大口径厚壁管均匀性热挤压工艺研究

通过虚拟正交试验研究不同热挤压工艺参数对厚壁管平均晶粒尺寸、组织均匀性及最大挤压力的显著性影响规律,确定其主要影响因素;利用数值模拟分析,研究主要影响因素对挤压管晶粒尺寸及动态再结晶率的影响,制定最优工艺参数;基于最优工艺参数分别进行数值模拟和工厂试验,采集数据进行对比分析。结果表明,铸坯预热温度、挤压速度和挤压比是影响管件晶粒大小及其均匀性的主要因素,当铸坯预热温度为1200℃、挤压比为9、挤压速度为40 mm·s-1时,厚壁管晶粒细小且分布均匀;数值模拟和试验结果在误差允许范围内,表明热挤压数值模拟模型可靠性高,可用于指导大口径厚壁管热挤压工艺的实际生产。

Inhomogeneity of density and mechanical properties of A357 aluminum alloy backward extruded in semi-solid state

The inhomogeneity of density and mechanical properties of A357 aluminum alloy in the semi-solid state were investigated.Numerical simulation and backward extrusion were adopted to study the preparation of cup shells.The results show that the relative density of the wall is the lowest in samples,and that of the base is the highest.With increasing the billet height,more time is needed for relative density of the corner to reach the maximum value,and the relative densities in every region improve evidently with increasing the pressure.The tensile stress was simulated to be the largest at the corner,and the hot tearings were forecasted to mainly appear at the corner too.By employing proper billet height and pressure,the extruded samples consisted of fine and uniform microstructures,and can obtain excellent mechanical properties and Brinell hardness.

Significant improvements in mechanical properties of AA5083 aluminum alloy using dual equal channel lateral extrusion

Dual equal channel lateral extrusion (DECLE), as a severe plastic deformation (SPD) process, was employed forimproving the mechanical properties of AA5083 aluminum alloy. Several experiments were conducted to study the influences of theroute type, namely A and B, and pass number on mechanical properties of the material. The process was conducted up to 6 passeswith decreasing process temperature, specifically from 573 to 473 K. Supplementary experiments involving metallography, hardnessand tensile tests were carried out in order to evaluate the effects of the process variables. The hardness measurements exhibitedreasonably uniform distributions within the product with a maximum increase of 64% via a 6-pass operation. The yield and ultimatestrengths also amended 107% and 46%, respectively. These significant improvements were attributed to the severe shear deformationof grains and decreasing pass temperature, which intensified the grain refinement. TEM images showed an average grain sizereduction from 100 μm for the annealed billet to 200 nm after 6 passes of DECLE. Finally, the experimental findings for routes A andB were compared and discussed and some important conclusions were drawn.

Effects of die geometry on non-equal channel lateral extrusion(NECLE) of AZ80 magnesium alloy

Non-equal channel lateral extrusion（NECLE） is a new process that can be used to attain higher grain refinement in comparison with equal channel lateral extrusion（ECLE）. The die design for this process was numerically and experimentally studied. After finding a good correlation between the numerical and experimental results, more comprehensive FE analyses were carried out. Different die geometrical parameters were considered and their effects on the induced plastic strain, stress distribution, velocity field and forming load of the process were investigated. It was found that by this process with a suitable set of die geometrical parameters, higher induced effective strain and more homogeneous strain distribution could be achieved in comparison with ECLE operation.

3D FEM simulations and experimental validation of plastic deformation of pure aluminum deformed by ECAP and combination of ECAP and direct extrusion

Rigid-viscoplastic3D finite element simulations(3D FEM)of the equal channel angular pressing(ECAP),thecombination of ECAP+extrusion with different extrusion ratios,and direct extrusion of pure aluminum were performed andanalyzed.The3D FEM simulations were carried out to investigate the load-displacement behavior,the plastic deformationcharacteristics and the effective plastic strain homogeneity of Al-1080deformed by different forming processes.The simulationresults were validated by microstructure observations,microhardness distribution maps and the correlation between the effectiveplastic strain and the microhardness values.The3D FEM simulations were performed successfully with a good agreement with theexperimental results.The load-displacement curves and the peak load values of the3D FEM simulations and the experimentalresults were close from each other.The microhardness distribution maps were in a good conformity with the effective plastic straincontours and verifying the3D FEM simulations results.The ECAP workpiece has a higher degree of deformation homogeneity thanthe other deformation processes.The microhardness values were calculated based on the average effective plastic strain.Thepredicted microhardness values fitted the experimental results well.The microstructure observations in the longitudinal andtransverse directions support the3D FEM effective plastic strain and microhardness distributions result in different formingprocesses.

大马肚隧道石碳系地层变形分析及施工对策

结合赣龙铁路(江西段)大马肚隧道出口端碳质页岩夹煤矸石地层施工实例,介绍了隧道围岩的收敛变形情况和力学分析以及相应采取的支护措施及施工对策,为今后类似隧道施工提供了一些判定标准和现场经验。

半空心铝型材挤压过程数值模拟与工艺参数优化

以半空心铝型材导流模具为例,运用HyperXtrude有限元分析软件对半空心铝型材的挤压过程进行数值模拟,并对挤压参数进行优化。采用正交试验分析了挤压速度、挤压筒温度、坯料温度和模具温度等挤压工艺参数对挤压流动均匀性的影响趋势。分析结果表明,以标准速度偏差SDV值大小作为评判挤出均匀性的标准,影响挤压均匀性大小的挤压参数排序为:挤压速度>挤压筒温度>模具温度>坯料温度。优化后的挤压参数为:坯料温度490℃、模具温度480℃、挤压筒温度420℃、和挤压速度1.5 mm·s-1。将优化后的挤压参数应用于模具设计并进行挤压成形试验,获得了挤压均匀性较好的合格型材。