关键词： 激光自熔焊   微观组织   力学性能   激光功率   AZ31镁合金  

摘要： 采用对接激光自熔焊方法焊接4 mm厚的AZ31镁合金,通过微观组织分析和力学性能测试研究了激光自熔焊工艺参数对镁合金激光焊接头焊缝成形、组织以及力学性能的影响。试验结果表明:采用试验范围内的工艺参数,可以获得焊缝成形良好、无明显焊接缺陷的接头。焊接速度从3 m/min增大到3.9 m/min,焊缝尺寸和接头抗拉强度变化较小。随着激光功率从2.4 kW增加到3.0 kW,接头抗拉强度逐渐减小。焊缝组织为晶粒均匀分布的等轴晶,其晶粒呈六角形,焊缝区硬度明显低于母材。当激光功率为2.4 kW、焊接速度为3 m/min时接头抗拉强度最高,为193 MPa。

关键词： 镁合金   微弧氧化   配方均匀试验   电解液   微观组织   耐蚀性  

摘要： 目的研究电解液中各电解质不同浓度配比下微弧氧化膜层的制备、微观结构及耐蚀性能,以确定最优配方。方法基于配方均匀试验方法,在硅酸盐系电解液中对AM60B镁合金进行微弧氧化处理。引入微弧氧化反应的可行性和微弧氧化膜层的成膜性两个试验指标,分别评判本研究中某电解液配方是否具有实际应用价值,以及评价在某个电解液配方下所制得膜层的合格程度。利用涡流测厚仪、扫描电镜(SEM)、X射线衍射(XRD)、电子探针(EPMA)、硝酸点滴实验以及电化学实验等方法,分别表征膜层的厚度、微观结构、物相组成、元素成分及耐蚀性能。结果当电解液中NaOH的质量浓度小于10 g/L时,方能获得表观完整且色泽均匀的微弧氧化膜层。当NaOH和KF的浓度配比接近,且两者之和约为Na_(2)SiO_(3)所占配比时,即Na_(2)SiO_(3)为19.24 g/L、NaOH为8.80 g/L、KF为11.96 g/L时,膜层中孔径的尺寸小,缺陷少,致密度最高,此时膜层的耐蚀性最好,与基体相比,该膜层的硝酸点滴耐蚀性提高了39倍,电化学耐蚀性提高了3个数量级。膜层主要由MgO、Mg_(2)SiO_(4)及少量的MgF_(2)、MgAl_(2)O_(4)组成,但含量有差别。结论实验设计方法的选择是保证本研究结果有效性的核心和关键。电解液中NaOH的浓度高低是决定某电解液配方是否具有实用价值的首要因素。只有Na_(2)SiO_(3)、NaOH和KF三者间具备适当的配比时,才能降低膜层中的微孔尺寸,减少微裂纹,提高其致密度,并能够在膜层中沉积更多的优质物相,这些是增强膜层耐蚀性的前提和保障。

关键词： AZ31镁合金   孪生   织构   高应变速率   变形机制  

摘要： 采用分离式霍普金森压杆(SHPB)测试预孪晶AZ31镁合金板材在应变速率分别约为800、1200和1600 s−1时的动态真应力−真应变曲线。通过自编程软件及电子背散射衍射(EBSD)技术分析预孪晶试样在高应变速率前后微观组织和织构的演变。结果表明:沿横向(TD)预压缩后再沿着轧制方向(RD)复合预压缩可促进AZ31镁合金板材中多孪晶变体及二次拉伸孪晶的激活。对于沿TD方向一次预压缩的试样,其法向(ND)高应变速率下的屈服强度急剧下降,这主要是由于退孪生的启动。然而,对于沿TD+RD复合预压缩试样,由于{1012}−{1012}二次孪晶和大量交叉孪晶变体的形成可以有效抑制退孪生行为,一定程度上提高了AZ31镁合金ND方向的屈服强度,并且拉伸孪晶的形成能够便利于启动更多的滑移系,改善了镁合金板材ND方向的塑形变形行为。

关键词： Magnesium alloy   Doublely-doped LDH film   Vanadate   Cerium   Anticorrosion  

摘要： A doublely-doped layered double hydroxide(LDH)film was produced on an anodized magnesium alloy *** Ce-doped Mg-Al LDH film was prepared by in-situ hydrothermal treatment method,and the intercalation of vanadate was realized by ion-exchange *** structure,morphology and composition of as-prepared LDH film were investigated by X-ray diffractometer,field-emission scanning electronic microscope and energy dispersive *** indicated that a uniform and compact LDH film was formed and the intercalation of Ce^(3+)and vanadate would change the crystal structure of *** results of the potentiodynamic polarization,electrochemical impedance spectra,hydrogen evolution and corrosion weight loss tests showed the Ce^(3+)and vanadate anions significantly improve the impedance of LDH film,and the active double-doped LDH film could effectively protect the magnesium substrate from corrosion.

