Improving weld formability by a novel dual-rotation bobbin tool friction stir welding

A novel dual-rotation bobbin tool friction stir welding (DBT-FSW) was developed, in which the upper shoulder (US) and lower shoulder (LS) have different rotational speeds. This process was tried to weld 3.2 mm thick aluminum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formability. Experimental results show that compared to conventional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process.     

海洋工程和船舶焊接变形预测方法研究

目前,影响海洋工程和船舶焊接结构质量的重要影响因素之一就是焊接变形,其产生的根本原因就是在焊接过程中因结构体受热不均、热梯度、残余应力等。基于此,本文对焊接变形预测的理论发展进程及其相关理论内涵进行详细阐述,并对基于神经网络的新型焊接变形预测理论的研究发展简单概述。     

钛合金激光清洗及其对激光焊接气孔的影响

采用砂纸打磨、酸洗、激光清洗等方式对Ti6Al4V钛合金进行焊前清洗。通过扫描电镜、白光干涉仪、能谱仪分析了各种清洗方式下的表面形貌、粗糙度和化学成分，研究了不同清洗方式及参数对清洗效果的影响。在均匀熔透和表面质量良好的同一激光焊接条件下，比较了不同清洗条件对气孔率的影响。合适的激光清洗可有效清除焊接试件表面氧化层，并改善表面粗糙度，得到较低的气孔率，其焊缝可达到中国航天工业行业标准I级焊缝要求。     

矿用直线振动筛结构故障分析

针对煤矿选煤厂直线振动筛工作过程中出现的结构故障问题,采用有限元仿真与现场测试结合的方法对振动筛出现故障的原因进行了分析研究。介绍了振动筛的主要结构及常见故障,并以某矿选煤厂发生大梁断裂的振动筛为例,对该振动筛进行三维建模和有限元模态分析,分析结果表明:随着模态阶次的增加,振型的变化逐渐由移动转为结构本身的扭曲变形。在该振动筛空载工作状态下,选用本质安全型便携式测振记录仪进行振动测试并处理测试信号,得到该振动筛的工作频率。结合模态分析结果和实际测试结果,判断出空载时频繁运行振动筛是造成其大梁断裂的主要原因。根据故障原因给出维护建议:应当尽量避免振动筛在空载或物料较少的状态下长时间运行;在振动筛投入使用前,应预先了解振动筛的工作状态及可能存在的薄弱环节,尽可能避免结构故障,保证振动筛可靠运行。     

煤与高岭石表面性质对凝聚过程的影响机制

煤泥水中含大量高岭石等黏土矿物，为其絮凝沉降带来较大的困难。为明确矿物性质对凝聚过程的影响机制，在应用扩展的DLVO理论计算煤和高岭石颗粒间作用力的基础上，采用聚焦光束反射测量仪监测了CaCl2用量为4.50 mmol/L时20 g/L的煤和高岭石的悬浮液在60, 100和150 r/min的搅拌转速下的凝聚过程。结果表明，颗粒间的静电作用力在颗粒表面间距2?200 nm范围内起主导作用，高岭石的电负性较大，在凝聚过程中更难发生靠近和碰撞；较高的转速可为颗粒提供较大的动量，有利于提高碰撞频率，缩短完成凝聚所需时间，实验条件下，煤和高岭石的凝聚时间分别由74和123 s缩短至47和89 s。疏水性作用力在颗粒表面间距小于2 nm的范围内起主导作用，决定了颗粒的黏附效率；煤因强疏水性，在碰撞后更易黏附，且能抵抗更高的流体剪切作用，可由19.32 μm凝聚形成100 μm的大凝聚体，而高岭石则因其亲水性难以得到较大粒度的凝聚体，均小于30 μm。     

Enhancing nugget size and weldable current range of ultra-high-strength steel using multi-pulse resistance spot welding

ABSTRACT

This paper presents an innovative approach that uses a pulse-profile to improve the welding quality of CP1180 steel in resistance spot welding process. Three pulses with two cooling times were used in the developed multi-pulse welding (MPW) schedule. The experimental results show that the first pulse increases the contact area between the sheets to improve the current flow pattern. The second pulse was designed to extend the sheet-to-sheet contact area and corona bond for preventing rapid nugget growth. Using these designs, the nugget size was maximised through the third pulse. The maximum nugget size using the designed MPW schedule was 18.5% greater than that of the single-pulse welding schedule and the weldable current range was extended by 130%.     

Development of a fast atom beam gun for surface-activated bonding

Surface-activated bonding (SAB), also called room-temperature bonding, is used in three-dimensional integration technology for semiconductor devices. An Ar fast atom beam (FAB) is used for SAB. However, conventional FAB guns must be replaced after hundreds of minutes of irradiation because carbon abrasion powders are generated by Ar ions sputtering in the gun. Therefore, this study develops a novel FAB gun with improved lifetime. The proposed FAB gun applies magnetic fields to guide Ar ions to reduce sputtering in the gun and improve irradiation efficiency. The proposed FAB gun indicates the possibility of improving gun lifetime.     

《电子显微分析》课程教学内容及方法研究

《电子显微分析》课程是目前高校材料类和生命科学类专业一门重要的专业选修课。根据《电子显微分析》课程特点，剖析了该课程的教学现状以及存在的问题。针对这些问题，在教学内容的设定、教学方式的调整及实践性教学的考核等方面做了一些思考。