关键词： AZ61镁合金   热变形   本构模型   Zener-Hollomon参数   动态再结晶  

摘要： 利用Gleeble-3500热模拟试验机,对均匀化退火处理后的铸态AZ61镁合金进行了等温热压缩变形实验,研究了合金在变形温度为220℃~380℃、应变速率为0.001 s^(-1)~10 s^(-1)条件下的热变形行为和组织演变特征,并基于双曲正弦模型建立了合金的本构模型。研究了Zener-Hollomon参数对热压缩变形组织演变的影响规律,揭示了高Z值、中等Z值和低Z值对应参数条件下的变形合金呈现不同的组织形貌特征,并阐明了随Z参数的逐渐减小,变形组织逐渐由失稳组织、不完全动态再结晶组织转变为粗化的完全动态再结晶组织,确定了合理的热成形工艺参数区间对应的lnZ数值范围为22.17~29.25。

关键词： 镁锂合金   复合挤压   涂层   制备   成型  

摘要： 镁锂合金作为目前最轻的金属结构材料之一,表现出优异的成形性能,具有比强度高和良好的阻尼特性等优点。因此其在工业方面的潜在应用价值引起了学术界和技术领域的关注。本案例涉及一种新的复合挤压制备Mg-Li/Al复合材料的方法。该方法具有以下几种优点:操作简单、节约能源、尺寸可控性好、一次成型即可获得较好的结合强度。挤压棒材表面涂层厚度均匀,硬度保持较高水平。通过压缩实验对复合材料棒、铸态合金以及常规挤压态合金进行了对比。实验表明:室温下,涂层包覆的Mg-Li合金挤压棒压缩强度约为335MPa,比铸态合金高32%,比常规挤压棒材高11%。

关键词： 镁合金   微弧氧化   水滑石   疏水性   耐蚀性  

摘要： 目的通过在微弧氧化膜上原位生长水滑石膜,提高镁合金的耐蚀性。方法首先分别在硅酸盐、磷酸盐和铝酸盐为主的电解液体系中制备镁合金微弧氧化膜。然后采用水热处理技术,通过加入硝酸铝与硝酸锌的混合溶液,制备微弧氧化/水滑石复合膜层。采用扫描电镜、X射线衍射仪、接触角仪和电化学腐蚀试验,分别研究了微弧氧化及复合膜层的显微形貌、物相组成、疏水性和耐蚀性。结果XRD表明,在不同的微弧氧化膜上均可原位生成水滑石膜。铝酸盐体系中制备的水滑石膜厚且致密,硅酸盐和磷酸盐体系中生成的水滑石数量少,不能完全封闭微孔及裂纹。在硅酸盐体系中于400 V和430 V条件下制备的复合膜层,接触角分别为74.3°和130.3°。磷酸盐和铝酸盐中制备的复合膜层的接触角低,无疏水性。硅酸盐中于430 V条件下制备的复合膜层,阻抗模值达到2×10^(7)Ω×cm^(2),耐蚀性提高10倍左右。结论原位生长水滑石膜可以封闭微孔,硅酸盐和铝酸盐体系中制备的复合膜层的耐蚀性提高,磷酸盐体系中制备的复合膜层的耐蚀性下降。微弧氧化的成膜电压对水滑石生长无显著影响。

关键词： 铝镁合金线   超强超细   增强技术  

摘要： 针对铝镁合金线在向超强超导超细微方向发展中出现的合金线丝强度降低、线间发粘、电阻率增大以及在拉拔过程中出现"裂、断、漏"等问题,采取晶粒细化剂石墨烯纳米化增强铝镁合金线材料的技术手段,调节合成方法提高合金材料超强超导能力,为开发出高强韧性能的铝镁合金线提供参考和借鉴。

关键词： AZ80镁合金   流动应力   本构模型   Zerilli-Armstrong模型  

摘要： 合理的本构模型是实现精确模拟镁合金挤压过程的关键,基于均匀化态AZ80镁合金在应变速率0.001~1 s^(-1)、变形温度523~673 K下的热压缩实验数据,建立了改进的Z-A模型来描述AZ80镁合金的热变形行为,并在此基础上,通过考虑应变对材料参数的影响,提出优化的Z-A模型。对两种模型预测精度进行定量分析表明:优化的Z-A模型对流动应力的预测效果较好,相关系数R和平均绝对相对误差E_(AR)的计算值分别为0.9962和3.60%;改进的Z-A模型的预测结果相对较差,其R值和EAR值分别为0.94和8%。比较分析表明,优化的Z-A模型具有良好的适应性,可以在整个应变范围内(0~0.9)很好地预测不同变形条件下的流动应力,因而工程适用范围广;改进的Z-A模型不能描述加工硬化-动态回复阶段的流动应力,因而预测精度较低。

关键词： AZ31 magnesium alloy   Extrusion   Shearing   Tube   Finite element method   Microstructure   Experiment and simulation   Grain refinement  

摘要： This paper presents a new forming technology for manufacturing the AZ31 magnesium alloy thin-wall tube. The direct extrusion process and continuous shearing-bending process are combined to produce thin-wall magnesium tube, abbreviated as "TESB" (tube extrusion-shearing-bending). The process has been studied based on the combination of experiments and numerical simulations, and the influences of temperatures, extrusion stresses, and friction factors on the forming process have been studied by Deform-3D simulation. And the mechanical properties and the grain size of the formed product have been tested. TESB technology has been proved to refine the grains of magnesium alloy tube effectively, and the mechanical property of the product can be improved. The better experimental extrusion conditions were also obtained by simulation, and the properties of the products under the condition of lubrication were better when the temperature was 400 degrees C. Three-dimensional finite element modeling is used to investigate the plastic deformation behaviors of wrought magnesium alloy during TESB process. Numerical results indicate TES could increase the cumulative strains effectively by direct extrusion and additional shearings. Experiments show that microstructures of magnesium alloy fabricated by TESB process can be refined to 50% of the original grain size with more uniform distribution. TES process could improve hardness of magnesium alloy obviously by comparing with which fabricated by direct extrusion.

