Applied Mechanics and Materials Vols. 217-219

Abstract: Heat treatment was carried out to the 1420 Al-Li alloy electron beam welding (EBW) joints after welding, and the microstructures of welded joints are analyzed systematically before and after post-weld heat treatment (PWHT). The observation of joint microstructure demonstrates that the grain morphology of weldment changes from equiaxed dendrites in as-welded (AW) condition into equiaxed grains after PWHT, and that the fine strengthening phases precipitate within the grain. The XRD analysis of phase constituent and TEM observation of weldment indicate that the main strengthening phases in 1420 Al-Li alloy weldment are spheroidal δ′(Al₃Li), β′(Al₃Zr) and rod-like T(Al₂MgLi) after PWHT. Furthermore, the δ′ phase precipitate free zone (PFZ) is found along the grain boundary. The scanning observation of joint fracture shows that Al-Li alloy EBW joint presents the characteristic of transgranular ductile fracture in AW condition. After PWHT, the Al-Li alloy welded joint presents the pattern of intergranular fracture. The variation of fracture mode is related to dispersed precipitation of δ′ phase and the formation of PFZ at the grain boundary in weldment after heat treatment.

Abstract: The process of twin-roll casting including pouring, solidifying, rolling and cooling can be accomplished in a very short time. Consequently, some important process parameters in the twin-roll casting that are difficult to be obtained in experiment can be acquired using numerical simulation. In this paper, a numerical simulation based on a 2D finite element model of vertical twin-roll strip casting of magnesium alloy has been conducted, and the thermal stress fields are significantly discussed. The influences of key process parameters consisting of submerged nozzle depth and nozzle spray angle have been studied. The thermal cracks on the surface of the strip are analysed according to the thermal stress distribution.

Abstract: This paper analyzed the structure of the thin walled brass cylinder, calculated the deformation degree and extrusion ratio, and designed the multistage cold extrusion process. According to the cold extrusion process, the multistage extrusion mold structure and transfer device were designed. Compared with the stamping process, multistage cold extrusion process has high material utilization, high efficiency, small investment in equipment and other advantages of high strength, high precision and small surface roughness in parts production.

Abstract: In this study, SEM and Köhlhoff etching were employed to follow the rolling texture and microstructure development in 93/7 brass that had been homogeneously cold rolled to different plastic strains. Correlated with FEM to rolling process, the effect of strain field on rolling texture and microstructure development in rolled 93/7 brass is conducted and reasonable conclusion is obtained.

Abstract: In the paper a inner-outer couple cooling technology of molten steel for 1240×200mm slab continuous casting, that is to set an inner cooler-U shape pipes in the mold, is put forward in order to enhance the efficiency of transmitting heat and improve the flow status of molten steel. The flow status of molten steel in inner-outer couple cooling mold is simulated by using fluid dynamics software. It is found that setting inner cooler in the mold can make molten steel flow status even, which partly act as electromagnetic trig and is favorable to inclusion in molten steel floating up.

Abstract: In the paper, the new machining process which was named non-abrasive cryogenic polishing will be introduced. The model of non-abrasive cryogenic polishing was set up. The dynamic simulation was analyzed by using Recurdyn. And the physical model was accomplished. By analyzing mass experiments, the ice tool material, metal material, rotate speed, polishing time and other parameters were found.

Abstract: At the entrance temperature of 300°C, the effect of mill temperature on the texture and microstructure evolution was worked to 85/15 α-brass by two rollings with mill temperatures calibrated as 28°C for one rolling and 55°C for another, in which TEM was employed to reveal the microstructures, and ODF to represent the related textures. From the experiment evidence, a detailed discussion was made and led to a conclusion: in current rolling, with recovery, mill temperature influences the rolling texture and microstructure development through chilling and the working temperature induced deformation mechanisms change, the former one affecting B intensities, by contrast, the latter one leading to a texture transition.

Abstract: Welding is the main means of the connection of tank, is also an important factor in determining tank quality. Applied Ansys software, finite element modeling, Choosed a reasonable heat source model to analyze the temperature distribution and variation of the weld, obtained the weld thermal stress distribution of the quantitative laws, it provides a good help to improve the security of the pressure vessel.

Abstract: The forming and springback of sail surface during the multi-point forming under force-displacement separated control (MPF-FD) was studied. Numerical simulation method was adopted to study the springback of sail surfaces with different radius, sheet thicknesses and forming forces. The results show that the springbacks on two directions influence each other. The springback on the bigger radius direction is on the leading role, and will influence that on the smaller direction. On the direction of the bigger radius, the springback is decreased with the increase of sheet thickness, forming force and decrease of the radius. On the direction of the smaller radius, the springback is decreased with the decrease of the sheet thickness and the increase of the forming force, and the radius has a small impact on springback.

Abstract: In allusion to the complex images of weld defects, weak contrast between the target and the background, a new segmentation method based on gray level difference transition region extraction is proposed. The paper analyzes the characteristic of weld defects, and then low-pass filtering and contrast enhanced are used to enhance the clarity. Finally, we extract the transition region and confirm a threshold for defects segmentation. The experimental results show that the method can extract the transition region more accurate, and segment the image much better in complex environment.