Morphology, microstructure, and mechanical properties of laser-welded joints in GH909 alloy

Chunming Wang,Yuanzheng Cai,Chongjing Hu,Xiong Zhang,Fei Yan,Xiyuan Hu 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.5

The experimental laser welding of GH909 alloy was conducted in this study. The morphology, microstructure, and mechanical properties of laser-welded joints were analyzed by scanning electron microscopy, energy diffraction spectroscopy, and other techniques. Results revealed that the microstructure of the welded joints mainly consisted of tiny cellular structures, dendritic structures, and equiaxed crystals. Pores appeared in the interdendritic regions because of the insufficient local feeding of molten metal during solidification. Nb segregation in the heat-affected zone caused liquation cracking, whereas C segregation further induced the formation of carbide precipitates along the grain boundaries during the welding thermal cycle. The instability of the keyhole significantly promoted the escape of the metal vapor/plasma from the hole; as a result, porosity defects formed in the weld. The average tensile strength of the test joints was 756 MPa, which is 93.1 % of that of the base metal. The average microhardness of the weld zone (250 HV) was higher than that of the GH909 alloy substrate (208 HV), peaking at 267 HV. Microcracks appeared along the grain boundaries, proving that the grain boundaries were the weakest areas in the joint.

Interaction between laser-induced plasma/vapor and arc plasma during fiber laser-MIG hybrid welding

Jun Wang,Chunming Wang,Xuanxuan Meng,Xiyuan Hu,Yangchun Yu,Shengfu Yu 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.6

Hybrid plasma is an important physical phenomenon in fiber laser-MIG hybrid welding. It greatly affects the stability of the process,the quality of the weld, and the efficiency of energy coupling. In this paper, clear and direct proofs of these characteristics are presented through high-speed video images. Spectroscopic analysis is used to describe the characterization of hybrid plasma. The hybrid plasma forms a curved channel between the welding wire and the keyhole during the fiber laser-MIG hybrid welding process. The curved channel is composed of two parts. The laser-induced plasma/vapor expands due to the combined effect of the laser and the MIG arc, forming an ionization duct, which is one part of the curved channel. The resistance of the duct is smaller than that of other locations because of the rise in electrical conductivity. Consequently, the electrical arc is guided through the duct to the surface of the material, which is the other part of the curved channel. The spectral intensities of metal elements in laser-MIG hybrid welding are much stronger than those in MIGonly welding, whereas the spectral intensities of shielding gas element in laser-MIG hybrid welding are much weaker.

A putative plastidial adenine nucleotide transporter, BRITTLE1-3, plays an essential role in regulating chloroplast development in rice (Oryza sativa L.)

Jia Lyu,Yihua Wang,Linglong Liu,Chunming Wang,Yulong Ren,Cheng Peng,Feng Liu,Yunlong Wang,Mei Niu,Di Wang,Ming Zheng,Kunneng Zhou,Shaolu Zhao,Fuqing Wu,Haiyang Wang,Jianmin Wan 한국식물학회 2017 Journal of Plant Biology Vol.60 No.5

Differentiation from proplastids into chloroplasts isa light- and energy-dependent process. How this process isregulated is still poorly understood at the molecular level. We herein report a new putative plastidial adenine nucleotidetransporter, BRITTLE1-3 (referred to as OsBT1-3), encoded bythe rice (Oryza sativa) White Stripe Leaf 2 (WSL2) gene. Loss of OsBT1-3 function results in defective chloroplastbiogenesis, severely reduced photosynthetic efficiency, andfinally a white stripe leaf phenotype in the first four leaves. The expression levels of genes related to chlorophyllbiosynthesis and photosynthesis are drastically reduced,accompanied with over accumulation of reactive oxygenspecies (ROS) in the wsl2 mutant. OsBT1-3 is targeted tothe chloroplasts and it expresses in almost all tissues inplants, especially in young leaves. OsBT1-3 consists of 419amino acids and exhibits features of all mitochondrialcarrier proteins, including a typical transmembrane-spanningdomain and a highly conserved sequence motif designatedas the ‘mitochondrial energy transfer signatures’. Phylogeneticanalysis shows that OsBT1-3 is a putative plastidialadenine nucleotide transporter and is most closely relatedto ZmBT1-2. Together, these observations suggest that thenew putative adenine nucleotide transporter, OsBT1-3,plays an essential role in regulating chloroplast biogenesisand maintenance of ROS homeostasis during rice seedlingde-etiolation.

