关键词： AZ31镁合金   铸造   夹杂   Al-Mn相  

摘要： 以AZ31铸态镁合金铸锭检测时发现的严重夹杂为研究对象,采用金相显微镜、扫描电镜等手段对夹杂物的形貌和分布进行了分析,使用能谱定量分析确定了夹杂物主要为Al-Mn相及铝锌碳氧化物。通过改进铸造工艺实现了夹杂物的防止,并对夹杂物成因进行分析讨论,提出了通过熔炼工艺和铸造工艺改善熔体质量的解决方案。

关键词： Ce   镁合金   ZnAlCe-LDHs   耐腐蚀性能   机理  

摘要： 利用一步水热法在AZ91D镁合金表面原位制备ZnAl-LDHs薄膜和ZnAlCe-LDHs薄膜,借助X射线衍射仪、扫描电镜、能谱仪和电化学阻抗谱等表征手段,研究Ce对镁合金表面ZnAlCe-LDHs薄膜形貌结构、化学组成及耐腐蚀性能的影响。结果表明,Ce离子加入不改变镁合金表面LDHs鸟巢网状形貌,但增加了薄膜的厚度以及纳米片的尺寸。EIS结果表明,ZnAlCe-LDHs薄膜与ZnAl-LDHs薄膜相比,自腐蚀电位正移0.05 V,腐蚀电流密度降低1~2个数量级,阻抗图中容抗弧半径明显增大,说明加入Ce离子可以增强镁合金的耐腐蚀性能。

关键词： AZ91 alloy   TIG   Heat input   Microstructure   Mechanical properties  

摘要： In the present study, the effect of heat input of gas tungsten arc welding on the microstructure and mechanical properties of AZ91 magnesium alloy was investigated. The microstructural studies were performed by using an optical microscope and scanning electron microscope equipped with energy dispersive X-ray spectroscopy, and tensile test was used to evaluate the mechanical properties. It was shown that, comparing to the base metal, a fine microstructure of alpha(Mg) and Mg17Al12 phase is formed in the weld metal and the size of alpha(Mg) phase slightly increased with heat input during welding process. The results also indicated that the thickness of partially melted zone increased with heat input. Tensile strength of welded samples was lower than that of the base metal and it decreases with increasing heat input. Failure of the welded specimens accrues in the partially melted zone. Studying of fracture surface revealed that the interface of alpha(Mg) and Mg17Al12 compound acts as crack initiation and growth path during the tensile test. Formation of cleavage steps in the fracture surface was the dominant fracture mechanism during tensile tests.

关键词： Magnesium alloy (AZ31B)   Finite element analysis   Damage mechanics   Orthogonal cutting   Cryogenic  

摘要： Magnesium alloys are biocompatible materials that are not only used in biomedical implants but also in many engineering load-bearing applications due to their high strength to density ratio. However, machining of these alloys is somehow challenging, for example, magnesium alloy (AZ31B) is prone to ignition risk at relatively low temperatures during various machining processes. This ignition risk can be avoided by performing machining under cryogenic conditions. In the present research work, 2D finite element-based analysis of orthogonal cutting process of magnesium alloy (AZ31B) is performed considering both cryogenic and dry machining environments. Finite element simulations are performed by varying the cutting speed and uncut chip thickness. A widely employed, damage-based Johnson-Cook flow stress model is exploited to perform coupled thermo-mechanical cutting simulations. Cutting forces and temperatures are the major output parameters of interest in the work. The resultant cutting forces predicted by FE analysis for cutting speed of 100 m/min and for uncut chip thickness of 0.1 mm vary by 19% and 16% for cryogenic and dry machining conditions, respectively, when compared with available experimental results from literature, whereas, in the workpiece body, temperature variations of 14% and 2% have been found for cryogenic and dry machining conditions, respectively. Promising results of numerical model may help to further investigate and optimize the process.

关键词： Mn   Morphology evolution   Atomic utilization ratio   Dilute Mg-Gd alloy   Hall-Petch constant  

摘要： The evolution of microstructure and mechanical properties of the dilute Mg-Gd alloy with Mn modification were investigated systematically in this paper. The results show that the combination of Mn and different processing states could adjust the solid solubility of Gd in the Mg matrix, thereby changing the morphology of the second phases and improving the properties of the alloy. With the addition of 0.8 wt% Mn into the Mg-4Gd alloy, the atomic utilization ratio of Gd atoms decreases from 61.5 to 51.8% during the water-cooling casting process, but it increases from 73.8 to 81.0% during homogenization treatment and increases from 72.3 to 84.1% during hot extrusion. Thus, the mean diameter of granular phases of the Mg-4Gd alloy is larger than that of Mg-4Gd-0.8Mn alloy after the isothermal heat treatment. The Mn addition has little effect on the Hall-Petch constant K(Y)and K(H)of Mg-4Gd alloy, but improves the sigma(0)value significantly due to the increase of the atomic utilization ratio of Gd atoms. Mn element can improve the mechanical properties of Mg-4Gd alloy, and the increase of yield strength and ductility of as-extruded Mg-4Gd-0.8Mn alloy is mainly attributed to grain refinement and the decrease of the texture intensity. Graphic The solid solubility of Gd in Mg matrix can be regulated by the combination of Mn and different processing states, thereby changing the morphology of the second phases and improving the properties of the alloy.

