Crystal Structure of 3S-hydroxy-7 Melleine

A new compound, 3S-hydroxy-7 melleine was isolated from the endophytic fungus Xylariasp No.2508 from the mangrove tree on the South China Sea coast. It was the first time that this kind of compound was isolated from marine fungus. The structure was elucidated by NMR data, infrared spectrum （IR） and mass spectrometry （MS）. In addition, its structure was determined by the single-crystal X-ray diffraction analysis. It crystallized in monoclinic, space group P21 with a=10.8884（19） A, b=7.2284（13） A, c=13.398（2） A,β=104.217（3）°, C10H10O4·H2O, Mr=212.20, V=1022.2（3） A^3, Z=4, Dc=1.379 mg/m^3, F（000）=448, μ=0.112 mm^-1, the final R=0.0498, wR=0.101 for 2407 observed reflections （I〉2σ（I））. The molecular backbone of the compound includes a benzopyran ring. By comparing with the melting point and the optical rotation of the known 3R-hydroxy-7 melleine in literature, the absolute configuration of the compound was determined as 3S. It didn＇t exhibit antibacterial activity against Gram-positive bacterium Staphylococcus aureus at 200 μg/disk in the preliminary test.

Residual-stress relaxation mechanism and model description of 5052H32 Al alloy spun ellipsoidal heads during annealing treatment

Marginal-restraint mandrel-free spinning is an advanced technology for manufacturing ellipsoidal heads with large diameter-thickness ratios.Nevertheless,the spinning-induced residual stress,which greatly influences the in-service performance of spun heads,should be removed.In this study,the effects of annealing on the residual-stress relaxation behavior of 5052H32 aluminum alloy spun heads were investigated.It is found that the residual stress first rapidly decreases and then remains steady with the increase in annealing time at the tested annealing temperatures.The relaxation of the residual stress becomes increasingly obvious with the increase in annealing temperature.When the annealing temperature is less than 220℃,there are no obvious changes in grain size.Moreover,the spinning-induced dislocations are consumed by the static recovery behavior,which decreases the residual stress during annealing.When the annealing temperature is approximately 300℃,the broken grains transform into equiaxed grains.In addition,static recrystallization and recovery behaviors occur simultaneously to promote the relaxation of the residual stress.Considering the different stress relaxation mechanisms,a model based on the Zener-Wert-Avrami equation was established to predict the residual-stress relaxation behavior.Finally,the optimized annealing temperature and time were approximately 300C and 30 min,respectively.

A strategy to control microstructures of a Ni-based superalloy during hot forging based on particle swarm optimization algorithm

In this study, a strategy based on the particle swarm optimization (PSO) algorithm is developed to control the microstructures of a Ni-based superalloy during hot forging. This strategy is composed of three parts, namely, material models, optimality criterions, and a PSO algo rithm. The material models are utilized to predict microstructure information, such as recrystallization volume fraction and average grain size. The optimality crite? non can be determined by the designed target microstructures and random errors. The developed strategy is resolved using the PSO algorithm, which is an intelligent optimal algorithm. This algorithm does not need a derivable objective function, which renders it suitable for dealing with the complex hot forging process of alloy components. The optimal processing parameters (deformation temperature and strain rate) are obtained by the developed strategy and validated by the hot forging experiments. Uniform and fine target microstructures can be obtained using the optimized processing parameters, which indicates that the developed strategy is effective for controlling the microstructural evolution during the hot forging of the studied superalloy.

Cu/Li Ratio on the Microstructure Evolution and Corrosion Behaviors of Al–xCu–yLi–Mg Alloys

The microstructure evolution and the corrosion feature of Al–x Cu– y Li–Mg alloys( x : y = 0.44, 1.65 and 4.2) were systematically investigated under the same artificial aging conditions. The relationships between types of precipitates and mechanical performance, as well as electrochemical behaviors, were discussed. Our results show that different types of precipitates can be obtained in alloys with different Cu/Li mass ratios, which significantly influences the mechanical performance of the alloys and substantial corrosion behaviors. Specifically, the analogous corrosion evolution in the aging Al– x Cu– y Li–Mg alloys was first ascertained to be derived from the growth mechanism of the precipitates at the grain boundary(GB). Moreover, a small number of GB precipitates can be obtained in the aged alloy with the lowest Cu/Li mass ratio, thereby resulting in the largest intergranular corrosion resistance. A higher proportion of the GB T1 phase in the continuous precipitates induces higher corrosion sensitivity in alloy with a high Cu/Li mass ratio.

Marginal-restraint mandrel-free spinning process for thin-walled ellipsoidal heads

Metal sheet spinning is an advanced near-net forming technology for the manufacture of thin-walled ellipsoidal heads.The exact control of dimensional accuracy,however,is a considerable problem for spinning thinwalled parts with large diameter-to-thickness ratios.In this work,a marginal restraint mandrel-free spinning process with two passes is proposed for the fabrication of thinwalled ellipsoidal heads without wrinkling.A finite element model is established and verified to study the influences of spinning parameters on the dimensional precision of thin-walled ellipsoidal heads.It is found that the spinning parameters considerably influence the deviations of wall thickness and contour characteristics.A small forming angle or small roller fillet radius during the first pass spining,as well as the small angle between passes or high feed ratio during the second pass spinning,can improve the wall thickness precision.Meanwhile,as the forming angle or feed ratio is increased during the first pass spinning,the contour precision initially increases and then decreases.During the second pass spinning,the contour precision can be improved at a small angle between passes,whereas it deteriorates at a larger roller installation angle.The optimized spinning parameters are obtained and verified by experiments.

Effects of spinning parameters on microstructures of ellipsoidal heads during marginal-restraint mandrel-free spinning

Marginal-restraint mandrel-free spinning is an advanced technology for manufacturing ellipsoidal heads with large diameter-thickness ratios.The effects of spinning parameters on the forming accuracy of ellipsoidal heads have been studied,and optimized spinning parameters have been obtained.The microstructure evolution of a workpiece is usually very complicated in the spinning process.In this work,the influence of spinning parameters on the microstructures of two-pass spun ellipsoidal heads is studied.It is found that the forming angle and feed rate of the first pass,angle between passes,and feed rate of the second pass significantly affect the microstructures.Meanwhile,the evolution rule of the microstructures near the inner and outer surfaces of the spun parts is almost consistent.A large forming angle,large angle between passes,or large feed rate of the second pass are beneficial to obtain uniform microstructures.A small or large feed rate of the first pass reduces the microstructure uniformity.To improve the microstructure uniformity between the inner and outer surfaces,the optimized spinning parameters are determined.