焊接工艺对SMA490BW耐候钢接头腐蚀行为的影响

目的 研究转向架焊接构架用SMA490BW耐候钢及其在不同焊接工艺条件下制得的焊接接头在模拟工业大气环境下的腐蚀行为。方法 采用周浸腐蚀试验方法,利用扫描电镜（SEM）、X射线衍射（XRD）和能谱（EDS）等方法,研究了腐蚀产物的表面形貌、锈层结构及相组成。结果 在模拟工业大气环境条件下,SMA490BW耐候钢母材、自动MAG焊接头、手工MAG焊接头的腐蚀失重率呈先增后减的变化规律,其中自动MAG焊接头腐蚀失重率最小,手工MAG焊接头腐蚀失重率最大,而SMA490BW耐候钢母材居于两者之间。耐候钢母材及其焊接接头腐蚀产物的相组成均为γ-FeOOH、α-FeOOH、Fe2O3和Fe3O4。经过150 h腐蚀后,耐候钢母材及其焊接接头腐蚀产物中Cr、Ni、Cu合金元素含量有所差异,其中自动MAG焊焊缝腐蚀产物中Cr、Ni、Cu合金元素含量最高,分别为1.79%、0.23%、0.17%。Cr、Ni、Cu合金元素将直接对耐候钢母材及其焊接接头耐腐蚀性产生影响。结论 与手工MAG焊接头相比,自动MAG焊接头耐蚀性较高的主要原因是焊缝中主要抑制锈层腐蚀的Cr、Ni、Cu合金元素含量较高。     

镁合金蜂窝板隔声性能分析

采用AZ31镁合金板材、AZ31镁合金蜂窝芯、铝合金蜂窝芯制备了镁合金蜂窝板和镁-铝蜂窝板,并测定具有不同结构参数的蜂窝板的隔声性能。预期高隔声镁合金蜂窝板应用于交通运输装备上,将可提高地板或壁板的减振降噪能力,极大改善乘坐的舒适性,提高能源效率。     

Measurement of the mass transfer coefficient at workpiece surfaces in heat treatment furnaces

The mass (e.g. carbon) transfer coefficient at a workpiece surface is an important kinetic factor to control the heat treatment process of the workpiece and to evaluate heat treatment equipment. The coefficient can be calculated from the carbon concentration at the surface of a sample carburized in a carburizing furnace for a given time. Two common measurement methods which use a thin plate and employ a component as samples respectively are evaluated and compared for sensitivity and uncertainty. The comparison shows that the use of a component produces higher measurement precision and also has the advantage in measuring the carbon transfer coefficients at different treated positions. This method is then extended and discussed methodologically. Also two equations are proposed to calculate the carbon transfer coefficient and its uncertainty, respectively. This method is also applied to measure the carbon transfer coefficient in a fluidized bed heat treatment furnace.     

Piezoelectric and mechanical properties of CaO reinforced porous PZT ceramics with one-dimensional pore channels

The formation of capillaries in sodium alginate gels is a dissipative process driven by unidirectional diffusion of divalent cations into sodium alginate sols. In the present work, we have prepared 3-1 type porous lead zirconate titanate (PZT) ceramics with oxides (CaO) being doped on a molecular level from the dissipative process by incorporating PZT particles into the sodium alginate gel matrix. By varying the concentration of cation solutions (CaCl₂) from 0.5 mol/L to 2.5 mol/L, both the microstructure, doping amount of oxides (CaO) and crystalline phase of the porous PZT ceramics were tailored. Accordingly, increase in the concentration of Ca²⁺ has led to a reduction in the relative permittivity (ε_r) first, and then an increase, while the piezoelectric coefficient (d₃₃ and d₃₁) demonstrated an opposite variation tendency. The prepared samples possessed a maximal HFOM value of 4755×10^–15 Pa⁻¹ when the concentration of Ca²⁺ was 1.0 mol/L. Addition of CaO was found to improve the compressive strength of porous PZT ceramics, which was preferential to promoting the stability and reliability for application.     

