汽车总装线上远程激光焊接能量评估

通过分析激光源的类型和结构,建立参数数据库,并结合机器人运动的动力学分析,本研究提出了汽车总装线上远程激光焊接(RLW)的能量评估模型。通过对简单焊件进行焊接实验,将传统激光焊接和远程激光焊接进行了对比,结果发现,焊接过程中机器人运动能量逐渐减少,而激光能量逐渐增加。处理时间和激光功率是影响远程焊接能源效率的主要因素。     

船用铝-钢复合过渡接头焊接试验研究

通过模拟焊后热处理试验,分析了界面温度与界面结合强度的关系,并以此为基础进行了船用铝-钢复合过渡接头焊接工艺试验。试验结果表明,铝-钢复合过渡接头焊后的组织和性能均能满足相关标准和产品技术协议的指标要求。     

Allotropic transformation induced stacking faults and discontinuous coarsening in a γ-γ′ Co-base alloy

The stability of a Co-based alloy designed to possess a microstructure comprising of L1₂, γ′ Co₃Ti-type precipitates embedded in an A1, γ Co solid solution matrix has been investigated. The alloy showed acute microstructural instabilities upon ageing at 700 °C, resulting in the degeneration of the γ-γ′ aggregate into i) a faulted Co-based martensite and Co₃Ti and ii) a lamellar aggregate of A3-Co and Co₃Ti. The faulted Co-based phase was formed by isothermal diffusionless transformation of the metastable A1-phase, whilst the lamellar aggregate was a discontinuous reaction product.     

Preparation,characterization and properties of polycaprolactone diol-functionalized multi-walled carbon nanotube/thermoplastic polyurethane composite

Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized to prepare thermoplastic polyurethane (PU) composites with enhanced properties. In order to achieve a high compatibility of functionalized MWCNTs with the PU matrix, polycaprolactone diol (PCL), as one of PU’s monomers, was selectively grafted on the surface of MWCNTs (MWCNT–PCL), while carboxylic acid groups functionalized MWCNTs (MWCNT–COOH) and raw MWCNTs served as control. Both MWCNT–COOH and MWCNT–PCL improved the dispersion of MWCNTs in the PU matrix and interfacial bonding between them at 1 wt% loading fraction. The MWCNT–PCL/PU composite showed the greatest extent of improvement, where the tensile strength and modulus were 51.2% and 33.5% higher than those of pure PU respectively, without sacrificing the elongation at break. The considerable improvement in both mechanical properties and thermal stability of MWCNT–PCL/PU composite should result from the homogeneous dispersion of MWCNT–PCL in the PU matrix and strong interfacial bonding between them.     

Synthesis and characterization of MgAl2O4 micro-rods by a molten salt method

Large amounts of MgAl₂O₄ micro-rods were successfully synthesized using the molten-salt technology. The effect of KCl contents on the formation of MgAl₂O₄ micro-rods was investigated. The structure and morphology of MgAl₂O₄ were investigated by means of powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy, respectively. The experimental results showed that the contents of KCl significantly influenced the formation of MgAl₂O₄ micro-rods. MgAl₂O₄ micro-rods could be prepared at 1150 °C with a weight ratio of 100:1 between the salt and the starting materials. The formation of MgAl₂O₄ micro-rods could be suggested to be due to the inhomogeneous nucleation and orientated growth perpendicularly to the surfaces of Al₂O₃ grains. An impedance-type humidity sensor was finally fabricated based on the as-prepared MgAl₂O₄ micro-rods. According to tests of the humidity performance, MgAl₂O₄ micro-rods might be suitable for high-performance humidity sensors.     

Fatigue analysis of multipass welded joints considering residual stresses

Gas metal arc welding (GMAW) is one of the most used joining method in the industry. However, one of the main problems of this process is the generation of residual stresses (RS). There are different approaches to predict the fatigue life of welded joints, but in general, these approaches do not consider the real value of RS. Therefore, the current approaches to estimate fatigue life of welded components are conservatives.This paper describes an alternative method to asses high cycle fatigue (HCF) life prediction based on numerically estimated RS values. Results have shown good correspondence for the HCF range, with a maximum average error of 15% in stress for the studied configurations. The proposed method can be used as a valid tool to optimise the geometry of the component and thus decrease the economic cost.     

Alloying behavior and novel properties of CoCrFeNiMn high-entropy alloy fabricated by mechanical alloying and spark plasma sintering

An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process.     

Effects of molecular modifications for water splitting enhancement of BiVO4

Combined organic (molecular adsorption) and inorganic (TiO₂ passivation) modifications for enhancing water splitting efficiency of porous bismuth vanadate electrodes are tested. The catalytic activity of BiVO₄ is increased after adsorption of a newly prepared ruthenium catalyst. TiO₂ passivation and sensitization with RuP dye does not show straightforward improvements to the complex photocatalytic behaviour depending on the configuration of the (two- or three-electrode) photoelectrochemical cell, type of the experiment and sample aging. The time constant for electron transport in BiVO₄ electrodes (in the range of seconds, revealed by electrochemical impedance measurements) was found to correlate with the stable photocurrent of the cells. The femtosecond transient absorption studies confirm the negligible effects of RuP on the population of the photoexcited carriers in BiVO₄. The transient absorption studies also show that the processes responsible for the differences in photocurrents of the modified BiVO₄ samples occur on a time scale longer than the first nanoseconds.     

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.