关键词： animal model   biocomposite   ex vivo   osteoporosis   polyelectrolyte   substituted hydroxyapatite  

摘要： Bone fractures/defects are normal in more established individuals experiencing osteoporosis. In this work, we have explored osteoblast bond, multiplication, and separation on biocomposites of bioactive dual minerals substituted hydroxyapatite/alginate-chitosan/graphene oxide porous biocomposites coated magnesium alloy (AZ91 Mg alloy). Hydroxyapatite is one the most important mineral constituents for bony which, due to its bioactive and histocompatible properties, is commonly used as a material for hard tissue substitution. However, the use of apatite as hard tissue implants is restricted due to its fragile nature and reduced mechanical properties. To overcome this defect and to generate suitable bone implant material, dual minerals substituted hydroxyapatite (DM-HAP) is combined with biodegradable polymer alginate-chitosan (ALG-CS). Graphene oxide (GO) is integrated into the biocomposite, which has long been believed for soft and hard tissue implants owing to its excellent structural and mechanical properties, to enhance the mechanical properties of the biocomposite. Graphene oxide grounds are most important for the reconstruction of bone;new, outstanding DM-HAP/ALG-CS/GO scaffold on Mg alloy has been developed. As developed coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX). Besides, the mechanical strength of the coating has also been assessed using adhesion and Vickers micro-hardness tests. In furtherer, the antibacterial activity of the composite was studied against Staphylococcus aureus and Escherichia coli and cell viability were observed in vitro against osteoblast cells and in vivo in rats. As a result, the results obtained propose that DM-HAP/ALG-CS/GO biocomposite can be believed as a prospective applicant for biomedical applications.

关键词： Incremental forming   Magnesium alloys   Numerical simulation   Fracture forming limit  

摘要： Magnesium alloys, because of their good specific material strength, can be considered attractive by different industry fields, as the aerospace and the automotive one. However, their use is limited by the poor formability at room temperature. In this research, a numerical approach is proposed in order to determine an analytical expression of material formability in hot incremental forming processes. The numerical model was developed using the commercial software ABAQUS/Explicit. The Johnson-Cook material model was used, and the model was validated through experimental measurements carried out using the ARAMIS system. Different geometries were considered with temperature varying in a range of 25-400 degrees C and wall angle in a range of 35-60 degrees. An analytical expression of the fracture forming limit, as a function of temperature, was established and finally tested with a different geometry in order to assess the validity.

关键词： Magnesium alloy   Four-point bending   AZ31B   Digital image correlation  

摘要： The mechanical response of magnesium alloy AZ31B is addressed thanks to four-point bending tests. These alloys are known to have an asymmetrical behavior in tension-compression. The bending test is, therefore, a good candidate to analyze this effect because it combines the two solicitations. Digital image correlation is used to measure the evolution of the strain fields during the test. Measurements of the shift of the neutral line (zero strain) of the specimen are then presented for samples taken in the rolling direction and the transverse direction. It is shown that the shift of this line is initially towards the side in tension and then shifts back toward the center of the sample. Due to this reversal of the sliding direction of the neutral line, some physical points of the tested specimen are subjected alternatively to compression and tension. Measurements show that these alternations are confined to the elastic domain. (c) 2021 Elsevier Ltd. All rights reserved.

关键词： AZ31 magnesium alloy   Spinning   Nanoindentation   Plastic deformation   Nanomechanical property  

摘要： The nanomechanical properties of an AZ31 magnesium alloy processed through spinning was systematically characterized with nanoindentation experiments using a Berkvoich indenter. The plastic deformation behavior of magnesium alloy was revealed by quantitatively studying microstructure evolution through spinning. Indentation depth, elastic recovery rate, yield strength, and hardening exponent were evaluated at the maximum loads. It was found that the grains observed by optical microscope were gradually refined. The nanoindentation plots revealed that the nanomechanical properties improved with the increase of spinning passes. Additionally, the calculated yield strength and hardening exponent of the cylinders were in the range of 42.0 +/- 0.5-125.5 +/- 0.6 MPa and 0.182-0.017 respectively with the increase of spinning passes. In summary, it was possible to evaluate the elastoplastic behavior of AZ31 magnesium alloy after spinning using the results of the nanoindentation tests.

关键词： Composite coatings   Filter cathodic vacuum arc   Magnesium alloy   Al?AlN   Bias voltage  

摘要： Al?AlN composite coatings were prepared using filtered cathodic vacuum arc deposition on AZ31 magnesium alloy substrates. With increasing substrate bias, AlN phase content increased and Al phase content decreased, resulting in increased hardness of the coatings. Transmission electron microscopy morphology of the composite coatings at 100 V bias showed that the metallic Al phase was embedded in the AlN matrix. The coatings significantly enhanced the corrosion resistance of the AZ31 magnesium alloy. The maximum hardness was 512 HV obtained at a bias of 300 V and a minimum corrosion current density was 1.913 ? 10-6 A/cm2 attained at a bias of 100 V. The effect of substrate bias on microstructure, coating thickness, and residual stress in the coatings was studied in details.