网格不敏感结构应力的焊接疲劳数据分布

为分析网格不敏感结构应力的焊接疲劳S-N数据分布具有高收敛性的机理,基于钛合金焊接接头疲劳试验数据,分别基于名义应力、主S-N曲线法中的结构应力及等效结构应力建立焊接疲劳数据坐标,并以最小二乘法拟合S-N曲线,应用粗糙集分析方法,以接头类型、相对板厚、载荷比、应力比等焊接疲劳主要影响因素作为条件属性,以疲劳数据对于S-N曲线的偏离度作为决策属性,对基于三种应力的焊接疲劳数据分布规律对比分析.结果表明,基于网格不敏感等效结构应力所建立的S-N数据分布更为集中和均匀,在预测焊接接头疲劳寿命方面具有更高的准确性.     

MIG焊叠加对6A01-T5铝合金FSW焊接头组织及性能的影响

研究了MIG焊叠加对6A01-T5铝合金FSW焊接头组织及性能的影响. 结果表明, MIG/FSW叠加焊缝熔合良好，叠加位置未出现气孔等缺陷，FSW焊核区及热影响区组织发生粗化，叠加位置附近微观组织出现明显改变；叠加区域硬度明显降低，尤其是FSW焊缝热力影响区和热影响区. FSW、中心叠加、前进侧热力影响区叠加和后退侧热力影响区叠加MIG焊接头的抗拉强度分别为219.8, 188.0, 195.4和191.4 MPa，MIG焊叠加降低了接头的抗拉强度，断口均表现韧性断裂特征；FSW焊接头及带有MIG叠加焊缝余高的三种接头中值疲劳强度分别为76.7, 65.0, 67.5和65.0 MPa，MIG焊叠加也使FSW接头的疲劳性能有所下降.     

Formation of linearly linked Fe clusters on Si(111)-7?×?7-C2H5OH surface

The Fe atoms were deposited on the Si(111)-7 × 7 surface, which has been saturated with the C₂H₅OH molecules. Then, the Fe clusters were formed on Si(111)-7 × 7-C₂H₅OH surface and in situ observed by the scanning tunneling microscopy (STM). The STM images showed that with the increase of Fe clusters, the size of clusters was about 5 nm and they self-assembled in straightly linked chain crossing the step to lower or upper terrace. X-ray photoelectron spectroscopy (XPS) was in situ carried out on the surface of Fe/Si(111)-7 × 7-C₂H₅OH samples before and after the introduction of thin air (4.5 × 10^-2 Langmuir) into the STM chamber. The XPS results showed that the Fe clusters are stable in the abovementioned thin air condition at room temperature. Based on the STM and XPS results, the driving force making one-dimensional straightly linked chain structure might be the magnetic force of the Fe clusters. The formation of straightly linked Fe clusters chains suggests the formation of single magnetic domain Fe clusters.

PACS

07.79.Cz, 81.15.-z, 75.75.Fk     

排气阀壳体铸造工艺的数值模拟优化

为消除排气阀壳体的渗漏缺陷,利用ZCAST数值模拟软件对原铸造工艺方案进行模拟,发现产生渗漏的区域属于后凝固的区域。对封闭式和开放式两种新设计浇注系统模拟后,发现开放式浇注系统充型平稳、液面上升稳定,解决了铸件打压渗漏问题,通过采用铬矿砂砂芯解决了局部出现夹砂的问题。     

Research on saggars of lightweight design used to prepare cathode materials for Li-ion batteries

The focus of lightweight refractory is equivalent volume replacement that uses lower-density raw materials to replace the original high-density raw materials. In this study, we employ porous mullite microspheres (PMM) to replace mullite particles to realize the weight-lighting of mullite–cordierite saggars used to prepare cathode materials for Li-ion batteries.To confirm that lightweight saggars satisfy the quality standards of production, we conducted various tests, including mechanical properties, thermal shock stability and corrosion resistance. Compared with samples with mullite particles, samples with PMM have a comparatively stable material structure and excellent performance. Furthermore, PMM reduce mullite consumption and enhance their resistance to prevent stress shedding in the corrosion process.