关键词： Friction stir spot welding   X-ray radiography   Interface structure   Microstructure   Magnesium alloy  

摘要： The flat friction stir spot welding using double side adjustable tools (Flat DSAT FSSW) was successfully applied to the joining of magnesium alloys in our previous research. In this study, the in-situ X-ray radiography observations using a high-intensity X-ray transmission device were carried out to investigate the interface development. In addition, the microstructure evolution at different welding stages was also studied. The mechanical properties of the welded joints were significantly affected by the minimum plate thickness of the joint, which was the distance from the tip of the unwelded interface to the bottom of the lower plate. The welding interface was well welded during the stage of the holding of probes, and the minimum plate thickness was eventually determined by the stage of raising the lower probe, which is the key stage affecting the joint properties. The in-situ X-ray radiography technique shows a significant advantage to reveal the welding process. In the tip area of the unwelded interface at low rotation speed welding condition, the grain growth was suppressed due to the limited heat generation, giving rise to refined microstructure. Moreover, a randomized texture was obtained owing to the weak material flow during the welding process and the introduced mechanical twins during the stage of raising the lower probe. The refined microstructure resulting from limited heat generation and randomized texture resulting from weak material flow contributed to the high strength welded joint.

关键词： AZ91D mg alloy substrate   cold-sprayed al coating   corrosion resistance   friction stir-spot-processing   intermetallic compounds   microhardness  

摘要： Magnesium-based alloys are appropriate materials for transportation applications owing to their high strength-to-weight ratio. However, the poor corrosion performance of Mg alloy limits its lifetime. In this study, the pure Al coating was deposited onto an AZ91D substrate by cold spraying, and then modified by friction stir-spot-processing. The interfacial microstructure and phase were studied in detail, and the effect of the intermetallic compounds on the microhardness and corrosion properties of the coatings was investigated. Results show that the sound and dense coatings were obtained after friction stir-spot-processing at 2400 and 2700 rpm. Al12Mg17 was found in the upper part of the 1/2 radius zone in the processed coating. The thin and thick IMCs were identified at the interface in the center and 1/2 radius areas, respectively. In the thick IMCs, mainly two types of multi-phase coexistence structures were observed. The four-phase coexistence structure dominated by Al3Mg2 revealed a higher microhardness than the three-phase coexistence structure dominated by Al12Mg17. In the processed coating, the upper part of the 1/2 radius zone containing Al12Mg17 exhibited a higher microhardness than the center zone. Moreover, the cold-sprayed Al coating provided more effective corrosion protection for the AZ91D substrate after FSSP.

关键词： Microstructure   Mechanical and corrosion properties   AZ91 magnesium alloy   New severe plastic deformation method   Hydrostatic cyclic expansion extrusion  

摘要： This research investigates the microstructural evolution, mechanical properties, and corrosion behavior of AZ91 magnesium alloy after the process of hydrostatic cyclic expansion extrusion (HCEE) at elevated temperature. The HCEE process is able to produce long length ultrafine-grained rods by applying high hydrostatic pressure. The results showed that ultrafine-grained microstructure appears after the consecutive passes of the process, which led to the higher hardness and strength with an increased elongation to failure in the processed rods at room temperature. The ultimate tensile strength and elongation to failure of the processed rod after two cycles of the HCEE increased more than 2 and 2.6 times, respectively. Moreover, an increase in hardness was more than 100% after the second cycle of the process and its distribution was more uniform. Furthermore, the ultrafine-grained microstructure after the HCEE resulted in the movement of potentiodynamic polarization derived curves to higher values of corrosion potential (E-corr) and lower current density (I-corr), which shows the capability of the HCEE process in improving the corrosion resistance of AZ91 magnesium alloy rods. These increases in corrosion resistance were further indicated by the Nyquist diagram derived from the electrochemical impedance spectroscopy scanning and evolved hydrogen amount after 208 h of immersion in 3.5% NaCl solution. The novel HCEE process shows further its capability in producing long length ultrafine-grained rods with superior mechanical and corrosion properties rather than other severe plastic deformation techniques.

关键词： composite coating   corrosion resistance   hydrothermal reaction   magnesium alloy   superhydrophobic  

摘要： A superhydrophobic ceria-based composite coating is developed to improve anticorrosion properties of AZ61 magnesium alloy, fabricating via chemical conversion method followed by hydrothermal treatment. The cerium conversion coating has a block structure with microcracks. After the hydrothermal treatment, a dense CeO2 layer, porous CeO2 nanorods, and stearic absorbing layers are grown stepwise on the conversion coating. And the composite coating is hydrophobic or even superhydrophobic and has almost no microcracks. As the hydrothermal reaction time increases, the water contact angle of the composite coating first increases and then decreases, and it reaches the maximum value of 152 degrees after hydrothermal treatment for 4 h. Both the dense CeO2 layer and the superhydrophobic stearic absorbing layer can effectively prevent the electrolyte from contacting the substrate;the corrosion current density of the superhydrophobic composite coating is lower than that of the hydrophilic composite coating and the cerium conversion coating, and has the best corrosion resistance.