粉锻连杆预成形坯在热锻过程中的致密化行为

Powder forging connecting rod technology combines the advantages of P／M and precision forging with high material utilization and mechanical properties, as well as high forging size precision. However, powder forging connecting rod with a complex geometry shape always has a problem of non-uniform density distribution. Deformation, densification studies of powder metallurgy connecting rod preforms during hot forging process are of critical significance for optimizing the connecting rod quality. The experiments will be conducted by hot forging sintered Fe-Cu-C powder metallurgy connecting rod preforms in the closed dies. The microstructures and the mechanical properties of the deformed materials will be evaluated. he hot forging process of sintered Fe-Cu-C powder metallurgy connecting rod preforms will be simulated by the adoption of bi variable material constitutive model of temperature and density, thermal wear model, damage model and contact model with FEM (Finite Element Method). Then, the models and numerical results are contrasted with the experiment results. The effects of the physical characteristics of preforms and processing parameters on density distribution and the material flow behaviors of the preforms during hot forging will be studied. Based on the numerical results and experiments results, the heat transfer models, mechanism for metal plastic deformation and densification during powder forging connecting rod will be established. This work can offer good help for the optimal design of the geometrical size of work blanks, processing parameter, and provide a theoretical basis for fabrication and design of high performance powder forged connecting rod.

粉锻连杆技术结合了粉末冶金和精密锻造的优点，具有材料利用率高、力学性能好、尺寸精度高等特点。然而粉锻连杆形状复杂，易出现密度不均匀的现象，研究预成形坯在热锻过程中的塑性变形和致密化行为对改善锻件质量具有重要的意义。本项目拟对连杆预成形坯（粉末冶金Fe-Cu-C材料）加热后在闭式模锻中锻造成的连杆进行材料的显微组织和力学性能分析。拟建立温度和密度双变量粉末冶金材料的本构模型，结合热磨损模型、损伤模型等采用有限元法对连杆预成形坯的热锻成形过程进行数值模拟。研究坯料物理特性、热锻工艺参数对热锻过程中预成形坯的金属材料流动行为及密度的影响。基于模拟得到的相关数据和实验结果，揭示热锻过程中材料的传热规律、材料的塑性变形和致密化机理，以指导优化实际生产中的坯料几何尺寸和热锻工艺参数，为制备和设计高性能粉锻连杆提供理论依据。

粉锻连杆技术结合了粉末冶金和精密锻造的优点，具有材料利用率高、力学性能好、尺寸精度高等特点。然而粉锻连杆形状复杂，易出现密度不均匀的现象，研究预成形坯在热锻过程中的塑性变形和致密化行为对改善锻件质量具有重要的意义。本项目对连杆预成形坯（粉末冶金Fe-Cu-C材料）加热后在闭式模锻中锻造成的连杆进行了材料的显微组织和力学性能分析。采用热压缩模拟试验研究了相对密度为0.8的粉末冶金材料(P/M, Fe-Cu-C)合金的流动行为。建立了粉末冶金Fe-Cu-C合金的材料本构方程、功率耗散(g)图和热加工图。然后，基于建立的材料本构模型，结合热磨损模型、损伤模型等采用有限元法对连杆预成形坯的热锻过程进行了模拟仿真。计算结果与实验结果吻合较好。研究结果表明，随着温度的降低和应变速率的增大，流动应力增大。相对密度为0.8的P/M Fe-Cu-C合金激活能为188.42 kJ/mol。应变量为0.4时，最优温度1333 K到1380 K 范围内可获得较好的热加工性。建立了粉末冶金材料的本构模型，采用有限元法对连杆预成形坯的热锻成形过程进行了数值模拟。将模拟结合和实验结果进行对比验证，研究了坯料物理特性、热锻工艺参数对热锻过程中预成形坯的金属材料流动行为及密度的影响。中间段因具有较大的变形速率和较快的冷却速率，更易发生开裂。相对于坯料与模具间的摩擦系数和模具预热温度而言，锻造速度和预成型坯的初始密度对坯料的致密化影响较显著。预成形坯在热锻过程中的密度随预成形坯的初始密度、锻造速度、坯料与模具间的摩擦系数和模具预热温度的增加而增加。通过正交优化法获得了最优的预成形坯几何尺寸设计方案和最优的热锻工艺参数的方案。揭示了热锻过程中材料的传热规律、材料的塑性变形和致密化机理，指导优化了实际生产中的坯料几何尺寸和热锻工艺参数，为制备和设计高性能粉锻连杆提供了理论依据。