Search

In this work, a novel five-step cold extrusion forging technology was proposed for fabricating a shaped charge liner with hyperboloid structure feature, in which three steps forming to develop the macroscopic hyperboloid shape and two steps annealing treatments to improve the microstructure and property of the liner. Besides, the preforming process was the focus of this investigation because the size structure, microstructure, and texture of the preform play a crucial role in the manufacture of the final forming process due to the heredity of dimension and microstructure, which also provides powerful process reference with the following forming steps. Based on the ABAQUS finite element (FE) platform, the cold extrusion process of the shaped charge liner preform was simulated, and the influences of forming parameters such as the initial billet size and friction coefficient between billet and dies on forming load, cavity filling, and strain distribution of the preform were investigated, respectively. The simulation results show that the optimal parameters of initial billet diameter and friction coefficient between dies and billet in cold extrusion preforming of shaped charge liner are 50 mm and 0.1, respectively. Additionally, the strain distribution of the shaped charge liner in the cold forming process was analyzed in detail. Finally, the experiment of the cold extrusion of the shaped charge liner preform was carried out to verify the feasibility of the cold extrusion process and the correctness of the simulation results. [ABSTRACT FROM AUTHOR]

Multidirectional forging (MDF) of Mg-Gd-Y-Nd-Zr alloy was performed under decreasing temperature condition. The grain refinement, microstructure and mechanical properties homogeneity of Mg-Gd-Y-Nd-Zr alloy during MDF process were investigated. The results show that the grain refinement mechanism of Mg-Gd-Y-Nd-Zr alloy during MDF process was dynamic recrystallization. The dynamic precipitations were observed after MDF process, which were mainly located at the grain boundaries and had a significant influence on the grain refinement, and the amount of dynamic precipitations increased as the MDF passes increase. The microstructure of the billet was not homogeneous due to the deformation and temperature inhomogeneity during MDF process. Optimization MDF process has been proposed, which benefited the microstructure homogeneity and reduced the amount of the dynamic precipitations. Based on the optimization MDF process, the elongation to fracture significantly increased. [ABSTRACT FROM AUTHOR]

Near-net shaping of Mg-RE alloy matrix composites has received increasing attention. In this work, stir casting followed by extrusion was adopted to fabricate Mg-RE alloy (WE43) matrix composites reinforced by micron-sized SiC particles. The microstructural evolutions of SiC/WE43 composites partially remelted from as-cast and extruded states were studied. Furthermore, the thixoformability of SiC/WE43 composites in different states was evaluated by thixoextruding a type of double-cup component. The microstructures of as-cast SiC/WE43 composites were optimized under the comprehensive effects of SiC particles and RE elements. The SiC/WE43 composite was fully recrystallized during hot extrusion, and the α-Mg matrix consisted of fine equiaxed grains. Although the as-cast SiC/WE43 composite consisted of satisfactory structures and can be successfully thixoextruded into the final component with good surface quality and no evidence of internal defects, the microstructures, Vickers hardness, tensile mechanical properties, and wear resistance were still inferior to those of the component thixoextruded from extruded composite. Moreover, the thixoextrusion process was analyzed schematically, and an ideal thixoforming process that should contain two stages was proposed. [ABSTRACT FROM AUTHOR]

The tribological properties of combinative addition of nano-MoS and nano-SiO to the base oil have been investigated with a reciprocating ball-on-plate tribotester for magnesium alloy-steel contacts. The results demonstrate that the optimum mass ratio of nano-SiO to nano-MoS is 0.25:0.75. The optimum combinative addition into the base oil reduces the friction coefficient by 43.8% and the surface roughness (Sa) by 31.7% when compared to that found with the base oil. Meanwhile, the combinative addition of nano-MoS and nano-SiO, in comparison with single nanoparticles addition, is more pronounced in terms of the lubrication film stability. The excellent tribological properties of the SiO/MoS combinations are attributed to the formation of physical adsorption films and tribochemical products during the rubbing process and the micro-cooperation of various nanoparticles with different shapes and lubrication mechanisms. [ABSTRACT FROM AUTHOR]

In order to improve the understanding of the hot deformation and dynamic recrystallization (DRX) behaviors of large-scaled AZ80 magnesium alloy fabricated by semi-continuous casting, compression tests were carried out in the temperature range from 250 to 400 °C and strain rate range from 0.001 to 0.1 s on a Gleeble 1500 thermo-mechanical machine. The effects of the temperature and strain rate on the hot deformation behavior have been expressed by means of the conventional hyperbolic sine equation, and the influence of the strain has been incorporated in the equation by considering its effect on different material constants for large-scaled AZ80 magnesium alloy. In addition, the DRX behavior has been discussed. The result shows that the deformation temperature and strain rate exerted remarkable influences on the flow stress. The constitutive equation of large-scaled AZ80 magnesium alloy for hot deformation at steady-state stage (ɛ = 0.5) was $$ \dot{\upvarepsilon } = 1.394 \times 10^{12} [\sinh (0.018\upsigma )]^{5.043} \exp ( - 169.610/RT). $$ The true stress-true strain curves predicted by the extracted model were in good agreement with the experimental results, thereby confirming the validity of the developed constitutive relation. The DRX kinetic model of large-scaled AZ80 magnesium alloy was established as X = 1 − exp[−0.95((ɛ − ɛ)/ɛ*)]. The rate of DRX increases with increasing deformation temperature, and high temperature is beneficial for achieving complete DRX in the large-scaled AZ80 magnesium alloy. [ABSTRACT FROM AUTHOR]