Advanced Materials Research Vols. 652-654

Abstract: Compression properties, microstructure evolution and deformation behaviors of cast and extruded AZ31 alloys are investigated. The results show that compressive yield stress, ultimate strength and ultimate compression ratio between extruded and cast AZ31 alloy are quite different. The yielding pattern of as-cast AZ31 alloy is continuous, and the yield pattern of extruded AZ31 alloy demonstrate an obvious yielding plateau mode. The angle between the fractures and specimens axis of as-cast and extruded AZ31 alloy is about 45°. A mass of reliefs and damage can be found on the specimen surface of as-cast AZ31 alloy and the twinning is main deformation sign in as-cast AZ31 alloy as seen a rough surface. The slip activity might be a predominant deformation mechanism in extruded AZ31 alloy judged by smooth surface after fracture.

Abstract: Serrated flow has been observed in AZ81 alloy during tensile deformation. The observed static strain ageing effect and negative strain rate sensitivity suggest that the serrated flow is due to interaction between dislocations and solute atoms, know as dynamic strain ageing (DSA). The Portevin-Le Chatelier effect is observed at temperatures between 150oC~200oC and 125oC~200oC. In the microstructure of deformed samples dislocations and twins is observed. It is suggested that the occurrence of the dynamic strain aging is associated with interactions between solute atoms and dislocations.

Abstract: Improving the extrusion die wear condition was significant to increase the products dimensional accuracy and die life time. In this paper, the hot extrusion process of spur-gear shaft is analyzed by finite element method, and the die wear distributions of different blank shapes and die structures are calculated using the modified Archard model considering the effect of die temperature. According to the results, using the preformed blank shape and floating die could reduce the die wear obviously.

Abstract: Horizontal V – shaped anvil forging method is introduced to control fibrous tissue flow direction through changing shape of anvil, to improve the anisotropy of mechanical properties of forgings. This method can provide effectively drawing out technology for heavy axial forgings with requirements on the transverse mechanical properties. In this paper pilot production for rectangular billet by the forging method with horizontal V - shaped anvil were carried out. The results show that the forging method with horizontal V-shape anvil can improve transverse mechanical properties, realize uniform forging for heavy axial forgings, the ratio between transverse and longitudinal mechanical property is about 1.0 in the same position for heavy axial forgings, and uniformity degree of mechanical properties is better.

Abstract: Front end bending often occurs in the heavy plate mills and roughing stands, which reduce productivity efficiency and the quality of the plates considerably. The effect of temperature difference between top and bottom surfaces of slab and reduction ratio on front end bending was investigated by 3D FEM and the mathematical model was induced. The hexahedral mesh was generated by HyperMesh and embed into the DEFORM system. The results show that the temperature difference leads to the asymmetric distribution of equivalent stress, strain and strain rate in the deformation zone. With the increment of temperature difference and reduction ratio the slab head bends more significant. Additionally, the slab front end perhaps bends to higher temperature side in double phase rolling because of resistance of deformation with different phase. Reducing temperature difference, reducing reduction ratio and avoiding double phase rolling is benificial to reduce front end bending in hot slab rolling.

Abstract: In this study a cyclic rotating bending process for microstructure control of metal tubes was newly proposed. The AZ31 magnesium alloy tube was conducted to investigate the effect of the rotating bending process on the microstructure and mechanical properties of metal tubes. The rotating bending process was carried out with rotation speed of 20r/min for 10min at the temperature of 150, 200, 250, 300 and 350°C. The rotating bending processes carried out with various conditions show that the grains in cross-section and longitudinal section of magnesium alloy tube were refined for all samples by the rotating bending process with rotation speed of 20r/min for different rotation numbers and temperatures. The rotating bending temperature shows a various effects on the mechanical properties. When the temperature was 200°C, the highest strength as well as ductility was obtained.

Abstract: Glass molding press is an efficient and promising process for glass lens manufacturing. Molding temperature and velocity are crucial factors for pressing, and the annealing rate directly influences the residual stress and volume change of the final lens. The research contributes to studying the key factors that influence the quality of the molded lens. In the paper, by incorporating stress relaxation and structural relaxation of the viscoelastic material, numerical simulation is undertaken to determine the proper process parameters. Furthermore, the whole process of a spherical lens molding is simulated to predict the final residual stress and volume change, also the influence of different annealing rates is estimated.

Abstract: This paper is focus on two-Pass Deep Drawing Forming of conical axisymmetric parts, study on the finite element simulation and test of multi-Pass deep drawing part. It carry on the finite element analysis and calculation using the ANSYS/LS-DYNA software platform, analyzing the simulation results such as stress , strain distribution and formability by post-processing LSPOST software. It was done multi-Pass deep drawing test using a set of combined type mould. Based on the multi-Pass forming test by using a set of combined type mould, comparison of simulation and test data can be obtained through the forming limit diagram. The result of simulation and test is basically the same and both reflect the formability.

Abstract: Multi-stage deep drawing process for rectangular cups with extreme aspect ratio using finite element analysis is performed. The process is mainly consists of four forming stages including blanking, drawing, ironing and trimming. However, main deformation of the rectangular cup is completed during the drawing-ironing procedure. Tool design and blank modification for the multi-stage deep drawing process are presented. To consider the deep drawing and the ironing operations, the multi-stage deep drawing process is applied to obtain the rectangular cup by using each numerical simulation models from first to fifth drawing. Based on the design results of the initial blank, the multi-stage deep drawing process is performed, but it is shown that severe earing phenomenon is occurred at the upper flange part. To solve the severe deformation at the upper flange due to normal anisotropy of the used sheet material, initial blank modification is carried out. The simulation results for the rectangular cup are compared with the final configuration before and after the modification of the blank shape. The predicted result is confirmed that the modified blank shape not only improve the quality of a deep-drawn product but also reduce the cost of production.

Abstract: Hot compression test for AZ3l magnesium alloy at deformation temperatures of 523-723K and strain rates of 0.01-10s-1 were carried out using Gleeble-3500 thermo-mechanical simulator. The experimental results show that the flow stress and microstructure vary apparently with deformation process parameters. Microstructure observations show that dynamic recrystallisation (DRX) takes place during the deformation. The characteristic with the dynamic recrystallization change with the process parameters.