusheng

Materials Reports 2019,33(19 ):3290 -3297. DOI:10.11896/cldb.18070252

Abstract （898）

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Save As the lightest metal structural materials, magnesium alloy has great application potential due to its high specific strength and specific stiffness. However, magnesium alloy is a hexagonal close packed structure with a limited number of active slip systems so that low ability of plastic deformation at room temperature becomes one of the major reasons limits the wider applications of magnesium alloy. Investigating and understan-ding the microscopic plastic deformation mechanism of magnesium and its alloys can provide further innovation to design alloys and optimize process.
The complex behavior and the mechanism of plastic deformation in magnesium and its alloys result in clarifying the relationships between microstructure, deformation condition and materials properties difficultly only using experimental methods. Since molecular dynamics (MD) is an important method to understand various properties and phenomena of atoms or molecules under microscale, it attracts increasing attention to be applied to study magnesium and its alloys.
It can calculate various thermodynamic and kinetic properties, and simulate atomic motion under specific loading conditions by using MD. Accordingly, recent reports pay more attention to the problems of dislocation and slips, twinning, and grain boundary about the microscopic deformation mechanism of magnesium and its alloys which basic slip system is basal slip, and the potential slip systems are prismatic and pyramidal slips. Generally, MD can be performed to explore the activity of slip systems under tension or compression, especially the slide and dissociation of 〈c+a〉 dislocation. In comparison with face-centered cubic and body-centered cubic metal, the contribution of twinning to plastic deformation is more obvious in magnesium and its alloys because of the less slip systems. There have been studies that discuss the nucleation conditions and the types of twins through setting initial defect, microstructure, solute atoms or other cases to simulate the nucleation and growth of twins. The study of grain boundaries can be related to the mechanism of polycrystalline plastic deformation such as fine grain strengthening and texture. Ho-wever, the size scale that can be achieved by MD methods is still difficult to simulate micron-sized polycrystals so that researchers tended to rea-lize the migration behavior and the interaction with other microstructures of grain boundaries in bi-crystals and nanopolycrystals. Important here is that the reliability of MD depends mainly on the accuracy of the interatomic potentials. In the early days, MD is only used in pure magnesium with the lack of interatomic potentials. And in recent years, with the improvement of interatomic potentials, especially the second nearest neighbor modified embedded-atom method (2NN MEAM), the investigations of magnesium and its alloys are increasing together with the development of interatomic potentials which can be used to describe binary magnesium alloys.
In this paper, the MD theory and method are introduced briefly, and go further to review the MD to study the microscopic plastic deformation mechanism of magnesium and its alloys. It summarized the application of MD in interatomic potentials of magnesium and its alloys, dislocation and slips, twinning, grain boundary, solute atoms and second phases. At the end, it presented several prospects about MD applied to magnesium and its alloys.

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Study on Hot Deformation Behavior and Microstructure Evolution Mechanism of AA7021 Aluminum Alloy Article

QIU Peng, WANG Jiayi, DUAN Xiaoge, LIN Hongtao, CHEN Kang, JIANG Haitao

Materials Reports 2020,34(8 ):8106 -8112. DOI:10.11896/cldb.19030088

Abstract （701）

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Research Progress on Light Alloy-Air Batteries Article

YAO Wanpeng, CAO Fuyong, LI Yan, QI Jiantao

Materials Reports 2020,34(13 ):13058 -13067. DOI:10.11896/cldb.19060032

Abstract （746）

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Save As a new form of energy, metal-air batteries have the advantages of high theoretical energy density, low price, good safety, wide range of temperature and so on. At present, there are four types of metal-air batteries which are popular and widely studied, including zinc-air battery, aluminum-air battery, lithium-air battery and magnesium-air battery.
Light alloy-air batteries use light alloy material with high energy density as anode, air electrode as cathode, alkaline or neutral salt solution as electrolyte, mainly including aluminum-air battery and magnesium-air battery. Aluminum and magnesium with high electrochemical capacity, low cost and abundant reserves are excellent candidate anode materials for metal-air batteries and regarded as a promising alternative to fossil fuels as an energy storage material. However, the performance of metal-air batteries using pure aluminum and pure magnesium is not good as expected at the beginning with enormous study problems. With the development of aluminum alloys and magnesium alloys, the application of light alloys in metal-air batteries greatly reduces the self-corrosion problem of metal anodes, improves the discharge activity of electrode and the overall performance of battery is significantly enhanced. For aluminum-air battery, the corrosion rate of the aluminum alloy electrode decreases due to the doping of Sn, In, Ga, Mg and other elements, while the utilization rate of the anode increases and the passivation film on the electrode surface is destroyed which achieves the activation effect. In the case of magnesium-air battery, Al, Zn, Mn, Li and other alloying elements can improve the corrosion resistance and the discharge capacity of batteries is also improved. The addition of some rare earth elements can refine the grain of light alloys and improve the corrosion and passivation problems of light alloy electrodes.
This paper introduces the basic principles of metal-air batteries, describes the performance of two types of light alloy-air batteries, analyzes the main problems existing in metal-air batteries and briefly introduces the solutions. This paper mainly focuses on the alloying mode of the anode of the battery and the performance of various light alloys in the batteries. The corrosion reasons and control measures in light alloy-air batteries are summarized and prospected.

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A Review on Deep Cryogenic Treatment of Aluminium Alloy Article

LIU Xuanzhi,GU Kaixuan,WENG Zeju,WANG Kaikai,CUI Chen,GUO Jia,WANG Junjie

Materials Reports 2020,34(3 ):3172 -3177. DOI:10.11896/cldb.19040288

Abstract （1172）

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Intergranular Corrosion Behavior of the Friction-stir-welded Joint of 7N01S-T5 Aluminum Alloy Plate Article

FANG Zhenbang, ZHANG Zhiqiang, LI Ying, YIN Hua, XING Yanshuang, HE Changshu

Materials Reports 2019,33(2 ):304 -308. DOI:10.11896/cldb.201902019

Abstract （610）

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Mechanical Behavior and Numerical Simulation of 7005 Aluminum
Alloy Under Dynamic Impact Article

XU Congchang, YE Tuo, TANG Ming, GUO Pengcheng, TANG Xu, WU Yuanzhi, LI Luoxing

Materials Reports 2019,33(4 ):670 -673. DOI:10.11896/cldb.201904020

Abstract （600）

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Effect of Multi-scale Microstructures on the Hydrophobicity of Aluminum Alloy Surface Article

WAN Yanling, ZHANG Meng, YANG Jian, YU Huadong

Materials Reports 2019,33(16 ):2715 -2719. DOI:10.11896/cldb.18070134

Abstract （583）

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