关键词： 镁合金   表面处理   润湿性   纤维金属层板   层间剪切强度  

摘要： 采用扫描电子显微镜(SEM)、短梁弯曲法对采用不同表面处理镁合金制备的玻璃钢/镁合金复合板(Glass Fiber Reinforced Plastic/Magnesium Laminate,GFRP/Mg)的界面形貌和层间剪切强度进行了观察、测试和分析。结果表明,经磷酸盐处理和高锰酸盐处理后,镁合金的表面自由能分别比仅打磨处理提高了约53.7%和64.6%,其表面润湿性得到了明显改善。但镁合金表面处理对GFRP/Mg复合板的层间剪切强度影响较小,采用三种不同表面处理镁合金制备的GFRP/Mg复合板的层间剪切强度相近。相对地,GFRP/Mg复合板的层间剪切强度受镁合金表面粗糙度的影响更大一点。当镁合金的表面粗糙度为0.92μm时,GFRP/Mg复合板的层间剪切强度比镁合金表面粗糙度为0.23μm时提高了13%左右。GFRP/Mg复合板的层间剪切失效主要以界面粘接破坏为主。

关键词： magnesium   superplastic forming   superplasticity   electron back-scattered diffraction(EBSD)   AZ41 magnesium alloy  

摘要： An AZ41 magnesium alloy in the hot-rolled condition without further thermomechanical processing to modify its microstructure was investigated to establish its suitability for use within a superplastic forming process and to establish optimum forming *** was assessed using elevated temperature tensile testing and hot gas bulging,across a range of strain rates(1×10^(−1)−1×10^(−3)s^(−1))and temperatures(350−450℃).Circle grid analysis with GOM Aramis cameras was used to understand peak strains and material thinning in relation to industrial forming *** forming EBSD and STEM analysis was conducted to understand the mechanisms responsible for the materials formability,with dynamic recrystallization being clearly *** elongation of 520%was achieved at 450℃ and 1×10^(−3)s^(−1);industrially relevant elongation was achieved at 1×10^(−2) s^(−1) at both 450℃(195%)and 400℃(170%).

关键词： AZ80镁合金   显微组织   力学性能   多向锻造   EBSD分析  

摘要： 为了改善铸态AZ80镁合金组织和性能,对均匀化处理的铸态AZ80镁合金进行了多向锻造试验,并采用金相分析、EBSD (电子背散射衍射)分析和拉伸试验等方法,进行了显微组织和力学性能的测试与分析。结果表明:与锻造前相比,多向锻造后的AZ80镁合金的平均晶粒尺寸减小了约76μm、抗拉强度增加了66 MPa、屈服强度增加了79 MPa、断后伸长率增大了6%,断裂方式从脆性断裂转变为韧性断裂,多向锻造后合金内部晶粒为细小的等轴晶。因此,多向锻造显著地改善了AZ80镁合金的内部组织、提高了AZ80镁合金的力学性能。

关键词： 镁合金   热处理   冲击韧性   缺口敏感性  

摘要： 采用冲击实验研究了热处理工艺对Mg-5Y-3Nd-1Gd-0.4Zr镁合金U型缺口和无缺口试样的冲击韧性的影响,同时研究了时效时间对于时效态样品冲击性能缺口敏感性的影响。结果表明:固溶处理后合金的冲击韧性最高,断口形貌具有韧脆混合断裂特征,而时效后合金的冲击韧性迅速降低,断口形貌呈现脆性断裂的特征。这是由于固溶处理后合金的组织为单相组织,晶粒间和晶粒内协调性好,而时效处理后组织中析出大量第二相,在冲击变形过程中这些第二相阻碍位错运动,导致材料强度提高而韧性迅速降低。随着时效时间的延长,合金的室温缺口敏感性几乎不发生变化。当冲击温度提高到200℃时,缺口敏感性相对室温增加,这是由于存在缺口时,冲击过程几乎不发生塑性变形。提高实验温度,有缺口试样的冲击韧性增幅比无缺口试样的冲击韧性增幅要小的多,试样缺口敏感性也会增大。

关键词： AZ80+0.4%Ce镁合金   热处理   减振系数   阻尼性能   抗拉强度  

摘要： 采用了Box-behnken试验设计方法,确定了设计变量的取值范围,完成了目标函数(抗拉强度和减振系数)回归方程分析,系统地研究了固溶和时效制度分别对AZ80+0.4%Ce镁合金阻尼性能的影响。结果表明:时效温度为抗拉强度主效应因素,影响减振系数的主效应因素是时效时间。热处理最佳优化参数为410℃×2.5 h+193℃×17.5 h,对应的响应值:抗拉强度为266.72 MPa,减振系数为0.176。对优化后的热处理方案进行试验验证,合金在最佳热处理参数下的抗拉强度实际达到271.4 MPa,减振系数为0.245。

关键词： Magnesium alloy   Strain rate   Fractograph   Hopkinson bar system   Scanning electron microscope   Material model  

摘要： The performance of a structure depends on its material characteristics under various conditions of loadings, strain rate, and temperature, and therefore, it is necessary to understand these characteristics properly for the safe and reliable design of structures. In this paper, the flow stress behavior of AZ81 magnesium alloy is determined under tensile, compressive, and flexural loads at different strain rates and temperatures. An electromechanical universal testing machine of capacity 250 kN is used to perform quasi-static tests (0.0001-0.1 s(-1)) under tension and compression;and three-point bending (flexure) tests using suitable fixtures at crosshead speeds (1-100 mm/min) for varying span lengths (80-160 mm) and orientations (flat and transverse) at room temperature, 25 degrees C. The thermal and fracture behaviors of the alloy at various temperatures (25 degrees C, 100 degrees C, 150 degrees C, and 200 degrees C) are studied under quasi-static tension (0.001 s(-1)). The heating rate of the tensile specimens is 20 degrees C/min and the soaking time is 15 min. Dynamic tensile (850-1,400 s(-1)) and compressive (1,900-3,300 s(-1)) experiments are conducted using appropriate arrangements of Hopkinson bar systems. The effects of specimen geometry on the flow stress of the alloy are observed under compression. Ductility and toughness are determined to establish the energy dissipation capacity of the alloy. Fractographs of the fractured tensile specimens are studied by scanning electron microscope (SEM). Also, the applicability of the existing Cowper-Symonds and Johnson-Cook models in the aforementioned loading conditions is discussed. (C) 2020 American Society of Civil Engineers.