焊接速度对自适应双轴肩搅拌摩擦焊接Al–Mg合金接头微观组织和机械性能的影响

The butt welds of 4-mm thick 5A06 aluminum alloy plates were produced by adjustable-gap bobbin-tool friction stir travel with travel speeds of 200, 300, and 400 mm/min in this study. The microstructure was studied using optical microscopy and electron backscatter diffraction (EBSD). Tensile tests and microhardness measurements were performed to identify the effect of the travel speed on the joint mechanical properties. Sound joints were obtained at 200 mm/min while voids were present at different positions of the joints as the travel speed increased. The EBSD results show that the grain size, high angle grain boundaries, and density of geometrically necessary dislocations in different regions of the joint vary depending on the recovery and recrystallization behavior. Specific attention was given to the relationship between the local microstructure and mechanical properties. Microhardness measurements show that the average hardness of the stir zone (SZ) was greater than that of the base material, which was only affected slightly by the travel speed. The tensile strength of the joint decreased with increasing travel speed and the maximal strength efficiency reached 99%.     

Review of the fatigue behavior of hard coating–ductile substrate systems

With the wide application of coating materials in aerospace and other fields, their safety under fatigue conditions in service is important.However, research on the fatigue properties of ceramic hard coatings started late, and a unified standard is yet to be established to evaluate the fatigue life of hard coating–ductile substrate systems.Studies also present different opinions on whether coatings can improve or reduce the fatigue life of substrates.In this paper, the influence of the properties of ceramic coatings on fatigue performance is reviewed, and the effects of coating on the mechanism of fatigue crack initiation in substrates are discussed, aiming to help readers understand the fatigue behavior of hard coating–ductile substrate systems.     

Effect of superplastic deformation on precipitation behavior of sigma phase in 3207 duplex stainless steel

Owing to excellent strength, toughness and corrosion resistance, duplex stainless steels(DSS) are widely used in constructional and petrochemical applications. Sigma phase, which has detrimental impact on the properties, is readily precipitated during hot working of DSS. However, precipitation behavior of sigma phase during superplastic deformation, which is the most significant processing method of DSS, is still unclear. In the current study,the effect of superplastic deformation on the precipitation behavior of sigma phase was investigated in 3207 duplex stainless steel. The result shows that superplastic deformation could prevent sigma phase precipitation generally by increasing mobility of grain boundaries and decreasing misorientation of the sigma phase boundaries, resulting in some sigma phase precipitated on the twin boundaries. Most of the sigma phase precipitated on ferrite-austenite interface with misorientation of 20–25°, while it precipitated in ferrite or austenite with the misorientation of 40°–45°. The orientation relationship between sigma phase and matrix matched well in austenite and on the ferrite/austenite interfaces, while it showed a small misfit in ferrite. The prevention effect of the superplastic deformation on the sigma phase precipitation was beneficial to quasi stable deformation stage,resulting in longer elongation.     

VHD真空精炼炉电极伺服控制系统静、动态特性的测试及辨识

本文根据对某钢厂引进电炉的电极伺服控制系统的静、动态特性的测试,辨识出具有死区非线性阀控缸系统的数学模型。该测试和辨识方法对同类电炉伺服控制系统具有一定的参考价值。     

关于模N的原根及其整除性的推广

设整数ｎ≥３存在原根，对给定的正整数１＜ｋ＜ｎ且（ｋ，ｎ）＝１，本文证明了如下的结论：对任意０＜ｘ≤１，０＜ｙ≤１，当ｎ充分大时一定存在模ｎ的两个原根ｒ及ｓ，ｒ≤ｘｎ，ｓ≤ｙｎ使得ｒｓ≡１（ｍｏｄｎ）ｋ｜ｋｒ＋ｓ。     

模糊优化法在滚削加工中的应用

文章采用了模糊优化设计方法对滚削加工中的加工变量进行了优化，同时又对滚削加工变量进行普通优化设计和非优化设计，将三者结果加以比较，从而得出模糊优化是目前优化设计中一种较为理想的方法。     

轧制时接触表面微观形体模型的优化

本文利用刚性微凸体和塑性微凸体的相互作用模型模拟轧制过程中轧辊与轧件的相互作用,根据塑性力学的上界原理,并借助于滑移线原理,优化处理了接触表面微观体形的模型,揭示了微凸体几何形状以及接触面连接强度对摩擦系数的影响。     

低压静电对活性污泥絮体物理特性的影响

本研究采用静电处理技术以改善活性污泥絮体的物理特性，以提高活性污泥的沉降性和脱水性。结果表明静电场对污泥颗粒的电位有明显的降低作用；随着静电场电流的增加，污泥颗粒的电位降低，电流１００ｍＡ为稳定转化点。当电流为１００ｍＡ时，生物絮体的物理特性最佳，这些结果对活性污泥法处理系统的改善有重要意义。     

国防价值工程应用环境的系统分析

本文阐述了国防价值工程应用环境的概念，系统地分析了国防领域推广应用价值工程的有利和不利因素，进而给出了应用国防价值工程应具备的基础条件。     

Sol－Gel法制备SrO－SiO_2玻璃的研究

本文用Ｓｏｌ－Ｇｅｌ（溶胶－凝胶）法制备了ＳｒＯ－ＳｉＯ２玻璃，初步探讨了在液－液不混溶区合成的最佳实验条件，研究了不同组成溶胶的胶凝时间、老化温度以及热分解条件．并通过热重分析、差热分析及红外光谱等测试手段对于凝胶及玻璃的性能进行了考察．