Green-revertible Chlorina 1 (grc1) is Required for the Biosynthesis of Chlorophyll and the Early Development of Chloroplasts in Rice

Jieqin Li,Yihua Wang,Juntao Chai,Lihua Wang,Chunming Wang,Wuhua Long,Di Wang,Yunlong Wang,Ming Zheng,Cheng Peng,Mei Niu,Jianmin Wan 한국식물학회 2013 Journal of Plant Biology Vol.56 No.5

The nuclear genes involved in chloroplast developmentand chlorophyll biosynthesis must be investigated tounderstand their functions in plant growth and development. In this study, we isolated and identified a unique leaf-colormutant of rice with a green-yellow phenotype before thefour-leaf stage and named the mutation green-revertiblechlorina 1 (grc1). The mutants had significantly lower plantheight, number of tillers, and panicle length and headedsignificantly earlier than the wild type. The levels ofchlorophylls, carotenoids, and chlorophyll precursors werealso lower. The mutation in grc1 affected chloroplastultrastructure, particularly thylakoid development. Geneticanalysis indicated that the green-yellow phenotype wascontrolled by a single recessive gene. We mapped the grc1gene to a 32.4-kb region on the long arm of chromosome 6. Through map-based cloning, we identified a 45-bp insertionin the genomic region of LOC_Os06g40080, which encodeda heme oxygenase. Expression of LOC_Os06g40080 wassignificantly down-regulated in the grc1 mutant. Subcellularlocalization showed that this heme oxygenase was localizedin the chloroplast. In summary, we isolated and identified thegene for grc1, which plays an important role in chlorophyllbiosynthesis and chloroplast development in rice.

Investigation of melting dynamics of filler wire during wire feed laser welding

Yangchun Yu,Wei Huang,Guozhen Wang,Jun Wang,Xuanxuan Meng,Chunming Wang,Fei Yan,Xiyuan Hu,Shengfu Yu 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.4

In order to investigate the mechanism of stability for the wire feed laser welding process, systematic experiments are carried out in this study for 5A06 aluminum alloy. By using high speed camera, the melting dynamics of filler wires with different feed positions and feed rates are studied. The results indicate that these two factors mainly influence the characteristics of the filler wire melting dynamics and determine the stability of the welding process. The melting dynamics of filler wire can be generally characterized by three different forms: explosion, big droplet and molten metal bridge. When the filler wire melts and transits to the molten pool in the forms of explosion or big droplet, the stability of the welding process is strongly disturbed, resulting in an undesirable weld quality. In contrast, when it is in molten metal bridge form, the welding process is more stable and a uniform weld bead is achieved.

Convolutional Neural Network with Expert Knowledge for Hyperspectral Remote Sensing Imagery Classification

( Chunming Wu ),( Meng Wang ),( Lang Gao ),( Weijing Song ),( Tian Tian ),( Kim-kwang Raymond Choo ) 한국인터넷정보학회 2019 KSII Transactions on Internet and Information Syst Vol.13 No.8

The recent interest in artificial intelligence and machine learning has partly contributed to an interest in the use of such approaches for hyperspectral remote sensing (HRS) imagery classification, as evidenced by the increasing number of deep framework with deep convolutional neural networks (CNN) structures proposed in the literature. In these approaches, the assumption of obtaining high quality deep features by using CNN is not always easy and efficient because of the complex data distribution and the limited sample size. In this paper, conventional handcrafted learning-based multi features based on expert knowledge are introduced as the input of a special designed CNN to improve the pixel description and classification performance of HRS imagery. The introduction of these handcrafted features can reduce the complexity of the original HRS data and reduce the sample requirements by eliminating redundant information and improving the starting point of deep feature training. It also provides some concise and effective features that are not readily available from direct training with CNN. Evaluations using three public HRS datasets demonstrate the utility of our proposed method in HRS classification.

