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采用3D有限元模拟、实验研究和理论分析,并在与传统等径角挤压工艺对比基础上,系统研究挤扭成形对等径角挤扭工艺固结纯铝粉末-包套过程的影响。模拟结果表明,在等径角挤扭法固结纯铝粉末-包套过程中,挤扭成形起反向背压作用,螺旋通道所提供的旋转剪切变形和高静水压力可大幅增加材料内部的塑性剪切应变,显著改善变形坯料的变形均匀性。在内角为90°、螺旋角为36.5°的方形截面通道模具上,经200℃下1道次等径角挤扭变形实验,成功将纯铝粉末颗粒固结为近致密的块体材料。有限元模拟与实验结果具有较好的一致性。显微组织观察和硬度测试实验结果表明,等径角挤扭法固结的块体材料晶粒更加细小,孔隙得到有效收缩焊合,组织性能均匀性更好。这是由于在等径角挤扭变形过程中剧烈剪切应变大大增加,同时挤扭成形所起的反向背压作用有效提高了Al原子的自扩散系数。
Based on the 3D finite element simulation, experimental study and theoretical analysis, the effects of squeeze-twisting on the solidification of pure aluminum powder-enveloping process by means of isokinetic squeeze-twisting process were systematically studied based on the comparison with the traditional isometry angular extrusion process. The simulation results show that in the process of pure aluminum powder-encasement by isokinetic squeeze-twisting method, the reverse backpressure action is exerted by squeeze-twisting forming, and the rotational shear deformation and high hydrostatic pressure provided by spiral channels can greatly increase the internal Plastic shear strain, significantly improve the deformation of blank deformation uniformity. The pure aluminum powder particles were successfully solidified into nearly dense block materials by square cross-section deformation test with one pass at 200 ° C on a square cross-section channel die with internal angle of 90 ° and helix angle of 36.5 °. Finite element simulation and experimental results have good consistency. The results of microstructure observation and hardness test show that the congruent grain size of the solidified material by isokinetic angle squeeze-twisting method is finer and the pores are effectively shrunk and welded, and the homogeneity of the microstructure is better. The reason for this is that the sharp shear strain is greatly increased during the isokinetic squeezing process, and the reverse backpressure caused by squeeze twisting effectively increases the self-diffusion coefficient of Al atoms.