A Novel Multiobjective Optimization Method Based on Improved Artificial Bee Colony Algorithm

Wu Chunming,Li Tingting,Wang Yanjiao 보안공학연구지원센터 2016 International Journal of Signal Processing, Image Vol.9 No.3

In order to improve the convergence and diversity of multiobjective optimization algorithms, the harmonic average distance is employed to improve the aggregating function combined L-rank value. Selection model and searching scheme of artificial bee colony algorithm and diversity maintaining scheme are improved in this paper. This novel many objectives optimization method based on improved artificial bee colony algorithm (ABC) in this paper is compared with other three many objectives optimization methods on 3 to 8 objectives DTLZ. Simulation results show that the proposed algorithm is superior to other algorithms in the diversity and convergence of solutions.

A study of surface quality and mechanical strength in 5083 aluminum alloy plates using pulsed laser cleaning

Ji Lin,Chunming Wang 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.10

In this work, pulsed laser cleaning was conducted on 5083 aluminum alloy plates for removing the oxide film and improving the surface quality. The chroma was innovatively introduced to evaluate the surface quality of cleaned samples. Samples with good cleaning quality were successfully achieved by means of process optimization involving single factor and orthogonal laser cleaning tests. The optimum cleaning parameters for desirable effect consisted mainly of average power of 40 W, scanning speed of 2500 mm/s and repetitive frequency of 85 kHz. On this basis, a well-formed welded joint can be obtained because of the removal of the oxide film on the surface of aluminum alloy. It has been found that the maximum stress and strain of joints subjected to laser cleaning were up to 102.5 % and 114.81 % of joints laser welded in the absence of laser cleaning, respectively. Significant improvement in mechanical strength was mainly attributable to effective suppression of porosities in welds on account of the removal of oxides with the assist of pulsed laser cleaning.

Influence of cleaning modes on the microstructure and performance of 5083 alloy substrate

Yunkai Li,Chunming Wang,Gaoyang Mi 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.9

In this study, the paint layer was removed on the surface of 5083 aluminum alloy using laser cleaning and mechanical grinding. The microstructure and performance of experimental samples were carefully investigated using scanning electron microscope, energy disperse spectroscopy and other methodologies. The results showed that compared with mechanical grinding, laser cleaning can improve the surface paint coating of aluminum alloy more effectively. The surface of the matrix formed uniformly distributed volcanic craters and small holes emerged at the spot junction after laser cleaning. The carbon and oxygen content on the substrate surface after laser cleaning was much lower than that after mechanical grinding. In addition, the corrosion resistance and coating adhesion of the substrate were obviously improved using laser cleaning. It was closely associated with refinement of the grains and reduction in surface roughness. We concluded that laser cleaning can be widely used to replace mechanical grinding in manufacturing on the premise of meeting industrial needs.

Porosity in fiber laser formation of 5A06 aluminum alloy

Yangchun Yu,Chunming Wang,Xiyuan Hu,Jun Wang,Shengfu Yu 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.5

The mechanism of porosity formation and its suppression methods in laser formation of aluminum alloy have been studied using a 4kW fiber laser to weld 5A06 aluminum alloy with SAl-Mg5 filler. It was found that the porosity formation is closely related to the stability of the keyhole and fluctuation of the molten pool in the laser welding aluminum alloy. The filling wire increased the instability of the keyhole and weld pool, thus further increasing the amount of gas cavities in the joint. Prefabrication of a suitable gap for the butt joint can provide a natural passage for the flow of the liquid metal, which can weaken, and even completely eliminate the disturbance of the filling wire on the formation of keyhole. The gap can also provide a passage for the escape of the bubble. Thus, this method can greatly decrease the sheet’s susceptibility to porosity. Moreover, for a thin sheet, if the power of the laser is sufficient to form a keyhole with stable penetration through the weld sheet, a weld bead without porosity can also be obtained because closing the keyhole is almost impossible.